Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. BIOLOGY AND HOST PLANT RELATIONSHIPS OF SCAPTOMYZA FLAVA LEAF MINER A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Entomology Plant Science Department Massey University Palmerston North New Zealand Ali Asghar Seraj 1994 In the Name of ALLAH the Most Merciful the Most Beneficent I dedicate this disertation to Imam Khomeini and the blessed my deceased brother Ali Mohammad Seraj ABST RAC T Scaptomyza flava Fallen (Diptera: Drosophilidae) is a leaf miner of Cruciferous plants (Brassicaceae). It occurs throughout New Zealand and in many other parts of the world. S. flava attacks living plants but also lays eggs on dead leaves and larvae can develop in dead and decaying plant material. However, survival to the adult stage is greater when larvae develop on live leaves. Females are polygamous and mating begins soon after emergence. Female flies start puncturing leaves with their ovipositor ca. 4 h. after emergence and produce peak numbers of punctures within the first 12 h. of their adult lives. It is during this peak time of puncture production that egg laying begins. Oviposition starts on the day following emergence and lasts for about two weeks. Mter this oviposition rate declines slowly. Eggs are laid mainly between 06.00 and 10.00 h. and between 17.00 and 20.00 h. with a peak between 09.00-10.00 h. and 17.00-18.00 h. The mean number of eggs laid per female per day is dependent on the availability of host plants and ranges from 20.9 to 4.4 eggs per day. Maximum oviposition varies between different host plant species. The total fecundity of some females was as high as 320 eggs (on turnip and in contrast less than 12 eggs on cauliflower) over a lifespan of about 12 days. The larvae destroys the parenchyma of leaves. Although only a small portion of the lamina is damaged by a single larva - approximately 5 cm2• Most plant injury is caused by feeding by the third-instar larva which lasts about one week. Sex ratios of adults were close to 1: 1 with a slight bias in favour of males. Feeding punctures and fecundity of S. flava increase greatly when given honey solution. For both sexes, longevity is affected by adult food source. Caged adult female S. flava lived significantly longer when provided with honey solution and yeast than when confined on glass plates and starved or allowed access to yeast and water only. Virgin females lived only slightly longer than mated females and unmated males lived significantly longer than all other groups. S. flava is an oligophagous insect with host plants restricted to the Brassicaceae. When S. flava adults were given a simultaneous choice of seven plant species for feeding and oviposition, there was a distinct hierarchical ordering in their ovipositional preference, with turnip, Chinese cabbage, and hedge mustard being preferred over all others. Percentage of punctures with eggs for turnip, Chinese cabbage and cauliflower (three main host plants of S. flava) in choice tests were 3.1, 3 and 6.4% and in non-choice tests 6, 5.4 and 28% respectively. In non-choice tests, females laid more eggs on Chinese cabbage and Abstract ii turnip than other Brassicaceae. Egg production was also different between host plants. Females oviposited means of 255, 165 and 48 eggs during their lifespan when maintained on turnip, Chinese cabbage and cauliflower, respectively. Peak egg production period varied between host plants; on cauliflower, peak production occurred 3-7 days from adult emergence and on Chinese cabbage and turnip between days 7-1 1 from emergence. There were also significant differences in total developmental times of the insect between three Brassicaceous host plants (cauliflower 41d, Chinese cabbage 33.7d and turnip 3 1d). There were significant differences in duration of the 3rd larval instar among the host plant species with the longest duration on cauliflower (8d). Fecundity of S. flava was positively correlated with female body weight and greater female weights resulted when insects were raised on turnip and Chinese cabbage compared to cauliflower. Although all leaf sizes andlor ages were accepted by the insects (with the exception of the smallest leaves) for egg laying, the number of feeding punctures and eggs per cm2 leaf increased with increasing leaf size andlor age. Nitrogen content of leaves did not vary significantly with age. Previous larval feeding experience on turnip and Chinese cabbage appeared to modify adult host plant preference, but previous feeding experience as larvae on a poor host, cauliflower, did not increase egg laying on that host by adult females. Recently eclosed adult S. flava may show positive experience effects on turnip (and slightly on Chinese cabbage). Over a two year period in the Manawatu adults and larvae of S. flava were present throughout the year with no evidence of diapause or aestivation. However, there were marked peaks during spring and early summer in numbers of adult flies caught, and again in autumn to early winter with troughs in early autumn and early spring. This pattern, obtained by sampling for adults, was paralleled by sampling for larvae. In a laboratory experiment simulated herbivore injury did not produce the same effect as feeding by S. flava. Total fresh-weight accumulation was reduced significantly with increasing levels of injury by S. flava feeding but this did not occur with artificial clipping. In another laboratory experiment, where individual plants were caged with 4 mated females for 24 h. reduced growth of Chinese cabbage and turnip occurred from ensuing larval damage.In two separate field experiments turnip tolerated low levels of leaf mining without reduction in weight of bulb but the net yield of Chinese cabbage was significantly reduced. In the name of Allah the most compassionate the most merciful By the Pen and by the record which men write ( The Holy Qur' an 68: 1 ) ACKNOWLEDGMENTS First of all I send my love to beloved Allah (God) for giving me the ability of learning. He is Endlessness, Lord of everything existing, Creator and sustainer of the Cosmos. Praise be to Allah, who hath guided us to felicity: never could we have found guidance, had it not been for the guidance of Allah. I send my love to our beloved prophets Mohammad, Jesus (lsa) and others (peace be upon them). Also I send my greetings to all their followers. I am immensely grateful and especially indebted to my supervisors Assoc. Professor Peter G. Fenemore and Dr. Marion Harris for close supervision and fruitful discussions concerning this work, and for their appropriate guidance, advice, generous comments, suggestions, encouragement and keen interest. Their critical and careful reviews of the manuscript have improved the English, especially the many helpful comments on my fIrst drafts. Any time I needed their help I was provided a friendly answer. lowe much of my interest and enthusiasm for leaf-mining insects to Dr. Holloway and greatly appreciate her help for providing insect identifications and who kindly agreed to describe Scaptomyza species. The author wishes to thank Mr. J. S. Dugdale for his taxonomical assistance. I have to record my thanks to Mr. Jan Maca of the Australian Museum for much aid in drawing up the descriptions. III Acknowledgments IV I would also like to express my deep thanks to other staff of Plant Science Department, Massey University in particular Professor Ken Milne, head of department and Lecturer Mr. Terry Stewart, and secretarial staff Mrs. Collen Hanlon, Mrs. Pamela Howell, Mrs. Hera Kennedy and Mrs. Lois Mather. I gratefully acknowledge the technical assistance of Mr. Hugh Neilson, Mr. Chris Rawlingson and Mr. Jonathan Dixon and I should like to thank very sincerely Mrs. Lorraine Davis for assistance in the preparation of the manuscript in the laboratory and field and for providing the necessary facilities. Staff of Plant Growth Unit have kindly permitted me to have access to their greenhouses and field areas. My gratitude is extended to Mr. Ray Johnston for valuable facilities for greenhouse and field work. I gratefully acknowledge the grant support provided (full scholarship) by a Fellowship from the Ministry of Culture and High Education of the Islamic Republic of Iran for this research. The presence of other Iranian post graduate students at Massey University made me feel at home. It is my pleasure to thank all of them and the writer is indebted to his colleagues for being friendly and providing a pleasant work environment. My sincere thanks are due to my wife for her support, patience, encouragement and for shouldering my share of our duty to educate our children. The patience and forbearance of my daughters Sarah, Motahareh and Narges and my sons Horr and Ali over the nights I was working late is appreciated. Their smiles have encouraged me to cope with difficulties. Finally, my family and myself have enjoyed the hospitality of the friendly and law-abiding people of New Zealand during our four years in this beautiful country. We would like to thank them all very much. C O N T E N TS Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Contents .................................................... v List of tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii List of plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XVI Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 C h a p t e r 1 : Literature review . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 5-54 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 definition, shape and distribution of mines and miners . . . . . . . . . . . . . .. 6 leaf-miners taxonomy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9 duration of mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " 11 adult biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " 12 host specificity and species diversity . . . . . . . . . . . . . . . . . . . . . . 15 biogeographic patterns of diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 comparison of plant species as hosts for leaf miners and host plant defense .... 18 leaf selection ................................. . . . . . . . . . . . . . .. 21 leaf abscission ............................................... 25 inter-intraspecific competition . . . . . . . ... . . . . . . . . . . . . . . . . . . ... . 28 natural enemies of leaf miners: parasitoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 predators . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 37 abiotic mortality factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 population dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 colour and discolouration of mines . . . . . . . . . . . . . . . . . . . . . . 43 the subsequent fate of the mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 effects of leaf-miners on cultivated plants and economic importance . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 45 Contents vi C h a p t e r 2 : The biology of Scaptomyza flava . . . . . . . . . . . . . . . . .. 55-114 rearing ...................... . . . . . . . . . . . . . . . . . . . . . . . .. 55 morphology and behaviour of insect . . . . . . . . . . . . . . . . . . . . .. . . .. 58 emergence ................................... . . ....... 60 sex ratio ............................................ " 62 mating, feeding and oviposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 66 eggs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 71 larvae ...... . ....................................... " 72 pupae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 production in time of "feeding punctures" and egg laying by S. jlava on Chinese cabbage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " 83 feeding and fecundity of Scaptomyza flava . . . . . . . . . . . . . . . . . . . . .. 92 longevity of Scaptomyza flava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 lifespan of mated and unmated adult Scaptomyza flava .... . ........ 105 number of adult insects emerging from a single leaf of Chinese cabbage ......................................... 1 12 the ability of Scaptomyza flava to develop in dead and decaying leaf material ......................................... 114 C h a p t e r 3 : Host plant relationships of Scaptomyza flava . . . • . . . 115-161 comparison of plant species as hosts for Scaptomyza flava .......... 1 15 effect of host plant species on body weight of adult S. flava .......... 129 life span, number of feeding punctures and number of eggs produced by Scaptomyza flava on three plant species . . . . . . . . . . . . . . . . . . . 132 host effects on the survival and developmental time of Scaptomyza flava ........................................... 136 preference for feeding and egg laying by Scaptomyza flava with respect to leaf age and size of Chinese cabbage .......... . ........ 141 effect of larval food plant on adult egg laying preference . . . .... . .. . 148 effect of adult experience on oviposition preference ................ 155 Contents Vll C h a p t e r 4: Seasonal life cycle and population density of S. flava . . 162-174 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 study site . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 162 sampling methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 a: sampling for adult flies . ... . . . . . . . . . . . . . . . . . . . 164 sticky traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 water traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 sweep netting . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 b: sampling for larvae and for leaf mining injury . . . . . . . 165 results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 C h a p t e r 5 : Damage assessment experiments with Scaptomyza flava 175-208 damage assessment experiments in laboratory and field with Scaptomyza flava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 introduction . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 175 a: laboratory experiment . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 176 b: leaf miner damage assessment field trial . . . . . . . . . . .. . . . . . 182 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. 182 materials and methods . . . . . . . . . . . . . . . . . . . . . . . . . . 182 results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 simulated insect damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 measurement of leaf area damaged by a single larva . . . . . . . . . . . . . . . 204 what density of leaf miner (S. flava) may kill plant seedlings? . . . . . . . . 206 C h a p t e r 6: General discussion . . . . . . . • . . . . . . • . . . . . . . . . . . . . . . • 209 R ef e r e n c e s . . .. . . . . . . . . . . . . . . . . .. . . . ... . . . . . . . . . . .. 223-278 Contents Vlll A p p e n d ie e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279-359 Appendix 1 : taxonomical notes on the genera Scaptomyza and Drosophila within the family Drosophilidae • . . . . . . . . . . . . . . • . . . . . . . . 280-330 the relation between the genera Scaptomyza and Drosophila . . . . . . . .. 280 family Drosophilidae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 280 the separating characters . . . . . . . . . . . . . . .. . . . . . . . . . . . . 281 external morphological characters . , . . . . . . . . . . . . . .. 281 inner anatomical characters . . .. . . . .. . . . . . . . . . . . . 282 the subgenera of Scaptomyza . . . . . . . . . . . . . . . .. . . . . . . . . 282 the borderline between Scaptomyza and Drosophila . . . . . . . . .. 283 Scaptomyza (Parascaptomyza) pallida (Zetterstedt, 1847) . . . . . . . . . .. 286 Scaptomyza graminum . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 Scaptomyza jlava (Fallen, 1823) ............................ 289 Scaptomyza australis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 " Family D r 0 s o p h iIi d a e" ......................... 306 key to genera of Drosophilidae in New Zealand . . . . . . . . . . . . 307 genus Scaptomyza Hardy . . . . . . . . . . . . .. . . . . . . . " 307 key to species of Scaptomyza in New Zealand ............. 307 Scaptomyza jlavella sp.n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 Scaptomyza graminum . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. 309 Scaptomyza fuscitarsis .................................. 311 key to Scaptomyza species occurring in New Zealand ............. 315 the phylogeny of Scaptomyza ............................... 323 Scaptomyza diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . 330 Appendix 2: some important leaf miner (Agromyzidae) pests . . . . . . . 331 Appendix 3: ability of adults to survive at low temperature • . . . 332-335 Appendix 4: oviposition in sun and shade . . . . . . . . . . . . . . . . . 336-339 Appendix 5: laboratory insecticide experiments with Scaptomyza flava 340 Contents IX Appendix 6: the ability of S. elmoi to develop on Chinese cabbage . . . 343 Appendix 7: seasonal life cycle of Scaptomyza flava . . . . . . . . . . 344-356 Table 6: Table 7: Table 8 : Table 9: numbers of Scaptomyza flava recovered by three different sampling methods from Chinese cabbage over a two-year period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 numbers of Scaptomyza flava recovered by three different sampling methods from turnip over a one year period . . . . 349 numbers of Scaptomyza elmoi & Scaptomyza juscitarsis captured by 10 sweep net samples from Chinese cabbage over a one year period . . . . . . . . . . . . . . . . . . . . . . . . . 352 plant measurements and numbers of larvae from samples of five Chinese cabbage plants . . . . . . . . . . . . . . . . . . . . 355 Appendix 8: cultural notes on host plants of Scaptomyza flava . . 357·359 Chinese cabbage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357 pests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 physiological disorders . . . . . . . . . . . . . . . . . . . . . . . . . 358 turnip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 diseases and pests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 cauliflower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 radish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 Contents Table 1: Table 2: Table 3: Table 4: Table 5: Table 6: Table 7: Table 8: Table 9: Table 10: Table 11: Table 12: Table 13: Table 14: Table 15: Table 16: Table 17: Table 18: x LIST OF TABLES sex ratio of Scaptomyza flava from laboratory colony. . . . . . . . .. 63 sex ratio of S. flava captured by sweep net in the field at Palmerston North from Chinese cabbage and turnip. ..... . . . . . 64 mean number of feeding punctures and eggs per female . . . . . . .. 85 time of feeding and oviposition activity of Scaptomyza flava females under laboratory conditions . . . . . . . . . . . . . . . . . . . . .. 86 production in time of "feeding punctures" and egg laying by S. flava on Chinese cabbage under greenhouse conditions . . . ... . . 87 mean number of feeding punctures and eggs per female in time relationship between the number of feeding punctures and food 89 source. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96 fecundity of S. flava with different food availability . . .. . .... . 97 the longevity (survival) of adults of S. flava with different food availability (without plant material) .. . . . . . . . . . .. . ... . . .. . 102 life span of Scaptomyza flava under greenhouse conditions . . . .. 110 number of adult insects from ten leaves of Chinese cabbage . . . . . 113 plant species used in studies of host discrimination by S. flava . . 1 18 number of feeding punctures and eggs on eight plant species in choice tests with Scaptomyza flava .. . . . ........ . ... . . ... . .. . . 122 number of feeding punctures and eggs on eight plant species in non-choice test with Scaptomyza flava . . . . . . . . . . . . . .... . .. 124 mean weights of adult S. flava according to sex and host. . . . . . . 131 mean life span, number of feeding punctures and number of eggs produced by Scaptomyza flava (during entire life time) on three plant species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 mean numbers of punctures, eggs and adults of Scaptomyzajlava and leaf area mined per plant .. . ... ... . . . . . � . . . . . . . . . . . . . . . . . 138 the mean durations (days) of the egg stage, the tree larval instar, the pupal period and total time from egg laying to adult death on the three plants species . . . .. . .. . . . ... .. . ............. . . .... . 139 Contents Table 19 Table 20: Table 2 1: Table 22: Table 23: Table 24: Table 25: Table 26: Table 27: Table 28: Table 29: Table 30: Table 31: Table 32: Table 33: Table 34: Table 35: Table 36: Xl mean leaf area and number of punctures and eggs according to leaf age . .... . ....... ........... ...... ........... 144 influence of larval food plant on adult feeding and egg laying preference ..... .... ..... ... . ... . ........ . ... .. .. . 149 effect of first adult feeding on plant preference .... .. . ....... 157 results of laboratory experiment to assess the effects of Scaptomyza flava on Chinese cabbage ............ ...... . . 178 results of laboratory experiment to assess the effects of Scaptomyza flava on turnip . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 mean total leaf area, leaf area mined and percentage leaf area mined of Chinese cabbage on two sampling dates. 1991/92 field experiment. . . . . . ... . .... . . . .. .. .. . ... ... .. . .... .. . 188 gross and net weights of Chinese cabbage at harvest .......... 189 mean total leaf area, leaf area mined and percentage leaf area mined of turnip on two sampling dates. 1991/92 field experiment .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 mean weights of leaves and bulb roots of turnip on 7/1/92 and at harvest .... . .. . . ........ . .. .. ... ... ... ... ..... . .. 192 mean total leaf area, leaf area mined and percentage leaf area mined of Chinese cabbage on two sampling dates. 1992/93 field experiment .. ...... .. .. .. . .. . . .. . .... . . . .. . .. . . . .. 193 mean total leaf area, leaf area mined and percentage leaf area mined of turnip on two sampling dates. 1991/92 field experiment " ................... .................. 194 mean number of adult Scaptomyza flava captured by sweep netting on Chinese cabbage on three sampling dates . .... ..... 195 mean number of adult Scaptomyza flava captured by sweep netting on turnip on three sampling dates . ....... . ..... .... 195 gross and net weights of Chinese cabbage at harvest ...... . . .. 196 mean weights of leaves and bulb roots of turnip at harvest . ..... 196 results of actual and simulated damage to Chinese cabbage ..... 202 leaf area damaged by single larvae of Scaptomyza flava . . . . . . . . 205 number leaves damaged by different number of S. flava adults . . . 208 Contents Appendix Table 1: Table 2: Table 3 Table 4: Table 5: Table 6: Table 7: Table 8: Table 9: comparison of characters of Drosophila subg. Lordiphosa, Scaptomyza subg. Bunostoma and two unplaced Scaptomyza Xli species from New Zealand. . .......................... 329 survival in days of adult S. jlava at low temperatures . . . . . . . . . 334 number of new emerged adult insects from I pair of Scaptomyza flava from Chinese cabbage plants in sun and shade. . ............. 338 mean number of live adult Scaptomyza flava in experiment 1 after 48 h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 mean number of live adult Scaptomyza flava in experiment 2 . . . . 342 numbers of Scaptomyza flava recovered by three different sampling methods from Chinese cabbage over a two-year period . . . . . . . . 344 numbers of Scaptomyza flava recovered by three different sampling methods from turnip over a one year period . . . . . . . . . 349 number of Scaptomyza elmoi & Scaptomyza juscitarsis captured by lO sweep net samples from Chinese cabbage over a one year period . . . .. . . . . . . . . . .. . . . . . . .. . . . . . . . . . . . . . . . . . . 352 plant measurements and numbers of larvae from samples of five Chinese cabbage plants . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 355 Contents Fig. 1: Fig. 2: Fig. 3: Fig. 4: Fig. 5: Fig. 6: Fig. 7: Fig. 8: Fig. 9: Fig. 10: Fig. 1 1: Fig. 12: Fig. 13: Fig. 14: Fig. 15: Fig. 16: Fig. 17: Fig. 18: Fig. 19: Fig. 20: Xlll LIST OF FIGURES types of mines . ...... ..... . .. . ... . ........ . .. . . . . . 53 after leaf mining .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 56 time of emergence of S. flava adults under greenhouse conditions . 61 time of feeding activity of Scaptomyza flava females under laboratory conditions ......... ... . ....... ... . .... . . . ... . .... 90 time of oviposition activity of S. flava females under laboratory conditions ......... ..... . . . ..... .. . . . .. . .. ..... . . , 90 mean no. feeding punctures and time to commencement of egg laying by S. flava on Chinese cabbage . . . . . . . . . . . . . . . . . . . . . . . . . .. 9 1 fecundity of S. flava with different food availability . . ...... . . 98 the longevity of adult S. flava with different food availability .... 104 comparison of plant species for feeding punctures by S. flava .. . . 125 no. of eggs laid by S. flava in choice & non-choice tests . . . . ... 125 pattern of feeding by S. flava on three host plants . . . . . . . . . . . . 135 pattern of egg laying by S. flava on three host plants . . . . . . . . . . 135 relationship between nitrogen content of leaf and leaf age of Chinese cabbage .. . ....... . . . ..... . ....... . . .. . . . ........ 147 relationship between no. of feeding punctures of Scaptomyza flava and leaf age of Chinese cabbage . . ... . .... . . ......... .. . . . . 147 relationship between no. of eggs of Scaptomyza flava and leaf age of Chinese cabbage " ................................. 147 effect of larval food plant on feeding preference by Scaptomyza flava adult flies (cauliflower reared) .......... . . ............. 153 effect of larval food plant on feeding preference by Scaptomyza flava adult flies (Chinese cabbage reared) .. ....... ............. 153 effect of larval food plant on feeding preference by Scaptomyza flava adult flies (turnip reared) . .... . ... ..... . . ... . . ........ 153 effect of larval food plant on egg laying preference by S. flava adult flies (cauliflower reared) ..... . . ..................... . .... 154 effect of larval food plant on egg laying preference by S. flava adult flies (Chinese cabbage reared) ...... ... ... .... . . . .. ........ 154 Contents Fig. 21: Fig. 22: Fig. 23: Fig. 24: Fig. 25: Fig. 26: Fig. 27: Fig. 28: Fig. 29: Fig. 30: Fig. 31: Fig. 32: Fig. 33: Appendix: xiv effect of larval food plant on egg laying preference by S. flava adult flies (turnip reared) ..................................... 154 effect of adult experience on feeding preference by S. flava adult flies ........................................ 161 effect of adult experience on oviposition preference by S. flava adult flies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 seasonal rainfall & relative humidity ..................... 169 seasonal temperature (max, mean, min) ................... 169 weekly sampling of S. flava on Chinese cabbage by two sampling methods .................................. 170 weekly sampling of S. flava on turnip by two sampling methods . 170 weekly sampling of S. flava adults and larvae on Chinese cabbage ......................................... 171 weekly sweep net sampling of S. flava on Chinese cabbage " ... 172 percentage of leaf area mined for Chinese cabbage by S. flava . . . 173 no. of S. elmoi & S. fuscitarsis captured by sweep netting ...... 174 the effects of Scaptomyza leaf miner on Chinese cabbage and turnip in laboratory (re: leaf area mined) ....................... 180 the effects of Scaptomyza leaf miner on Chinese cabbage and turnip in laboratory (re: weight of leaves and bulb root) .... 180 Figs. 1-4: phallic organs of the Scaptomyza species. ................ 293 Figs. 5-6: spermatheca, parovarium, ventral receptacle S. griseola, and S. apicalis (flava) . . ... .... ......... ......... . ....... 293 Figs. 7-10: posterior spiracles of 3rd instar larvae.. .................. 294 Fig. 11: wing indices of Scaptomyza and their dependence on the wing length. ......................................... 295 Fig. 12: frequency of Scaptomyza pallida and S. graminum during collecting periods. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 296 Figs. 13-17: male genitalia of Parascaptomyza species ................ 302 Contents Figs. 1 8-26: Figs. 27-38: Figs. 39-44: Figs. 45-48: Figs. 49-54: Figs. 55-56: Fig. 57: Fig. 58: Figs. 59-60: Figs. 6 1 -67: Figs. 68-8 1 : Figs. 82-85: -- ---------- -- -- - - - xv male genitalia of Scaptomyza species . . . . . . . . . . . . . . . . . . .. 302 male genitalia of Scaptomyza species . . . . . . . . . . . . . . . . . . . . 303 male genitalia of Scaptomyza species. . . . . . . . . . . . . . . . . . . . 304 genitalia of Scaptomyza australis from newly discovered distributions 305 wings of the Scaptomyza species . . . . . . . . . . . . . . . . . . . . . . 3 14 head of the Scaptomyza species . . . . . . . . . . . . . . . . . . . . . . .. 3 14 some characters of the family Drosophilidae (holloway, 1 990). 3 16 profIle of scutellum (from the left side) of the Scaptomyza species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 17 acrostichal hairs on thorax of the Scaptomyza species compared with Drosophila species (holloway, 1990). . . . . . . . . . . . . . . . . 3 1 8 male genitalia of Scaptomyza and Drosophila species. . .. . . . . . . 326 spennatheca of Scaptomyza and Drosophila species. . . ....... . 327 testes and paragonia of Drosophila Jenestrarum and Scaptomyza species. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 Contents Plate 1: Plate 2: Plate 3: Plate 4: Plate 5: Plate 6: Plate 7: Plate 8: Plate 9: Plate 10: Plate 11: Plate 12: Plate 13: Plate 14: Plate 15: Plate 16: Plate 17: Plate 18: Appendix: Plates 1-2: Plate 3: Plate 4: Plate 5: - - -- -- --�---------------- - -- - XVI LIST OF PLATES rearing cages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 adult female Scaptomyza flava (dark form) . . . . . . . . . . . . . . . .. 59 anaesthetic operation tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 feeding punctures of S. flava in leaves of Chinese cabbage . . . . . 70 single egg of Scaptomyza flava . . . . . . . . . . . . . . . . . . . . . . . .. 73 eggs laid in leaf tissue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 73 larvae of Scaptomyza flava . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75 blotch mines on Chinese cabbage leaves . . .. . . . . . . . . . .. . . . 77 increasing severity of damage on leaves of Chinese cabbage by Scaptomyza flava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 77 blotch mines on cauliflower leaves . . . . . . . . . . . . . . . . . . . . . . 78 blotch mines on turnip leaves . , . . . . . . . . . . . . . . . . . . . . . . .. 78 plants of Chinese cabbage undamaged and heavily damaged by Scaptomyza flava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 pupa of S. flava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 small cylindrical oviposition cages (foreground) . . . . . . . . . . . . . 95 comparison between feeding punctures with male and female S. flava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 cylindrical cage used for choice tests . . . . . . . . . . . . . . . . . . . . . 120 square cage used for non-choice tests . . . . . . . . . . . . . . . . . . . . 120 area meter Mk2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 ovipositor of female S. flava ............ . ............ 319 external male genitalia of S. flava . . . . . . . . . . . . . . . . . . . . . . . 320 proboscis of adults S. flava . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 longitudinal rows of acrostic hal bristles S. flava . . . . . . . . . . . . . 322 INTRODUCTION Dipteran leaf miners are a large and widespread group of small flies, most with larvae attacking a wide range of plants. Most simply mine leaves but a few are gall makers (Hill, 1987). Some species are cosmopolitan, others solely temperate and some restricted to the tropics. The range of host specificity is great, from broad polyphagy to restricted monophagy on a single genus of host plant. About 1 50 species are regularly associated with cultivated plants, and these were the subject of a monograph by Spencer (1973); the total number of species recorded is about 1 800 (Hill, 1 987). The leaf-mining larvae are characterized by making long winding tunnels (mines) in the leaf lamina; the tunnel appears whitish because of light reflection from the air trapped in the mine. Some species make blotch mines but this is generally more characteristic of other groups of leaf miners. Sometimes the mine starts in a linear manner and terminates in a large blotch. Pupation takes place usually in the mine but a few species pupate in the soil or in leaf litter. Some crop plants are mined by different species of leaf miners in different parts of the world where they are allopatric in distribution, but some flies have overlapping distribution (i.e., sympatric), and some are cosmopolitan. The end­ result is that in any one locality some crops are attacked by several very similar leaf miners simultaneously. Most leaf mining Diptera are from the family Agromyzidae but the larvae of some drosophilids have the leaf mining habit. The identification of drosophilid leaf miners is extremely difficult and many species are only distinguishable by the male genitalia, but at generic level 1 Introduction 2 there are some differences in acrostichal hairs on the thorax (Hackman, 1982). The crops most likely to suffer multiple leaf miner fly infestation (including Agromyzidae and Drosophilidae) are those belonging to the families Leguminosae, Gramineae, Solanaceae, Compositae, Chenopodiaceae, Cucurbitaceae, and Brassicaceae. In New Zealand there are more than 30 species of native leaf mining insects, although only two, both flies, can be regarded as pests (Wise, DSIR fIles). The cabbage leaf miner, Scaptomyza flava (Fallen) , is probably one of the most common leaf miners in New Zealand. These minute flies have been greatly neglected in this country. Scaptomyza flava commonly infests many cruciferous vegetables especially in the young plant or seedling stages. It occurs as a pest in temperate zones and at the margins of the subtropics. S. flava is widespread in Europe, Asia, North America, Australia, and throughout New Zealand. The insect was not regarded as a major pest of brassica plant species in the North Island by Cumber and Eyles (1961a), but it has become increasingly important within the last few years as a pest of Brassicaceae plant species in the agricultural area of the Manawatu and other parts of New Zealand. Other Scaptomyza species are present in New Zealand, but little is known of their biology. Damage by S. flava is caused by the mining of the larvae within the leaf tissue and also by the feeding and ovipositional habits of the adult female. Under favourable environmental conditions populations of it may reach high levels. The literature concerning S. flava is very limited, although Holloway (1990) reported some details of host plants. Brassica leaf miners in New Zealand have previously been misidentifIed, Introduction 3 and attempted biological control failed probably due to mis-identification of the target (McGregor, 1989). The leaf miners were shown to be not Agromyzidae but two species of Drosophilidae: Scaptomyzajlava (Fallen) and S. graminum (Fallen) (DSIR files). The initial assumption that the "brassica leaf miner" was Chromatomyia syngenesiae was wrong. Two factors that have complicated research on Scaptomyza jlava have thus been misidentification of species and also lack of basic biological knowledge. The information presented in this thesis should contribute to the overall understanding of host plant utilization by this insect and to the development of more comprehensive and soundly based pest management strategies. Studies have been conducted on various aspects of the biology, ecology and host plant relationships of Scaptomyza jlava to better understand its role as a pest of Brassicaceae plant species. The symptoms and extent of damage caused and the relationship of insects to their host plants are of fundamental importance to understanding pest biology and abundance and critical to the development of pest management systems. My research has been directed towards determining the basic biology and behaviour of Scaptomyza on selected hosts, the economically important brassica species (Chinese cabbage, turnip and cauliflower). The main objectives of my research programme were to develop information that would enable a comprehensive picture to be built up of: seasonal life cycle, simple population dynamics, ecology and behaviour of Scaptomyza jlava, pest status; this to involve determining the relationship between pest incidence and yield/quality of produce for two vegetable brassicas, and aspects of host plant relationships including preference for feeding and oviposition. Inlroduction 4 To achieve this I did the following: 1. Carried out a literature reVieW of leaf mining insects with particular reference to Dipterous leaf miners of Cruciferae and to the Australia I New Zealand region to cover taxonomy (see Appendix 1), host-plant relationships, ecology and control, 2. to improve my taxonomic understanding of the Drosophilidae, I spent two periods with Diptera taxonomists in Auckland (DSIR), and Australia (CSIRO), 3. collected larval samples from a range of cultivated and wild Cruciferous plant species affected by leaf miners and reared out adults. A reference collection of authoritatively identified specimens was established, 4. determined the occurrence and seasonal life cycle of the leaf miner on two types of vegetable brassicas at Palmerston North, 5. assessed experimentally the effects of Scaptomyzaf!ava on the growth and yield of two vegetable brassicas, and 6. investigated various aspects of the insect's host-plant relationships. - - - - - - ----------- -- -- - - - Chapter 1 L ITE R ATUR E R E V I E W INTRODUCTION I The development of specialised feeding habits by insects is in some cases characteristic of the species concerned. Leaf-mining insects are one such specialised group and feed on tissues between or in the epidermal layers of leaves for all or part of their larval development. Possible advantages of this feeding habit include avoidance of digestibility reducing compounds in certain leaf tissues, protection from natural enemies, and amelioration of harsh external weather conditions, particularly protection from desiccation during dry periods. Leaf mining Diptera are very common on seedlings, young plants and in some cases mature plants of most cultivated Cruciferae (cabbage, turnip, cauliflower, broccoli, radish, watercress, bittercress and fodder brassicas) in New Zealand, but very little is known about them as to their ecology, host plant range, natural enemies and pest status. In the past, confusion has existed as to species involved. As pointed out by Hering (195 1 ) , two groups of plant feeding insects have for a long time attracted special attention from entomologists. These are the gall makers and leaf miners. In both cases the insect larva lives and feeds inside plant tissue i.e. is endophagous, and does not merely chew from the outside. This particular interest derives from both the distinctive form of leaf mines and the often remarkable structure of galls. The uniformity of pattern is often very pronounced and characteristic for a particular species. In many cases this makes it I Major publications concerned with leaf mining insects are "Biology of the leaf miners" (Hering, 1951) and "Bionomics of leaf-mining insects" (Hespenheide, 1991). Most of my knowledge concerning the leaf miner literature comes from studies of them (especially the comprehensive review of Hespenheide). These published reviews provide a good starting point for those interested in these kinds of insects (leaf miners). Chapter 1: Literature Review 6 easier to identify the genus or species of insect responsible from its feeding pattern rather than from examination of the insects themselves (Hering, 1951). Most insects that live in galls or mines are highly specialised and show a number of adaptations to their habitat (Houser, 1923 cited by Hering, 1951). Cecido}ogy, the study of galls, was studied systemically considerably earlier than its sister science, hyponomology or the study of mines, which only fully developed in the twentieth century. Leaf-miners were flrst mentioned by Beckmann in 1681 who discussed and illustrated the strange fonns which had appeared in great numbers the previous year on cherry trees in the Frankfurt / Oder area in Germany (Basden, 1954). The popular conception at this time was that these mines represented little serpents which had descended from the skies or emanated from the foul air of the local swamps. However, Beckmann was able to show that the mines were caused by insects and illustrated the lepidopterous larvae responsible. Then in 1737, Reaumur discussed and illustrated Agromyzid leaf-miners on Sonchus oleraceus L., Trifolium, Ranunculus and Lonicera. These species were not given names but are readily identifiable from their host-plants (Hering, 1951). DEFINITION, SHAPE AND DISTRffiUTION OF MINES AND MINERS Mines may be defined as feeding channels formed by insect larvae inside the tissues of plants, in which the epidermis, or at least its outer wall, remains uninjuried (Hering, 1951). Thus miners are insects which feed in such channels for at least part of their larval lives (Claridge and Wilson, 1982). Naturally, the mine cavity is extended inside the green parenchyma of a leaf, but in the same way, feeding channels, which can be designated as mines, may be established inside the parenchyma of fruits, stems or roots. The channels established in different types of pith tissue of the stem, roots and fruit and which lie below the green parenchyma layer of the organ in question obviously do not fall within the same category as leaf mines (Hering, 1951). - - - - - -��-�--- - - - - - - - - Chapter 1: Literature Review 7 Potter (1989) has pointed out that some insects that specialize on young leaves, including certain leaf miners, appear to be resource limited in that natural or experimental induction of a secondary leaf flush results in increased feeding damage or rapid population increase. The physiologically essential aspects of insect leaf-mining activity, i.e. feeding exclusively on parenchyma or epidermis cells and simultaneously being cut off from the outer world by a dividing barrier (Stiling and Strong, 1984), are also to be found in a whole series of other feeding patterns occurring not in leaves but in other plant organs. In such cases there is a clear relationship to leaf-mining from the point of view not only of plant anatomy but also of insect classification, even though they are usually less conspicuous and diverge widely in form from leaf-mines (Hering, 1936 cited by Hering, 1951). Essentially the same families and genera are concerned; in many instances even the same species, either through choice or compulsion during later stages of development, change their habits for example, from leaf-mining to stem­ boring. If the leaf is very small and provides insufficient food for the larva, it may move on through the petiole into the stem (Hering, 1951). Leaf miners show spatial patterns in distribution and are of particular interest because they are often abundant and can affect growth and reproduction of both native and cultivated species (Collinge and Louda, 1988). Hespenheide (1991) mentioned that the distribution of leaf-miners has been discussed at several different spatial scales; between different habitats, among and within plants within a single habitat, and among and within leaves of a single plant. A leaf mining moth, Stilbosis quadricustatella, exhibited a clumped distribution of mines among leaves of the evergreen oak. Mines tended to be on large, peripheral, and undamaged leaves so that leaves were often multiply mined. Over successional gradients, major faunal components change between annuals, which are dominated by Agromyzids, and perennials which are dominated by Lepidopterans; a large number of species occur on perennials and earlier plant stages have a greater density of miners Chapter 1: Literature Review 8 (Godfray, 1984 cited by Hespenheide, 1991). Within habitats, miners are unequally distributed among trees (Bultman and Faeth, 1986 cited by Hespenheide, 1991), in some cases preferring younger trees over older ones (Martin, 1956 cited by Hespenheide, 199 1) . Densities often decrease from edges to the interior of a habitat, in one case because of parasite pressure (Stiling et ai. , 1982 cited by Hespenheide, 199 1). The distribution and abundance of leaf miners on some trees should not be viewed as the turnover of reproductive populations on individual trees, but rather as the immigration and failed colonization of species whose movements encompass several trees (Connor et aI. , 1983). Connor et al. (1983) investigated the leaf miner guilds of several species of oak: trees to determine to what extent species distributions are maintained by in situ reproductive recruitment and to what extent by continued immigration. Complementary caging experiments were performed to exclude immigration and to exclude in situ recruitment from overwintering populations. Collinge and Louda (1988) have reported that oviposition and leaf mining damage were concentrated on the lower central leaves of a stem in Drosophila leaf miners. Within a plant (usually a tree), miners may prefer upper portions of the canopy (e.g., the larvae of Cameraria hamadryadella and C. cincinnatiella form a solitary blotch mine in the upper portion of oak leaves) (Hinckley, 1972) or more usually, lower portions, for example, the mines of Lithocolletis salicifoliella are found on the underside of the leaves (Martin, 1956), or show no preference. One phenomenon suggesting that resource limitation was or is an important factor in the population dynamics of some insects is the presence of spacing or oviposition-deterring pheromones (Quiring and McNeil, 1984). Such preferences are usually presumed to be for sun or shade (Bultman and Faeth, 1988), but shaded plants may show more damage than preferred plants in the sun (Collinge and Louda, 1988), and miners may prefer leaves in the sun but survive better in the shade (Bultman and Faeth, 1986). They demonstrated that total insect herbivore load on bittercress is greater on plants in the shade and that there were increases in the water associated soluble (nitrate) nitrogen concentrations in leaves. Story et al. (1979) stated that feeding activities of adult leaf miner on turkey oak, Brachys tessellatus shifted to the more shaded middle and lower Chapter 1: Literature Review 9 crown levels during the warmer days of late May and June. The hypothesis that generally higher levels of herbivory on bittercress Cardamine cordifolia A. Gray (Cruciferae), especially by leaf miners, are related to the earlier phenological development of plants in the sun was tested in field studies in Colorado by Colling and Louda ( 1989). The dominant insect at the site was the Drosophilid leaf miner Scaptomyza nigrita. Adult flies were at least twice as frequent on bittercress plants in sun-exposed than in shaded areas, and were most active from mid-day to late afternoon. Female flies were on average 26% larger than male flies, but there were no differences in size of adults between the two habitats. Larval damage to bittercress was generally much greater on plants in sunny areas than on those in the shade, possibly due to the increased activity of ovipositing flies in these areas (Collinge and Louda, 1989). LEAF -MINER TAXONOMY· Leaf miners which feed only within the tissues of leaves are restricted to the orders Lepidoptera, Diptera, Coleoptera and Hymenoptera. Leaf mining insects therefore fonn a distinct feeding guild (in the sense of Root, 1973 cited by Claridge and Wilson, 1982) which is taxonomically very diverse. The greatest diversity of forms and number of species are in Lepidoptera (fossil lepidopterous leaf mines demonstrate the age of some insect-plant relationships), then in the fly family Agromyzidae and relatively fewer in the Coleoptera and Hymenoptera (Hespenheide, 1991). In Slovenia / Yugoslavia, MaCek (1972) recorded 1 18 species of leaf miners from 5 1 weed species. Diptera predominated, with Coleoptera, Hymenoptera and Lepidoptera being only sparsely represented. In Germany Bachli et al. (1985 cited by Macek, 1972), described 1 1 hitherto unknown leaf-mines and allocated positions in Hering's classification. In two cases the insects responsible for the mines were known genera of Lepidoptera and in 6 cases, perhaps those of Coleoptera or Hymenoptera. Fifteen new types of leaf­ mines caused by larvae of Diptera were described and classified by Zoerner (197 1 ). Of these, nine were caused by Agromyzids, two by Chironomids, one by Cecidomyiids, one by a Drosophilid and two by unknown Diptera. For Britain and a fauna of nearly 1 Taxonomy of Scaptomyza flava leaf miner has been elaborated in Appendix 1 Chapter 1: Literature Review 10 700 species of leaf miners the proportions were 57% Diptera, 33% Lepidoptera, 8% Coleoptera, 3% Hymenoptera (Godfray, 1985). This overall pattern is probably maintained in most localities (Askew and Shaw, 1974), but varies from habitat to habitat (Askew, 1980; Godfray, 1985) and shows some change with geography, perhaps especially in the relative importance of the Coleoptera and Agromyzidae. Leaf-mining flies are predominantly Agromyzidae, but leaf-miners also occur in the Anthomyiidae (Godfray, 1986), Drosophilidae (Collinge and Louda, 1988,1989) and Ephydridae (Stiling et aI. , 1982, 1984), among others. Agromyzids have been extensively studied, perhaps because of their temperate distribution, but also because of their economic importance. Some important Dipterous leaf miner pests (Agromyzidae) and a full list of leaf miner species associated with British trees is given by Claridge and Wilson (1982). Major families in the Lepidoptera include the Cosmopterygidae, Gelechiidae, Gracillariidae, Heliozelidae, Incurvariidae, Lyonetidae and Nepticulidae (Simberloff and Stiling, 1987). Thus leaf-mining microlepidoptera form a large assemblage whose larvae mine the leaves of both angiosperms and gymnosperms. Beetle leaf-miners are concentrated in the three families: Buprestidae, Chrysomelidae, and Curculionidae. Hymenoptera that mine leaves are sawflies of the family Tenthredinidae (Toumi et aL, 198 1 cited by Hespenheide, 199 1 ). In New Zealand two orders, Diptera and Lepidoptera are important as leaf miners. Diptera include Agromyzidae: Beet leaf miner (Liriomyza chenopodi Watt), hebe (koromiko) leaf miner (Liriomyza spp.), Phytobia spp. , and kaka beak leaf miner Phytomyza syngenesiae Hardy); and Drosophilidae: Scaptomyza flava, S. flavella, S. elmoi, and S. fuscitarsis. A study during 1974-75 recorded 4 1 Agromyzid flies and, while no recent study of the moth miners has been made, there were 18 recorded species by 1923 (Scott, 1984). In Spencer ( 1976) 16 known species of Agromyzidae hitherto in New Zealand and subantarctic islands have been revised, and 19 new species are described: Cerodontha sylvesterensis, Hexomyza coprosmae, Liriomyza oleariae, L. wahlenbergiae, L. craspediae, L. watti, L. plantaginella, L. hebae, L. vic ina, L. pen ita, L. homeri, Melanagromyza senecionelia, Phytoliriomyza cyateae, P. Chapter 1: Literature Review 11 bicolorata, P. huttensis, P. convoluta, P. tearohensis, Phytomyza imporvisa, and P. [yllL Lepidoptera leaf-miners in New Zealand include the families Gracillariidae and Nepticulidae. DURA TION OF MINING Hering (1951) has pointed out that a comparison of the time required by a mining larva for its development with the duration of the larval stage of free-living insects shows that in the majority of cases mining insects have a shorter larval development than external feeders. Although details of extremely short larval stages may be based on inaccurate observation, owing to the minute, hair-like early channel being frequently overlooked, it is nevertheless a fact that the larval stage, especially in the fIrst larval generation, is often extraordinarily short. Webster and Parks (1913 cited by Hering, 1951) recorded that in an American species of Liriomyza the duration of the larva stage was four days and that the shortest time of development from oviposition until the emergence of the imago was 18 days. Similar short periods of development are found in many other miners, especially in the genus Nepticula. Two principal reasons may be adduced to explain the shortening of the larval stage by comparison with free-feeding forms. The larva of mining insects which live inside the mine and feed exclusively on mesophyll, consumes qualitatively highly nutritious food but apparently quantitatively less than free-living larvae (Crawley, 1983). It is not forced to eat quantities of indigestible food of low nutritive value like the free­ feeding larva, which in addition to the green leaf tissue with its high protein content is also compelled to eat the epidermal cells (Chapple, 1929) which are often thickened by a cuticle, as well as many strengthening elements in the leaf, such as are found in the vicinity of the vascular bundles. The mining larva can thus develop with a far smaller quantity of food; as the larval stage is essentially devoted to the consumption of food, it is naturally shortened by its abundant supply. That this is the decisive factor is shown by the fact that even in its living quarters inside the leaf the larva seeks to avoid as far as possible having to consume the more indigestible substances (Hering, 1951). Chapter 1: Literature Review 12 ADULT BIOLOGY Male and female of leaf miners usually mate more than once (Story et al., 1979). The nonn of protracted copulation is nearly 1 hour (Parella, 1987). Pre-oviposition feeding by adults can be extensive and damaging to plants-both hosts and nearby plants. It has been estimated that alfalfa blotch leaf miner (Agromyza Jrontella) females make over 3700 feeding perforations (with their ovipositor), equivalent to 1.1 cm2 per female in damage to alfalfa. Dehiscence of leaflets by adult feeding occurred when adult populations reached high levels (Hendrickson and Barth, 1978). Egg-laying has been measured for relatively few species (Askew and Shaw, 1979; Condrashoff, 1964; Martin, 1956; Miller, 1973) and depends on food resources for the adults in those cases examined. Dimetry (1971) found that different food sources affected fecundity and the oviposition period of Liriomyza congesta. Females provided honey laid more eggs over a greater period of time than females provided other food sources. Labeyrie (1957) reported that some Lepidoptera with access to water laid twice as many eggs as those denied it (mean of 84), and that adults provided with honey in addition to water laid 3 times as many eggs as those not fed (absolute maximum 336). Charlton and Allen (1981) observed that the fecundity of Liriomyza tn/olii increased greatly when given honey. They also suggested that aphid honeydew and floral nectars could increase leaf miner popUlations. Adult female L tri/olii (Burgess) lived significantly longer when confIned on tomato leaves than when confmed on glass plates and starved. Continuous exposure of adults to aphid honeydew on tomato leaflets resulted in increased fecundity of females relative to adults exposed to tomato foliage without honeydew (Zoebisch and Schuster, 1987). Most leaf mining insects lay eggs singly (e.g., Linomyza trifolii and Scaptomyza jlava) , but a few species lay eggs in a group from which the larvae will fonn a communal mine. For example Pegomya nigritarsis is a gregarious leaf-mining fly attacking Rumex and larvae from one clutch of eggs all inhabit the same mine (Godfray, 1986). Chapter 1: Literature Review 13 Total time required for development is dependent on temperature; for example for alfalfa blotch leaf-miner it is 52 days at 16.7", 36 days at 20°, 3 1 days at 22.8 ° and 27 days at 25.6°e (Parella, 1987). William and Robert ( 1978) determined median developmental rates at constant temperatures between 10° and 25°e for all immature stages of the alfalfa blotch leaf-miner Agromyza jrontella. The preoviposition period and adult male lifespan were also determined. Larval survival was maximum at 200e and minimum at lye although the developmental rates differed little between these two temperatures. The developmental rate-temperature relationship for egg period ranged from 3.5 to 12.4 days. The relationship was sigmoid for each larval instar. The total larval period ranged from 5.9 to 16.4 days. The relationship was exponential for pupae. The pupal period ranged from 15.9 to 6 1.5 days. Developmental rates for pupae under constant temperatures yielded valid simulations of adult emergence patterns under fluctuating temperature regimes in the field. Survival varies widely among different leaf miner species and depends much on feeding habits, life history and protection of young (pedigo, 1989). Insects that feed on a wide variety of food sources and protect their young to a degree have greater survival potential (Pedigo, 1989). In the latter instance, viviparous birth types generally have less mortality of newborns than oviparous birth types (S. flava is oviparous birth type). This is because the offspring are in a protected environment, inside the females, much longer than are those of oviparous species. It is now more than 40 years since Dethier (1954) remarked that "no one attractant alone performs the service of guiding an insect to its proper host-plant, food or mate, and that the desired end is achieved only by a complex array of stimuli, such as chemical, light, temperature and humidity, acting in harmony. " For many plant-feeding insects, the selection of an oviposition site is a critical stage in their choice of host. This is especially t:r:Ie when the newly hatched offspring are not capable of searching for additional hosts (e.g. leaf-miners, but see Miller and Strickler, 1984). Thus the choice of feeding site lies with the adult female. Chapter 1: Literature Review 14 Miller and Miller ( 1 986) used the term "acceptability" to describe the likelihood that a plant will be accepted if it is encountered and "suitability" to encompass the various aspects of host quality that affect insect performance. Studies of survivorship in leaf-mining insects usually means larval survivorship. Mortality of eggs is either infrequently estimated (Day and Watt, 1 989; Pottinger and LeRoux, 197 1 ; Turnbow and Franklin, 1981 cited by Hespenheide, 199 1 ), or often underestimated in death-assemblage studies (Connor, 1 988 cited by Hespenheide, 1 991), and may result from parasitoids, predation (Pottinger and LeRoux, 197 1 cited by Hespenheide, 199 1 ), or unknown causes (Pullin, 1985). Turnbow and Franklin ( 198 1 ) found that of a total of 346 eggs oviposited on 200 leaves of turkey oak (Quercus laevis) by leaf miner adults (Brachys tessellatus), only 1 3.3% hatched. The others were lost to parasitism ( 1 3%), predation (35. 1 %) and miscellaneous or undetermined causes (infertility, desiccation, thermal death, undetected parasitism, etc.) (38.5%). Unknown factors of leaf miner mortality might include bacterial, fungal, and viral diseases, host plant nutrition, and abiotic forces such as weather (Faeth and Simberloff, 1 98 1 ). Some authors (e.g., Newman and Clark, 1 929 cited by Mazanec, 1 987) speculated that bush fIres would cause high mortality of leaf miner larvae aestivating in soil (Mazanec, 1 978). Over-winter mortality is usually a combination of terrestrial predators and abiotic factors (Hespenheide, 1 991) . According to Bultman (1988), leaf-miner survival on oaks was less than expected for four of fIve species when co-occurring on leaves with conspecifics than when mining with heterospecifics or alone. The mortality factors of oak leaf miner in New Zealand are discussed in detail by Swan ( 1 973). Survival of leaf miners may be a negative function of clumping among and within leaves. Small-leaved branches and trees appear to be less susceptible to leaf miner attack because adult females deposit fewer eggs overall, and eggs are more frequently laid singly on leaves of inadequate size for development or are more frequently clumped on leaves with competing conspecillcs (Faeth, 1 99 1 ). ------------- - - - - - - - - - Chapter 1: Literature Review 15 HOST SPECIFICITY AND SPECIES DIVERSITY "Leaf-miners have generally narrow host preferences. Most are monophagous, a smaller proportion oligophagous, and only a few are polyphagous (Liriomyzidae)" (Hespenheide, 1991). Thus polyphagy is unusual among leaf-miners. In a survey of Agromyzids associated with British Umbelliferae, Lawton and Price ( 1979) found that a combination of geographic area, plant size, leaf form, and occurrence in aquatic habitats explained about 50% of the variation in size of the fauna when effect of each plant's local abundance and the number of occupied habitats within its geographic range were examined by Fowler and Lawton (1982), addition of the latter explained a total of 6 1 % of variation. Scaptomyza spp. adults have been collected from tomatoes (Berlinger et ai., 1988; Collins, 1 956), banana (Bachli, 1973), some flowers, grass, radish (Torrent, 1955), cauliflower, turnip (Frey, 1 95 1 cited by Stapel, 1961 ), cabbage (Szwejda, 1 974), endive, lettuce, spinach (Osmelak, 1 983), hedge mustard, onion, flax, cucurbits, swede (Hardy et aI. , 1 979), carrot, broccoli, garden pea, watercress, nasturtium (Holloway, 1990) and many other crops and wild plants (Singh and Bhatt, 1 988). Although the cosmopolitan genus Scaptomyza contains about 400 species or slightly over one-quarter the number of known Drosophila species, only four occur in New Zealand. The highest populations of Scaptomyza juscitarsis in New Zealand were taken from swedes (Cumber and Eyles, 1961b). Harrison ( 1959) recorded this species in association with rotting swedes, but it occurred on all types of crops studied with the exception of pampas. Its frequent occurrence in association with maize suggests that it may breed in moist materials held in leaf axils and sheaths (Scott, 1984). Scaptomyza juscitarsis Hardy was taken on 52 occasions by Cumber and Eyles ( 1961a) and is present throughout the North Island of New Zealand. In pastures leaf miner species composition is strongly related to plant species composition, but modified by plant structure under different grazing treatments. There is a strong successional trend in miner assemblies, even when the effects of changes in Chapter 1: Literature Review 1 6 plant composition have been taken into account. Conversely, local variation in miner species composition generally reflects food plant distribution alone. Grazed treatments have fewer mines than controls, but there are also species specializing in grazed areas, despite the abundance of their food plants elsewhere. There is a weak: indication that miner species in grazed treatments are more likely to fluctuate in abundance than those in ungrazed controls (Stering et ai., 1992). Opler ( 1974) showed that the number of species of leaf-mining insects on California oaks was very closely related to the geographic area occupied by the oaks. BIOGEOGRAPIDC PATTERNS OF DIVERSITY "Most basic ecological studies of leaf-miners have been carried out in temperate zone localities (England, California) or at the margins of the subtropics (Florida, Arizona), although a few economically important tropical species have also been studied. Leaf-miners are common in the tropics and it is clear that these faunas differ from those in temperate zones" (Hespenheide, 199 1 ). Within Australia, many lepidopteran leaf miner species are widely distributed both geographically and ecologically (occurring in a range of woodland and other ecosystems), with extension of their natural geographical range. Powell ( 1980) quotes Opler as having found leaf miners on half of 102 tree species in Costa Rica (Hespenheide, 1985). Although beetles are a minor component of temperate zone faunas, they are much more numerous in the tropics. Scaptomyza spp. are found everywhere (endemic). These species occur on cabbage in Poland (Michalska, 1 973; Szwejda, 1 974; and Pol, 1974) and Islamic republic of Iran (personal observations), on turnip in England (Frey, 1954) and India (Gupta, 1 970175; Gupta and Singh, 198 1 ; Kumar and Gupta, 1 992), on field and forage crops in the following places: Tasmania (Bock and Parsons, 1977), Japan (Kaneko and Tokumits, 1 969; Okada, 1973), Nepal, Taiwan, Portugal (Rochapite, 1979), Afghanistan (Hackman, 1969), Czechoslovakia (Maca, 1972), Mongolia (Okada, 1973), Italy, Algeria, Jamaica, France (Rossi and Rossi, 1979), Peru (Ramirez, 1988), Slovenia (Yugoslavia) (Macek, 1972), Egypt (Hafez and Ziady, 1970), Nearctic, Germany (Becker, 1 908; Chapter 1: Literature Review 17 Sturtevant, 1918 cited by Bachli et al., 1985) and Switzerland (Bachli, 1973,1974). They have been recorded from Canada (Torrent, 1955), Chile (Hedqvist, 1977), and collected from tomatoes in New Jersey, USA. Scaptomyza caliginosa is a species endemic to the island of Hawaii (Takada, 1970; Montague and Kaneshiro, 1982; Roger and Lewin, 1985). Scaptomyza (Bunostoma) australis Malloch is a common species widespread throughout Australia (Bock and Parsons, 1977; Rockwell and Grossfield, 1977) and most recently reported as well from Norfolk and Pitcairn Islands (South Pacific Islands) (Bock, 1986; Grimaldi, 1990). New species are described by McEvey ( 1990) from Madagascar and Mauritius; two are classified in Scaptomyza s.str. and one in the subgenus Parascaptomyza; the latter species closely resembles S.(P.) pallida Zetterstedt. Harrison ( 1959) found the grey pasture fly, Scaptomyza juscitarsis to be widespread but not abundant in the pastures of North Island of New Zealand. Its host is not known but Scaptomyza spp. (Drosophilidae) are regarded as leaf miners in grasses. Scaptomyza graminum was recorded in small numbers at three sites. This species has been also reared from brassicas. Scaptomyza flava is also widespread in Europe, Asia and North America. In the latter area it appears to be an introduction which has spread in association with cultivated members of the cabbage group' (Bock, 1977). The leaf-miner Liriomyza trifolii has been reported to cause almost near collapse of cow pea, Vigna unguiculata, crops (Jackai and Daoust, 1986) in Tanzania (Price and Dunstan, 1983; Singh and Merrett, 1980). This same species is also known to attack cow peas in the USA and in central and South America (Chalfant, 1976; Daoust et al. , 1985). In Southeast Asia this species is capable of causing significant yield reductions (Singh et aI. , 1978). A long-term survey ( 1965-1989) (Macek, 1990) showed that leaf-miners were not very widespread on cereal weeds in Slovenia and that their levels of infestation were seldom high enough to markedly injure the weeds. Leaf-mining Diptera are also recorded as damaging in Egypt (Hafez, Ziady and Dimetry, 1970). Chapter 1: Literature Review 1 8 Pest species of Agromyzidae are widely distributed throughout the world and infest many important crops. New Zealand has 41 described species of Agromyzidae in the genera Cerodontha, Hexomyza, Liriomyza, Melanagromyza ,Phytoiiriomyza, and Phytomyza (Spencer, 1976). Some species present in New Zealand are serious pests overseas, but their pest status in New Zealand is uncertain. The cosmopolitan pest Liriomyza brassicae Riley is not recorded as a significant pest in New Zealand. Appendix 2 shows some important Agromyzidae leaf miner pests. Holloway ( 1990) has pointed out that in New Zealand, different species of Scaptomyza were bred from the following plants: Scaptomyza flava: Adult flies were bred from leaves of cabbage, turnip, swede, radish, broccoli, garden pea, wild mustard, watercress, and nasturtium (Tropaeolum majus). S. elmoi: Adult flies have been reared from leaves of radish and Senecio glomeratus (previously known as Erechtites). S. juscitarsis: Adult flies were bred from leaves of broccoli and watercress and were swept from grass, carrot and swede. S. flavella: No breeding was recorded (it is represented in NZAC [New Zealand Arthropoda Collection] only by the type series from Mokohinau Is.). COMPARISON OF PLANT SPECIES AS HOSTS FOR LEAF MINERS AND HOST PLANT DEFENCE Host plant species is one factor that may influence insect behaviour and numbers of eggs laid. Host plant qUality may affect amount of adult feeding, number of eggs laid and survivorship of juvenile stages through alterations in leaf nutrition or toxins. Soluble foliar nitrogen is considered a reliable estimate of the amount of protein available to the herbivore, and therefore indicative of plant nutritional quality (for reviews, see Feeny, 1970). For a general treatment of host-seeking behaviour in phytophagous insects see Chapter 1: Literature Review 19 Ahmad and Allen ( 1983). Saxena ( 1969) pointed out that host-plant location may be essentially by random, or at least undirected, movement, so that contact with suitable plants is by chance, or by orientation in response to some perceived properties of the plant. From a distance the latter can only be by visual or chemical means (Fenemore, 1988). Each phytophagous insect species is associated with a group of plants, large or small in number, which we designate as its food-plant range. The food-plant range of some insects is often correlated with natural taxonomic plant groupings (genera or families, etc. ), but the food plants of many insects are distributed in an apparently random pattern among plants without special regard to botanical affInities. In host-plant selection insects make a number of decisions. An insect continuously evaluates the information from its surroundings, compares this impression with its own internal standards, and decides to continue or change its motor patterns (Visser, 1986). Host selection in phytophagous insects consists of a sequence of behavioral responses to an array of stimuli associated with host and nonhost plants. The oviposition step is particularly crucial in the leaf miner insects, because the hatching larvae are often relatively immobile and thus depend on the judicious choice of food plant by the adult female (Renwick and Chew, 1994). Phytophagous insects vary greatly in the number of parasitoid species they support (Price et ai., 1980). Host plant characteristics may cause much of this variability by directly or indirectly affecting herbivore vulnerability to parasitoids (price et al. , 1980). Direct effects occur when such plant characteristics as glandular leaf trichomes or gall structures (Cornell, 1990) impede parasitoid searching, or when plant odours or nectar attract parasitoids (Gross and Price, 1988). Leaf trichomes can interfere with access to the leaf surface (Ezcurra et ai., 1987). Tildenia inconspicuella (Lepidoptera: Gelechiidae) on horsenettle (Solanum carobinense) is apparently forced to be endophytic and suffers higher parasitism because of dense trichomes, whereas Tildenia georgei on ground cherry (Physalis heterophylla var iambigue) where trichomes are thin and flexible, is more vagile and can escape parasitoids (Gross and Price, 1988 cited by - - - - - - - - - -- -------------- - - - - - - Chapter 1.' Literature Review 20 Hespenheide, 1991). Three main host plants of Scaptomyza flava differ in colour, cauliflower being dark green, turnip light green and Chinese cabbage yellowish, though these terms can only be vague descriptions of the colours of plants. To describe colours more precisely requires consideration of hue, saturation, and intensity (brightness). A specific colour can attract insects to plants for oviposition (Finch, 1986; Prokopy et ai. , 1983b). Female Delia radicum flies use leaf colour to distinguish between turnip, radish and green cabbage prior to landing, preferring green cabbage (Prokopy et al., 1983b). The pattern of multi-leaved plants plays a significant role in determining landings, suggesting that the total area and colour of foliage is important to plant-seeking flies (Nottingham, 1988). Chemical properties play an important role in host plant selection. Plant chemistry is probably the most important source of information contributing to the fInal decision by a insect to oviposit or not (Renwick and Chew, 1994). One method of dealing with chemical defense might be to avoid tissues with defensive compounds and to mine cell layers without them (Feeny, 1970). However, only one of 1 8 species of leaf miners studied on oak in Florida restricted mining to cell layers low in tannin (Faeth et aI., 198 1). Cell growth in the vicinity of leaf miner eggs, encapsulation of endoparasitoids eggs, venation of leaves and abscission of mined leaves can be other host defense mechanisms (Hespenheide, 1991) . The role of competition in structuring phytophagous insect communities encompasses two distinct perspectives. Janzen ( 1973) proposed that insects that feed on plants "automatically compete with all other species" on the plant. Conversely, Lawton and Strong ( 1981) contended that " resource-based competition does not occur 'automatically' at low or even moderate levels of phytophagy", and concluded competition is relatively unimportant in structuring phytophagous insect communities. - - - - - -------------- - - - - - - Chapter 1: Literature Review 2 1 Competition between leaf-miners and externally feeding larvae may (Faeth, 1985, 1986) or may not (Hawkins, 1988) be mediated by parasitoids. Plants of Cardamine cordifolia that were experimentally stressed had increased herbivory by the leaf-miner Scaptomyza nigrita. In two other situations, one experimental (Potter and Redmond, 1989) and one natural (Auerbach and Simberloff, 1984), stressed trees experienced leaf-miner outbreaks after defoliation (Hespenheide, 199 1 ). Distribution and damage of Scaptomyza nigrita Wheeler on its host bittercress, Cardamine cordifolia A. Gray (Cruciferae), a native perennial crucifer, were examined over two growing seasons in relation to leaf position by Collinge ( 1987). Concentrations of defensive compounds (glucosinolates) and of nutritive compounds (total nitrogen, free amino acids, soluble carbohydrates) were also examined. The fly-host plant relationship was studied in sun and shade habitat at two sites. Oviposition and leaf-mining damage were concentrated on the lower central leaves of the stem in both habitats. These mature leaves had lower glucosinolate concentrations than new leaves and total insect herbivore load on bittercress was greater on sun than on shade plants (Collinge, 1987). Collinge and Louda (1988) tested the hypothesis that light intensity was the direct, proximal mechanism causing significantly higher vulnerability of bittercress clones in the sun to herbivory by S. nigrita Wheeler. Leaf-mining damage was significantly higher on artificially-shaded plants, the opposite of expectation. Shading plants shifted their growth pattern toward that of naturally-shaded plants. No significant differences were detected in leaf water status or glucosinolate concentrations, eliminating water stress and variation in defensive posture for mediating the between habitat differences in levels of herbivory. LEAF SELECTION Leaf selection is an important aspect of plant/insect interactions because, for some phytophagous insects such as leaf miners, oviposition by the adult insect determines where the larva will feed (Faeth et aL, 198 1 ). Most endophagous insects such as leaf miners cannot move to more suitable plants or leaves as many external-feeding insects can. Therefore, natural selection for oviposition should act to minimize risks - - - - - - - -- ------- -- - - - associated with host plant (and other phytophagous insects and natural enemies under field conditions). Host plant factors influencing plant quality include size and position of leaves, nutritional and defensive chemistry, physical barriers, and phenological changes (e.g., qualitative seasonal changes in leaves or leaf abscission) . Previous or concurrent feeding by other phytophages may alter physical and chemical aspects of the leaf or reduce leaf size so that insufficient area remains for development. Finally, attack by predators and parasitoids may render certain leaves less suitable for oviposition and development if search for hosts on different leaf types is nonrandom (Schultz, 1983). Many folivorous insects prefer young leaves over mature ones when both resources are simultaneously available (Cates, 1980; Fowler and Lawton, 1982). Other phytophages completely restrict feeding to young leaves (Feeny, 1970; Rockwood, 1974; Auerbach and Strong, 1981). This pattern is related to the generally higher food quality of young leaves (potter, 1989). This restriction can be imposed by synchrony between bud break and termination of diapause (Feeny, 1970), or chemosensory cues can lead to oviposition preference or avoidance of mature leaves (Auerbach and Strong, 1981; Faeth et ai., 1981a). Chemical and physical differences between young and mature leaves presumably form much of the basis for leaf-age preferences among phytophagous insects. Young leaves generally have higher protein, amino acid and water concentrations and are less tough than mature leaves (Scriber and Slansky, 1981). Morphological differences between young and mature leaves also may impose selective pressures determining leaf­ age preferences. Young rolled leaves of Heliconia protect Hispine beetle larvae from most parasitoids and predators (Auerbach, 1982). Larvae of four species of leaf-mining Lepidoptera commonly found on water oak, Quercus nigra (L), restrict feeding to young leaves. Two of the phenologically restricted leaf-mining species feed only on supple, first-flush leaves produced in March and April. Peripheral leaves may be more heavily mined than interior ones (Simberloff and Stiling, 1987). The dispersion of mines among leaves is often aggregated rather than uniform, but this varies among species (McNeil and Quiring, 1983). ------- - - - Chapter 1: Literature Review 23 "Leaf size may not influence but usually does; smaller leaves are preferred by smaller species, or larger leaves are simply preferred (Bultman and Faeth, 1986 cited by Hespenheide, 1991) . Large leaves may increase the probability of survival of single larvae, but may also increase the density of mines; communal mines have been suggested to be an adaptation for exploiting larger leaves " (Hespenheide, 1991) . Tuomi et al. ( 1981) demonstrated that leaf miners on multiply-mined leaves occupy large leaves and that larval mass is a negative function of the number of mines per leaf. Leaf size selection by endophagous insects may only become important when densities are sufficiently high that insects are forced to occupy leaves with other insects or when an individual insect requires large portions of a leaf for development. Stilbasis juvantis did not select leaves different in size from those available for colonization on individual trees (Faeth, 1985). However, larval weights may vary considerably among individuals utilizing the same leaf (petitt and Wietlisbach, 1992). Zucker ( 1982) has shown an inverse relationship between leaf size and concentrations of phenolics in narrow leaf cottonwood. Choosing the correct leaf is particularly crucial when an insect is confined to a single leaf for a majority of its lifetime as are leaf miners (Hering, 195 1). If large leaves are superior we would expect them to be preferentially selected for oviposition (Tuomi et aI., 198 1 ). Leaves chosen for oviposition by leaf miners are usually undamaged and may be either younger (4 of 18 species) or older ( 14 of 18 species) (Godfray, 1984). Stilbosis juvantis selected intact leaves over damaged leaves for oviposition (Faeth, 1985). Of 141 mines observed, the expected distribution, based on 55% leaves damaged and 45% undamaged for all trees ( 1 8 oak trees, Quercus emoryi), is 75.5 mines on damaged and 63.5 on intact leaves; the observed distribution was significantly different (Faeth et at. , 198 1) . Successful emergence was greater for S. juvantis on intact leaves (70.2%) than on damaged leaves (5 1 .4%). Stilbosis juvantis on damaged leaves experienced significantly lower survivorship, owing to increased parasitism, than did miners on intact leaves (Faeth, 1985). Chapter 1: Literature Review 24 "Mines may be more frequent toward the base of the leaf or toward the apex or be randomly distributed (Gross and Price, 1988). When more than two mines occur on a leaf, they are often on opposite sides of the midvein (Auerbach and Simberloff, 1984). Mines may be superficial or full-depth, and the two sides of a leaf may serve as discrete habitats for superficial miners (Connor, 1984). Mines of different species may co-occur on leaves more frequently than expected by chance without apparent competition, perhaps because of preferences for different portions of the leaf' (Hespenheide, 199 1 ). Mining larvae in many cases retain throughout their life the same type of mine and in this way feed consistently only in upper surface or in lower surface mines. In other cases, however, larvae change the type of mine on one or more occasions (Nielsen, 1978). Such changes in feeding behaviour frequently occur after completing a moult and often run parallel to changes in the structure of the mouthparts, which are now adapted to a different type of food (Martens and Trumble, 1987). There are many linear mining dipterous larvae which initially live on the under­ side of the leaf in the spongy parenchyma, later continuing their channel in the palisade parenchyma on the upper-side, and then often transfer the last part of the channel back to the under-side, where they can pupate in a less exposed position (Parella, 1987). Such a double change of the side of the leaf can be frequently observed in the polyphagous Phytomyza atriconis Mg. The change from a linear mining to a blotch mining existence can also often be found to be related to moulting. The depth of the mine in the leaf tissue is also subject to remarkable variations during the course of a larva's life. In general the type of depth with which feeding commences is retained throughout. What starts as a full depth mine does not later become upper surface or under surface, and vice versa. However, a few exceptions do exist. The initial channel of Philophylla heraclei L., for instance, is normally a full depth mine on the leaves of Umbelliferae, the subsequent blotch on the other hand is upper surface and greenish (Fig. 1.12) (Hering, 195 1 ). - - -------------------- - - - Chapter 1: Literature Review 25 Sometimes mines have a distribution among leaves (Heads and Lawton, 1983). However, mine placement within leaves frequently is non-random because of either preference for certain leaf locations or avoidance of conspecific eggs. Selective pressures should result in females ovipositing in leaves which promote increased larval development and survival (Mitchell, 1975; Larsson et al., 1986 cited by Colling and Louda, 1988). Therefore, larval occurrence and damage should reflect qualitative and quantitative differences in leaf quality detectable by the ovipositing female (Chew, 1977; Rausher, 1979 cited by Colling and Louda, 1988). Adult females of some leaf-mining species appear to sample plant qUality. For example, agromyzid females puncture holes in the leaf cells with their ovipositor and then "test" the sap (Hering, 195 1); it is not clear whether they are merely sampling the leaf tissue or are actually feeding. However, mandibular chemoreceptors exist in many insect species, including dipteran crucivores that feed on plants, which are sensitive to characteristic host plant chemicals and primary nutrients (Chapman, 1982). LEAF ABSCISSION The importance of leaf abscission in the popUlation dynamics of insects was fIrst recognized by Clark ( 1962) for psyliids, and later by Owen (1978) and Faeth et ai., ( 198 1 ) for leaf-mining and other sessile insects. They studied a number of species of dipteran, lepidopteran and coleopteran leaf miners whose development is restricted to a single leaf, and reasoned that for leaf-mining insects early leaf fall will most likely lead to mortality unless the larvae is near pupation, or has pupated (Connor, et al. 1994). Recent studies by Preszler and Price ( 1993) showed that premature leaf abscission has a strong negative impact on some endophagous insects (e.g., leaf miners) while others, which nearly complete feeding by the time of early leaf abscission, do not suffer increased mortality in abscised leaves. They investigated the causal relationship between leaf mining and leaf abscission by experimentally isolating the effect of leaf mining on leaf abscission. They concluded that: (i) Early abscission of mined leaves is - - - - ---------------- Chapter 1: Literature Review 26 an important mortality factor for some leaf miners (e.g., Phyllonorycter species). Phyllonorycter survival was greatly reduced in these abscised leaves. (ii) Leaf-mining by Phyllonorycter was associated with increased early leaf abscission. An egg removal experiment demonstrated that leaf mining induced an increase in leaf abscission. (iii) The induction of early leaf abscission was dependent upon the timing of herbivory and simulated herbivory (mechanical damage). Early mechanical damage induced leaf abscission, late mechanical damage did not. Mines which expanded early were more likely to induce leaf abscission than mines which expanded more slowly. Circumstantial evidence strongly suggests that Dipteran and Lepidopteran leaf miners can induce early leaf abscission on a variety of woody plants (e.g., Faeth et aI., 198 1 ; Maier, 1982; Owen, 1978). Other reports show early abscission of mined leaves to be a major mortality factor for some leaf miners (Owen, 1978; Askew and Shaw, 1979; Faeth et aI., 198 1 ; Potter, 1985 cited by Simberloff and Stiling, 1987), though Pritchard and James ( 1984a) found for two Phyilonorycter species that abscission causes <3% of larval death. Kahn and Cornell ( 1989) argued that leaf abscission may not increase mortality of leaf miners for two reasons. One reason for lack of a nagative effect was that leaves were not dropped until mines had pupated in the leaf. Second, some leaf miners form "green islands" of healthy tissue around themselves when the leaf falls. Engelbrecht et al. ( 1986 cited by Simberloff and Stiling, 1987) suggested such islands may be generated by high cytokinin levels. Faeth (1986) reported green islands for Stilbosis juvantis on emory oak, but Simberloff and Stiling ( 1987) have found none for S. quadricustatella. Kahn and Cornell ( 1989) also argued that, because some parasitoids do not search the ground, a miner might be better off there. Faeth et ai. ( 1986) showed that mined leaves abscised significantly earlier in three oak species and constituted one third of the mortality of two species of miners. Most researchers believe that abscission is a general response to damage and not an attempt to adjust miner numbers (pritchard and James, 1984). The clumping of mines by Stilbosis larvae seems to increase the likelihood of early abscission. This increase appears to be due to the clumping and not to the type of leaves -- - - -- - - - - ------- -- - - Chapter 1,' Literature Review 27 chosen. When the leaf abscises early, miners are likely to die; this is the greatest source of larval mortality. Stiling et al. ( 1984) state that premature leaf fall is by far the largest source of larval mortality in Hydrellia valida (Diptera: Ephydridae). Auerbach and Simberloff ( 1989) noticed that dominant sources of larval mortality of a leaf-mining moth on aspen (Quercus calliprinos) leaves were premature leaf abscission and death from unknown causes. Abscission timing determines the effect on herbivore demography. The amount of early abscission is affected by extent of injury, the timing of damage or both (Maier, 1989). When miners in an abscised leaf of oak were very near to pupation, abscission killed them (Simberloff and Stiling, 1987). Delayed (4 to 5 months) post-hatch development of larval Phytomyza iUcis synchronizes adult emergence with leaf flush and postpones early leaf abscission of infested leaves (James and Pritchard, 1988). Leaflets mined by a single larva of Agromyza jrontella in third-cutting alfalfa abscised an average of 1 2.9 days after the larva emerged from the leaflet to pupate in the soil. Abscission of mined leaflets was detectable in fust and second cutting alfalfa only if harvest was delayed at least 10 days (Hendrickson and Dysart, 1983). Fourth-instar larvae of Coptodisca on Vaccinium had 90% survival from abscised leaves (Maier, 1989), and for the univoltine leaf-mining moth, Lithocolletis quercus on Quercus calliprinos (Auerbach and Simberloff, 1988), leaves on vegetative shoots abscised significantly earlier if mined than if unmined. Hendrickson and Barth ( 1978) reported that mined leaflets tended to abscise more rapidly than unmined leaflets on potted alfalfa maintained in rearing rooms. I observed the same phenomenon with Chinese cabbage, turnip and cauliflower in the field and under greenhouse conditions. Faeth (1991 ) showed that leaf abscission rates are greater in unshaded leaves compared to shade leaves and this can explain some variation in larval distribution and Chapter 1: Literature Review 28 mortality. Others (Askew and Shaw, 1979; Faeth et al. , 198 1 ; Potter, 1985; Stiling et al., 1 984; Auerbach and Simberloff, 1989) have shown that premature leaf abscission reduces survival of leaf miners. High rates of premature leaf abscission for unshaded leaves (Bultman and Faeth, 1986) may contribute partly to lower densities in this region if females also select leaves based on their propensity to abscise (leaves were censused for densities before most premature abscission associated with mining occurs so differential leaf abscission cannot account for differences in densities). However, unshaded leaves are typically smaller than shade leaves in Emory oak trees. INTER - INTRASPECIFIC COMPETITION Interspecific competition is unlikely without intraspecific competition (Strong et al., 1984). Over the last several years ecologists have questioned the importance of competition, particularly in phytophagous insect communities (Rathke, 1976; Bultman and Faeth, 1985). Cases in which insects do compete often involve sedentary insects which feed on discrete patches of food for extended periods of time. For example, competition was documented for eight species of leatbopper on American sycamore (McClure and Price, 1975) and for two leatbopper species on stinging nettles (Stiling, 1980). Sedentary insects, such as leaf miners, may experience food or space limitation if putative competitors are in the same food patch. Most leaf-mining insects feed on single leaves for the entire larval stage. Hence, competition seems more likely between leaf miners than between more mobile insects, which can move within and between plants while foraging. For phytophagous insects, experimental field studies demonstrating intraspecific competition at natural densities are few. By experimentally caging individual sycamore leaves, McClure and Price ( 1975) showed intraspecific competition in several species of the leaf hopper genus Erythroneura. For leaf miners, however, Faeth and Simberloff ( 198 1 ) contend that natural enemies, particularly hymenopteran parasites, keep populations far below levels at which intraspecific competition occurs. Chapter 1: Literature Review 29 Two major forms of intraspecific competitive interactions have been described. Scramble (Nicholson, 1954 cited by Quiring and McNeil, 1983) or exploitation (Birch, 1957; Miller, 1967 cited by Quiring and McNeil, 1983) competition occurs when individuals do not interact aggressively but compete for the use of a limiting resource. Interference competition denotes interactions that limit access to a necessary resource or requirement. In its most extreme form this results in contest competition where there is a winner, which obtains as much of the governing requisites as it needs for survival and reproduction, and a loser which does not (Quiring and McNeil, 1983). "Intraspecific competition can either take the form of cannibalism, in which one larva kills a conspecific that occurs with it in a mine (interference competition), or of preempting the conspecific's use of the leaf by mining it fIrst (exploitation [starvation] competition)" (Hespenheide, 199 1). A form of larval interference competition, by the production of chemicals affecting conspecific, has been suggested for several Drosophila species, concurrent with exploitation competition for the available resources (Neilson, 1968; Quiring and McNeil, 1983). Competition among members of the same species is frequently observed in nature (Fox, 1975; Polis, 198 1 ; Inove, 19834; Persson, 1983; Stiling et al., 1984 cited by Dohse and McNeil, 1988). Intraspecific competition depends on the presence of at least two mines in a leaf and then on either large numbers of mines (Wallace, 1970) or large mines relative to the size of the leaf (Guppy, 1981 ). It may not occur at all when densities of mines are low, or be relatively minor as a source of mortality (Askew and Shaw, 1979). Martin (1956) has pointed out that in larva-larva competition, attacks were provoked by the introduction of larvae into tenanted mines, and the results were observed. The fust larva to sense the presence of the other immediately attacked and killed it by tearing a hole in the central portion of the abdomen and consuming the body fluids. The larva on the defensive did not, as a rule, put up much resistance. The size of the larva involved did not seem to have any bearing on the outcome of the struggle, the smallest individual often being the victor. In the fust and second instars, the bodies of the dead larvae were usually moved to the frass pile, whereas in the third instar they were moved to the margin of the mine (Martin, 1956). - - ------------ Chapter 1: Literature Review 30 In the aspen blotch miners, larval competition occurs only in the fIrst three instars (Martin, 1956). Competition between larvae of similar age of Agromyzajrontella, second instar larvae are very aggressive, active cannibals while third instar larvae generally do not attack each other (Quiring and McNeil, 1984). When interactions between third instars occur, they only last a few seconds and do not result in death. Thus it appears that third instar larval behaviour changes depending on the size (or behaviour) of the opponent, while the fIrst and second instar larvae attack any individual encountered. Although interspecillc competition of phytophagous arthropods may be rare, intraspecillc competition could be important in maintaining individual populations at levels below which interspecifIc competition would occur (Faeth and Simberloff, 198 1 ). Experimental field studies demonstrating intraspecillc competition of phytophagous insects at densities usually found in nature are few. McClure and Price ( 1 975) showed that populations of leaf hoppers can compete both intra- and interspecillcally during certain times of the growing season, although not to the extent of excluding any species. Stiling ( 1980) demonstrated that field populations of leaf hoppers on stinging nettles could reach densities where intra- and interspecillc competition occurred. In both examples intraspecillc competition was deemed to be greater than interspecillc competition. Exploitation competition depends on multiple mines in a leaf as well as their size and distribution on the leaf. In the field confluent mines of Labdia occurred on 17% of multiply mined Acacia phyllodes and on less than 8% of all mined phyllodes (New, 1979). Although multiple mines are readily induced in the laboratory, most field samples have few mines per phyllode and the incidence of confluent mines is low. "Interference" between larvae is thus likely to be relatively rare, as is food shortage; the completed larval mine may comprise only a small proportion of available phyllode area, the incidence of "untenable" oviposition is thus low (New, 1979). As many as 2 1 0 mines of Perditha can occur on jarrah leaves; 64 insects matured in one leaf with 178 mines, but the usual maximum is 40-60 (Wallace, 1 970). Some leaves were mined so intensely Chapter 1: Literature Review 3 1 that no larvae matured and the leaf was totally consumed. If the number of mines per leaf increases, either survival (Guppy, 198 1 ) or pupal weight (Bultman and Faeth, 1 986) or both decrease (Stiling et ai. , 1984). Guppy ( 1 98 1 ) noted that survival of the larvae of alfalfa blotch leaf miner was higher in leaflets with solitary mines than in those with multiple mines; only 25% of the leaflets with two mines gave rise to two mature larvae; three larvae seldom survived in a single leaflet. Success in contest competition depends upon superior combative abilities while exploitation competition requires rapid accumulation of the limiting resource and (or) a lower minimal mass required for survival (Quiring and McNeil, 1983). Field studies on lepidopterous leaf miners have found intraspecific competition to be of minor importance (Dye, 1982), but in some Diptera leaf miners (alfalfa blotch leaf miner) intraspecific competition is a major mortality factor, both in laboratory and field conditions (Quiring and McNeil, 1983). Interference (cannibalism) reportedly occurs in several species other than Agromyza Jrontella (Diptera: Agromyzidae), although it has been reported not to occur in some species (Simberloff and Stiling, 1987 cited by Hespenheide, 1 99 1 ). Swan ( 1 973) considered that cannibalism is an important mortality factor in high infestation of oak leaf miner (Phyllonorycter messaniella) in New Zealand. Overall mortality from cannibalism was 1 1 % for Phyllonorycter on apple in Japan and increased with larval density to nearly 50% for approximately 25 larvae/leaf (Sekita and Yamada, 1979). Larval mortality owing to interference competition (cannibalism) among similarly aged larvae of the alfalfa blotch leaf miner, Agromyza Jrontella during the first two larval instars, and exploitation (starvation) competition during the third and fmal instar, increase in density-dependent manner. Larval competition caused 53% mortality of Lithocolletis salicifoliella on Phyllonorycter tremuloides (Martin, 1 956). The effect of competition among same-aged larvae of the vegetable leaf-miner Liriomyza sativae Blanchard was investigated by Petitt and Wietlisbach ( 1 992) in laboratory studies over a range of densities from 0. 1 to 2.9 larvae per cm2 of lima bean primary leaf area. Both exploitative and interference competition occurred among larvae. Cannibalism was observed primarily between first or second - ------------- Chapter 1.' Literature Review 32 ins tars , and was not density-dependent at < 1.0 fIrst instars per cm2• Exploitative competition occurred between third instars at higher densities. Greater mortality of oak: leaf miners in high-density treatments resulted from increased mortality of miners on singly mined leaves compared to those on singly mined leaves in low-density treatments (Bultman and Faeth, 1986). Larval mortality owing to interference (cannibalism) during the fIrst two larval instars, increased in a density­ dependent manner. Pre pupal and pupal mortality increased and pupal weight decreased as larval density increased (Bultman and Faeth, 1986). Quiring and McNeil (1984) have pointed out that in some species, adults of Agromyza frontella (Diptera: Agromyzidae) will cannibalize younger individuals. When two larval mines of Lithocolletis salicifoliella (Lepidoptera: Gracillaridae) coalesced, one larva attacked and killed the other. In rare cases, the coalescence of mines resulted in the death of all larvae concerned (Marten and Trumble, 1987) . There is little supporting evidence that competition increases larval susceptibility to parasitoids. NATURAL ENEMIES OF LEAF-MINERS InterspecifIc competition is comparatively uncommon because many populations are kept rare, relative to the availability of potentially limiting resources, by the impact of natural enemies-insect parasitoids, insect predators, birds, pathogens, etc. Hence the major processes acting in many conite work vertically through the food chain, not horizontally with other pecies in the same trophic level. (Strong et al., 1984). The effects of natural enemies are much more important than intraspecific competition by a ratio of at least 2: 1 . PARASITOIDS The foraging behaviour of parasitoids is the subject of numerous studies because of the direct link between successful searching and parasitism (see Casas, 1989) Parasitoids of leaf-miners are much more easily studied because leaf-miners are Chapter 1: Literature Review ------ -- - 33 relatively immobile compared to external feeders and are more conspicuous than other endophytic forms such as gall-makers. Possible adaptations for the leaf mining habit include avoidance of digestibility-reducing compounds in certain leaf tissues (Feeny, 1970), protection from desiccation during dry periods (Hering, 195 1) , and reduction of predation and parasitism by concealment within the leaf (Faeth, 1980). There is, however, little experimental evidence demonstrating that the leaf-mining habit is indeed adaptive in any of these respects. To the contrary, there is evidence, at least in regard to reducing predation, that leaf mining is not particularly advantageous. When leaf miner densities are high parasitoids may be an important source of mortality. Parasitoids may kill leaf-miners by oviposition and subsequent feeding by the parasitoid larva, as well as by feeding of the adult parasitoid on the larval host. The principal enemies of leaf miner insects are undoubtedly parasitic Hymenoptera, which penetrate the mines with their eggs placed in or on the bodies of the mining larvae. They also destroy many larvae merely by feeding on their body fluids. These Hymenoptera belong mostly to the Chalcidoidea, especially the family Eulophidae, with Ichneumonoidea being generally much less strongly represented (Askew and Shaw, 1974). Host feeding by adults is difficult to separate from plant antibiosis (Askew and Shaw, 1979 cf West, 1985), but has been observed or measured in the field or in laboratory studies and at times appears to be a more frequent cause of host death than oviposition (Simberloff and Stiling, 1987 cited by Hespenheide, 1991 ). Egg parasitoids of leaf-miners have been little studied, although a number of parasitoid taxa are involved and host mortality rates can be high. Mymarids have been reared from eggs of the Buprestid genus Taphrocerus, and up to 70% of Taphrocerus eggs are parasitized toward the close of the season (Claridge and Wilson, 1982). Two species of Eulophidae were reared from B. tessellatus on oak and 13% of eggs were parasitized. Other egg parasitoids have been reared from PachyscheZus psychotriae and emergence holes have been seen in eggs of Hispine beetles. Swan (1973) compared the levels of oak leaf miner infestation in Nelson (New - --------------- -- Chapter 1,' Literature Review 34 Zealand) and found that the nwnber of mines per leaf on Quercus robur had declined from more than 40 mines per leaf prior to the release of parasitoids, to around 2.3 miner per leaf in 1 969- 1 970. In an analysis of the parasitoids of leaf-miners of British deciduous trees, Askew and Shaw ( 1 979) found that most belonged to three subfamilies of the Eulophidae, with a fourth Eulophidae subfamily parasitizing weevils and pteromalids parasiting agromyzids. There are fewer ichneumonid than braconid parasites of leaf-miners, perhaps because leaf-miners are too small to be exploited by the relatively larger Ichnewnonids (Shaw and Askew, 1976). A broader perspective both in tenns of geography and in host taxa would lengthen the list of parasitoid taxa (Marten and Trumble, 1987). Braconids are often important parasitoids (Mair, 1989; Goppy et al. , 1 988), as are pteromalids and chalcidids on tropical Buprestidae and Hispines as well as tachinids on Hispinae (Hespenheide, 1 99 1 ). Twenty-one species of parasites were reared from natural populations of the chrysanthemum leaf-miner, Chromatomyia syngenesiae Hardy (Diptera: Agromyzidae), 1 5 endoparasites and 7 ectoparasites. The rank order of importance of the parasites on Sonchus spp. and Senecio spp. was significantly correlated (Cornelius and Godfray, 1 984). There is little supporting evidence that competition increases larval susceptibility to parasitoids (Osmelak, 1 983). Foraging behaviour of parasitoids has received some attention. In the field, mines are detected in flight, apparently visually, although the mode of distinguishing suitable plant hosts is unknown. Laboratory experiments suggest plant hosts are located chemically, mines by vision, and feeding larvae by sound (Sugimoto and Ishii, 1 979 and references therein). Parasitoids might mediate competition between miners and externally feeding herbivores by being attracted to damaged leaves (Faeth et ai. , 1979, 1980), but experimental damage had no effect on parasitism (Hawkins, 1990). Oviposition in or feeding on the host is influenced by host density (Sugimoto and Ishii, 1979). Parasitoid longevity and rates of foraging, oviposition, and �ost feeding have been shown in the field (Bultman and Faeth, 1985) or experimentally to be temperature dependent (Sugimoto and Ishii, 1979). - -------------- Chapter 1: Literature Review 35 Relatively little attention has been paid to the potential influence of mine morphology on susceptibility to parasitism. The observation that Eulophids parasitizing tentifonn miners have longer ovipositors than those parasitizing other types of mines suggests tentifonn mines may be a defense against parasitoids. Unusual larval refuges have been observed in several tropical Hispines that may reduce parasitism. Notable examples of biological control of leaf-mining herbivores have been achieved for the Hispines Promecotheca coeruleipennis and Promecotheca cumingi on coconut Cocos nucifera in Fij i and Sri Lanka, respectively, as well as for Agromyza frontella in the United States (Drea and Hendrickson, 1986). The braconid parasitoid Opius dis situs Muesebeck is reared and released at the Land, EPCOT Centre, Florida, to reduce damage caused by Liriomyza sativae (Petitt, 1988). crnc (Commonwealth Institute of Biological Control) began a survey of parasitoids of Scaptomyza spp. in Pakistan in March 1 97 1 but found none [DSIR (Department of Scientific and Industrial Research) fIles]. In some studies rates of parasitism are higher later in the season (Gross, 1988; Miller, 1 973 and Wallace, 1970), while, in others, they have been higher on the fIrst than on the second host generation (Askew and Shaw, 1 979; Maier, 1982), although either overall mortality was greater in the second generation (Askew and Shaw, 1979) or parasitism was higher again in the third generation. Rates of parasitism have been shown to vary with leaf size (Connor, 1984). Also this rate in some cases was dependent on density and in other cases density independent (Heads and Lawton, 1983; Sekita and Yamada, 1979). Rearing records are presented by Shaw and Askew ( 1 976) for 14 species of Braconidae and 13 species of lchneumonidae from leaf-miners of the orders Lepidoptera, Hymenoptera and Coleoptera in England. Braconids were more abundant and specialised than Ichneumonids in the parasite faunas of leaf-miners on both deciduous trees and low-growing plants. Although seldom comprising a major element in the parasite Chapter 1: Literature Review 36 complex on deciduous trees, braconids were sometimes numerically the dominant parasites on low-growing plants. Moderate to heavy infestations of Liriomyza munda and L pictella (Diptera: Agromyzidae) were sustained in alfalfa during the hot summer months, late July to early October, in the Sacramento and San Joaquin Valleys, California. L pictella is more numerous during the early part of the growing season, L. munda during the hotter months. Parasites destroy most of the immature stages of the two species from April to June. Parasitization drops to less than 50% from July to September but increases slightly in autumn (Jensen and Koehler, 1970). Some species of Stigmatomyces (Ascomycetes) are parasitic on some Dipterous leaf miner, for example: S. scaptomyzae on Scaptomyza spp. in the USA, Venezuela, France and Poland (Watt, 1923 cited by McGregor, 1989). Dacnusa scaptomyza (Hymenoptera: Ichneumonidae), parasitises the dipterous leaf-miner Scaptomyzajlaveola (Valentine, 1967). Scaptomyzella flava is parasitised by Dacnusa temula and Pleurotropis jlavis (Valentine, 1967). A number of Hymenoptera have also been reared from dipterous pupae. These include Phaenocarpa (Asobara) persimilis Papp (Braconidae: Alysiinae) and two Chalcids, Hemiptrasenus semialbiclava Girault (Eulophidae) and Trigonogastrella sp. (pteromalidae) (Spencer, 1 976). Many Chalcids and Ichneumonids are recorded parasitizing Agromyzidae, and under nonnal conditions population control is effected by these natural enemies, which are undoubtedly major factors in maintaining population equilibrium (Szwejda, 1974). Biological control of alfalfa blotch leaf-miner Agromyzajrontella, was attained in 1 98 1 in Delaware by using the exotic parasite species Dacnusa dryas (Hymenoptera: Braconidae), and Chrysocharis punctifacies (Hymenoptera: Eulophidae), which were released at two Newark fields in 1977 and became established in 1978. During the pre-establishment period, parasitism in the first cutting was 1 8% by native parasites; yearly maximum number of mines per stem in first cutting was 1 0 to 25. In 198 1 , imported and native parasites produced 7 1 % parasitism and reduced host populations to an average maximum of two mines per stem (Hendrickson and Barth, 1978). Chapter 1: Literature Review 37 In New Zealand two species of Hymenoptera have been recorded as parasitizing Chromatomyia syngenesiae before introductions for biological control began. These were Chrysocharis sp. (Eulophidae) probably C. pubicomis [DSIR (Department of Scientific and Industrial Research) ftles] and Dacnusa areolaris Nees (Braconidae). Watt ( 1 923 cited by McGregor, 1989) recorded 90% parasitism of Chromatomyia syngenesiae larvae but did not identify the species and Kelsey (1937) claimed that 40-65% parasitism of C. syngenesiae was normal. This parasitoid was presumably D. aerolaris. Hemiptarsenus sp. (Eulophidae) has also been recorded from Cerodontha australis (Valentine, 1967). This was probably Hemiptarsenus semialbiclavus. Cumber and Eyles (196 1 ) recorded Hemiptarsenus sp. associated with various crops including brassicas. Diglyphus isaea Walker (Eulophidae) apparently established in New Zealand on C. syngenesiae before its introduction for leaf-miner control (McGregor, 1989). Parasitoids already present in New Zealand may restrict populations of potentially damaging agromyzid leaf miners. McGregor ( 1989) concluded that further biological control attempts for Agromyzidae are not warranted. First priority for leaf-miners on brassicas in New Zealand must be identification of the insects and the extent of their damage (Pearson and Goldson, 1980). PREDATORS The effectiveness of natural enemies of arthropods can be directly influenced by morphological characteristics of the host plant or secondary plant compounds (Vinson, 1 976). Plants may also affect natural enemies of arthropods through induced physiological modifications of the host or prey which render them either more or less suitable for predation (Moraes and McMurtry, 1987). The major vertebrate predators of leaf miners are probably birds (Hering, 195 1 ) , which are frequently observed on isolated trees (Faeth and Simberloff, 198 1) . Faeth (1980) considered predation on leaf miners to be energetically feasible for birds when at least 10% of the leaves were mined. For large predators, searching for and opening leaf mines when they are at low densities would seem energetically prohibitive because of the small size of leaf miners relative to those - �----------------------- --- Chapter 1: Literature Review 38 of most external feeding insects. Although it seems that leaf mining larvae might be a more suitable food item for invertebrate predators, there have been only a few accounts of invertebrates other than ants, hemipterans, lacewings and mites feeding upon leaf miners. Some birds particularly titmice, are known to peck open leaf mines, and predacious Hemiptera sometimes feed upon the larvae through the leaf epidermis. It is likely, however, that leaf mining larvae suffer much less than exposed phytophagous larvae from predator attack (Askew and Shaw, 1974). Observations of ants preying upon leaf miners in temperate zones are rare (Hering, 195 1). But according to Faeth ( 1980b) certain ant species are important invertebrate predators of leaf miners and are commonly found in agriCUltural fields. All stages of the jarrah leaf miner are eaten by predators. A small number of eggs, usually at sites of high leaf miner population density, were eaten by an unidentified predator, probably a mite (Mazanec, 1987). Predation on leaf mining larvae by non-arthropods is recognised by torn, empty mines. the general pattern is illustrated by the numbers of larvae eaten by birds. In the study by Mazanec ( 1987) the numbers of larvae eaten amounted to 32.7% of total. Predation by birds depends on the leaf miner occurring at the canopy levels they exploit. Unlike the parasitoids, the avian predators tend to attack only the large larvae. They consumed the highest number of jarrah leaf miner larvae, but caused the lowest percentage of mortality (Mazanec, 1987). Spraying with dieldrin on sweet potato for weevil control had an adverse effect on parasitisation (Hinckley 1963), and he attributed the subsequent outbreaks of two species of lepidopteran leaf-miners to elimination of ant predation. An inverse relationship between predation by Parus and density of Phytomyza might result from the difference in scale between the foraging of the larger bird and the dispersion of the smaller mines, rather than to numbers of prickles (Heads and Lawton, 1983). ltamies and Ojanen ( 1977 cited by Hespenheide, 199 1), on the other hand, found Chapter 1: Literature Review 39 that leaves of Alnus with greater numbers of mines of Lithocolletis spp. had higher predation rates by Parus spp. They also suggested that the birds preferred full size mines and thus avoided parasitized larvae that were smaller, and consequently had a greater influence on the populations of the moths. Parus species also prey on Rhynchaenus larvae (Pullin, 1985). Larvae of Perthida were found in the stomachs of 9 species of birds. Mazanec ( 1 985) has shown that large larvae of Perthida glyphopa were the most preyed upon (33%) by 9 species of birds at intermediate population densities. At high popUlation density, 3 species of ants collected some 30% of the fallen mature larvae and a further 2 1 % were eaten by earwigs, Carabid beetles and ants during summer aestivation. The importance of predators on Phyllonorycter messaniella (oak: leaf miner) in New Zealand is unknown, but a number are known to attack P. blancardella in Canada (Thomas and Hill, 1989). Although studies of leaf-miner mortality have concentrated on larvae, adults are also susceptible to predation and have evolved antipredator defense. Hispine chrysomelids are often involved in mimicry complexes, usually with beetles in the Lycidae or Lampyridae (Bale, 198 1) , that are probably Mullerian in character. Leaf­ mining Buprestidae of the genera Taphrocerus and Leiopleura have been hypothesized to mimic flies (Hendrickson and Plummer, 1983). ABIOTIC MORTALITY FACTORS Weather conditions (temperature, precipitation, wind) have been postulated to be the most important overall cause of dramatic changes in pest abundance in ecosystems. Weather may directly influence the physiology (e.g., developmental rate and water regulation) or behaviour (e.g., locomotion, orientation and dispersal) of an insect, and/or indirectly affect the insect population through its effect upon the host plant and natural enemies (Nestel, et al., 1994). Indirect effects of temperature and/or precipitation upon the population of the leaf-miner are less clear. It has been argued that climatic events can induce insect Chapter 1: Literature Review -- --�------- - - - 40 outbreaks by decoupling the relationship between parasitoids and hosts (Risch, 1987). Climatic stress may increase the availability of nitrogen in the host plant, making the tissue more palatable to the herbivore, and/or disrupt the plant chemical defence. In the case of meristematic feeders (leaf miner), this mechanism may be more important than the direct effect of weather in the regulation of the insect population (Nestel et al. , 1994). Temperature is a key environmental factor determining the duration of survival and life stage of insects (Adler, 1987; McCreadie and Colbo, 1 990). The time that an organism can survive at a temperature can be related to such factors as duration of exposure, external or internal (e.g. , leaf miners) activities, and acclimation or hardening (Baust, 1 982). Abiotic mortality factors include the coincidence factors in which cool weather delays larval development as the leaf matures. Freezing injury can encourage leaf miner outbreaks by inducing an abundance of soft, protein rich young leaves late in the adult activity period, when availability of vulnerable leaves becomes limited. However, frost caused some overwintering pupae of apple leaf miner to die (potter and Redmond, 1 989). The action of wind or rain weakens and opens mines and could be a mortality factor (pullin, 1985); this may especially be a problem in the wet tropics. The coffee leaf miner Leucoptera Coffeella Guerin-Meneville (Lepidoptera: Lyonetiidae) population increased significantly during the period of intermediate temperature and low precipitation. Elevation also affected the population load of the insect: leaf miner populations were larger at low elevations (where temperatures are high and precipitation low) than at high elevations (Nestel et aI., 1 994). Duration of each stage of the alfalfa blotch leaf-miner, Agromyza jrontella decreased with rise in temperature up to 25T but none of the stages survived 30 °C (Goppy, 198 1). Median developmental rates at constant temperatures were between 10 and 25 °C for all immature stages of the alfalfa blotch leaf-miner, Agromyza jrontella. Larval survival was maximum at 20 and 25 °C although developmental rates differed little between these two temperatures. The role and importance of climate and weather Chapter 1: Literature Review 41 in the dynamics of insect populations has long been recognized by insect ecologists and agricultural entomologists (Nestel et aI., 1994). POPULATION DYNAMICS There are at least 10 400 known secondary plant substances, and an estimated 100 000 - 400 000 unknown ones, implying that plants have a considerable impact on dynamics of insect herbivores (Stiling, 1988). Host plant influences on insect population dynamics can be subtle but profound. A host plant not only directly affects herbivore development, fecundity and mortality, but acts indirectly as well through interactions with herbivore natural enemies (Price et ai., 1980). Hespenheide ( 1991 ) states that the number of generations per year, generation times and occurrence of diapause are interrelated. Most temperate species of leaf miners undergo a winter season diapause. However, Opler ( 1978, 198 1 cited by Hespenheide, 1991 ) found that California leaf-miners feeding on evergreen oaks had fewer annual generations, longer larval periods, lower populations, greater host specificity, and were larger in size compared to those using deciduous oaks. Finch ( 1986) observed the importance of soil type and compaction, and Rockwood (1974) suspected sandy soil to be more conducive than moist forest soils to successful insect population growth, but Mopper et al. ( 1984)'s results did not support these observations. They found no significant differences in miner overwintering success between soil types, or moisture regimes. However, soil predators, which they did not examine, may influence pupal survival (Mopper et at., 1984). Diapause can occur at any stage with species overwintering as eggs, larvae, pupae, or adults, but it commonly occurs in the egg or pupal stage (the latter being most common in leaf miners [Hering, 195 1]) as these do not require food and can remain in ---------�--- -- - - - - - Chapler 1: Literature Review 42 an inactive condition for long periods. According to Condrashoff ( 1964) pupae or prepupal larvae are the most common diapausing stage of leaf miners. Larvae of several species of leaf-miners feeding on evergreen trees exhibit protracted development and continue to mine through the winter, pupating and emerging when new leaves are flushed in the spring (Auerback and Simberloff, 1989; Potter, 1985; Potter and Kimmerer, 1986). Some leaf miners form "green islands" on abscised leaves and survive and mature long after the leaf has fallen in winter (Hering, 195 1). Condrashoff (1964) states that the aspen leaf miner spends its hibernation as an adult. Explanations of outbreaks or cycles in herbivore population density fall into two broad categories: extrinsic and intrinsic causes. The extrinsic explanations include parasitism and predation, pathogens (Myers, 1988 cited by Ruohomaki and Haukioja, 1992), variation in plant resistance (Benz, 1974 cited by Ruohomaki and Haukioja, 1992), climatic factors or some combination of these (Watt and Leather, 1988). Explanations based on intrinsic factors propose that some inherent mechanisms in individuals cause density fluctuations. For instance, the genotype of individuals may be different at different population densities, so that at low, but not at high densities, population growth is rapid. This may contribute to mass outbreaks taking place more or less regularly (Ruohomaki and Haukioja, 1992). When refoliation coincided with emergence of ovipositing leaf miner adults, Acrocercops sp. and Neurobathra strigijinitella densities increased dramatically, indicating that both species are at times limited by availability of young leaves (Auerbach and Simberloff, 1984). An insect outbreak is a rapid increase in the abundance of a particular species that occurs over a short period of time. The concentration of nitrogenous compounds available in plant food, estimated by foliar nitrogen and amino acid concentrations, has been used to explain the occurrence of herbivore-insect outbreaks (White, 1978 cited by Silvanima and Strong, 1991 ). Host-plant qualities are detennined in part by concentrations of nutrients, of noxious phytochemicals and morphology (cuticular toughness, type and number of trichomes, etc.). Total nitrogen content can influence insect generation time, efficiency of food use and abundance of natural enemies rNay, --- -- -----.�------- Chapter 1: Literature Review 43 1972 cited by Silvanima and Strong, 1991 ). All three of these factors can affect insect mortality rates. Insect abundance and distribution also may be directly affected by the availability of nitrogen (Silvanima and Strong, 1991) . No clear population cycles were detected in a ten-year period study of Rhynchaenus Jagi (a beech leaf mining weevil) in Ireland (there were years of sustained decline, but not enough evidence to suggest a cycle) (Day and Watt, 1989). Adults and larvae of Agromyza Jrontella share the same food resource and the presence of nutrition holes indirectly modifies the population dynamics of Agromyza Jrontella in several ways. At high population densities, both exclusion (starvation competition) and interference intraspecific larval competition (cannibalism) are important mortality factors. The number of nutrition holes per leaflet is high under such conditions (Quiring and McNeil, 1984). COLOUR AND DISCOLOURA TION OF MINES There is usually a distinct variation of colour between mines and surrounding leaf. Feeding channels in other parts of the plant, such as roots, pith of the stem and fruits, are less conspicuous and do not show the peculiarities which are characteristic of each species, as clearly as is the case with leaf-miners. It is not always the mine itself which stands out so distinctly as a result of its different colouration; in some cases the mine is less obvious but its surroundings are discoloured in a characteristic fashion due to the influence of the mine. Both the colour of the mine and the discolouration of the surrounding leaf are frequently of great value for determining the species of the mine­ producer (Hering, 195 1) . A. Colour of the Mine: The colour of the mme, which often deviates strikingly from that of its surroundings and emphasises clearly every detail of its shape, is usually the result of the fact that parts have been eaten out of the plant tissue. Air normally penetrates the Chapter 1: Literature Review 44 resulting cavities and this produces a different colour from that of the rest of the leaf. The colour of the mine may also vary according to which parts of the leaf have been eaten away. It is often possible to deduce which tissue has been removed from the leaf, from the difference of colour of the mine without having to make a microscopic examination of the inside of the leaf. The colour also varies according to the type of light in which the mine is examined (Hering, 195 1 ). The various types of mine colouration range over: Light green in transmitted light, grey-green in direct light. Yellowish green in both direct and transmitted light. Darker green than that of the rest of the leaf (arises not from the production of a cavity but from the filling up of this cavity). Pure to yellowish white in direct and transmitted light. Silvery white in direct light. Silvery white with patches of rust-brown. Greenish-white mottling (particularly common and striking in mines of the genus Lithocolletis). A reddish-brown colouration of the mine may be based on two separate causes. Brown to deep black. Red to blue anthocyanine colouration. B. Discolouration: The mine may be as follows: - Ringing of discolouration surrounding the mine. - Necrobioses (necrotic areas). - Red or blue caused by anthocyanines. - "Green islands" in the autumnally discoloured leaf. THE SUBSEQUENT FATE OF THE MINE In most cases, mines have a one-to-one relationship with the larvae which make --- - - ---- - -- ----�- - - - - - Chapter 1: Literature Review 45 them. The mines also persist for some time after a larva has ceased to feed, and are relatively conspicuous (Sterling et ai., 1992). When the larva is mature it leaves the infested part of the plant in order to pupate. It is important for anyone wishing to identify a mine to know what changes occur in mines after the larva has completed its feeding. Two different possibilities must be taken into account: - The larva pupates inside the mine, i.g. , some Lepidoptera leaf miners. - The larva leaves the mine and pupates outside. This applies to the majority of mines. In this case mined parts are soon destroyed (with dampness, rain and etc.) making leaf mining identification difficult. Faeth ( 1985) recovered all available mines of oak on abscised leaves from leaf litter. Over 75% of the mines were recovered in the leaf litter. All miners recovered in the litter had either emerged or died; none was still feeding. For each leaf mine he recorded whether it occurred on a damaged (manually or herbivore-damaged) or an intact leaf, and its fate. EFFECTS OF LEAF-MINERS ON CULTIVATED PLANTS AND ECONOMIC IMPORTANCE Wit ( 1985) stated that whether quantitative damage occurs to cultivated plants or not depends on the type of crop, the growing stage, the amount of insect injury, and plant growth factors. He studied the relation between artificial simulation of insect injury to the leaves, and yield in spring cabbage to obtain information on the threshold values to be used for leaf-miners in this crop. The effects of four percentages of defoliation (0, 25, 50, 75%) applied at four or five treatment dates during the preheading stages of the crop, were investigated. Sensitivity to defoliation increased during the period from transplanting to head-formation reaching a maximum after plants had reached a tota1 1eaf area of approximately 2000 cm2• In plants of this size the author deduced that a 5% reduction of the leaf area would cause a yield reduction of 3%. Chapter 1: Literature Review 46 Because the amount of leaf area mined affects photosynthesis, leaf-miners often prefer shaded or older leaves (Hileman and Lieto, 1 98 1 ) that are less productive photosynthetically. For example with 1 5-50 mines of the pear leaf miner photosynthesis decreases 10-30% respectively (Fujiie, 1982). Shading invariably reduces net photosynthetic rate and levels of foliar sugar, starch and protein, reduces leaf thickness, increases leaf area, and apparently reduces levels of some noxious secondary compounds in leaves (Schultz, 1983). Changes in leaf chemistry with shading, if widespread, suggest phytophagous insects might prefer shade plants owing to the reduction of secondary compounds, or avoid them because of low levels of sugars and proteins compared to unshaded leaves. On the other hand, photosynthesis may be affected in disproportion to the area mined if the leaf is abscised prematurely (Hespenheide, 1 99 1). Palisade mesophyll tissue removed from mature leaves of Phaseolus lunatus L. by Liriomyza trifolii (Burgess) was replaced with photosynthetically active cells, permitting virtually complete recovery from injury (Martens and Trumble, 1987). No significant differences in biomass production or levels of ribulose- l ,5-biophosphate carboxylase were observed between damaged and control plants. Decreases in photosynthesis did not exceed 10% for leaves with approximately one-fourth of the leaf area mined. According to Livene and Daly ( 1966) the trifoliate leaves of rust-attacked primary bean leaves can increase their photosynthetic rate almost twice. Furthermore, the trifoliate leaves tend to be more resistant to continuous L. trifolii infestations, although secondary rust-infections impair their function. For potato, it has been postulated that a leaf-miner may be responsible for virus dissemination (Bethke and Parrella, 1985). Leaf-miners typically cause a relatively small amount of damage to an individual tree because of low population densities and minor damage from single mines. Densities of individual species and cumulative density of all leaf-miners were less than 1% on Betula pendula (Godfray, 1 985). Heavy attack by leaf-miners (up to 80% leaf destroyed by larvae), may result in complete defoliation of plants in outbreak: situations (Notly, 1 948, 1956 cited by Hespenheide, 1 99 1) . Condrashoff (1964) reported that when 80-90% of leaf surfaces of aspen plant ---�----- - --- - - Chapter 1: Literature Review 47 contained mines, about one half the epidennis on a tree was destroyed, and growth reduced. When more than 90% of leaf surfaces were affected by aspen leaf miner, Phyllocnistris populiella Cham (Lepidoptera: Gracillariidae) the leaves dried and shrivelled and dehisced. Other than larvae, heavy feeding damage (>50% of the leaf area destroyed) was caused by adult of locust leaf miner on woody plants (Williams, 1989). However, outbreaks of locust leaf miner are often described as patchy in distribution and short in duration. At high infestation levels, the wheat sheath miner, Cerodontha australis (Agromyzidae: Ephydridae) is capable of suppressing ryegrass growth in many parts of the world (Barker et ai., 1984). Alfalfa yield losses caused by alfalfa blotch leaf miner averaged 7.7% in some years in USA (Hendrickson and Day, 1 986). The economic injury level for Leucoptera leaf miners (Lepidoptera) on coffee was calculated at 30 large mines per stem, which causes an 1 1 % yield loss (Notley, 1 956). The economic impact of Liriomyza leaf-miners in the United States and throughout the world has been considerable; in California alone it was estimated that the chrysanthemum industry lost approximately 93 million US dollars ($ 93 000 000) to Liriomyza trifolii from 198 1 through 1 985. During the past 1 5 years there has been a dramatic increase in the economic importance of Liriomyza leaf-miners (Parella, 1987). The leaf-miner Liriomyza trifolii has been reported to cause almost near collapse of cow pea Vigna unguiculata L. crops in Tanzania. The cosmopolitan pest Liriomyza brassicae is not recorded as a significant pest in New Zealand. Infestations of Phyllonorycter crataegella (Clemens), the apple blotch leaf miner, averaging more than two mines per leaf caused premature fruit drop from 'McIntosh' apple trees in eastern New York and reduced fruit set the following season (Reissig et aI. , 1982). Infestations of alfalfa blotch leaf miner averaging more than four mines per leaf reduced the size of 'Red Delicious' apples. In western New York, varying populations of P. blancardella (F), the spotted tentifonn leaf miner, had little effect on the growth or production of two apple cultivars during the initial year of infestation but - - - - - --------����----- - - - - - - - - - - - - Chapter 1: Literature Review 48 reduced fruit set and consequent production during the following season. Leaf-miners can produce other effects on plants. The locust leaf-miner Odontota dorsalis is destructive to its noneconomic host Robinia pseudoacacia, but has become of economic importance because of its use of such alternate larval hosts as soybean, Glycine max (Poos, 1 940 cited by Hespenheide, 1991), and ornamental plants (Hespenheide, 1 99 1). Reports on adult leaf miner feeding under field or laboratory conditions are scarce. A few investigations revealed that leaf miner adults can cause feeding damage on leaves of plants in addition to damage caused by their larvae (Bale and Luff, 1 978). They and an anonymous writer ( 1960 cited by Bale and Luff, 1 978) reported that the beech leaf mining weevil, Rhynchaenus jagi, made feeding holes in eighteen tree and shrub species other than beech and two of them were the most acceptable plants if beech was not available. The oil palm leaf miner beetle, Coelaenomenodera elaeidis (Chrysomelidae: Hispinae) has become a major pest throughout West Africa and cyclic outbreaks resulted in serious damage to foliage and reduced production of oil palm, Elaeis guineensis, (Bernon and Graves, 1 979). Plant damage relates directly to the extent of tissue destroyed by mining. Mines may be so extensive that a significant loss of effective photosynthetic tissue results and the plant becomes unthrifty. Also the mines may be so extensive that there is deterioration of commercial or aesthetic value of the plants (Aiello and Vogt, 1986; Hespenheide, 1973). In New Zealand damage from leaf-miners is seldom serious, although leaf-miners are usually quite conspicuous and often common. However, sometimes economic injury is inflicted. Although the leaf-miner host range is very wide, some species such as kaka beak (Clianthus puniceus) leaf-miner (Liriomyza clianthi) restrict themselves to one or a few species of plant. Commonly leaf-miner species are capable of mining many members of one plant genus, e.g., Hebe (koromiko) miners and oak leaf-miner. The wheat sheath miner is the most common leaf mining insect in New Zealand pastures (Barker, 1984). Although, it is not an economic pe�t it contributes to the overall pest fauna in suppression of pasture growth (Barker, 1984). ---------------- ----- - - - - Chapter 1: Literature Review 49 Chromatomyia syngenesiae Hardy has been regarded as not economically important in cultivated crops in New Zealand (Valentine in DSIR mes). The economically damaging leaf-miners of Cruciferae in New Zealand are not Agromyzidae but two species of Drosophilidae: Scaptomyza flava Ellen and Scaptomyza graminum [known then as Scaptomyza elmoi (nSIR fIles)]. Leaf-mining Agromyzidae do not appear to be as economically important in New Zealand as they are overseas. This may be because the most serious pests such as Liriomyza trifolii are not present or because economic injury levels have not been assessed. The spread and host range of oak leaf miner in New Zealand were recorded by Wise ( 1953a, 1953b, 1954, 1955, 1958 cited by Thomas and Hill, 1989). The high incidence of mines on exotic hosts together with attack on apple and the indigenous forest species Nothofagus spp. were seen as a major threat to the fruit-growing and forestry industries (Given, 1959 cited by Thomas and Hill, 1989). The role of Scaptomyza spp. as leaf-mining pests of brassicas in New Zealand is not understood as no pest assessment studies of Scaptomyza spp. have been carried out. There are no published records of damage attributed to Scaptomyza spp. in New Zealand, although Cumber and Eyles ( 1961 b) associated Scaptomyza fuscitarsis with various crops. The New Zealand Arthropod Collection contains Scaptomyza elmoi reared from various brassicas, Tropaeolum majus L. and Pisum sativum L. (B. A. Holloway pers. comm.). The genus Scaptomyza contains known pests of brassicas in other parts of the world (Cumber and Eyles, 196 1) . Conversely, leaf-miners have been considered for biocontrol of pest plants; of Lantana camara by Octotoma and Uroplata (Harley, 1969; Winder and Harley, 1982, 1984 cited by Hespenheide, 199 1 ) and of Echium plantagineum by Dialectia (Wapshere and Kirk, 1977 cited by Hespenheide, 199 1 ). The possible interactions of the snail Bostryx conspersus with a species of the Drosophilid genus Scaptomyza was discussed by Ramirez (1988). Larvae and eggs of Scaptomyza were found in 4.4% of individuals of Bostryx conspersus examined, and could be the biological cause of mortality of the snail in its fIrst stages. Chapter 1: Literature Review 50 Very few Agromyzidae have been used extensively or even actively considered for possible control of weeds but one species, Phytomyza orobanchia Kaltenbach, has been conspicuously successful in controlling Orobanche (broomrape) which affects a variety of crops in the U.S.S.R.; another, Ophiomyia lantanae Froggatt has been introduced to many parts of the world where Lantana (Verbenaceae) has become a problem, but its effectiveness in controlling Lantana has been very limited. Three further species have been or are being investigated for possible use against Convolvulus arrensis L. (field bindweed), Cuscuta (dodder) and Stn·ga (witchweed); these are Melanagromyza convolvuli Spencer, Melanagromyza cuscutae Hering and Ophiomyia strigalis Spencer. A long-term survey (1965-1989) showed that leaf miners were not very widespread on cereal weeds in Slovenia and that their levels of infestation were seldom high enough to markedly injure the weeds. Of the 1 18 species of miner recorded on 5 1 weed species, Diptera predominated, with Coleoptera, Hymenoptera and Lepidoptera being only sparsely represented (Macek, 1990). In New Zealand, like the endemic Melanagromza senecionella Spencer, Chromatomyia syngenesiae also infests the weed ragwort (Senecio jacobaea L.) (Asteraceae) and has been considered to have limited potential as a biological control agent for this weed (Kelsey, 1937). Kelsey also suggested that Phytomyza syngenesiae Hardy might have some value in controlling ragwot in New Zealand. Chapter 1: Literature Review Fig . '! Fi9A -- --- - - - - Fig. 2.. 5 1 3. Solidago: opbiogenous stigmatonome of Dizygomyza posticata Mg., on the right a pan with greater magnification shows the primary (P) and secondary (S) feeding lines, the "herring-bone" pattern. 4. Galeopsis: Heliconome of Liriomyza eupatorii Kaltenb. 5. Ulmus: Visceronome of Nepticula viscerella Stt 6. Lonicera: Asteronome of Phytomyza (Napomyza) xylostei Kaltenb. Fig. 1 : Types of mines (From Hering, 1951). Chapter 1: Literature Review 52 7. Taraxacmn: Asteronome of Liriomyza strigata Mg. along the leaf veins. 8. Acer platanoides: ptychonomes of Lithocolletis plaJanoidella de Joan. Left, in the centre of the leaf; right, within a folded oven comer of the leaf. 9. Section of an upper surface mine of Lithocolletis (E_ epidermis, P _ palisade parenchyma, S_ spony parenchyma, K_ frass, G_silk). Top left, an early epidermal mine. 10. Prunus domestica: ophistigmatonome of Nepticula plagicolella Su. Fig. 1 : Continued. -------------------- - - - - - Chapter 1: Literature Review 11. Arctostapbylos: Coleophora arctostaphyli Med. a) Initial mine b) Later mines and case cut-out 53 12. Apium: Philophylla heraclei L. (celery fly), initial channel full depth and transparent, later blotch upper-surface, greenish. 13. Saxifraga rotlIDdifolia: Early linear mines, blotcb mines, and areas cut out (Incurvaria trimaculla HS). 14. Malus: Callisto denticulella Thbg. First instar epidermal mines and folded over leaf-edges. 15. Polygonum: Euspilapteryx phasianipennella Hb. with initial mines and later leaf cones. Fig. 1 : Continued. - ------------ Chapter 1: Literature Review 1. Betula: Incurvaria pectinea Hw. a) Leaf after construction of cases b) mined leaf. 54 2. Sallie Ophionome of Phyllocnistis saligna Z., leaf_stem cortex leaf. At the end, the edge of the leaf is curled over the pupal chamber. 3. Acer platanoides: carponome of Nepticula sericopeza Z. 4. Silene: linear mine of Liriomyza strigata Mg. on the gall of Gnomoschema cauliginella Schmid. Fig. 2: After leaf mining (Hering, 1951). - --- - ---- C h a p t e r 2 THE BIOLOGY OF SCAPTOMYZA FLAVA 1 INTRODUCTION An intriguing characteristic of the leaf miner Scaptomyza flava female is that she makes hundreds of punctures with her ovipositor in host plant leaves for feeding. This feeding probably greatly enhances her reproductive capacity (Minkenbreg, 1988b). While feeding, a female also may assess the nutritional value of the leaf, which may influence the decision whether to continue feeding and ovipositing or to leave (Bethke and Parrella, 1985). Because the larvae usually restrict their feeding to one leaf, the ovipositing adult female insect thus "detennines" where, and therefore what food, her offspring will eat. The thesis of this chapter is an understanding of behaviour and aspects of biology of Scaptomyza flava regardless of its host plants. REARING MA TERIALS AND METHODS Rearing of adult Scaptomyza flava was carried out in a greenhouse at ambient temperature (about 20DC-uncontrolled temperature). An initial stock of larvae was obtained from infested Chinese cabbage and turnip plants growing in the field at Palmerston North. Rearing colonies were maintained in terylene net cages over aluminium and wooden frames (Plate 1). Most larvae emerged from their mines and dropped to the floor of the rearing cage to pupate. Pupae were removed from the floor of the cage with a soft camel hair brush and soft forceps and placed in potting medium, and allowed to emerge. 1 Some parts of this Chapter modified from a paper presented to XIX International Congress of Entomology. 1992. Beijing-China. Chapter 2: The biology oj Scaptomyza j1ava 56 Plate 1 : Realing cages Chapter 2: The biology of Scaptomyw flava 57 water plus 10% honey solution imbibed in a cotton wool pad were provided as food for emerging flies. Host plants were placed in an oviposition cage (50 x 50 x 50 cm) and exposed to 100-200 flies. Potted plants of Chinese cabbage Brassica rapa chinensis group (Brassica campestris spp. pekinensis) and turnip Brassica rapa L. were used (plants were grown in pots in a greenhouse until they were 1 8-28 cm tall [about 1 month old] before use). After 3-4 days plants were exchanged for new ones. When it was necessary to replace plants, the oviposition cage was placed beneath a light or exposed to sunlight. The positively phototactic adults flew to the top of the cage when the plant was disturbed, enabling the old plants to be exchanged for new ones. Wild flies were sometimes added to this colony from field and nursery plantings of the respective hosts. Plants with eggs were held in clean fIne gauze cages (for approximately 2 weeks) until larvae had begun to form large blotch mines in the leaves. This occurred 2-3 days before the larvae dropped from the leaf to pupate in the potting mix or the cage substrate. After about two weeks new adults emerged. Another method was sometimes used to rear adult insects from an infested plant by removing a leaf and placing it in a petri dish arena (9 cm diameter) containing either a piece of moist cotton wool or fIlter paper attached inside to the top and bottom. Most larvae from the host leaf pupated in the cotton. When adult flies emerged they were placed in an oviposition cage or used in experiments. Larvae and adult insects were preserved in 70% ethyl alcohol in glass vials. Voucher specimens that have been collected from different plant species during two years (including weekly sampling of fIeld plots) have been deposited in the insect collection of the Plant Science Department, Massey University, Palmerston North, New Zealand. The life-cycle of Scaptomyza flava was determined under laboratory conditions with respect to the duration of larval instars, pupal and adult stages. Observations were also made on feeding, mating and egg laying behaviour. Chapter 2: The biology of Scaptomyza flava ---- -- - MORPHOLOGY AND BEHAVIOUR OF INSECT ADULT 58 The adult flies are small, about 3 mm long (tip of the head to the tip of the abdomen) with a wing spread of 6 mm (from wingtip to wingtip). The colour is very variable. Some are quite yellow (most insects reared in the laboratory and most spring and summer flies from the field) and some are greyish-brown or black (autumn and winter ones) (plate 2). Host and leaf selection is accomplished by the ovipositing female who cements eggs singly to the lower leaf surface. If the exposure period of plants for oviposition during rearing was prolonged, diminutive adult insects with wide variation in size resulted due to larval overcrowding. Scaptomyza }lava has been reared from the plants listed below collected in the Manawatu. Many specimens of an Agromyzid leaf miner were also reared from Cineraria and Sow thistle (Sonchus oleraceusl. Common name Botanical name 1 . Turnip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brassica rapa ssp rapa 2. Chinese cabbage . . . . . . . . . . . . . . . . . . . . . BTassica rapa chinensis group 3. Cauliflower . . . . . . . . . . . . . . . . . . . . . . . . . Brassica oleracea vaT botrytis 4. Broccoli . . . . . . . . . . . . . . . . . . . . . . . . . . . . BTassica oleracea var italica 5. Radish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , Rhaphanus sativus 6. Wild turnip . . . . . . . . . . . . . . . . . . . . . . . . . . . BTassica rapa ssp sylvestris 7. Wild radish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rhaphanus raphanistrum 8. Hedge mustard . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sisymbrium officinale 1 Cineraria leaf miner, Phytomyza atricomis Mg., is the commonest leaf miner in New Zealand. It is of European origin and is almost worldwide in distribution (Wise, DSIR fIles). This pest also is active on sow thistle, chrysanthemum, pea, ragwort, groundsel, marigold, dahlia, dandelion, nettie, and scotch thistle (Wise, DSIR files). Chapter 2: The biology of Scaptomyza flal'a 59 Plate 2: Adult female Scaptomyza flava (dark fOlm) Chapter 2: The biology of Scaptomyza flava 60 EMERGENCE To establish the time of emergence of the adults, large numbers of pupae (from the rearing cages) were checked hourly between 05.00 and 1 8.00 over a period of several days in December 1991 (sunrise: 05.42, sunset: 19.47). The pupae were placed in an environmental chamber at 20 ± 2aC uncontrolled humidity and natural daylength. Observations were started on day 10 following fIrst formation of pupae. RESULTS Adults emerge through the ventral anterior end of the puparium with the aid of the ptilinum. This process may take from 5 to more than 40 minutes. Newly emerged adults exhibit a positive phototactic response and climb up the side of a cage or up the stalk of a plant where they remain quiescent for a period of approximately 30 min while expanding their wings and body. The body is fully sclerotized and coloured within 30 min-3 hr (personal observations). Emergence of both sexes occurs almost entirely during early daylight hours. The data show that out of a total of 565 adults 545 (96.5 % ), emerged between 05.00 and noon, with the largest proportion emerging (42 %) between 06.00 and 07.00. Fourteen of twenty adults which emerged in the afternoon emerged before 14.00. No emergence occurred between the hours of 18.00 and 04.00. The pattern of emergence is shown in Fig. 3. Adult females emerged before males (unrecorded data). Though this has been recorded for other species (e.g., Spodoptera littoralis) (Baker and Miller, 1974), the earlier emergence of males is more common (Singer, 1982). Earlier female emergence may be due to the length of time required for ovary maturation (Hamilton, 1986; Hamilton and Zalucki, 1991 ). In agro-ecosystems flies are likely to emerge near to host-plants, but under some circumstances distances to host plants may be greater (personal observations). Chapter 2 : The biology of Scaptomyza flava Fig. 3: Time of emergence of s. flava adults under greenhouse condition C/J .... - � ""0 cj r.;...... o � !l) .D 1 E ::l Z 5 6 7 8 9 1 0 1 1 � Time of day (Hours) � 1 2 1 4 1 6 I p·M· 1 1 8 61 --------------- - Chapter 2: The biology of Scaptomyza flava 62 SEX RATIO The sex ratio is an important fitness character of any sexual reproducing organism. Sex ratios of animal species often approximate 1: 1. The commonness of the 1:1 sex ratio was originally explained by the equal investment theory of Fisher ( 1930 cited by Ishihara and Masakazu, 1993), which is based on frequency-dependent selection. However, some species have been found to produce offspring with biased sex ratios. Several factors that may result in adaptive biased ratios have been suggested: local mate competition (Werren, 1980 cited by Ishihara and Masakazu, 1993), local resource competition (Clark, 1978 cited by Ishihara and Masakazu, 1993), and physiological condition dependent on maternal rank in a group (Clutton-Brock et aI., 1984 cited by Ishihara and Masakazu, 1993). Recent studies by Ishihara and Masakazu ( 1993) showed that secondary sex ratios in adults have also been found to deviate from 1: 1 due to differential mortality during development, theoretically due to competition for resources, territories mates, etc. Little has been published on the sex ratio of Scaptomyza. Mopper and Whitham (1992), mentioned that plant variety may strongly influence sex ratios, so insects were collected from Chinese cabbage from the laboratory colony and from the field. MA TERIALS AND METHODS To detennine the sex ratio of Scaptomyza flava, I checked 2 groups of insects, 400 puparia from the laboratory colony on Chinese cabbage (flies were sexed as they emerged from puparia kept in petri-dishes in the laboratory at room temperature [ca. 20°C]) and over 440 flies (typical morph) captured by sweep net from plots of Chinese cabbage in the field. Natural daylength (at a 15:9 [LD] hours photoperiod with photophase from 05.00 [sunrise] to 19.55 [sunset, summer time is not included]) was that in January 1992. Chapter 2: The biology of Scaptomyza jlava 63 Flies were anaesthetized with carbon dioxide (C02) or ethyl acetate vapour to facilitate sexing (Plate 3). Flies were sexed using the end abdominal character. The pooled sex ratio was tested for confonnation to a 1 : 1 ratio using the X2 statistic. RESULTS Results are summarized in the Tables 1 and 2. Table 1 : Sex ratio of Scaptomyza flava from laboratory colony. Sample Date No. of puparia No. of males No. of females 1 1 -7.6. 9 1 100 52 48 2 1 -7.7.91 100 5 1 49 3 1 -7.8 .91 1 00 56 44 4 1 -7 .9.9 1 1 00 5 5 45 Total 400 2 1 4 1 8 6 �ean percentage 53.5 % 46.5 % The sex ratio of adults emerging from pupae in the laboratory did not deviate significantly from a 1 : 1 ratio (mean of 46.5% female and 5 3 . 5% male for four samples) (Table 1). For field captured adults the corresponding values were 48.4% females and 5 1 .6% males (Table 2). Thus under greenhouse and field conditions males were about 7% and 3% more numerous than females respectively. The Che statistic is calculated as: X2 = � (Ob-Exi/Ex Ob=Observation Ex=Expectation. Chapter 2: The biology of Scaptomyza flava 64 Table 2: Sex ratio of S. f1ava captured by sweep net in the field at Palmerston North from Chinese cabbage and turnip. Sample No. of No. of No. of Date flies males females 8.8.91 50 25 25 6.9.91 70 36 34 11.10.91 80 43 37 8.11.91 100 52 48 1.12.91 140 7 1 69 Total 440 227 2 13 �ean percentage 5 1 .6% 48.4% The value for chi-square at one degree of freedom, for the 5% level of probability is 3.84 1 . This is not significantly different from expection of 50:50. Thus the sex ratio does not depart significantly from 50 : 50 in the laboratory and field data. If one sex is more costly to produce than the other, then according to Fisher (1930) it is expected to be the less frequent sex. compared to balanced sex ratio, sex ratio biased inconsistent (non-significant) towards males should result in poor potential population fecundity in Scaptomyza flava, and this should be of deleterious in a species whose oviposition period is not restricted to a few days. Chapler 2: The biology of Scapromyz.a j7al'a 65 Plate 3: Anaesthetic operation tools ��- ��-��������-�-- - - - - Chapter 2: The biology of Scaptomyw flava 66 MATING, FEEDING AND OVIPOSITION INTRODUCTION Mating behaviour of adult leaf-miners has not been extensively studied. Leaf­ miner matings may be single, at least for female Lepidoptera (Powell, 1980), but beetle matings are known to be multiple (Story et aI. , 1979). Protracted copulation is known for both groups (Kirkendall, 1984; Pottinger and LeRoux, 1 97 1 ; Story et al. , 1979), and post copulatory escort behaviour has been described for the hispine Odontota dorsalis (Kirkendall, 1984). Among Diptera oviposition behaviour has been studied primarily for the Agromyzids Phytomyza on Ranunculus spp. in relation to egg and larval density (Sugimoto, 1 980) and Agromyza on alfalfa (Quiring and McNeil, 1987). Both Agromyzids puncture the leaves with the ovipositor for both oviposition and for feeding; Agromyza females mark eggs with an oviposition pheromone (McNeil and Quiring, 1983) that can influence the outcome of larva-larva competition (Quiring and McNeil, 1 984). In experimental choice situations, female Agromyza rank unexploited leaves above marked leaves or those with many nutrition holes above these with 1ate-instar larvae (Quiring and McNeil, 1987). The average number of perforations made during the lifespan of the female alfalfa blotch leaf-miner Liriomyza trifolii was 3769 (Hendrickson and Barth, 1978). The mating behaviour of insects is often very complex and varies greatly in different species. The factors that bring the sexes together may be chemical signals (sex attractants), acoustical signals, or visual signals (light flashing, dances and other courtship manoeuvers in many flies), and the high degree of specificity in this behaviour acts as an isolating mechanism to prevent the mating of different species (Southwood, 1 975 cited by Stiling, 1988). Chapter 2: The biology of Scaptomyza flava 67 MA TERIALS AND METHODS Mating and oviposition behaviour of Scaptomyza flava were studied under laboratory conditions. I set up 10 small cages and released 1 pair of newly emerged adults in each, on one month old Chinese cabbage plants. cages were placed in a greenhouse under ambient lighting (L: 12 D: 12) photoperiod and ca. 18 ± 2"C temperature with 75 ± 10% RH (relative humidity). I observed insects and leaves under a stereo microscope hourly. Length and width of eggs were measured using an eyepiece micrometer. To detennine that S. flava females are polygamous, two preliminary experiments were established under greenhouse conditions: In the fIrst experiment, one female and three males were released onto plants in a cage. To distinguish them wings of two of the males were stained either green, blue or not stained. They were recaptured, by aspiration, several days after release and were subsequently identifIed and re-stained. During one week it was observed that the female mated with all three males. In a second experiment, a single pair of insects was released into a cage with a potted plant and each two days the male was replaced with a fresh one. The same female was observed to mate with three different males. The potential frequency of mating in the male was determined by placing one newly emerged male and female in an oviposition cage. The following day the male was transferred to another oviposition cage with a new l -day-old unmated female, and this was repeated daily until the male died. There were 24 replications. RESULTS Mating. The majority of males and females mate within 24-48 hr of emergence. The females are polygamous and copulate soon after emergence. Almost all females have mated within 48 hr. The sexes may remain coupled for as little as 5 minutes, but the norm is protracted copulation taking 20 min- l hr, with maximum mating time about Chapter 2: The biology of Scaptomyza flava 68 2 hr. Males and females mate more than once. The males mated on average 4.88 times (range 1- 12). One pair of adults mated on 5 consecutive days, and another pair was observed mating on 4 separate occasions within the same day. Still another pair was observed in copulation 10 different times over a period of 15 days. Mating was observed to take place at various times between 9 a.m. and 7 p.m., but more generally occurred during early morning hours. During copulation, the male assumes a position behind the female at about a 60° angle above her body. In the more typical position, the male's forelegs clasp the mesothorax of the female, his middle legs clasp the female's abdomen, and his hind legs spread the female's wings. The wings of the male are folded in the normal resting position (held over the body), their tips touching the leaf. The male brings his abdomen forward to connect to the female genitalia as the male's hind legs move to rest on the substrate. This position is maintained throughout copulation. Aggressive behaviour between males of Scaptomyza flava during mating has not been observed in the laboratory under severely crowded conditions (about 2000 insects under one cage 50 x 50 x 50 cm). Sometimes females walk slowly forward during mating. Feeding and oviposition. The behavioural repertoire of females included flying, alighting on leaves, arching of the body so that the tip of the abdomen touched the leaf surface. When a female initiates a leaf-puncturing sequence, the first event observed, regardless of host plant (turnip, Chinese cabbage, cauliflower, etc.), is a bending of the abdomen to position the ovipositor perpendicular to the leaf. The ovipositor contacts the leaf through a series of rapid thrusts. Once the ovipositor has penetrated the leaf surface, the thrusts becomes slower and more deliberate. At this point the female damages mesophyll cells (parella, 1987). The females feed by using their ovipositor to make perforations of the epidermis (in the upper and underside surfaces of the leaves) (Plate 4). The female of Scaptomyza, after producing a incision, quickly backs over the wound and sucks upon the exudation. Gravid females laid eggs more than once before leaving the leaf. Feeding punctures may be either scattered or concentrated in one area, while - - - - -------------- -- - - - Chapter 2: The biology of Scaptomyw flava 69 the eggs are deposited more at random in the leaf. Sometimes eggs, and thus mines, were aggregated on leaves of host plants so that two or more mines coalesced. But eggs were limited to one at each discrete site or hole. The time required to make a perforation averaged 22 seconds (range 6-65 sec, 20 observations), and the time used in feeding averaged 7 sec (range 5-10 sec , 1 2 observations). Eggs were laid within 20-32 sec (mean 2 5 sec, 3 0 observations) after the fly had alighted on the leaf. The punctures used for oviposition are made in practically the same manner as the ones used for feeding. The punctures used for oviposition were obviously bigger than others. Females tend to make punctures and feed on a small area of a single leaf until disturbed. For example: one female made 44 pinholes in a 1 cm2 area during 2 hr of observation. The average length and width of these feeding holes was 0.43 mm (range 0.3-0.5) and 0.27 mm (range 0. 175-0.3) (25 observations) respectively; the area of a single pinhole was thus approximately 0. 12 mm2, but puncture size varies with the size of the adult female. In the field, the number of feeding punctures per leaf varies widely, but at times is sufficient to cause noticeable damage. For example, in one sampling (December 199 1 , 40 leaves) punctures ranged in number from 10 to 900 per leaf (the equivalent of ca. 1 .2 to 108 mm2 [= 1 cm2] of leaf), with an average of 86 (the equivalent of ca. 10 mm2 of leaf). Thus under field conditions leaves with multiple attacks are quite common. Pinhole density on a leaf was counted under a binocular (magnification x 80). Feeding by adults before oviposition can thus be extensive and damaging to plants- both hosts and nearby plants. Leaf puncturing can reduce photosynthesis (Livene and Daly, 1966), growth and vigour of the whole plant (Hendrickson and Barth, 1978) and when leaf miner densities are high, host plant leaves can be completely girdled by mines that cause foliage to die and sometimes may kill young plants (laboratory and field observations, Table 36). Dehiscence of leaves in response to adult feeding occurred when adult popUlations reached high levels (as seen in the laboratory). Eggs are deposited in a large percentage of leaf punctures. ( 'htll'lI'/" 2. Th,' !>",Iog\ oj .'i' (/I)I"III \'�., P. /I'" 70 Plate 4: Feed ing punctures of S. flawl 1 11 leaves of Ch inese cahhage ----------- - - - - Chapter 2: The biology of Scaptonryza flava 7 1 Observations during the scotophase indicated that the number of flies on the plants increased after natural darkness commenced (even under artificial light) but no feeding punctures were produced during darkness. Under laboratory and greenhouse conditions, most gravid females began oviposition within 24-48 hr. after emergence. Eggs are deposited over several consecutive days (usually 2- 15) ; the majority of eggs are laid between days 4 - 9 of adult life. Eggs per female in constant association with males averaged 255 (range, 145- 32 1 ) (on Chinese cabbage plant) (see Table 16 in Chapter 3). On Chinese cabbage, cauliflower and turnip, eggs have been observed only on lower surfaces of leaves. Aged females spent more time on the lower surfaces of the leaves, produced few feeding punctures, and apparently were more dependent upon plant exudations for food. Usually, just before death, the female (and male) adults were found on the cage floor where they exhibited weak and erratic movements when disturbed. EGGS The form of insect eggs varies considerably. Most Diptera eggs are elongate (Chapman, 1982). The whitish, translucent egg of ScaptomyzaJlava is deposited through the adaxial or abaxial leaf surface into punctures made by the ovipositor. The average length of the egg is 0.36 mm (range 0.3-0.45) and width 0. 1 5 mm (range 0. 1 -0.2)(25 observations). Eggs are laid singly, but often in close proximity to each other (though not in a cluster) . The period of egg development (incubation) varies with temperature and averaged six days (range 2-8 days, 35 observations) under laboratory conditions. As the eggs develop they become opaque, and gradually the yellowish brown cephalopharyngeal Chapter 2: The biology of Scaptomyza flava 72 skeleton of the fIrst instar larva can be seen. At eclosion, the larva is oriented with its anterior extremity, which contains the mouthhook, at the terminus of the egg furthest from the original oviposition puncture made by the female. Scaptomyza flava females laid a greater proportion of eggs on the edge of cauliflower leaves (against major veins and near leaf margins) but a greater proportion of eggs towards the centre of Chinese cabbage leaves. In cauliflower, because of leaf wax, eggs have never been observed on the dorsal surface of the leaves, the fly always laying on the lower surfaces. (personal observation, unrecorded data). The egg is clearly seen through the epidermis of the leaf by means of a lens (under a stereo microscope) (Plates 5 and 6). LARVAE Damage to plants by Scaptomyza flava is caused mainly by the larvae, which mine leaves and reduce yield or the aesthetic value of plants. The larva is somewhat cylindrical and typically maggot-like. The anterior end tapers and the posterior end is truncate (Plate 7). The fIrst instar larva begins feeding immediately after eclosion and feeds constantly to mine the leaves until it is ready to emerge from the leaf and pupate. It feeds in different areas of the leaf mesophyll layer, especially the parenchyma such that sometimes only the upper and lower transparent cuticular layers remain. On Chinese cabbage, oviposition punctures and hence larval mines are close to the main vein. In contrast on cauliflower, the majority of punctures and larval mines are around the leaf margin. When larvae are forced to compete for resources because of crowding, they may tunnel into leaf stalks and into the main vein of leaves. Where more than one larva is present in the leaf, they usually come together near the main vein, but each larva of Scaptomyza flava preserves its own microecological niche. Larvae were not observed sharing a single mine. Chapter 2: The biology of Scaptomyza j7ava 73 Plate 5: Single egg of Scaptomyza flava Plate 6: Eggs laid in leaf tissue Chapter 2: The biology of Scaptomyza flava 74 The ftrst instar larva is transparent when newly emerged, soon becoming a faint green as it commences feeding on the leaf tissue. The second instar larva is light yellow­ green, whereas the third instar larva becomes a rich yellow- green. The dark green chlorophyll-like matter in the intestines is clearly visible in this instar. The teeth of the black sclerotized mandibles, or mouth hooks, extend into the oral opening. The mandibles are united at the base and appear to work together as a unit. The mouth hooks are clearly visible in all instars. Mter eclosion the larva fonns a narrow translucent feeding channel. Starting from the point of hatching at the oviposition puncture, a thin pencil line-like mine denotes the trace of a Ll larva. This linear mine widens gradually from about 0.5 mm to 1 .0 mm at the first moult. This is followed by long linear or serpentine and broader mines by second instar larvae (the linear mine gradually widens to about 5 mm at the second moult). The third instar larvae widen the mine gradually into an irregular blotch. The mine gradually expands and may cover ca. 100 mm2 area (on big leaves) (Plates 8 till 12). I observed up to seven fully developed mines on a single Chinese cabbage leaf. In such case, leaves are sometimes completely destroyed during 2 weeks (in the laboratory) or 3 weeks (in the field) (20 leaves observed in each case). Larval movement within the mines is of a peristaltic type. As the larvae increase in size, their dorsal and ventral sides contact the top and bottom of the mines, aiding them in their movements. In a heavily mined leaf, the larvae often have to move some distance to fmd green leaf tissue. This is particularly true of the third - instar larvae. In doing so they progress in the manner described, quickly eating any green tissue encountered. Larvae extrude frass through mines, where it adheres to the leaf and slowly accumulates; the larval faecal pellets are not very conspicuous as they are deposited at the side of the mine. Sometimes, because of severe damage by the larva to the whole plant, the plant may die (more than 100 observations). Larvae of Scaptomyza flava are unable to leave one leaf and enter another. But when removed from a mine and placed on a cut leaf surface, larvae of any size mine into the new leaf and begin feeding almost immediately (personal observation, unrecorded data). Chapter 2: The biology oj Scaptomyza flava 75 Plate 7: larvae of Scaptomyza flava -- - - - - ------------ --- -- - - - - CluJpter 2: The biology of Scaptomyza flava 76 Larvae move via peristaltic action of their hydrostatic skeleton. There are three moults and larval instars. The fourth instar occurs between puparium formation and pupation. A series of larvae were examined microscopically to determine the average size of the mouth hooks. Cephalopharyngeal skeleton lengths were measured to determine the number of larval instars. Measurements were made from a dorsal viewpoint. Sex of larvae was not determined. The data show that there are distinct mouth hook (cephalopharyngeal skeleton) sizes for each larval instar. A knowledge of instar number is important for an understanding of the timing of population events, the effects of natural enemies, insecticides and the duration of damaging stages (Hamilton and Zalucki, 1991). Larvae were dissected from the leaves of plant species on several dates and preserved in 70% alcohol for subsequent head-cephalopharyngeal skeleton length measurement. The average length of fIrst instar larvae is 0.4 mm (range 0.375-0.450, 50 observations), the second instar is 2.3 mm (range 1 .9-3.6, 50 observations), with the cephalopharyngeal skeleton about 0.25 mm in length. The third instar larva is 4.4 mm (range 3.5-5 mm, n= 50) and fourth instar is 5.5 mm (range 5.4-5.6 mm, n= 25). The mature fourth instar larva averaged 5.8 mm with a cephalopharyngeal skeleton about 0.50 mm long. In a severe infestation (e.g., about 60 larvae in each leaf) occasionally half of the body of a larva is inside and other half is outside of the leaf and sometimes larvae have been seen moving on the leaf surface. 01<111(,1 2 /Iii !>/(ilng, IIf S, (/I'(nl/l \�.(/ j7(/ \ ( / 77 Plate 8: B lotch m i nes on Chi nese cahhage leaves Plate �: I ncrcasing sevel; ly of damage on leaves of Ch inese cahhage hy S. j7ava Cllt/I'II" 1· n,,· ',,0101:' of S, (/1'101/1 1:',/ J7(/\(/ 78 Plate to: B lotch m i n�s on caul i llowcr leavcs Plate ] 1 : B lotch I11 I 11CS on t urn ip Icavcs Plate 12 : Plants of Chinese cabbage undamaged (left) and heavily damaged by S. flava Chapter 2: The biology of Scaptomyza jlava 80 When a larva of S. jZava is ready to pupate it cuts a semicircular slit in the leaf surface, usually at or near the end of the mine. This slit may be located on the upper or lower leaf surface, but depends on the mining location of the larva within the mesophyll. The larva emerges with characteristic peristaltic locomotion. Movement outside the mine is the same as within and is accompanied by a rolling motion, which usually forces the larva to fall from the leaf to the ground to form the puparium, after evacuating its gut. Larvae occasionally pupate within or on leaves or at the base of leaves or stalks. Larvae exit leaves during early daylight hours, with the majority of emergence occurring before 0900 hr. Under laboratory and greenhouse conditions (room temperature in August and September 1991 ), mean development times of each stadium (calculated only for those individuals that reached adulthood) were : 1 st ins tar 2 days, 2nd instar 2.4 days, 3rd instar 2.6 days and 4th 1 day (or third instar 3.6 days), a total time of 8 days as larvae. Despite the fact that the duration of L3 instar is only 1 .3 times longer than L l , the volume of leaf tissue consumed by L3 is much greater than the L l . Mature larvae placed in a petri-dish pupate quickly (about one day). PUPAE At the end of the feeding phase the third instar departs from the food (host) and burrows into the soil (sometimes larvae enter diapause within their natal leaf [in the mine]) to pupate. When ready to pupate, the larva becomes shorter and thicker. The third-instar skin forms the puparium, in which the pupa stage is formed. The puparia are at fIrst light yellow and within 24 hr. become brown (plate 13). The lateral sides of the pupa are subparallel and tapered rather Sharply at the ends, flattened ventrally and arched dorsally. They average 3 ± 0. 1 mm in length (n= 25). In the field most pupae are formed in soil crevices adjacent to host plants (personal observation, unrecorded data). Pupal development took on average 14 days (range 1 0- 18 days, 50 observations) in November and December 199 1 under laboratory conditions (no temperature control). Chapter 2: The biology of Scaptomyw flava 8 1 After the adult emerges, the empty puparium is a light brown, rather brittle structure, with a torn dorsal lid-like section left hanging open at the anterior end. A hyaline soft, pliable sac, which enveloped the developing adult, is left inside the puparium. The entire life cycle can be completed in about 28 days at approximately 1 8 ± 2°C, natural daylength (under a I lL : 13D photoperiod), and 75 ± 3% RH (early spring). Average duration of each stadium is: - Egg: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 days, 20% of total development. - Larval stage: . . . . . . . . . . . . . . . . . . . . . . . . 8 days, 30% of total development. - Pupa: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 days, 50% of total development. Total development time: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 days, 100%. Males and females required nearly the same time to develop (unrecorded data). Chapter 2: The biology of Scaptomyza flava 82 Plate 13: Pupa of S. flava - - -- - --------------� - - - - PRODUCTION IN TIME OF "FEEDING PUNCTURES" AND EGG LAYING BY S. FLAVA ON CHINESE CABBAGE INTRODUCTION Scaptomyza flava is unusual among phytophagous insects in that adult females make small punctures in leaves of host plants with their toothed ovipositor from which both sexes may feed on the exuding juices. Only a small proportion of these punctures is utilised for the deposition of eggs (see detail literature review and in the section "Comparison of plant species as hosts for S. flava"). It could be important to determine the sequence in time of the formation of punctures and the commencement of egg laying. An experiment was therefore undertaken using Chinese cabbage plants and individual pairs of insects to investigate this. MA TERIAL AND METHODS Puncturing activity: To confIrm that Scaptomyza flava females require additional nutrient for commencement of egg laying, a small experiment was undertaken under greenhouse conditions and with the following treatments: 1 ) Single pairs of newly emerged adult insects confmed without plant material for fIrst 24 hr. 2) Single pairs of newly emerged adult insects confmed with plant material (potted Chinese cabbage plant) for fIrst 24 hr. In the subsequent three 24 hour periods insects in both treatments were provided with a fresh potted Chinese cabbage plant. There were 5 replications for each treatment For each treatment and for each 24 hour period the number of feeding punctures and eggs were determined. 83 - - - - ------------------- Chapter 2: The biology of Scaptomyza jlava 84 Time of feeding and oviposition: Observation suggested that feeding and oviposition by adults were crepuscular activities. To confmn the time of feeding and oviposition activity, two experiments were undertaken under laboratory conditions. In the first experiment there were 14 sampling intervals (treatments) replicated 5 times in separate containers. Treatments (Hours): 05.00, 06.00, 07.00, 08.00, 09.00, 10.00. 12 .00. 14.00. 16.00, 17.00, 1 8.00, 19.00, 20.00 and 2 1 .00. At each time a single pair of 2 day old adult flies was placed in a gauze cage containing plant material (one potted Chinese cabbage plant) and removed after 1 hour. The numbers of feeding punctures and eggs were then counted. The second experiment was conducted in a greenhouse conditions during November 1992. The greenhouse environment consisted of natural photoperiod ( 14L: lOD) with ambient temperature of l3 to 19°C and 60 to 94% relative humidity. Single potted Chinese cabbage plants at the 3-4 leaf stage were placed in square cages 30 x 30 x 30 em with fme mesh terylene net cloth screen ceiling and walls. Moist paper towels were placed on the floor of the cages. Individual pairs of newly emerged ( 1 to 2 hour old) unfed adult insects were introduced into each cage (flies had to be exposed to plants immediately after emergence to prevent excessively high initial feeding punctures and egg laying). Cages were restocked with a fresh plant every 4 hours until eggs started to be laid. Sequences and durations of activities were recorded and for each interval the number of eggs and punctures were determined by counting under a stereo microscope. In preliminary tests it had been established that eggs were not laid during the hours of darkness (though a few punctures were formed). Therefore plants were not renewed overnight. There were 1 0 replications each consisting of one pair of insects. RESUL TS The results of these experiments are summarised in Tables 3, 4, 5, and 6 and in Figs. 4, 5 and 6. ------- - - - - -- - - - - Chapter 2: The biology of Scaptomyl1l flava Table 3: Mean number of feeding punctures and eggs per female Trt 1st 24 hours 2nd 24 hours 3rd 24 hours Total means Mean Mean Mean Mean Mean Mean No. of No. No. of No. of No. of No. of No. of No. of holes of holes! eggs holes eggs holes eggs eggs 1 - - 72 1.2 142 1 .2 107 1.2 2 200 1.4 252 6 710 18 414 8.5 85 The results in Table 3 show that insects deprived of plants during the first 24 hours after emergence laid fewer eggs over the subsequent two 24 hour periods compared to insects that had access to plants for the first 24 hours. In treatment 1, this delay may also be due to delay in mating (no host plant present for first 24 h). However, insects initially without access to plants also produced fewer leaf punctures, during the 2nd and 3rd 24 hours periods so may have been weakened by this deprivation. The results of the second experiment (Table 4) showed that practically all of the feeding punctures were produced and eggs deposited between 6-10 a.m. and 5-8 p.m. (sunrise: 05.50, sunset: 20.45). Prior to 06.00 hours females that had mated showed little feeding and no egg laying activity but one hour later these activities had begun. By 10.00 hours, activities had reached a peak and means of 5.2 eggs and 42 feeding punctures occurred between 09.00 and 10.00. The frequency of feeding and oviposition declined subsequently to 14.00. The decrease in these activities was correlated with an increase in the temperature and light intensity. From 16.00 hours, feeding and oviposition activity increased from means of 12 and 2.3 per hour respectively to means of 42 and 5.4 per hour by 19.00. The pattern of feeding and oviposition activity in time is shown in Figs. 4 and s. 1 Holes: Feeding punctures Chapter 2: The biology of Scaptomyza jlava 86 Table 4: Time of feeding and oviposition activity of Scaptomyza flava females under laboratory conditions Numbers of egg laid and feeding punctures between indicated hours Hours Mean Number of feeding Mean No. of eggs per punctures female 05.00-06.00 10 0 06.00-07.00 34 3 . 1 07.00-08.00 35 4 08.00-09.00 38 3 .9 09.00-10.00 42 5.2 10.00-1 1 .00 9 1 .6 1 1 .00-12.00 4 0 12.00-14.00 3 0 14.00-16.00 8 1 16.00-17.00 1 2 2.3 17.00- 18.00 40 5 1 8.00-19.00 42 5.4 19.00-20.00 2 1 4 20.00-2 1 .00 2 0 Table 5: Replication ,!. 1 2 3 4 5 6 7 8 9 10 - - - - - -------- - - - - - - - Production in time of "feeding punctures" and egg laying by Scaptomyza flava on Chinese cabbage under greenhouse conditions Day 1 Time ... 08.00- 12.00 - 16.00 - 12.00 16.00 20.00 No. of holes 5 36 99 No. of eggs 0 0 0 No. of holes 50 20 300 No. of eggs 0 0 0 No. of holes 25 25 37 No. of eggs 0 0 0 No. of holes 3 6 40 No. of eggs 0 0 0 No. of holes 50 0 1 1 No. of holes 1 10 No. of eggs 0 No. of holes Replicates 105 No. of eggs 6 - 10 0 commenced at No. of holes 60 16.00 No. of eggs 0 No. of holes 1 50 No. of eggs 0 No. of holes 30 - - --�------- Chapter 2: The biology of Scaptomyza flava I Day 2 05.00 08.00· 12.00 ·0.800 12.00 ·16.00 801 10 52 1 8 2 10 0 0 2 30 10 0 0 0 1 39 1 1 1 0 0 0 1 50 3 3 25 4 2 0 0 0 5 2 4 0 0 0 44 6 3 0 0 0 80 10 0 0 0 0 200 15 2 1 No. of feeding punctures (holes). 2 No. of eggs. I 16.00 05.00 ·20.00 ·08.00 25 50 0 0 10 1 10 0 0 1 5 1 50 0 0 0 80 10 30 0 0 30 2 0 60 0 0 1 10 200 0 13 0 17 88 Day 3 I 08.00 12.00 ·12.00 ·16.00 0 45 0 5 1 1 88 0 6 0 80 3 15 40 2 10 0 1 0 45 2 5 0 50 0 1 2 10 Chapter 2: The biology of Scaptomyza flava --- -- - - - - - 89 The results of the third experiment (Tables 5, 6) show that each female makes between 141 and 550 (mean 258) feeding punctures before commencing egg laying and that there is a period of approximately 24 hrs. after emergence before egg laying begins. Two pairs of insects (replications 5 and 10) did not produce any eggs but caused some feeding punctures. Table 6: Mean number of feeding punctures and eggs per female in time Time 41 8 12 17 22 26 30 34 42 46 50 54 Holes 59 22 93 28 32 43 3.3 8 1 2 77 39 42 Eggs 0. 1 0.5 0.6 0 0 2 1 .2 4 DISCUSSION All ten individual flies (Tables 5-6, the third experiment) commenced making leaf punctures within four hours after emergence and two out of ten females produced peak numbers of punctures within the fIrst 12 hours and before egg laying commenced. With other individuals peak numbers of punctures did not occur until about the time that egg laying commenced. Where there was an early peak there was also a second peak once egg laying began. This is shown clearly in the mean values for all ten pairs of flies (Fig. 6). Egg laying did not commence until at least 22 hours following emergence (Table 5). This delay in commencement of egg laying and the pattern of feeding suggest that Scaptomyza females require additional nutrients for oviposition (pre-oviposition feeding). Additional nutrients to those obtained from host plant leaf juices are important to obtain maximum fecundity and they obtain these by feeding on leaf juices that are released by the puncturing activity of the ovipositor. 1 hours from emergence. 2 See results of the fIrst experiment (puncturing activity test) in this section. Chapter 2: The biology of Scaptomyzaj7.ava Fig. 4: Time offeeding activity ofS·flava females under laboratory conditions <.0... o .... Cl) .n E ::; z 5 6 7 8 9 1 0 1 2 2 4 5 6 7 8 9 A.M. Time of day (Hours) P.M. Fig. 5: Time of oviposition activity of Sflava females under laboratory conditions 4- o .... Cl) .n E -' z 6 7 8 9 1 0 1 2 2 4 5 6 7 8 Time of day (Hours) A.M. P.M. 90 Fig . 6 : 1 ifJ 0() b() OJ c3 times as long with honey and males with honey solution survived >4 times as long compared to those that had access only to water. The greatest lifespan was for those fed honey solution with water and yeast also available (Table 9, Fig. 8). There was no significant difference between the lifespan of leaf miners provided with water only and yeast plus water, but for males there was significant improvement in lifespan when yeast was available as well as honey solution. Similar results were obtained for Liriomyza trifolii species by Dimetry ( 197 1 ), Zoebisch and Schuster ( 1987), Pedigo ( 1989), Kircher and Al-Azawi ( 1985), House ( 1 974), Wyatt ( 1967) and Hollingsworth and Burcombe ( 1 970). Honey apparently provides necessary nutrients to increase longevity significantly. It may also be concluded that access to water allows mobilisation of food reserves not available to starved flies (Hollingsworth and Burcombe, 1970), but that maximum longevity requires additional nutrients provided by honey solution. Further studies are required to determine which components present in honey are responsible for the effects on longevity observed in this study. The results suggest that longevity may be greater in the field if carbohydrate food sources are available. Nectar is such a potential food source and more field observations are needed to determine if female leaf miners exploit nectar from crop or weed flowers. The presence of aphid infestations on either crop plants or weeds associated with Chinese cabbage and turnip plants may also provide food for adult leaf miners via their honeydew, thus increasing their biotic potential. Fig . 8: Chapter 2 : The biology oj Scaptomyzaf/ava The longevity of adult S.flava with different food availability Starved Water Yeast Treatments Honey Honey & Yeast 1 04 LIFESPAN OF MATED AND UNMATED ADULT SCAPTOMYZA FIAVA INTRODUCTION "Costs of reproduction occur when an increase in current reproductive rate leads to a drop in lifespan or in future fertility" (partridge and Fowler, 1 990). It is well known that sexual activity reduces longevity in Drosophila (Service, 1 989). Virgin females (Smith, 1958; Partridge et al., 1986 cited by Service, 1989) and virgin males (Partridge and Andrews, 1985 cited by Service, 1989) live longer than mated flies. However, the deleterious effects of sexual behaviour on longevity are reversible: when the sexual activity of mated flies is terminated, their death rates become similar (after a short time lag) to those of same-aged virgins (partridge et al., 1986). Thus, sexual activity appears to represent a short-term risk or hazard with respect to survival. This pattern of effects has been interpreted as evidence that mating does not cause an acceleration of senescence and that the shortening of lifespan by sexual activity does not involve the ageing process, i.e., somatic deterioration (Partridge and Andrews, 1985 cited by Service, 1989). Based on their observations of the effects of mating on male lifespan, Partridge and Andrews (1985) have argued that selection for increased longevity in Drosophila melanogaster (Rose and Charlesworth, 198 1 ; Luckinbill et al., 1984; Rose, 1 984 cited by Service, 1 989) may in fact be selection for reduced sexual activity or, more generally, for reducing short-term mortality risks. Differences in female lifespan appear to be associated with changes in age-specific fecundity (Service, 1 989). The results of several studies have implied that egg-production is costly to female insects, by reducing their survival. For instance, the lifespan of female Drosophila subobscura is increased after sterilization by high temperatures (Smith, 1958 cited by partridge et al. , 1 987) or by X-irradiation (Lamb, 1 964). In these examples a strong case for an effect on lifespan of egg-production per se was made by the demonstration that the lifespan of mutant ovaryless females was unaffected by the same experimental 105 Chapter 2: The biology of Scaptomyza flava 106 treatments (Partridge et aI., 1987). In contrast to these fmdings, a study of the lifespan and egg-production rates of female Drosophila melanogaster whose exposure to males was experimentally varied suggested that the reduced longevity of females kept with males could not be caused by variation in egg-production rates (Partridge et aI., 1 986). Exposure of females to males may affect female longevity directly (Partridge et aI., 1987). Unlike Drosophila subobscura females, Drosophila melanogaster females regularly remate (Newporty and Gromko, 1984), and this or some other consequence of exposure to males may result in reduced longevity. Partridge et al. (1987) manipulated egg-laying rate environmentally. Flies that laid fewer eggs lived longer, but differences in total body weight between experimental groups were not consistent with the hypothesis that increased fecundity caused greater mortality through reduced somatic investment. Thus, higher egg-laying rates may also represent an increased short-term hazard, similar to that associated with mating activity, rather than an acceleration of somatic deterioration. If this is the case, then the increased longevity obtained in selection experiments may result from a reduction in the short­ term risk attributable to egg laying. According to this interpretation, females in long­ lived populations are exposed to lower levels of risk (early in life) because they have reduced fecundity. The aim of the present study was to investigate whether mating and egg­ production reduce longevity of Scaptomyza flava. MA TERIALS AND METHODS An experiment was conducted to determine the lifespan of virgin and mated female and male Scaptomyza flava under greenhouse conditions and natural daylength (April 1 993, 1 3 h light : 1 1 h dark cycle). All experimental transfer of insects was done Chapter 2: The biology of Scaptonryza flava 107 using minimal carbon dioxide anaesthesia (after passage through water to maintain humidity) (Plate 3) on flies not less than three hours from eclosion. This procedure has been shown to be without significant effect on Drosophila female fertility or longevity (Partridge et al., 1986). During this study, ambient temperature ranged from 8 to 15°C and relative humidity from 65 to 98%. Sample size was 10 adult flies per treatment. Two one-month old (at the 3-4 leaf stage) potted Chinese cabbage plants were placed in each of 4 cages, which contained: 1 . - 10 unmated females. 2. - 10 mated females. 3. - 10 unmated males. 4. - 10 mated males. All cages were provided with free water. Clean white paper was placed on the floor of each cage. To obtain unmated flies, two methods were used: 1) they were collected at eclosion (less than four hours old from a colony reared on Chinese cabbage. Because adults do not mate until they are >1 day old [Chapter 2] , there was no opportunity for females to mate within rearing cages), 2) pupae were separated individually into small glass tubes and emerged flies were removed daily. For supplying fertilized females, flies after emergence were housed in groups with males in cages with Chinese cabbage plants for 3 days to ensure they were inseminated (preliminary laboratory and greenhouse observations indicated that most males mated within 24 to 48 hours after emergence). Thereafter mated females remained isolated in their cages for the remainder of their lives. Mated male flies were obtained two days following emergence. Chapter 2: The biology of ScaptomyZil flava 108 As virgin and mated females produce punctures on leaves plants were renewed every four days until all flies had died. No leaf punctures were observed in the cages in which males were held (Plate 15) so plants in these cages were not renewed. Cages were checked daily and the number of dead insects recorded until all had died. Deaths were recorded and dead flies removed from the cages at the same time each day. Based on reports of Picard ( 1913, cited by Partridge et ai., 1986) and Attia and Mattar ( 1939, cited by Partridge et al., 1986) that unmated females of some insects deposit a limited number of eggs, plants which were exposed to unmated females were checked for eggs. Data were analyzed with a general linear models procedure (SAS Institute, 1985). Where significant differences in the variables occurred, means were separated using LSD test (P s 0.01 ). Chll(ller 2: 1'1", hilling\' 11/ S( {/"IIIII/r�{j Jl<11'(1 Plate 1 5 : Com parison he tween fee d i n g punctures w i t h male and fem a le S. j7ava Left. Lea!" e x posed to !"t,;male n ics Right . Lca f ex posed to m;,l Ic n ics 109 Chapter 2: The biology of Scaptomyw j1ava 1 10 RESULTS AND DISCUSSION Results are summarized in Table 10. Table 10: Life span of Scaptomyza flava under greenhouse conditions (with plant material) Treatment Mean life span (Days) Range (Days) Unmated female 17.5 B 5 - 46 Mated female 17. 1 B 8 - 26 Unmated male 26.3 A 14 - 56 Mated male 8.5 C 4 - 14 Means in each column accompanied by the same letter are not significantly different at p :$ 0.01 ( ANOV A followed by LSD (lsd = 0.65) test for separation of means). Surprisingly, the effect of mating on lifespan of female was opposite from my predication on survivorship of Scaptomyza flava. The increased lifespan in my experiments of virgin males compared to virgin females was unexpected. A shorter lifespan in mated males of Busseola fusca was observed by Usua ( 1970). Some (unfertilized) eggs were laid by unmated females (mean 5 per female) but neither I nor Usua (1970) have observed any development in eggs laid by such virgin females. All such eggs laid by virgin females collapsed within two days and failed to develop. Unmated males lived significantly longer (26.3 days) than all other groups (P :$ 0.01 ) and about 3 times as long as mated males (8.5 days). However, virgin females ( 17.5 days) did not live significantly longer than mated females (17 . 1 days). Taken the results of the experiment suggests that exposure to females may be potentially more Chapter 2: The biology of Scaptomyza flava 1 1 1 damaging to male survival. Contrary to my expectation, mating and egg production by females did not increase female death rate. The results overall therefore are equivocal with respect to Partridge and Andrews (1985) results, as in some species of Drosophila mating and egg laying do lower survival (Partridge et al., 1987). The difference in longevity between male and female could be attributed to different amounts of body fat. Luckinbill et al. (1988) also found that mating had a more pronounced effect on male longevity than on female longevity in some Drosophila species. In natural, these may be an interaction between the two effects, both because elevated egg-laying rates have been shown to lead to more frequent re-mating by female (Gromoko and Gerhart, 1984 cited by Partridge et al., 1 987). For female flies, the difference in mean longevity between virgin and mated ones is unaffected by mating status, as shown by the absence of statistical interactions between them. NUMBER OF ADULT INSECTS EMERGING FROM A SINGLE LEAF OF CHINESE CABBAGE MA TERIALS AND METHODS Ten infested leaves of Chinese cabbage obtained from the rearing colony were placed individually with their stems into small water containers and covered with small PVC acetate sheet cages until all eggs hatched, larvae fed and pupated and new adults emerged. The experiment was set up under greenhouse conditions. Ambient temperature approximated 20°C, 70 (±3)%RH and natural daylength was about 14 hours. The experiment was set up between 0800 and 1000 hours. At the end of the experimental period numbers of emerged adult flies were recorded. RESULTS Results presented in Table 11 show that from each leaf between I to 5 adults emerged. 1 12 Chapter 2: The biology of Scaptomyza flava 1 13 Table 11 : Number of adult insects from ten leaves of Chinese cabbage Leaf Area of leaf No. of emerged ( cm 2 ) adults 1 60 5 2 55 4 3 54 4 4 53 3 5 45 3 6 44 1 7 41 1 8 40 2 9 39 1 10 35 2 Mean 46.6 2.6 THE ABILITY OF SCAPTOMYZA FIAVA TO DEVELOP IN DEAD AND DECAYING LEAF MATERIAL INTRODUCTION Pomace flies or small fruit flies (Drosophilidae) are generally found around decaying vegetation and fruits. The larvae of most species occur in decaying fruits and leaves (Borror et al., 198 1 ). As Scaptomyza flava is taxonomically placed within the Drosophilidae in contrast to most other leaf mining Diptera, two experiments were conducted to determine whether this species can breed in dead and decaying leaf material. MA TERIAL AND METHODS Environmental chambers were maintained at 14:10 L:D photoperiod, and relative humidity of 40 - 70%. Data were collected daily. In the fIrst experiment, several Chinese cabbage plants were exposed to newly emerged adult flies in a cage until some eggs were laid. The leaves were then cut from the plants and placed into separate cages. Moist tissues were placed under the leaves and watered each day. After 2-3 days the leaves were well decayed. In the second experiment, 1 0 pairs of newly emerged male and female S. flava were confmed in a cage. Some decayed leaves of Chinese cabbage were placed in the cage for 3 days then removed. RESULTS AND DISCUSSION In both experiments larvae of Scaptomyza flava developed in the decaying leaf material, pupated and produced adult insects. The number of adults from the fIrst experiment was 80 and from the second experiment 25. From this brief experiment it is apparent that Scaptomyza flava will lay eggs and larvae can develop in decaying leaves of Chinese cabbage. However, the number of emerging adults was greater when the flies fIrst laid their eggs in live leaves. 1 14 C h a p t e r 3 HOST PLANT RELATIONSHIPS OF SCAPTOMYZA FLAVA1 COMPARISON OF PLANT SPECIES AS HOSTS FOR SCAPTOMYZA FLA VA INTRODUCTION One of the most crucial events in the life cycle of phytophagous insects is the selection of a suitable site for oviposition. Newly hatched larvae of many insects are relatively immobile (e.g. , leaf miners) , and depend on the ability of their mother to find the best source of food for their successful growth and development. The driving forces affecting host finding and acceptance or rejection of a host are governed largely by surface (e.g. , polar extracts, nonpolar compounds [Renwick and Chew, 1994]) and nutritional qualities of the plant, competition, and coincidence of favourable conditions that ensure success of offspring (Capinera, 1993). Host selection by phytophagous insects can be considered as "choice behaviour" with the choice being made at different stages in the sequence leading up to host acceptance (Browne, 1977 cited by Visser, 1 988). Some insects "choose" solely after contact with the plant. Here the frequency with which different plants, hosts and nonhosts, are visited depends only on their apparency and relative abundance. Other insects perceive plant characteristics at a distance and initially "choose" according to these impressions (Visser, 1988). However, in this case, after this initial choice is made, 1 Some parts of this Chapter modified from a paper published In Entomologia experimentalis et applicata. 1 994. pp. 1 1 5 Chapter 3: Host plant relationships of Scaptomyza flava it should be noted that the insect probably continues to "choose" as it proceeds through the sequence leading up to oviposition (Harris, 1 994 personal communication). Plant chemistry almost certainly provides cues for location of the host as well as poses problems for the larvae after hatching. However, other plant characteristics, such as morphology, may influence the interaction of insects with their host plants (Vaugun and Hoy, 1 993). Cruciferous plants have a distinctive biochemistry, characterized by the presence of one or more enzymatic hydrolysis products of glucosinolates (mustard oil glucosides) (Kjaer, 1 976) a group of naturally occurring anionic compounds whose known number totals almost 1 00 (Pivnik et ai., 1 992). These are hydrolysed by enzymes (e.g., enzyme myrosinase) within the plant cell to produce volatile chemicals including isothiocyanates (Cole, 1 976) or mustard oils, nitriles and other compounds, depending upon pH and other conditions (Chew, 1 988). Some hydrolysis probably takes place during normal catabolysis, particularly during early seedling development. It also occurs rapidly when plant tissue is damaged (Pivnik et ai., 1 992). Glucosinolates are secondary plant substances which are believed to have evolved as a chemical defence against herbivores (Rhoades and Cates, 1 976; Feeny, 1 976 cited by Nottingham, 1 988). Insects that are specialized to feed on cruciferous plants are able to detoxify these chemicals (Nottingham, 1 988) and in many cases use them as host­ finding cues and feeding and oviposition stimulants (e.g., Nottingham, 1 988). However, a number of insect species feed primarily or exclusively on plants containing glucosinolates. Many of these insects are known to suffer no adverse effects from naturally occurring concentrations of glucosinolates and isothiocyanates. It has been well documented that at least some crucifer-specialist insects are also attracted by one or more of the isothiocyanates (Chew, 1988) . For example, gravid female cabbage root flies use isothiocyanates as host-finding cues and glucosinolates as oviposition stimulants (Hawkes et aI., 1 97 8 cited by Nottingham, 1 98 8). Host preference is associated with higher oviposition rates, increased female longevity, shorter developmental time, and higher survival in all life stages (van Lenteren and Noldus, 1 990). 1 1 6 Chapter 3: Host plant relationships of Scaptomyza flava 1 17 Many studies have investigated the interactions between insects and host plant species but the relationship between Scaptomyza flava and its host plants has not been reported other than the general observation that it is usually found associated with Cruciferous plants. As neonate larvae of Scaptomyza flava are incapable of moving from plant to plant, the choice of feeding sites of larvae is detennined entirely by ovipositional preference of the adult female. Because Scaptomyza flava had not been studied in regard to its oviposition behaviour, I was unable to predict which plants might be especially suitable for survival and reproduction. Therefore, a study was initiated to detennine host-feeding behaviour using a range of common plants from the family Brassicaceae compared to plants from other families. The strong correlation between the presence of glucosinolates and the host range of some insect such as cabbage butterflies has led to numerous studies based on the assumption that these compounds are responsible for host recognition (Renwick and Chew, 1994). In this study I fIrst examined selection by S. flava for feeding and oviposition between 8 plant species including 5 species within the family Brassicaceae. The specifIc objectives of this study were to ( 1 ) detennine if S. flava will accept plants other than Brassicaceae and (2) compare a range of brassicas as host plants for S. flava. MA TERIALS AND METHODS The experiments were conducted under ambient greenhouse conditions in the Plant Growth Unit (PGU), Massey University. Feeding and oviposition preferences of adult females were determined for eight plant species (five cruciferous, one composite and two grasses). Preference was measured by the number of feeding punctures and by the number of eggs laid on the plants in choice and non-choice tests. Temperature in the experimental chamber was maintained at 14 ± 2°C [night] and 22 ± 2°C by day. Natural daylength (at a 10: 14 [L:D] hours photoperiod with photo phase from 07. 15 [sunrise] to 17. 15 [sunset]) was that in July 1993. The experiments began between 09.00 and 1 1 .00 hours when the flies were introduced to the test arenas. Chapter 3: Host plant relationships of Scaptomyza flava 1 18 The following plant species were evaluated (Table 12): Table 12: Plant species used in studies of host discrimination by S. flava Common Name Scientific N arne Family 1 - Turnip . . . . . . . . . . . . . . . . . . . . . . . . . . . Brassica rapa (Brassicaceae) 2- Hedge mustard . . . . . . . . . . . . . . . Sisymhrium officinale (Brassicaceae) 3- Chinese cabbage . . . . . . . . . . . . . . . . . Brassica chinensis (Brassicaceae) 4- Radish . . . . . . . . . . . . . . . . . . . . . . . . Rhaphanus sativus (Brassicaceae) 5- Cauliflower . . . . . . . . . . . . Brassica oleracea var botrytis (Brassicaceae) 6- Lettuce . . . . . . . . . . . . . . . . . . . . . . . . . . . Lactuca sativa (Compositae) 7- Wheat . . . . . . . . . . . . . . . . . . . . . . . . . Triticum aestivum (Gramineae) 8- Prairie grass . . . . . . . . . . . . . . . . . . . . Bromus willdenowii (Gramineae) All plants were raised from seed in a greenhouse with the exception of hedge mustard which was collected from the field (plants about 10- 15 cm high) and placed into pots. Seeds were germinated in greenhouse media (peat, sand, pumice, dolomite, superphosphate and lime) in plastic pots (20 cm diameter) in an outdoor growth chamber (controlled environment with 20 ± 1°C temperature and 70 ± 10% RH) with enough light and fertilizer for plant growth to continue. Except for wheat and prairie grass seedlings were transplanted at cotyledon opening into pots ( 10 cm diameter) . A single transplant was planted in each pot except for wheat and prairie grass where plants were not transplanted and each pot contained a group of plants (5 plants for prairie grass and 10 for wheat). Plants were overhead watered on alternate days for the fust 4 weeks and were also kept moist by capillary matting and perforated plastic fIlm on the bench. Plants selected for choice and non-choice experiments were mostly at the 3-4 true-leaf stage (26 - 30 days after sowing, ca. 24 cm tall). Newly emerged adult S. flava used in choice and non-choice experiments were Chapter 3: Host plmlt relationships of Scaptomyza flava 1 19 treated identically before exposure to test plants. Flies were sexed under a binocular microscope after being anaesthetized by CO2• The insects used in experiments were about 50 to 60 generations removed from field populations and were from a laboratory colony raised on Chinese cabbage. When the experiments were terminated, plant foliage was examined for the presence of feeding punctures and eggs with transmitted light under a dissecting microscope. To measure oviposition I divided each leaf into four quadrants by marking four segments equidistant along the midvein, then drawing a line perpendicular to the midvein. The number of eggs (or feeding punctures) occurring in each quadrant were then counted. Test plants were stored in a coolroom (4°C) until assessments could be made. Clwice tests: In these tests, experiments were conducted in the test chamber described above, in five arenas (cylindrical cage, 85 cm in diameter and 90 cm in height made from net fine cloth) (Plate 16), each of which contained eight potted plants (one of each plant species) arranged at random in a circular formation 10 em apart and 14 cm from the cage walls. Groups of four male-female pairs of newly emerged adult S. flava were introduced into each cage and left for four days (19.7. 1993 - 23.7. 1993) to permit mating, feeding and egg laying. The flies were then removed, and the distribution of feeding punctures and eggs among leaves was recorded. The experimental design was a randomized complete block. The strata of variation were between the five blocks (cages) and between the 8 treatments within blocks. The experimental "whole treatment" units were pots of one plant and the allocation of treatments (different plant species) within blocks was randomised and their order was changed for each replicate. The results were subjected to two-way analysis of variance. When the analysis of variance showed significant treatment effects (P $ 0.05), Fisher's protected least significant difference (LSD) test was used to separate means at P $ 0.0 1 (Milliken and Johnson, 1984). Regression analysis (SAS Institute, 1 985) was used to evaluate the relationship between numbers of feeding punctures and eggs per leaf. Chapter 3: Host plant relationships of Scaptomyzajlava 120 Plate 16 : Cylindrical cage used for choice tests Plate 17 : Square cage used for non-choice tests Chapter 3: Host plant relationships of Scaptomyza flava 121 Non-choice tests: In the non-choice test, eight single pots of each plant specIes were placed separately in each test arena (square cages [30 by 30 by 30 cm] of terylene net). There were three arenas (replications) for each species. The arenas were assigned at random to positions in the greenhouse (Plate 17). The flies were sexed and paired up at random. Four newly emerged (3 hours old) male + female adult flies were placed in each cage and left for 4 days. RESULTS The results of choice tests are presented in Table 13 and of non-choice tests in Table 14. Figures 9 and 10 compare the numbers of feeding punctures and of eggs in choice and non-choice tests respectively. Choice tests: In a choice situation, on the basis of feeding punctures and of eggs laid, plant species fell into three groups: L turnip, hedge mustard, Chinese cabbage and radish with large number of feeding punctures and moderate numbers of eggs; 2. cauliflower with few feeding punctures and fewer eggs than the fIrst group; 3. lettuce, wheat and prairie grass (i.e., non-Brassicaceous plants) with no feeding punctures and no eggs. There were significant differences in total number of feeding punctures on the cruciferous plant species; most for radish, least for cauliflower and intermediate for turnip, hedge mustard and Chinese cabbage. Some differences between species within this group in the total number of eggs laid were also significant. Turnip received significantly more eggs than radish and cauliflower, and cauliflower received fewer than all other species. There was no significant correlation between number of feeding Chapter 3: Host plant relationships of Scaptomyza flava 122 punctures and eggs deposited (Table 13; Fig. 9). I have observed that S. flava selected intact leaves of Chinese cabbage and turnip over damaged leaves (by rust, aphids and white flies) for oviposition (uninjured plants received increased feeding and were always chosen over injured plants, regardless of species or age). Table 13: Number of feeding punctures and eggs on eight plant species in choice tests with Scaptomyza }lava Plant Mean No. Mean No. eggs Percentage of species punctures per pot punctures per pot with eggs turnip 229.5 b 7.2 a 3 . 1 hedge mustard 1 8 1 .3 be 4.5 ab 2.5 Chinese cabbage 132.4 e 4.0 ab 3 radish 347.5 a 2.5 b 0.7 cauliflower 15.5 d LO c 6.4 lettuce O d O c - wheat O d O c - prairie grass O d O c - Treatments accompanied by the same letter are not significantly different at P ::; 0.05 (ANOVA followed by LSD [lS�UIlCtures = 53.87; Isdeggs = 6.29] test for separation of means). Chapter 3: Host plant relationships of Scaptomyza flava 1 23 Non-choice Tests: Two major differences occurred between the non-choice tests and choice tests. First, radish received significantly fewer punctures than turnip, hedge mustard and Chinese cabbage, and was not significantly different from cauliflower. Secondly, an appreciable number of feeding punctures were made on wheat (significantly more than cauliflower) and eggs were deposited in 2.5% of these. Numerically per pot ( 1 0 plants per pot), wheat received as many eggs as cauliflower, hedge mustard and radish. No significant difference (p > 0.05) occurred between turnip and Chinese cabbage for feeding or oviposition but there was a significantly higher number of feeding punctures on hedge mustard, Chinese cabbage and turnip compared to cauliflower (Table 14; Fig. 10). Approximately 1 .3-fold and 3.5-fold more eggs were deposited on Chinese cabbage than on turnip and cauliflower respectively. When the percentage of punctures with eggs was calculated for each species (column 4, Tables 13, 14) cauliflower had by far the highest value at 6.4% and 28% in choice and non-choice tests respectively. For all other species on which eggs were laid it was less than half this. In the presence of radish or lettuce only (non-choice test), 40 and 6 feeding punctures per pot were made by S. flava compared with 347 and 0 respectively when those and other plants were provided simultaneously (choice test). On Chinese cabbage, most eggs were laid near the midrib of the leaf. In contrast on cauliflower, the majority of feeding punctures were around the leaf margin. Chapter 3: Host plant relationships of Scaptomyza flava 1 24 Table 14: Number of feeding punctures and eggs on eight plant species in non - choice test with Scaptomyza flava Plant Mean No. Mean No. eggs Percentage of species punctures per pot punctures per pot with eggs turnip 202 B 1 1 . 3 A 6 hedge mustard 3 3 1 . 8 A 2.2 B 0.6 Chinese cabbage 269.7 AB 14.6 A 5.4 radish 40.3 CD 3. 1 B 7.7 cauliflower 15. 1 D 4.2 B 28 lettuce 6 D O B 0 wheat 85.4 C 2. 1 B 2.5 prairie grass O D O B - Treatments accompanied by the same letter are not significantly different at P $ 0.01 (ANOVA followed by LSD [ls'4unctures = 66.54; lsdeggs = 4.3 1] test for separation of means). Chapler 3: Host plant relarionshlps of ScaplOmyza flava Fig. 9 : Con1parison of plant species for feeding punctures by Scaptomyzajtava Turnip Mustard Cabbage Radish Caulif Lettuce Treatments Wheat P.grass Fig. 1 0: No. eggs laid by Scaptomyzajlava in choice & no-choice tests Turnip Hedge Cabbage Radish Caulif Lenuce Wheal P.grass Treatments no-choice lesl 125 Chapter 3: Host plant relationships of Scaptomyw flava 1 26 DISCUSSION My results argues that apart from some anomaly plant, Scaptomyza flava female accepted only plant from Brassicaceae family. In the choice experiment reported here Scaptomyza flava typically selected only plants from the family Brassicaceae for feeding and egg laying. However, under non-choice conditions poor and moderate acceptance of lettuce and wheat respectively also occurred. The eggs on the leaves of these non-host plants collapsed within a day or two and failed to develop. Thus, in accordance with field records of plant species affected (Michalska, 1973; Szwejda, 1974; and Pol, 1974), S. flava showed clear preference for plants within the Brassicaceae based on number of feeding punctures and of eggs laid. On Chinese cabbage, the majority of feeding punctures were void of eggs (3% and 5.4% of punctures with eggs in choice and non-choice tests respectively). In contrast on cauliflower, 6.4% and 28% punctures contained eggs in choice and non-choice tests respectively. Thus although the leaves of cauliflower appear to be less suitable than other Brassicaceae for feeding, they are well accepted for egg laying. Scaptomyza flava showed very similar feeding and ovipositional preference for Chinese cabbage and turnip in both choice and non-choice tests with numerical differences not significantly different. In non-choice tests, S. flava produced significantly more feeding punctures on hedge mustard than on turnip. However, when able to choose between hedge mustard and turnip the difference was not significant. In contrast, radish was preferred over other Brassicaceae for feeding in choice tests but received few feeding punctures in non­ choice tests and not significantly greater than cauliflower. When insects exist in an ecosystem provided with several host species, they may prefer to feed and oviposit on some hosts more than the others (Dethier, 1 954; Holdren Chapter 3: Host plant relationships of Scaptomyza flava 127 and Ehrlich, 1 982; Carolina et al. , 1 992). Insects may be expected to be more selective and show strong preferences given a choice between host and nonhost plant species. However, in the absence of highly preferred hosts, a nonpreferred plant may be accepted (Carolina et al., 1992). In these experiments (Chapter: 3, Effect of adult experience on oviposition preference) S. flava flies preferred cauliflower least of the five Brassicaceae offered. There is no obvious reason for this but turnip and Chinese cabbage have a much softer leaf than cauliflower and may be easier to puncture with the insect's ovipositor. On the other hand, selection of plants for oviposition is detennined both by the physical nature of their surfaces and by chemical factors which are detected only on contact (Fenemore, 1988). Surface texture of substrates may play an important role in oviposition preference of Scaptomyza flava. Soft or wax-textured surfaces, i. e., leaves of cauliflower (cauliflower leaves have a very different leaf wax structure from turnip and Chinese cabbage) were less suitable than other Brassicaceae for feeding, but they were accepted for oviposition sites. Although percentage of punctures with eggs on cauliflower was relatively high, damage to leaves was relatively low. No data are available to explain this but it could be due simply to physical condition of cauliflower leaves compared with Chinese cabbage and turnip. General morphology of leaves may also influence oviposition preference. However, leaf hair density does not appear to have an effect on feeding and oviposition of Scaptomyza flava; relatively high leaf hair densities of turnip compared to Chinese cabbage do not apparently inhibit penetration of the leaf surface for feeding and egg-laying. Of the three non-Cruciferous plant species evaluated, flies fed and infertile eggs were laid on wheat under non-choice conditions. This suggests that, under extreme conditions, S. flava may oviposit on plants other than Brassicaceae. Non-choice tests addressed several questions unanswered by choice tests. In choice tests, reduced number of eggs laid on cauliflower could have resulted from (a) fewer females accepting treatments, (b) females accepting treatment but laying fewer Chapter 3: Host plant relationships of Scaptomyza flava 1 28 eggs, or (c) some combination of these factors. The fIrst possibility begs the question of why even a small number of females would accept altered treatments, when the more host plants were available. A possible explanation in that some females were less discriminating because they (a) had matured eggs more rapidly than other females and, therefore, were showing behaviour effects of "time-dependent responsiveness" (Papaj and Rausher, 1 983) or (b) were stimulated to oviposit on the unaltered host, but reacting to proximity of other treatments or crowding on the unaltered cauliflower (or wheat), laid eggs on what would normally be a less stimulately treatment (Singer, 197 1 ) . CONCLUDING REMARKS All fIve Brassicaceous plant species tested may be regarded as acceptable adult hosts because sustained feeding occurred on each though to a much lower extent on cauliflower than the other species. One non-Brassicaceous plant (wheat) can also be considered as marginally acceptable for adult feeding and perhaps would be oviposited on to a small degree if females had no other choice of plants. No measurable feeding or oviposition occurred on prairie grass or lettuce even under non-choice conditions. Therefore, these species should not considered as hosts for Scaptomyza flava. Scaptomyza flava ' s distinct preferences between species within the family Cruciferae (= Brassicaceae) suggests that development of host plant resistance might be a possible control strategy for this pest in the future. Also these results support the hypothesis that host preference of ovipositing females is an important factor in the utilization of cruciferous crops by S. jlava flies. It is possible that some populations of S. flava have broadened their host range beyond cruciferous plants. A factor conducive to host plant expansion is limited access to preferred hosts (Singer, 197 1 ; Miller and Miller, 1986). The absence of other leaf miners on Chinese cabbage, turnip, radish and cauliflower in the Manawatu area has allowed S. flava to exploit this niche without competition. In summary, I have found that oviposition of S. jlava adult is considerably more complex than early studies. Further studies are needed to quantify the fitness of S. flava (both larvae and adults) developing on Cruciferous plant species compared with others. Chapter 3: Host plant relationships of Scaptomyza flava EFFECT OF HOST PLANT SPECIES ON BODY WEIGHT OF ADULT SCAPTOMYZA FlAVA INTRODUCTION 129 The body weight of newly-emerged adults depends on the diet regime and host­ plant species on which the insect developed (Borrer, 198 1) . For leaf miners this is related to the food quality of host leaves within species. Physical changes in the morphology or toughness of leaves or shoots can also be important (Potter, 1989). Body weight (and size) is the most comprehensive predictor of male fitness in Drosophila (Pitnick, 1991). In laboratory Drosophila melanogaster populations larger males inseminate more females during the first 2 weeks of life (Partridge and Farquhar, 198 1 , 1 983 cited by Pitnick, 1991 ). In some insects, males transfer fecundity-enhancing, sperm-associated nutrients to females during copulation (Butlin et al., 1987 cited by McLain et aI., 1990). Because a larger male may transfer a greater quantity of nutrients, female fecundity may also covary with mate size (McLain et aI., 1990). In contrast, female size and weight are positively correlated with fecundity (the number of eggs produced) in some insects (McLain et aI., 1990). Fecundity of females is known to vary with adult size (weight) in many insects, and the nutritive value of different larval food plants might influence the final body weights of larvae, and hence of pupae and adults (Fenemore, 1977). Many authors have shown a positive correlation between adult weight and fecundity (Chutter, 1970; McCreadie and CoIba, 1990). Meisner et al. (1974) recorded fecundity of potato moth, Phthorimaea operculella differing widely according to the larval food. The purpose of the present experiment was to elucidate the effect of three larval food plants on adult body weight of Scaptomyza flava. Chapter 3: Host plant relationships of Scaptomyza jlava 1 30 MA TERIALS AND METHODS Potted plants of turnip, Chinese cabbage and cauliflower were placed into separate cages containing adult insects and left for 3 days (6/8/1993 - 9/8/1 993). There were 20 males and 30 females per cage and each cage contained 1 0 plants. After eggs were laid the flies were removed. The infested plants were held separately under clean fme gauze cages for eclosion of larvae, formation of pupae and emergence of the new generation of adult flies. In order to weigh adults, individual insects were sucked up by an aspirator, and placed in a plastic cup with a lid (diam 5 mm by 40 mm) of a known weight. The cups plus insects were weighed on a microbalance Mettler AE 1 63 (Mettler Instrument Corporation, Highstown, N. J.), and mean weights for males and females were calculated. Data were analyzed with a general linear models procedure (SAS Institute, 1 985). Where significant differences in the variables occurred, means were separated using LSD test (P :$ 0.05). RESULTS Adult male and female weights, as affected by host are shown in Table 15. Greater adult weights for males resulted when insects developed on turnip or Chinese cabbage compared to cauliflower. For females the trend was the same as that for males, with the heaviest females developing on turnip and Chinese cabbage and lower weight when raised on cauliflower. Males and females weighed 21 .7% and 22.3 % more, when reared on turnip than on cauliflower and Chinese cabbage respectively. Combining host types, adult males weighed an average of 33 % less than adult females (Table 15). Fecundity of Scaptomyza flava is positively correlated with female body weight (compared Tables 15 and 1 6) and this is the common pattern among insects (Gwynne, 198 1 ) . Chapter 3: Host plant relationships of Scaptomyza flava 1 3 1 Table 15: Mean weights of adult S. flava according to sex and host. Host Weight of adult insect in mg n dd n � � Turnip 55 0.92 a 49 1.39 a (range: 0.7 1- 1 . 1 2) (range: 1 .22- 1 .57) Chinese 49 0.90 a 55 1 .30 ab cabbage (range: 0.82- 1 .(0) (range: 1 .2 1 - 1 .47) Cauliflower 50 0.72 b 50 1 .08 b (range: 0.53-0.86) (range: 0.84- 1 .04) Total 1 54 84.6 1 54 1 25.6 Means within a column followed by the same letter are not significantly different (P :::; 0.05). LIFE SPAN, NUMBER OF FEEDING PUNCTURES AND NUMBER OF EGGS PRODUCED BY SCAPTOMYZA FIAVA ON THREE PLANT SPECIES INTRODUCTION The host plant is a very important factor in determining a leaf miner's lifespan. Many leaf miners are quite specific in their host preferences. The host plant of a leaf miner may affect it in many way: its growth, development, reproduction (certain leaf miners require specific types of host plant before they can lay eggs), behaviour and lifespan (Auerbach and Simberloff, 1984). To determine how adult longevity, feeding and reproduction varies between different host plant species an experiment was conducted with Chinese cabbage, turnip and cauliflower. MATERIALS AND METHODS The experiment was undertaken under greenhouse conditions. Temperature was not regulated (range 10 - 1 8 °C by day, mean 14°C). Natural daylength was that in April 1993 (sunrise:06.40, sunset I8. 10). Tests were run between 14 - 28 April. Plants were raised from seed in pots in a greenhouse. Plants selected for experimental use were about the same size and age, and were at the 3-4 leaf stage. There was a single plant per pot for each plant species. Plants were exposed in square cages (30 x 30 x 30 cm) to groups of 2 males + 1 female of newly emerged adult S. flava (=1 replicate) . The insects were about 50 to 60 generations removed from field populations and were raised in a glasshouse on Chinese cabbage and turnip. Plants in each cage were replaced with a fresh one every 3 days until the female insect had died. Because fecundity may be influenced by access to males, any males that died were immediately replaced so that the female would always have access to two males. There were 10 replications of each treatment. For each interval the mined leaves were assessed for the number of punctures and eggs using a zoom stereomicroscope with a magnification range of XlO-20. To 132 Chapter 3: Host plant relationships of Scaptomywjlava 133 estimate average daily egg deposition, I divided total fecundity over the lifespan by the lifespan in days to yield the mean number of eggs per female per day. Data were analyzed with a general linear models procedure (SAS Institute, 1 985) to examine the relationships between adult longevity, daily egg deposition and lifetime fecundity. Where significant differences in the variables occurred, means were separated using LSD test (P ::;; 0.01). RESULTS AND DISCUSSION Results are summarised in Table 16 and Figures 11 and 12. Table 16: Plant species Turnip Chinese cabbage Cauli- flower Mean life span, number of feeding punctures and number of eggs produced by Scaptomyzajlava (during entire life span) on three plant species Life span Mean No. of Mean No. of Mean No. Mean No. of female feeding punctures! of eggs! of (days) punctures / day female eggs/day female 1 2.2 A 1 158 A 95 255 A 20.9 (7-17) (650-1 800) ( 145-32 1 ) 1 0.7 B 800 B 75 165 B 15.4 (7- 14) (392-1 100) (32-286) 1 0.8 B 394 C 36 48 C 4.4 (7- 14) (220-907) ( 12- 105) Means in each column accompanied by the same letter are not significantly different at P ::;; 0.01 ( ANOVA followed by LSD test for separation of means). -------------- - - - - -- Chapter 3: Host plant relationships of Scaptomyza flava 134 The lifetime totals of feeding punctures on plants, were significantly different between the three plant species; most for turnip, least for cauliflower and intermediate for Chinese cabbage (P ::; 0.01). There were also significant differences in the total number of eggs laid on the plant species with the same rank as for feeding punctures (P ::; 0.01) . The area of a single pinhole was ca. 0. 12 mm2• Therefore average total leaf area destroyed by the feeding of one adult female was 1 39, 96 and 47 mm2 for turnip, Chinese cabbage, and cauliflower, respectively. The life span of S. flava females was significantly longer on turnip than on Chinese cabbage or cauliflower but there was no difference between Chinese cabbage and cauliflower. Average fecundity according to host plant ranged from 48 to 255 eggs deposited over the total life span. The number of eggs laid on turnip was >5 fold as many as on cauliflower and the number of eggs laid on Chinese cabbage was slightly more than half of the total number on turnip. The majority of feeding punctures on Chinese cabbage, turnip and cauliflower were made between days 3- 1 1 , 7- 1 1 and 3-7 of adult life respectively and the majority of eggs on Chinese cabbage and turnip were laid between days 4-9 of adult life but peak oviposition on cauliflower occurred 2-4 days following emergence and had declined to low levels by age 9 days (Fig. 12). Chapter 3: Host plant relationships of Scaptomyzaf/ava Fig. 1 1 : Q) "@ S 0.05) in number of eggs laid and adults emerged between Chinese cabbage and turnip, but cauliflower received significantly fewer eggs and produced fewer adults (P :::; 0.01). Very low number of eggs were laid in this experiment for unexplained reasons. Incubation time of eggs laid on cauliflower and duration of the pupa stage was longer than on turnip and Chinese cabbage. This combined with markedly fewer punctures, and slightly lower survival on cauliflower suggests that this is a less suitable host plant for Scaptomyza flava than turnip or Chinese cabbage. Mortality from egg to adult emergence was apparently low for all 3 plant species, though numbers of eggs observed was low. This low mortality could be due to the absence of predators under greenhouse conditions and to the low density of larvae. Lower survival may occur under field conditions. Which physical or chemical factors of these three Cruciferous host affect Scaptomyza flava development rate are unknown but differences in nutritional composition of host plants may well influence rate of development. PREFERENCE FOR FEEDING AND EGG LAYING BY SCAPTOMYZA FLA VA WITH RESPECT TO LEAF AGE AND LEAF SIZE OF CHINESE CABBAGE INTRODUCTION Various factors influencing leaf selection by ovipositing leaf miners have been identified. For example, leaf size, leaf age, position, and as well as previous herbivore damage, affect leaf selection for oviposition by some adult leaf miners (Auerbach and Simberloff, 1989). Because leaf miners and gallers spend a major portion of their lives attached to one site on the host (Mitchell, 1983 cited by Clancy et aI., 1993), the size of the leaf often provides a good index of the resource available to the herbivore and thus enables one to quantify the subset of resources used by each to estimate the influence of leaf size on the fecundity and survival of the herbivores (Whitham, 1978; Van Driesche, 1983; Price, 1992 cited by Clancy et al., 1993). The size and age of leaves or other plant parts is typically an important factor influencing oviposition choice, survival, and pupal or adult biomass of sedentary herbivorous insects such as leaf miners and gall formers (Clancy et al., 1993). Leaf phenology has been suggested to play an important role in the demography and population dynamics of herbivorous insects (Connor et ai., 1994). Apart from phenological effects on ontogenetic changes in the chemistry, moisture content, toughness and pubescence of leaves and their potential effects on insect growth, survival, reproduction and host selection, two distinct aspects of leaf-phenology have been proposed to affect populations of herbivorous insects: the timing of leaf production and the timing of leaf fall (Connor et at., 1994). In some leaf miners (e.g., Lithocolletis quercus), females strongly prefer young leaves but their discriminatory powers are not perfect (pittara and Katsoyannos, 1992). Besides leaf age, the other cue related to leaf selection is leaf size. The size and shape 141 Chapter 3: Host plant rekltwnships of Scaptomyza flava of a potential oviposition site is of great importance (Pittara and Katsoyannos, 1992). Results of studies on several different leaf miners have demonstrated that some (but not all) species select bigger leaves or shoots over smaller ones (Clancy et ai. , 1 993). For example Mopper and his co-workers ( 1984 cited by Clancy et aI., 1993) found that leaf area was positively correlated with the density of microlepidopteran leaf miners on sand live oak. In general, other leaf miner studies have also found positive relationships between leaf size and mine density (e.g., Hileman and Lieto, 198 1 ; Tuomi et at., 198 1 ; Simberloff and Stiling, 1987; Sato, 1991 cited by Clancy et ai., 1993). Leaf size apparently influences how females disperse eggs and the probability of survival for their offspring (Faeth, 1991). Often, leaves are also selected according to leaf nitrogen content (McNeil and Southwood, 1978; Mattson, 1980; Scriber, 1984). In this case, a leaf of high quality is defIned as a leaf containing much nitrogen. Some authors (e.g. , Hanna et at. , 1987; Minkenberg and Fredrix, 1989) claim that the variation in nitrogen level among leaves may explain the distribution and growth of leaf miner populations to some extent. I therefore performed a series of experiments to examined the selection of leaves of Chinese cabbage by Scaptomyza flava according to leaf age, area and nitrogen content I hypothesized that such choice should be critical for this leaf miner. MATERIALS AND METHODS Ten individual naive females, each with two 3-day-old males, were caged in enclosed arenas over individual Chinese cabbage plants (4-5 leaf stage). Plants were placed in a greenhouse under ambient and artificial lighting (LI4:D10) photoperiod with the photophase between 0600 and 20.00, and ca. 18 ± 2°C temperature with 80 ± 4% RH. Light was provided by three fluorescent tubes of the daylight type and during most 142 Chapter 3: Host plant relationships of ScaptomyZll flava 143 of the photophase also by natural daylight entering from windows. The light intensity (irradiance), at the level of the cages with the flies, varied between 4 and 15 WJm2, depending on the outdoor illumination. The nuptial chambers (square cages 30 x 30 x 30 cm) were large enough so that the insects could fly freely around the plants. The insects were provided with honey solution and left for 72 hours from 912/1993 when plants were removed from cages. At the end of this period, the number and position of all feeding punctures and eggs were recorded for each individual leaf within each plant, starting with the outer (older) leaves, and working progressively to the smallest and youngest leaf in the centre of the plant. The area of each leaf was also measured. Samples of undamaged leaves were taken for N analysis. Analysis of leaf nitrogen : Nitrogen content may vary with the age of the plant, the age of the leaf and growing conditions. Thus leaf samples for analysis leaf nitrogen content were taken on 121211993 from plants grown at the same time under similar conditions and same leaf age as those I used for experiments with insects. Leaves were removed and immediately taken to the laboratory. Leaf samples were dried at 60°C (in an oven) for 3 days before extraction. Before commencing digestion of leaves, tubes were weighed and tube weights recorded. All glassware used for analysis was fIrst acid-washed in 2 M HCL (made with deionised water). To prepare the samples for analysis the following method was used (as described by Mahimairaja et aI. , 1990). Nitrogen was determined by Kjeldahl method (McKenzie and Wallace, 1954) (Kjeldahl digestion solution allows measurement only of organic N and NH4 -N): 250 g K2 S04' 2.5 g Selenium powder, 2.5 litres Conc. H2 S04' In digestion tube weigh approximately 0. 1 g of dry herbage accurately and add 4 mls digestion solution. Heat to 350 °C for 4-5 hours, or until solution clears. Make up to 50 mls using distilled water. Chapter 3: Host plant relationships of ScaptomyZil flava Shake and pour into numbered vial Store in fridge. Measurements were made using an autoanalyser. 144 The effect of leaf size on the leaf nitrogen was examined by analysis of variance and comparison of means. RESULTS Four of the ten females produced no leaf punctures or eggs. Results are presented in Table 19 and Figs. 13, 14 and 15, for the remaining six. Table 19: Leaf age First (oldest) Second Third Fourth Fifth (youngest) Mean leaf area, number of punctures, eggs and nitrogen content according to leaf age Leaf No. of No. of No. No. of Nitrogen size punctures punctures of eggs! content (cm2) per cm2 eggs cm2 Mmol/kg 79 a 330 a 4.3 23 a 0.3 3948 (68-88) (20-450) a ( 1 -60) a a 60 b 292 a 4. 1 9 b 0. 1 5 4378 (55-87) (40-800) a (1-21) b a 58 b 203 a 3.5 4 b 0.06 5422 (43-78) (20-550) a ( 1 - 1 1 ) be a 37 c 74 b 2 5 b 0. 1 3 4670 (21 -45) ( 10- 180) b (0-25) b a 1 3 c 2 c 0. 15 O c 0 4678 (5-20) (0-8) c c a Treatments accompanied by the same letter are not significantly different at P ::; 0.05. Chapter 3: Host plant relationships of ScaptomyZIJ flava 145 The questions addressed in this study were: Is feeding or oviposition affected by leaf size? Do flies prefer (in sense of Singer [ 1986]) leaves of certain nitrogen level, for feeding and oviposition? The results show that nitrogen content was not related to leaf age. Although all leaf sizes (ages) were accepted by the insects (with the exception of the smallest leaves for egg laying), the number of feeding punctures and eggs per cm2 leaf decreased with decreasing leaf size (age). Thus younger leaves were not favoured for feeding or egg laying (Table 19, Figs. 13, 14 and 15). DISCUSSION AND CONCLUSIONS Based on findings for other leaf miners (Hering, 195 1 ; Whitham, 1978; Mopper et aI., 1984; Bultman and Faeth, 1986a; Craig et aI., 1989, 1990; Clancy et aI., 1993), I predicted that Scaptomyza flava would select larger Chinese cabbage leaves for feeding and oviposition. My results support this prediction. Scaptomyza flava spent considerably more time on older leaves than on younger ones (personal observation, unrecorded data) in my experiment, which supports the conclusions of Vaugh un and Hoy (1993) that host preference can change with host age and leaf type. In contrast to these results some workers found that some insects selected young leaves for oviposition over old ones (see detail in the introduction). Thus leaf size appears to be correlated with preference for feeding and oviposition by S. flava. Scaptomyza flava females feed on sap that exudes from leaf punctures. It is possible that increased numbers of punctures on older leaves are associated with the increased difficulty of extracting sufficient nutrient from older leaves. However, as a choice of leaf age was freely available, this explanation is not likely. Leaf size apparently influences how females disperse eggs and the probability Chapter 3: Host plant relationships of Scaptomyw. flava 146 of survival for their offspring (Faeth, 199 1 ). It is likely that variation in leaf sizes exerts the greatest influence on pattern of density and dispersion at the time of colonization via reduced oviposition and aggregated dispersion of eggs. That mean leaf size of cruciferous explains a significant amount of variation in density of Scaptomyza flava. The positive relationship observed between leaf area and within-leaf miner density supports Mopper et al. 's ( 1984) fmdings on the selection of large leaves for oviposition. Murai (1974) suggested that ovipositing lepidopteran miners tend to avoid laying eggs on small leaves, or on leaf regions with previously deposited eggs. In a developing field situation plant phenology may also be important (Collinge, 1987), because the lower leaves are the first available and are present at the time of oviposition. Some lower leaves die before the average leaf miner completes development While these results show that Scaptomyza has preference for certain leaf ages, the mechanism by which discrimination occurs is unclear. Although I cannot currently resolve these uncertainties, some of above mentioned hypotheses cannot be eliminated without considerably more work. Chapter 3: Host plant relationships of Scaptomyza!lava Relationship between n.itrogen content 34�iiiii� oldest second third Leaf age fourth youngest Fig. 14: Relationship between number of feeding punctures of S. flava and leaf age oldest oldest second third fourth Chinese cabbage leaf age second third Leaf age fourth youngest youngest 1 47 EFFECT OF LARVAL FOOD PLANT ON ADULT EGG LA YING PREFERENCE INTRODUCTION According to Hopkins' Host Selection Principle (Hopkins, 1917), the selection of a plant species for egg laying by adult female insects is influenced by the plant species on which the females developed in the larval stage. Hopkins' Host Selection Principle has been controversial since it was fIrst put forward in 1917 (Hopkins, 1917) and there is little published data in its support. "A shift into a new niche or adaptive zone is, almost without exception, initiated by a change in behaviour . . . . . With habitat and food selection - behavioral phenomena playing a major role in the shift into new adaptive zones, the importance of behaviour in initiating new evolutionary events is self-evident" (Mayr, 1963). To detennine whether Hopkins Host Selection Principle applies to Scaptomyza flava, an experiment was undertaken with three host species, Chinese cabbage, turnip and cauliflower. MATERIALS AND METHODS Scaptomyza flava was reared on 3 plant species, Chinese cabbage, cauliflower, and turnip. Plants were chosen to be about the same size and age (3-4 leaf stage). In the fIrst phase, plants of the 3 species were placed into separate cages containing adult insects (newly emerged unfed adults were obtained from a colony reared on Chinese cabbage) and left for 4 days (221311993 - 26/3/1993). There were four males and four females per treatment Mter eggs were laid the flies were removed. The infested plants were held separately under clean fme gauze cages for eclosion of larvae, 148 Chapter 3: Host plant relationships of Scaptomyza flava 149 fonnation of pupae and emergence of the new generation of adult flies. In the second phase, 8 males and 4 females obtained as described above from rearing on each of the three plant species were released into cylindrical cages (85 cm diameter, 90 em high) (n=3), each containing 2 plants of the 3 plant species arranged randomly in a circular formation. Seventy-two hours later the numbers of feeding punctures and eggs on each plant were counted. Three replications were run over the next four weeks. A one-way analysis of variance (ANOV A) was undertaken. Comparisons among treatment means were subjected to LSD test (P � 0.05). RESULTS Results are presented in Table 20 and Figures 16 to 21. Table 20: Influence of larval food plant on adult feeding and egg laying preference 1) Adult insects raised as larvae on cauliflower1 : Plant Mean no. Percentage of of punctures punctures Cauliflower 5 c 1 .5% Chinese cabbage 250 a 70.5% Turnip 100 b 28% Total 355 100% Mean Percentage no. of of eggs eggs 1 b 9% 6 a 55% 4 a 36% 1 1 100% 1 Within a column, treatments accompanied by the same letter are not significantly different at P � 0.05. Chapter 3: Host plant relationships of Scaptomyza flava 2) Adult insects raised as larvae on Chinese cabbagel : Plant Mean no. of Percentage punctures of punctures Cauliflower 95 b 3% Chinese cabbage 1700 a 49% Turnip 1650 a 48% Total 3445 100% 3) Adult insects raised as larvae on Turnipl: Plant Mean no. of Percentage of puncturesZ punctures Cauliflower 61 C 4% Chinese cabbage 485 B 34% Turnip 866 A 62% Total 1412 100% Mean no. of eggs 39 ab 60 a 24 b 123 Mean no. of eggs 19 b 14 b 27 a 60 150 Percentage of eggs 32% 49% 19% 100% Percentage of eggs 32% 23% 45% 100% 1 Within a column, treatments accompanied by the same letter are not significantly different at P $; 0.05. 2 Within a column, treatments accompanied by the same letter are not significantly different at P ::; 0.01 . Chapter 3: Host plant relationships of Scaptomyzajlava 1 5 1 4) Mean total numbers of feeding punctures and eggs from insects raised as larvae on each plant Plant Feeding punctures Eggs Cauliflower 1 1 8 .33 c 3.58 c Chinese cabbage 1 148.3 a 4 1 .3 a Turnip 478 . 1 7 b 20.4 b Within a column, treatments accompanied by the same letter are not significantly different at P ::; 0.05. DISCUSSION In terms of total feeding punctures and eggs laid, flies reared on Chinese cabbage produced significantly more than those reared on turnip, which in turn produced more than those reared on cauliflower. This suggests that Chinese cabbage is the better quality host plant. Flies reared on turnip produced significantly more feeding punctures (P $; 0.01 ) on turnip than on Chinese cabbage or cauliflower (Table 20[3]). Also they deposited significantly more eggs on turnip (P $; 0.05) compared with Chinese cabbage and cauliflower. Flies reared on Chinese cabbage produced an equal number of feeding punctures on Chinese cabbage compared to turnip, but showed a distinct preference for Chinese cabbage for egg laying. However, flies reared on cauliflower showed no preference for cauliflower and made most feeding punctures and laid most of their eggs on Chinese cabbage. Chapter 3: Host plant relationships of Scaptomyza flava 152 Thus, although there was significant preference for both egg laying and feeding on turnip in the case of insects raised on that plant and similar slight preference in the case of Chinese cabbage, this was not the case at all for cauliflower where rearing on that plant induced no preference. The results from the present experiment appear to support the principle in the case of Chinese cabbage and turnip, though not for cauliflower. However, the results should be viewed with caution due to the limited number of insects used and the fact that the laboratory colony, from which the test insects were drawn, had been maintained for a considerable number of generations on Chinese cabbage. Further experiments with large numbers of insects of field ongm would be desirable before it can be claimed that this is a true case of Hopkins' Host Selection Principal. Chapter 3: Host plant relationships of Scaptomyzaflava Fig. 16: Cauliilower Chinese cabbage Larval food plant (cauliflower) 19 1 7 Effect of larvalfood plant onfeeding adult S. Cauliflower Chinese cabbage Larval food plant (Chinese cabbage) Fig. 1 8: Effect of larval food plant on feeding preference adUlt s. Chinese cabbage Turnip Larval food plant (turnip) 1 53 Chapter 3: Host plant relationships of Scaptomyza flava Caulif10wer Chinese cabbage Turnip Larval food plant (cauliflower) Fig. 20: Effect of larval food plant on egg laying preference by adult S.flava .... o tfi. Cauliflower Chinese cabbage Turnip Larval food plan! (Chinese cabbage) 154 EFFECT OF ADULT EXPERIENCE ON OVIPOSITION PREFERENCE INTRODUCTION The role of learning in host selection by phytophagous insects has received a good deal of attention over the last few years (see reviews by Jermy, 1986; Papaj and Prokopy, 1989; Lee and Bemays, 1990; Papaj and Lewis, 1993). Much of this attention has focused on what is commonly known as induction of preference, that is, increased preference for a plant food as a result of feeding experience with the food. A number of recent laboratory and field studies on insects have demonstrated that early experience of adult insects with host plants can affect subsequent responses to hosts (prokopy et ai. , 1982; Papaj, 1986 cited by Hoffmann, 1988). Most studies have reported positive experience effects, where insects show a tendency to be attracted to, or oviposit on, the host to which they were exposed. Positive experience effects are usually interpreted as evidence that insects can learn to remain associated with particular hosts (show habitat fidelity). However, negative experience effects (where insects avoid the host they were previously exposed to) have been found in some cases (Hoffmann, 1988; Blaney and Simmonds, 1985). The larval environment does not appear to strongly affect host preferences in phytophagous insects and relevant adult experience can only occur in the period between eclosion and departure from the larval host. The length of this period will depend on the dispersal behaviour of the young adults and the extent to which hosts of the same type are aggregated. Experience effects in recently eclosed adults have been studied particularly in experiments with Drosophila (Jaenike, 1982, 1983; Hoffmann, 1985 cited by Hoffmann, 1988). A limitation of some of these studies has been that the experimenter rather than the insect determined the length of exposure to a host. Adults were held on hosts in confined containers for at least 3 days, and it is unknown whether 155 Chapter 3: Host plant relationships of Scaptomyza jlava 156 recently eclosed individuals would stay near their larval environment for so long. Forced exposure to a host can also lead to changes in host response unrelated to learning. For example, insects may become starved as a consequence of confmement on a nutritionally poor host, and apparent positive learning effects may result if the starved adults are less discriminating than individuals kept on a high quality host (Hoffmann, 1988). For this experiment three plant species were chosen which in previous experiments had shown high numbers of eggs (Chinese cabbage), intermediate numbers (turnip) and low numbers (cauliflower). MA TERIALS AND METHODS Five, recently eclosed female Scaptomyzajlava plus 10 males from the laboratory rearing colony (on Chinese cabbage) were released at 08.30 hours into screen mesh square cages (30 x 30 x 30 cm). Three potted plants were placed in each cage spaced 20 cm apart. There were four treatments: L all three plants of cauliflower (non-choice experience). 2. all three plants of Chinese cabbage (non-choice experience). 3. all three plants of turnip (non-choice experience). 4. one plant each of cauliflower, Chinese cabbage and turnip (choice experience). The insects were allowed to feed on the plants for 24 hours. During this time no eggs were laid (plants were checked for possible eggs). The following day, between 08.30 and 09.00, the insects (two males and one female from each cage) were removed from the cages by aspirator and transferred to cages of the same size, each containing one plant of the three species. The experimental design was a randomized complete block with four treatments and eight replications (single females). After 48 hours the numbers of feeding punctures and eggs on each plant were recorded. A video camera (Panasonic F15) was set up on a dissecting microscope with zoom lens for counting punctures and eggs on a television screen. Chapter 3: Host plant relationships of Scaptomyza flava 1 57 RESULTS The results obtained are given in Table 21 and Figures 22 and 23. Insects fIrst allowed to choose between the three plant species (Table 21, treatment 4) preferred Chinese cabbage for feeding and egg laying over turnip and cauliflower in the second phase of the experiment. No eggs at all were laid on cauliflower. The same order of preference was shown when insects were fIrst exposed to cauliflower (Table 21, treatment 1). When insects fIrst fed on Chinese cabbage (Table 21, treatment 2) there was an unexpected preference for turnip. However, when insects fIrst fed on turnip (Table 21, treatment 3) there was no difference subsequently between turnip and Chinese cabbage, either for feeding or egg laying. In all treatments, including fIrst exposure to cauliflower, cauliflower was the least preferred species. Table 21: Effect of first adult feeding on plant preference 1) Adult insects fIrst fed on cauliflower: Plant Mean No. of Percen- punctures per plant tage Cauliflower 22 b 5% C. Chinese 285 a 67% Turnip 1 1 8 b 28% Total 425 100% Mean No. of Eggs per replication 1 .5 b 6 a 3.5 b 1 1 Percen- tage 1 3.6% 54.4% 32% 100% Chapter 3: Host plant relationships of Scaptomyza flava 2) Adult insects fIrst fed on Chinese cabbage: Plant Mean No. of punctures per plant Cauliflower 8 b C. Chinese 60 b Turnip 162 a Total 230 3) Adult insects fIrst fed on Turnip: Cauliflower 12 b C. Chinese 226 a Turnip 234 a Total 472 Percen- tage 3.5% 26% 70.5% 100% 2.5% 48% 49.5% 100% 158 Mean No. of Eggs Percen- per replication tage 0.25 b 3% 1 .87 ab 30% 4 a 67% 6 100% 1 b 7% 7 a 50% 6 a 43% 14 100% 4) Adult insects fIrst allowed to select between cauliflower, Chinese cabbage and turnip (control treatment): Cauliflower 4 c 1 % O c 0% C. Chinese 226 a 62% 15.6 a 67% Turnip 135 b 37% 7.6 b 23% Total 365 100% 23.2 100% Chapter 3: Host plant relationships of Scaptomyza flava 1 59 5) Mean total numbers of feeding punctures and eggs from insects fust fed on each plant I Plant I Feeding punctures I Eggs I Cauliflower 141 .6 a 3.6 be Chinese cabbage 76.72 b 2.01 c Turnip 157.3 a 4.6 b Control treatment 120.9 a 7.9 a Within a column, treatments accompanied by the same letter are not significantly different at P � 0.05 DISCUSSION Little is yet known about the role of learning in host selection by Drosopbilidae insect species. Lewis and van Emden ( 1986) discussed examples of the effects of previous feeding experience on an insect's subsequent preference for host plants and a number of studies have documented induced feeding preferences in insects (Jenny et a!., 1968; Wiklund, 1973; Phillips, 1977; Barbosa et ai., 1979; Jenny et a!., 1982; Ferguson et a!., 1991 ). In this experiment, previous feeding experience of adult Scaptomyzajlava on cauliflower and Chinese cabbage did not enhance feeding and egg laying preference for these hosts. Considering the total numbers of leaf punctures produced after exposure to each plant species, insects allowed to feed on cauliflower for 24 hours produced the lowest number of punctures. This is in agreement With the results of the experiment "Comparison of plant species as hosts for Scaptomyza jlava". The total number of punctures was highest after exposure to turnip. Chapter 3: Host plant relationships of Scaptomyza flava 1 60 Egg numbers overall were low especially after exposure to cauliflower. It is possible that the 48-h period over which the experiment was conducted was not long enough to allow full expression of fecundity. The general conclusion from this experiment is therefore that exposure of adult S. flava for 24 hours to one plant species did not increase preference for that species for production of feeding punctures. The extent to which the host fidelity occurs in the field may depend on the nature of the resources that Scaptomyza flava flies encounter after eclosion. Rather than occurring because of adult experience, host fidelity may occur if individuals encounter fresh plants of the same type as their larval or adult host near the eclosion site (non-choice situation) (Hoffmann, 1988). Chapter 3 : Host plant relationships of Scaptomyza jlava Fig . 22: Effect of adult experience on feeding preference by S.jlava adultjlies Fig. 23: ..... c ro 1 C= Chinese cabbage turnip cauliflower Turnip C. cabbage Cauliflower Control Plant on which adult insects first fed Effect of adult experience on oviposition preference by Sjlava jlies .C= Chinese cabbage turnip Cauliflower Turnip C. cabbage Cauliflower Control Plant on which adult insects first fed 1 6 1 C h a p t e r 4 SEASONAL LIFE CYCLE AND POPULATION DEVELOPMENT OF SCAPTOMYZA FLA VA INTRODUCTION Many population studies reported in the literature considered key-factors and density-dependent processes which govern insect population dynamics, but only a few species of two-winged flies have been studied in this respect (Hovemeyer, 1 992). Scaptomyza leaf miners appear to have been little studied previously, and life cycle data on Scaptomyza flava in New Zealand, are lacking probably because the insect was considered to be a minor pest. The need for basic biological studies on Scaptomyza flava has been enhanced by the increasing importance of this leaf miner as a pest of cultivated Brassicaceae. Studies by Minkenberg ( 1990) showed that the host plant and its growing conditions and temperature have a considerable effect on the life history of some leaf miners (e.g., Agromyzid flies). A few studies have addressed the effects of temperature on the development and reproduction of the leaf miner Liriomyza bryoniae (Minkenberg and Helderman, 1990). STUDY SITE Studies of the seasonal life cycle and biology of Scaptomyza spp. were carried out on Massey University Plant Orowth Unit land (POU) at Palmerston North, Manawatu, New Zealand over a 2-year period from October 1 990 to September 1 992. The study site was located in a 5 ha. field in grass and mixed vegetable cultivation. The climate of the area is classified as humid temperate with no distinct summer dry season. In order to gather information on the prevailing temperature and precipitation during the 162 Chapter 4: Seasonal life cycle and. . . . . . leaf-miner survey, the meterological data of agroclimatic station in the region was provided. Mean annual rainfall at the nearest weather station (AgResearch Grasslands) approximately one kIn away is 1 240 mm (mean of 30 years. December has the most rain [ 1 10 mm] and February the least [70 mm]). Mean temperatures of the hottest (February) and coldest (July) months at that station (mean of 30 years) are 1 8°C (6YF) and 6°C (43°F), respectively. The site was on a silt loam soil at an altitude of 30 metres, longitude of 17Y.37 n and latitude of 40°.23 'S. Figures 24 and 25 summarize the weather pattern over the two year study period. A small area was repeatedly sown with Chinese cabbage Brassica rapa chinensis group (Brassica campestris spp. pekinensis) and turnip Brassica rapa L plants at approximately 2 monthly intervals from June 1 990 to June 1992 (vegetative growth of Chinese cabbage and turnip extend throughout the year). Two rows each of approximately 25 metres length were sown of each plant species on each date. SAMPLING METHODS Sampling is an integral part of any seasonal population determination programme. The number of samples required is determined by the degree of precision required plus other factors such as sample variability, and distribution and abundance of the pest population. An estimate of the pest population that has a standard error within 25% of the mean is considered acceptable for crop protection entomology (Southwood, 1978; Stewart and Sears, 1 989). The seasonal field population trends of Scaptomyza flava were followed in the field area during 1990 - 1 992 by sampling at weekly intervals. Sampling of each sowing commenced once a number of mature sized leaves had developed on each plant. Once plants become overmature and started to flower sampling 163 Chapter 4: Seasonal life cycle and ..... was transferred to a new sowing of younger plants. In order to obtain abundance estimates two life stages were sampled : (i) adults and (ii) larvae (which were still within their mines). A: SAMPLING FOR ADULT FLIES 1 64 Three collection methods were tried for determining numbers of adult Scaptomyza present within the planted area: i) Sticky traps ii) Water traps iii) Sweep netting I) STICKY TRAPS Sticky traps provide a simple method of obtaining relative measurements of insect populations. Sticky traps can also detect early pest infestation more efficiently than intensive unit area sampling because they serve to collect and flx the insects within the trap area (Southwood, 1978; Heinz et at., 1992). Sticky traps consisted of yellow cylinders of approximately 25 cm height x 15 cm diameter mounted on a post approximately 1 metre above soil level. Each cylinder was covered with a removable acetate sheet smeared with insect trapping grease. Sticky traps were operated over October and November 1 990. m WATER TRAPS Two yellow plastic buckets (30 cm diameter) part filled with water plus a little detergent were used as water traps and were partly sunk into the ground between rows. Chapter 4: Seasonal life cycle and. ... . . 1 65 Water traps were operated and examined weekly for 12 months from late November 1990 through November 199 1 . ID) SWEEP NETTING The sweep net is one of the most common methods used for sampling insects on cruciferous plant species. However, the sweep net gives only a relative estimate of the actual population density. Factors such as row spacing, insect developmental stage, plant growth characteristics (plant height being the most important factor), and time of day may affect efficacy of sweep net sampling (Studebaker et aI., 1991) . Sweep net samples were taken usually between 0900 and 1 000 hours weekly throughout the study period from November 1990 to September 1992. Only during very heavy rain was sampling suspended. A net of 38 cm diameter (generalized insect sweep net) was used to make 10 arm length sweeps brushing lightly through the foliage of the plants while walking along a row and covering a strip of about 100 m by 70 cm. Netted samples were transferred to clear plastic bags in the field, sealed, and brought back to the laboratory for counting, sorting and identification. Mter killing by ethyl acetate vapour or anaesthetizing by CO2, specimens of Scaptomyza were separated from the rest of the catch and identified to species (S. flava, S. fuscitarsis and S. elmoi). Voucher specimens have been deposited in the insect collection of Massey University of New Zealand. Student's t-test (SAS Institute, 1985) was used for comparison of numbers of adult Scaptomyza flava swept from Chinese cabbage compared to turnip. B: SAMPLING FOR LARVAE AND FOR LEAF MINING INJURY In 199 1 , to determine populations of larvae, random samples of 1 0 Chinese cabbage and 10 turnip leaves were taken each week from the centre rows of the plots (in order to avoid edge effects) throughout the year. Larvae were dissected free from mines under a stereomicroscope, counted, then killed and preserved in 75% ethanol. Chapter 4: Seasonal life cycle and. ..... 166 At fortnightly intervals from November 1 99 1 to December 1992 five Chinese cabbage and five turnip plants were taken at random (according to table of random numbers) from the centre area of the plots. In this programme for Chinese cabbage and turnip whole-plant samples were used to obtain estimates of larval population density. Plants were cut off at ground level and returned to the laboratory for close inspection. Measurements were made on each plant to determine leaf area (area of each leaf and total leaves), area mined, height of plant from crown to the tip of the highest leaf, number of leaves, and number of larvae. I also compared mean leaf area of the two host plants to ensure that any variation in miner density was not simply due to leaf size differences. To determine total leaf area and mined area (in cm2) a MKll leaf area meter was used (Plate 18). RESULTS AND DISCUSSION The results are summarised in Tables 6, 7 and 9 of Appendix 7 and Figures 26 to 31 and are discussed under four headings: 1 . comparison of sampling methods for adults, 2. relative numbers of adults on Chinese cabbage compared to turnip, 3. seasonal changes in abundance of adults and larvae on Chinese cabbage, and 4. numbers of Scaptomyza elmoi and Scaptomyza juscitarsis. 1. Comparison of sampling methods for adults Sticky traps caught 8 Drosophila adults during the 6 weeks that they were operated but no Scaptomyza were captured and traps were abandoned for further sampling. Numbers of adult Scaptomyza flava caught each week by sweep netting and water trapping on Chinese cabbage for the 12 months from November 1 990 are shown Chapter 4: Seasonal life cycle and. ..... 1 67 in Fig. 26. Similar data for turnip is shown in Fig. 27. Generally, peaks and troughs in numbers were paralleled by the two sampling methods but sweep netting caught consistently higher numbers. As the effectiveness of water traps is dependent on flight activity of insects, and as this in turn may be affected by prevailing weather conditions it was decided to cease water trapping after 12 months and to base comparisons over the 2 year study period on sweep net sampling data. 2. Relative numbers of adults on Chinese cabbage compared to turnip The fluctuations in numbers of adults from Chinese cabbage and turnip, both by water trap and sweep net sampling, were closely similar over 1 2 months from November 1990 (Figs. 26 and 27). However, numbers swept from turnip for the period were somewhat higher than from Chinese cabbage (but differences were not significant, t-test: t= 1 .83, P > 0.05) especially over the winter months of June, July and August. 3. Seasonal changes in abundance of adults and larvae on Chinese cabbage Seasonal changes in numbers of adults on Chinese cabbage as determined by sweep netting and of larvae from leaf sampling are shown on Fig. 28 for the period November 1990 to November 199 1 and in Fig. 29 for adults only for 24 months from November 1 990. Adults and larvae were present throughout the year with no evidence of diapause or aestivation. However, there was considerable variation in numbers from month to month. There is a pattern of higher numbers of flies during spring and early summer (October - December) and again in autumn to early winter (May - July) with lower numbers in early autumn (March - April) and early spring (September - October). Numbers of larvae paralleled and slightly preceded the peaks and troughs in numbers of adults (Fig. 28). Chapter 4: Seasonal life cycle and. ... . . 1 68 Prevailing weather conditions and stage of growth of the host plant, in addition to overall seasonal temperature changes, may play a major role in determining numbers. There was particularly heavy rainfall in February 1992 (Fig. 24) and this was followed by low numbers of adults in March and April. The same pattern is apparent to a lesser extent in January/February 1 99 1 (high rainfall) followed by low numbers of adults in April. Although I have no any reason to believe that my 2 year-study was in any way atypical. Data were obtained on adult flies and larval activity from traps operated over 2 year period, the results do not enable fmn conclusions to be drawn as to dates of generation number. From the above results, I draw the following conclusions: ( 1 ) Scaptomyza flava leaf miner population in Brassicaceae field varied as the season progressed; (2) S. flava were more aggregated at the earlier part of the summer and winter; (3) with no evidence of cease over the winter or summer months. Observations indicated that the infestation was generally heaviest in the plants along the edge of the planted area (unrecorded data). The reasons for this are not known but within the planted area adults can disperse to host plants in any direction, but at the edges, because of their close relationships with the host, they have only a 1 800 range for such movement. 4. Numbers of Scaptomyza elmoi and Scaptomyza fuscitarsis Small numbers of the closely related species Scaptomyza elmoi and Scaptomyza juscitarsis were collected in sweep net samples from both Chinese cabbage and turnip. Data for the 1 2 month period from November 199 1 is presented in Fig. 31 (and Table 8 of Appendix 7). Laboratory experiments (Appendix 6) showed that S. elmoi is saprophagous in habit and does not oviposit or develop in living leaves (of Chinese cabbage). The insects captured by sweep netting in the field are therefore unlikely to have developed from the turnip or Chinese cabbage plants. Chapter 4: Seasonal life cycle and . . . . . . - -- -;:;:=--======:;::;;:::==:;:::::::=;:::;:::::;=====;=-===:::;::�- -� Fig. 24: [Seasonal Rainfall & Relative Humidity I IS �------------------------------------------------------� .q l "0 's � 1 Pd ";2 1 ::;; :E l c: "§ Nov.9CDoc. 1..,..9 1 Fib. M" chApril y June J y Aug, Scp<. OcL Nov. Dec. Jan.92 Feb. MarcilApril o Ul 2 1 3 � IV 14 e. E I E ;:.-.. 5 1 c: o g E § IV � 4 Fig . 25: Date - Rainfall (nun) - R. hwnidity (%) Seasonal Temperature (Max., Mean, Min.) NovSODec.. Jan.91 Feb. MarchApril y Juno J Y Augt.ut.Sept. Oa.. �Ov. � Jan.91Pcb. :M..i.rc.bApoJ Date -- Max. temperature - Mean temperature -- Min. temperature 1 69 Chapter 4: Seasonal life cycle and . . . . . . Fig. 26: VJ c.. Q) Q) � VJ o .- --­VJ Q) 4:: t;...., o o c Weekly Sampling ofS.jlava on Chinese cabbage by two samplIng methods Date (Months) Fig. 27: Weekly Sampling oJScaptomyzajlava on turnip by two sampling methods Date (Months) 1 7 0 Chapter 4: Seasonal life cycle and . . . . . . Fig. 28: Weekly Sampling of Scaptomyza flava adults and larvae on Chinese cabbage Adults: total no'/1 0 sweeps Larvae: total no.l1 0 leaves Date (Months) 1 7 1 Chapter 4: Seasonal life cycle and . . . . . . Fig .29: Weekly Sweep Net Sampling of S.jlava on Chinese cabbage Date (Months) 172 Chapter 4: Seasonal life cycle and . . . . . . Fig . 30: Percentage of leaf area mined for Chinese cabbage by Scaptomyza jlava 173 July Aug. Sep. Oct. Nov. Dec. Jan.93 Chapter 4: Seasonal life cycle and . . . . . . Fig. 3 1 : No. oiS. elmoi and S.fuscitarsis captured by sweep netting o ...... Nov. 9 1 Dec. Jan. 92 Feb. March April May June July August Sept. Oct. Date (Months) 174 s . elmoi C h a p t e r 5 DAMAGE ASSESSMENT EXPERIM:ENTS IN LABORATORY AND FIELD WITH SCAPTOMYZA FLAVA 1 INTRODUCTION Scaptomyza flava is a dipterous leaf mmer that commonly infests many cruciferous vegetables especially in the young plant or seedling stages. It is common throughout New Zealand but no damage assessment experiments have previously been reported. It has multiple generations per year with no distinct donnancy. Adult flies feed on leaf tissue of host plants, creating small pinholes in the epidermis which affect the marketability of leafy cruciferous crops such as Chinese cabbage and water cress. Larvae create irregular blotch mines in leaves and may affect growth and yield of plants. Insect damage in cabbage crops can be the result of injury to the leaves during the preheading stages, or of injury to the head. The flrst type of injury can cause the formation of a smaller head, thus a lower weight of yield (quantitative yield reduction); the second type generally gives cosmetic damage (qualitative yield reduction) (Wit, 1985). Criteria to estimate the damage thresholds for qualitative yield reduction are generally very subjective and dependent on long and short tenn market situations. Whether quantitative damage occurs or not depends on the type of crop, the growing stage, the amount of insect injury, and growing factors (Wit, 1 982). Straka ( 1 979) found economic damage (above 3%) when 8.9-10.4% of the leaf area was destroyed in early cabbage, and 10.7-1 3.7% in late cabbage. I Modilled from a paper published in Proceedings of the 46th New Zealand Plant Protection Conference. 1993. pp. 45-49. 175 Chapter 5: Leaf miner damage assessment experiments 176 In order to assess the ability of Scaptomyza flava leaf miner to affect the growth and yield of two cruciferous vegetables (Chinese cabbage and turnip), several experiments were conducted in the laboratory and field. Chinese cabbage was chosen because it is a leaf vegetable the tops of which are harvested and utilized; thus any leaf mining injury will directly affect the product. In contrast turnip was selected as it is a root vegetable the leaves of which are not normally harvested for human use. Any leaf mining injury would therefore be indirect in its effect on the harvested part, the bulb root. A: LABORATORY EXPER�ENT MA TERIALS AND METHODS Turnip seed Brassica rapa L. and Chinese cabbage Brassica rapa chinensis group (Brassica campestris spp. pekinensis) seeds were sown in seed boxes in a glasshouse on 15 November 199 1 . Ten days after sowing, the seedlings were transplanted individually into plastic flower-pots ( 1 0 em diam.) which were kept in a growth room at 20 ± 1 °C during the day (about 1 6 hours of light) and 1 5 ± 2°C during the night ( about 8 hours darkness). After 20 days in the growth room (one month old plants), 1-2 day old adult Scaptomyza flava obtained from the rearing colony were released onto the plants, which were kept individually under small cages. At this stage the average number of leaves per plant for turnip was 5 and for Chinese cabbage 4.5. There were six treatments as follows, each replicated four times, in a completely randomized design: Chapter 5: Leaf miner damage assessment experiments 1 ) plants without any insects (control plants). 2) plants with one pair of adult insects per cage. 3) plants with two pairs of adult insects per cage. 4) plants with three pairs of adult insects per cage. 5) plants with four pairs of adult insects per cage. 6) plants with six pairs of adult insects per cage. 177 After 1 day, the plants were removed from the cages and mines allowed to develop. When larvae were fully fed and had pupated (8 weeks after sowing), plants were harvested by cutting off at ground level ( 16 days after infestation). The following were measured for each plant; a) fresh weight of tops (whole plant cut off at ground level), b) total leaf area, c) leaf area mined for each leaf, and d) fresh weight of the bulb root (for turnip only after lifting washing and drying). RESULTS Results for Chinese cabbage and turnip respectively are summarised in Tables 22 and 23. Figures 32-33 illustrate the effect of S. flava on the amount of leaf area mined and fresh weight of leaves of Chinese cabbage and turnip. Also Fig. 33 shows the effect of leaf miner on weight of bulb root of turnip. Table 22: Results of laboratory experiment to assess the effects of ScaptomyZll }lava on Chinese cabbage Pairs of adults per Total leaf area Leaf area Leaf area Fresh weight plant for 24 hr. (cm2/plant) mined mined (%) of leaves (cm2/plant) (glplant) 0 586.75 a 0.00 a 0 40 a 1 pair 465.25 ab 1 8.50 ab 4 28 ab 2 pairs 362.00 b 15.00 ab 4 22 b 3 pairs 414.75 ab 20.25 b 4.8 26.5 b 4 pairs 454.25 ab 30.25 b 6.6 27.7 b 6 pairs 502.25 ab 80.07 c 16.4 24 b Within a column, means with the same letter are not significantly different (p::; 0.05). Table 23: Pairs of adults per Results of laboratory experiment to assess the effects of Scaptomyza }lava on turnip Total leaf Leaf area Leaf area Fresh Fresh area mined mined weight of weight of plant for 24 (cm2/plan t) (cm2/plant) (%) leaves bulb root hr. (glplant) (glplant) 0 531 .75 a O a 0 26.77 a 7.25 a 1 pair 450.25 ab 8.50 bc 1 .9 25.20 abc 3.72 ab 2 pairs 428.75 b 10.00 cd 2.3 26. 10 ab 4.30 ab 3 pairs 441.75 b 12.25 cd 2.8 22.97 abc 2.82 ab 4 pairs 390.50 b 3.25 ab 0.8 17.75 c 1 .40 b 6 pairs 463.25 ab 15 .75 d 3.4 1 8. 15 be 2.02 b Within a column, means with the same letter are not significantly different (P$ 0.05). Chapter 5: Leaf miner damage assessment experiments 179 DISCUSSION The results for Chinese cabbage and turnip are discussed separately. Chinese cabbage: The degree of injury to the plant was closely related to the density of the leaf miners. The area of leaf mined for Chinese cabbage (Table 22) increased with increasing numbers of adult insects released but not in direct proportion. For example one pair of adults resulted in 18.50 cm2 (3.9 %) of leaf mined but four pairs of adults produced only 30 cm2 (6.6 %) of leaf mined rather than an expected 73 cm2• This could be due to interference between females during oviposition with increasing numbers confmed to relatively small plants. Also at high pest density interference between individual larvae may occur and closely adjacent injuries to the leaf may exert less effect than ones widely spaced. Even six pairs of adults per plant resulted in only 80.07 cm2 of leaf area mined or approximately 16.4% of total leaf area at the tennination of the experiment. Nevertheless, all treatments, with the exception of one pair of adults per plant, significantly reduced total leaf weight; however, there were no differences between treatments with increasing adult insect densities. Total leaf area, including that mined, showed no significant differences compared to untreated except for an anomalous reduction associated with two pairs of adults per plant Turnip: The area of leaf mined for turnip (Table 23), except for an anomalous figure with four pairs of adults, increased in about direct proportion to numbers of adults but there was not a close linear relationship (r= 0.69). Regarding fresh weight of leaves and bulb roots, there was a significant difference between the control plants and treatments with 4 pairs and 6 pairs of adults. Significant reduction of bulb root occurred only with 4 or 6 pairs of adults per plant Chapter 5: Leaf miner damage assessment experiments Fig. 32: The effects of Scaptomyza leafminer on C.cabbage & turnip in the laboratory 1 2 3 4 6 No. of insects (pairs) Fig. 33: The effects of Scaptomyza leafminer on C.cabbage & turnip in the laboratory o 1 2 3 Number of insects (pairs) 4 6 - C.cabbage Turnip leaves Turnip bulb root 1 80 Chapter 5: Leaf miner damage assessment experiments 1 8 1 It seems that turnip may compensate to a considerable extent for damage from larvae to leaves. This compensatory growth prevented significant loss of root weight for treatments with up to 3 pairs of adults per plant A single pair of adult insects per plant gave a bulb root weight little more than half that of untreated control, but the difference was not significant due to high variability. It is apparent from these results that plant compensation in turnip is an important factor that must be considered when determining pest control actions. It is likely to be a dynamic process which will vary throughout the growth of the plant. Taylor ( 1968) has reported that only injury to the older leaves of turnip plants affects root weight, perhaps because in turnip, older leaves are more important than young ones in exporting photosynthetic assimilates to the roots. In the experiment with Scaptomyza flava larvae fed mainly on the older leaves, some of which were badly injured. However, attacked plants mostly retained their older leaves as long as unattacked ones (except for severely damaged leaves that dropped before maturity). B: LEAF MINER DAMAGE ASSESSMENT FIELD TRIAL INTRODUCTION In damage assessment experiments a common approach is to alter the pest density with chemicals, by applying different kinds, concentrations, times or number of applications of insecticide. There can be a problem of interplot interference due to pest movement between pesticide-treated plots. There is the added complication of possible movement of pesticide by drift or run-off or of unplanned repellency if plots are too close or movement is not prevented by careful choice of the droplet size or consideration of the wind direction. Yields are measured on plots receiving different treatments, with different degrees of pest infestation and yield / infestation regressions calculated. The control of leaf mining pests is generally difficult, as the insects are protected for a major part of their life cycles by the leaves they are attacking. A spray must either penetrate the leaves to kill the young insect in the mine during they leave the mines during a later stage of their life cycles. It is difficult to fInd a spray which will penetrate leaves in suffIcient quantity to kill the insects but not damage the plant. To kill the insects after emergence from the mines it would be necessary to know the life history in detail and then attempt to fmd a spray that would be effect give in killing the insects at some unprotected stage (Hill, 1987). Chemical control involves the use of insecticides with penetrate action in order to kill the larvae in situ, and some systemic chemicals are also effective. To other alternative is to use insecticides against the adult flies on the plant foliage prior to oviposition and this method requires very careful timing. The objective of the trials was to create different levels of leaf miner attack during the growth of Chinese cabbage and turnip by the application of different insecticide treatments and to determine harvested yields in relation to the degree of leaf miner injury earlier in crop life. 1 82 Chapter 5: Leaf miner damage assessment experiments 1 83 MA TERIALS AND METHODS Experiment 1 : 1991 / 1992 Chinese cabbage (Brassica rapa spp. chinensis group), variety "Chi-Hi- Li", and turnip (Brassica rapa spp. rapa), variety "Snow ball" , were sown in field plots with 40 cm spacing between rows on December 5th 199 1 . Plots were four 3 m rows. The seedlings were thinned to about 1 5 cm spacing between plants. Insecticide was applied with treatments designed to provide different levels of leaf miner suppression. On commercial Brassica crops Scaptomyza is probably normally controlled by insecticides applied for control of other pests such as white butterfly, diamondback moth and aphids. Each treatment was replicated four times in a randomized complete block design for both turnip and Chinese cabbage. Data were analyzed by linear regression analysis (General linear model SAS) and a two-way ANOV A and treatments compared using LSD test at 0.05 leveL The treatmentsl were as follows: L Control, no insecticide applied (Scaptomyza allowed to develop freely). 2. Perrnethrin (Ambush 50 EC) (a contact insecticide) applied at full label rate of 100 ml Ambush 50 EC 1 ha. as a dilute spray. 3. Permethrin applied at 112 label rate (50 ml Ambush 50 EC 1 ha.) 4. Pirimicarb (a contact 1 systemic insecticide) applied at full label rate (250 g Pirimor 50 EC / ha) for the first application plus acephate (Orthene 75 EC at lkg / ha) for the second application. 1 Insecticide treatments were selected on the basis of results from laboratory tests (see Appendix 5). Chapter 5: Lea! miner diunage assessment experiments 1 84 Sprays were applied with a knapsack sprayer at approximately 700 I water per ha. Prior to each spray application ten plants were selected at random from the centre rows of each plot and total leaf area and leaf area mined measured. At maturity the effects of leaf miner attack were determined by taking random samples of 1 0 plants from the centre rows of each plot (in order to avoid edge effects) and recording gross fresh weight of plants after cutting at ground level, and net weights after damaged leaves were removed. In addition for turnip, the fresh weight of washed bulb roots was recorded. The timetable of sowing, sampling and spraying was as follows: Sowing date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 05. 12. 1 99 1 Seedlings thinned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6. 1 2. 199 1 First sampling (before fIrst spraying) . . . . . . . . . . . . . . . . . . . . 24. 1 2. 1 99 1 First spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24. 1 2 . 199 1 Second sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " 07.0 1 . 1992 Second spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 09.0 1 . 1 992 Third sampling (Turnip only) . . . . . . . . . . . . . . . . . . . . . . . . . 1 0.02. 1 992 Harvest: Chinese cabbage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.0 1 . 1992 Turnip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0.02. 1 992 Total leaf area and leaf area mined were measured by an Area Meter MK2 (Webb, 1 989). The great advantage of this system is that the measured areas are seen on the monitor so that discrimination between different areas can be controlled before the measurements are made. Areas of different tone on the same object can be measured independently by adjustment of the threshold control of this machine. For measurement of irregular blotch mines, the blotch areas may be measured as a proportion of the whole for a single leaf, or as a direct percentage if required (Plate 18). Chapter 5: Leaf miller damage assess1I1elll experiments 185 Plate 18: Area Meter MK2 Chapter 5: Leaf miner damage assessment experiments 1 86 Experiment 2: 1992 I 1993 A similar experiment was established. Chinese cabbage variety "Chi-Hi-Li", and turnip variety "Snow ball" were sown in field plots with about 50 cm spacing between rows. The plants were thinned to about 20 cm spacing between plants. Plots were 4 rows x 3m. The treatments were as follows: 1 . Control; no insecticide applied. (Scaptomyza allowed to develop freely). 2. Pennethrin (Ambush 50 EC) (a contact insecticide) applied at full label rate of 100 ml Ambush 100 EC I ha 3. Pennethrin applied at 112 label rate (50 ml Ambush 50 EClha.). 4. Pennethrin applied at 114 label rate (25 ml Ambush 50 EClha). Sprays were applied with a knapsack sprayer at approximately 700 I water per ha. The timetable of sowing, sampling and spraying was as follows: Sowing date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24. 1 1 . 1992 Seedling thinned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15. 12 .1992 First spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28. 12 .1992 First sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 06.01 . 1993 First sweep netting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 07.01 . 1993 Second spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 08.01 . 1993 Third spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.0 1 . 1993 Second sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 8.01 . 1993 Second sweep netting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.01 . 1993 Fourth spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.01 . 1993 Fifth spraying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28.0 1 . 1993 Sixth spraying (turnip only) . . . . . . . . . . . . . . . . . . . . . . . . . . 04.02.1993 ----------------- -- - � - - Chapter 5: Leaf miner damage assessment experiments 187 Third sweep netting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 02.02. 1993 Harvest: Chinese cabbage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 02.02. 1993 Turnip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.02. 1993 The experiment was a randomized complete block design with four replications. The results were subjected to two-way analysis of variance (ANOV A). Multiple regression analysis (SAS) was used to evaluate the relationship between gross weight and net weight per plant of Chinese cabbage (comparisons among treatment means were subjected to LSD test [SAS Institue, 1985] for separation of means at 0.05 level). On 1 st and 2nd sampling dates, 5 plants were picked from the middle row of each plot and total leaf area and leaf area mined measured by Area Meter MK2 (Webb, 1989). At maturity the effects of leaf miner attack were detennined by taking random samples of five plants from each plot and recording gross fresh weight of plants after cutting at ground level, and net weights of Chinese cabbage after a cohort of mined leaves were removed from the experimental plants. For turnip the fresh weight of bulb roots was recorded in addition to leaf weight. To compare populations of adult insects, sweep net samples were taken ( 10 ann length sweeps brushing lightly through the foliage the Chinese cabbage and turnip plants while walking the length of rows) on three dates ie., one or two days before spray applications. RESULTS The results of the two field experiments are summarised in Tables 24 to 33. Chapter 5: Leaf miner damage assessment experiments 1 88 Table 24: Treatment Untreated Permethrin 50 g aifha Permethrin 25 g aifha Pirimicarb 1 25 g ailha + Acephate 750 g ailha Mean total leaf area, leaf area mined and percentage leaf area mined of Chinese cabbage on two sampling dates. 1991192 field experiment. Leaf samples 24/12/91 Leaf samples 711192 Total leaf Leaf Leaf Total Leaf Leaf area (cm2) area area leaf area area mined mined area mined mined (cm2) (%) (cm2) (cm2) (%) 144.58 a 1 . 1 7 ab 0.75 95.45 a 1 3 .07 a 1 3 1 38.72 a 2.65 a 2 97.45 a 0 1 .6 c 2 1 2 1 .20 a 0 b 0 99. 82 a 0.72 c 0.75 1 28.82 a 0 b 0 97.50 a 06.55 b 7 Figures in each column accompanied by the same letter are not significantly different at P$ 0.05 ( ANOVA followed by LSD test for separation of means). Chapter 5: Leaf miner damage assessment experiments 189 Table 25: Gross and net weights of Chinese cabbage at harvest Treatment Weight of head at harvest Gross weight (g) Net weight (g)l Untreated 149.74 a 1 1 8.01 a Pennethrin 145.79 a 1 35.05 a 50 g ai/ha Pennethrin 1 34.92 a 1 1 6.09 a 25 g ai/ha Pirimicarb 1 34. 10 a 1 1 2.22 a 1 25 g ai/ha + Acephate 750 g ai/ha Within each column, means with the same letter are not significantly different (P ::;; 0.05). 1 After removal of outer leaf miner damaged leaves. Chapter 5: Leaf miner damage assessment experiments 190 Table 26: Mean total leaf area, leaf area mined and percentage leaf area mined of turnip on two sampling dates. 1991192 field experimenf Treatment Leaf samples (24112/91) Leaf samples (911192) Total Leaf Leaf Total Leaf area Leaf leaf area area area leaf mined area cm1 mined mined area cm1 mined cm2 (%) cm2 (%) Untreated 1 49.35 a O a 0 160.30 a 38.45 a 24 Pennethrin 1 67.00 a O a 0 148.7 ab 3.67 c 2 50 g ailha Pennethrin 1 52. 1 5 a 1 .22 a 0.75 1 28.05 b 4. 17 c 3 25 g ailha Pirimicarb 1 59.20 a O a 0 160.72 a 1 8.02 b 1 1 1 25 g ailha + Acephate 750 g ailha Figures in each column accompanied by the same letter are not significantly different at P $ 0.05 ( ANOVA followed by LSD test for separation of means). 1 Continued on Page 1 9 1 ---- ---------------- - - - - Chapter 5: Leaf miner damage assessment experiments 191 Table 26 (Continued from page 190): Treatment Leaf sample (101211992) Total leaf area (cm2) Leaf area Leaf area mined mined (cm2) (%) Untreated 206 b 8 ab 4 Permethrin 272 a 3.5 b 1 .5 50 g ailha Permethrin 250 a 5 b 2 25 g ailha Pirimicarb 208 b 1 3 a 6 1 25 g ailha + Acephate 750 g ailha Figures in each column accompanied by the same letter are not significantly different at P � 0.05 ( ANOVA followed by LSD test for separation of means). Chapter 5: Leaf miner damage assessment experiments 192 Table 27: Treatment Untreated Permethrin 50 g ailha Permethrin 25 g ailha Pirimicarb 1 25 g ailha + Acephate 750 g ailha Mean weights of leaves and bulb roots of turnip on 7/1192 and at harvest Plant sample Weight of leaves Weight 7/1192 at harvest of bulb 10/2192 root (g) Weight of Weight Gross Net 10/2192 leaves (g) of bulb weight weight root (g) (g) (g)l 3 1 .4 c 3.8 b 8 1 .95 6 1 .57 c 1 32.3 bc b 5 1 .4 ab 8.4 a 1 3 1 .7 a 1 2 1 . 1 a 230.3 a 52.5 a 7.7 a 1 1 5. 1 a 92.70 b 193.8 ab 39.0 be 5.4 b 8 1 .35 b 59.25 c 1 1 8.4 c Within each column, means with the same letter are not significantly different at the 5% level of probability. I After removal of outer leaf miner damaged leaves. Chapter 5: Leaf miner damage assessment experiments Table 28: Treatment Untreated Permethrin 50 g ailha Permethrin 25 g ailha Permethrin 1 2.5 g ailha Mean total leaf area, leaf area mined and percentage leaf area mined of Chinese cabbage on two sampling dates. 1992/93 field experiment 611193 18/1/93 Mean Mean Leaf Mean Mean total leaf leaf area total leaf leaf area per area mined area per area plant (cm2) mined (%) plant mined (cm2) (cm2) (cm2) 1 39 a 4 b 2.9 433 b 1 3.7 b 1 64 a o a 0 536 a 0.3 a 172 a 3.7 ab 2. 15 501 ab 7.5 ab 154 a 0.6 ab 0.39 506 ab 1 .0 ab 193 Leaf area mined (%) 3.2 0.05 1 .5 0.2 Treatments accompanied by the same letter are not significantly different at P � 0.05 (ANOV A followed by LSD test for separation of means). Chapter 5: Leaf miner damage assessment experiments 194 Table 29: Treatment Untreated Permethrin 50 g ai/ha Pennethrin 25 g ai/ha Permethrin 1 2.5 g ai/ha Mean total leaf area, leaf area mined and percentage leaf area mined of turnip on two sampling dates. 1992/93 field experiment 6/1193 18/1193 Mean Mean Leaf Mean Mean total leaf leaf area total leaf leaf Leaf area area per area mined area per area mined plant (cm2) mined (%) plant mined (%) (cm2) (cm2) (cm2) 1 15.6 a 5 b 4.5 294.8 a 10.7 b 4.2 1 32.2 a 1 . 1 a 0.85 268.3 ab 6.3 ab 2.5 142.8 a 0.5 a 0.35 258.2 a 0.9 a 0.3 1 54.3 a 0.9 a 0.99 235.7 b 2.5 ab 1 .2 Figures in each column accompanied by the same letter are not significantly different at P $ 0.05 ( ANOVA followed by LSD test for separation of means). Table 30: Treatment Untreated Pennethrin 50 g ai/ha Pennethrin 25 g ai/ha Pennethrin 1 2.5 g ailha Mean number of adult Scaptomyza flava captured by sweep netting on Chinese cabbage on three sampling dates 7.1.1993 19.1.1993 2.2.1993 40.6 c 32 b 33 a 5.2 a 17.2 a 35 a 15.3 b 17.5 a 50 b 14.5 b 27.8 ab 67 c Within a column, means with the same letter are not significantly different (� 0.05). Table 31: Treatment Untreated Pennethrin 50 g ailha Permethrin 25 g ailha Permethrin 1 2.5 g ailha Mean number of adult Scaptomyza flava captured by sweep netting on turnip on three sampling dates 7.1.1993 19.1.1993 2.2.1993 24 a 20 b 29 a 22 a 10 a 22 a 22 a 17 b 28 a 23 a 9 a 27 a - Within each column, means with the same letter are not significantly different (p ::; 0.05). Table 32: Gross and net weights of Chinese cabbage at harvest Treatment Weight of head at harvest Mean gross weight Net weight (g) (g/plant) Untreated 2 1 8 a 152.4 b Perrnethrin 38 1 .5 a 300.7 a 50 g ailha Perrnethrin 348.4 a 238.6 ab 25 g ailha Pennethrin 367.5 a 221 .9 ab 1 2.5 g ailha Within each column, means with the same letter are not significantly different(p � 0.05). Table 33: Mean weights of leaves and bulb roots of turnip at harvest Treatment Weight of head at harvest Mean gross weight Net weight (g) (glplant) Untreated 1 12.5 a 225 a Permethrin 124.7 a 242 a 50 g aiJha Permethrin 124.2 a 267.8 a 25 g aiJha Permethrin 1 13 . 1 a 23 1 .5 a 12.5 g ailha Within each column, means with the same letter are not significantly different(p � 0.05). Chapter 5: Leaf miner damage assessment experiments 197 DISCUSSION The results for Chinese cabbage and turnip are discussed separately. Chinese cabbage: The leaf area mined on untreated control plants was less than on turnip in both seasons, reaching a maximum of 13% in January 1992. Permethrin at full label rate gave the most effective suppression of leaf miner (Tables 24, 28). Based on gross weights of heads at harvest, leaf miner had no effect on yield in either season (Table 25) but in 1992/93 net weight of heads (Table 32), after removal of leaf miner damaged outer leaves, was significantly lower for untreated control plants compared to the full permethrin treatment. This difference was not significant in 199 1/92. The number of adult insects captured by sweep netting of Chinese cabbage on 7. 1 .93 and 19. 1 . 1993 was significantly greater on the untreated control plants compared to other treatments (Table 30). Turnip: Percentage leaf area mined reached a peak of 24% on untreated control plants in January 1992 but had declined to 4% by harvest. The contact insecticide (permethrin) at full label rate gave the most effective suppression of leaf miner and percentage area mined on sprayed plants at no time exceeded 2% (Table 26). The gross weights of leaves and of bulb roots of untreated control plants were significantly less than at the full rate of permethrin (table 27). In 1992/93 (Experiment 2) (Table 29), due presumably to poor weather conditions, leaf miner infestation was at a low level and did not exceed 5% leaf area mined on unsprayed control plants. There were no significant differences at harvest between treatments in gross weight of leaves or of bulbs (Table 33). Chapter 5: Leaf miner damage assessment experiments 198 CONCLUSION It is concluded that Scaptomyza can reduce the yield of both turnip and Chinese cabbage, in the case of the former by reducing effective leaf area and thus indirectly affecting yield and with the latter by directly damaging outer leaves of the head, which then require removal at harvest. In the Manawatu such effects are unlikely to occur every year based on two season's experience. SIMULATED INSECT DAMAGE INTRODUCTION Clipping treatments have been used to simulate the effects of herbivory in numerous studies. The adequacy of this approach has been reviewed by Baldwin (1990) with mixed conclusions. The fidelity with which clipping reproduces the effects of damage by insects depends on the particular plant variable and the specific pairing of plant and herbivore. The final conclusion by Baldwin ( 1990) was that clipping more frequently than not does not adequately simulate real herbivory. However, as Baldwin ( 1990) also discussed, the advantages of using artificial clipping techniques are numerous and not easily discarded. Use of real herbivory within large manipulative experiments has proven difficult because of logistical problems associated with managing a large population of herbivores. If clipping represents a good model for herbivore damage, then increased replication, more precise placement of damage, and tighter timing of a defoliation event are possible (Welter, 199 1 ). Another compelling reason to use artificial clipping techniques instead of real herbivory is the need in some experiments to uncouple plant susceptibility from plant tolerance to herbivory. Susceptibility refers to plant characteristics that influence the amount of damage from herbivory sustained by a plant. Tolerance refers to characteristics that influence a plant's ability to sustain damage without significant changes in the marketable portion of the crop. Susceptibility to herbivory can vary with many different treatments including plant cultivar, abiotic stress factors, or other biotic stress agents such as nematodes. If plants differ in their relative susceptibility, then exposure to equal numbers of herbivores does not result in equal levels of damage. Therefore, use of clipping techniques, where appropriate, may allow particular experiments to be concluded that would be logistically impossible otherwise (Welter, 1991) . 199 Chapter 5: Leaf miner damage assessment experiments 200 The effects of pest attack on crop yield are often investigated by attempting to cause similar injury artificially to plants by partially or completely removing heads or leaves. The main difficulty associated with this approach is that of exactly simulating natural pest attack, which often has most effect on yield at a critical stage in crop growth. The recovery of the crop after damage in the field may be different to that in experiments. Plant compensation and growing conditions may also be different under field conditions. In all cases the amount of damage should be monitored in terms of leaf area or dry weight in order to compare artificial with natural damage. Although many studies have documented an increase in plant yield after either actual or simulated damage caused by herbivorous insect populations (Southwood and Norton, 1973; Kolodny- Hirsch and Harrison, 1982), relatively few studies have demonstrated the basis of plant compensation for such injury. In studies where increased cell division has been demonstrated in response to damage, the potential for compensation by leaves was related to the stage of leaf development at the time of injury; growth from meristemic tissue ceased when immature leaves reached 25 - 75% of mature size (Bardner and Fletcher, 1974). Any additional growth then occurred in response to cell enlargement (Wall and Berberet, 1979). Palisade mesophyll tissue removed from mature leaves of Phaseolus lunatus (L) by the leaf-mining herbivore Liriomyza trifolii was replaced with photosynthetically active cells, permitting virtually complete recovery from injury. Decreases in photosynthesis did not exceed 10% for leaves with approximately one-fourth of the leaf area mined (Martens and Trumble, 1 987). As part of my programme to investigate the effects of Scaptomyza on vegetable brassicas quantitative yield reduction in Chinese cabbage was investigated. In this experiment insect injury to the leaves was simulated by partial defoliation in comparison with Scaptomyza flava damage. Chapter 5: Leaf miner damage assessment experiments 201 MA TERIALS AND METHODS Leaf miner damage to potted Chinese cabbage plants was compared to artificial simulation of damage by removing different amounts of leaf area. The experiment was executed according to a completely randomized design with 3 treatments, each replicated four times. The Chinese cabbage plants were one month old at the commencement of the experiment. Treatments were as follows: 1 . Control plants: No insects released on them, no leaf area removed. 2. Real herbivory: 10 pairs ( 10 � and 10 � ) of adult � 72 h old Scaptomyza flava (obtained from the rearing colony) were released onto the plants and removed after 2 days (22/211992 to 2412/1992). 3. Simulated damage plants: After the larvae which developed on plants of treatment 2 were fully grown (immediately before pupation), the area mined on each leaf was measured by an Area Meter MK2 (Webb, 1989). Holes were then punched in leaves, to an equivalent leaf area using scissors and a cork borer. The holes were made alongside the midrib (because most leaf mines were concentrated near the midrib of Chinese cabbage leaves). Care was taken not to damage the midrib. The percent area damaged by either Scaptomyza flava larvae or the clipping regime was conf'mned with the leaf Area Meter. The plants were protected from insect infestation. About 2 weeks after insects of treatment 2 had pupated new adults began to emerge and were removed. The plants were considered mature just before flowers became apparent (about two months old). Twenty-one days after defoliation treatment, all plants were harvested by cutting off at ground level and measured (overali length of head) and weighed. The results were subjected to analysis of variance. Photoperiod throughout the experiment was 14: 10 (L:D). Chapter 5: Leaf miner damage assessment experiments 202 RESULTS The mean lengths and weights of the Chinese cabbage heads from each treatment are given in Table 34, together with significance values. Table 34: Results of actual and simulated damage to Chinese cabbage Treatment Mean length of head Fresh weight of head, (cm ) mean total per plant(g) Untreated control 2S.S0 a 87.75 a Simulated damage plants 2S.50 a 67.50 ab I Plants exposed to insects I 24.S0 a I 43.00 b I Treaunents accompanied by the same letter in each column are not significantly different at P � 0.05 (ANOV A followed by LSD test for separation of means). Measuring the length of a Chinese cabbage head essentially measures the length of the longest leaf. Under the conditions of this experiment, simulated herbivory and leaf mining activity by Scaptomyza jlava had no effect on mean length of heads as shown in Table 34. However, the fresh-weight of heads from plants subject to leaf miner injury was significantly (P ::; O.OS) lower (less than half) that of uninjured control plants. DISCUSSION Artificial simulation of injury did not produce the same effect as actual leaf miner injury. Although the artificial treatment removed a similar amount of leaf area to Chapter 5: Leaf miner damage assessment experiments 203 that caused by leaf mining larvae, the injury was imposed at a time when leaf mines were fully developed. This could account for the decreased effect. These results agree in part with Welter ( 1 99 1 ) . He found that total dry-weight was reduced significantly for increasing levels of defoliation by artificial herbivore and by tobacco horn worm. A variety of physiological mechanisms are likely to play a role in plant compensation for herbivore damage (McNaughton, 1 979; Martens and Trumble, 1987). Thus the effect of insect feeding depends not only on the amount eaten, but also on other factors such as the time when it occurs and the method of feeding. Leaf miners feed primarily in the palisade parenchyma tissue (Parrella et ai., 1985), leaving a continuous band of frass at the top, sides, or, more commonly, the bottom of the mine (Martens and Trumble, 1978). Artificial simulation of such injury is likely to be much more difficult (or impossible) compared to biting I chewing insects. MEASUREMENT OF LEAF AREA DAMAGED BY A SINGLE LARVA INTRODUCTION A number of laboratory and field studies have reported the proportion of a leaf mined by a single miner: Agromyza, 27% (Guppy et al., 1988) of alfalfa; Coptodisca, 7.6% of vegetative and 47% of floral leaves of Chamaedaphne (Hileman and Lieto, 198 1) . New ( 1976, 1979) has calculated the actual weight of leaf consumed by individual miners (Acrocercops plebeia). Guppy (198 1 ) reported that the area consumed by a single larva of alfalfa blotch leaf miner Agromyza Jrontella (based on a sample of 25 alfalfa leaves) during its life span ranged from 0.20 to 0.78 cm2, average 0.39 cm2• The range in area consumed is large; however, mine size may depend on thickness of the leaf. Hendrickson and Barth (1978 cited by Guppy, 1981 ) have pointed out that one larva consumed an average of 0.64 cm2 of alfalfa leaflet; however, their results were based on more tender laboratory­ grown plants. MATERIAL AND METHODS In order to determine the area of leaf that is damaged by an individual Scaptomyza jlava larva one pair of newly emerged adult insects were released onto each of 4 Chinese cabbage plants for 24 hr then removed. As soon as the eggs hatched, all except one larva on each leaf were killed by pricking with a pin. There were 5 such leaves for each planL When the larvae were fully fed and had pupated, the leaf area affected by each larva was measured. 204 Chapter 5: Leaf miner damage assessment experiments RESULTS AND DISCUSSION Results are presented in Table 35. Table 35: Plant 1 2 3 4 Mean Leaf area damaged by a single larvae of Scaptomyw flava Mean leaf area damage per larva (cm2) 7.2 7 5 1 .2 5. 1 205 The mean leaf area consumed by each larva during its life time was 5. 1 cm2 but with a wide range from 1 .2 to 7.2 cm2 (20 observations). This represents ca. 1 2% of the Chinese cabbage leaf area. These differences in leaf area damaged may be due to differences in either leaf size (ranged from 10 to 65 cm2, averaging 40.8 cm2), or size, age (larval stage) and sex of larvae, though all developed from eggs laid over a 24 hr period. Further studies are required to determine the reasons for this wide variation. WHAT DENSITY OF LEAF MINER ( SCAPTOMYZA FIAVA) MA Y KILL PLANT SEEDLINGS? INTRODUCTION Sometimes in the field and under laboratory conditions dead leaves and even small dead plants were observed due to damage by Scaptomyza leaf miner. Thus an experiment was undertaken to determine what density of leaf miner is capable of killing seedlings of Chinese cabbage under laboratory conditions. MA TERIALS AND METHODS On 27th April, 1992 different numbers of adult Scaptomyza flava were released onto seedling Chinese cabbage plants ( 4-6 leaf stage) in individual containers in the glasshouse (one plant per pot). Each pot was covered with an inverted transparent plastic cylinder from which the bottom had been removed. The pot and cylinder were joined with sticky tape. Either 5, 10, 15, 20 or 30 pairs of adult Scaptomyza flava were introduced into pots and the open tops closed with a piece of mesh cloth (for ventilation), held in place by a rubber band. After either I , 2, or 3 days the flies were removed. Treatments were as follows (15 treatments each with 4 replications): 1 . 5 pairs o f adult insects released for . . . . . . . . . . . . . . . . . . . . . . . . . 1 day · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 days · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 days 2. 10 pairs of adult insects released for . . . . . . . . . . . . . . . . . . . . . . . . I day · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 days · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 days 3. 15 pairs of adult insects released for . . . . . . . . . . . . . . . . . . . . . . . . 1 day 206 Chapter 5: Leaf miner damage assessment experiments 207 · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 days · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 days 4. 20 pairs of adult insects released for . . . . . . . . . . . . . . . . . . . . . . . . 1 day · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 days · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 days 5. 30 pairs of adult insects released for . . . . . . . . . . . . . . . . . . . . . . . . 1 day · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 days · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 days In each case after removal from the oviposition cage, plants were placed under a clean fIne gauze cage for eclosion of larvae. Plants were retained until leaf mines developed and there were established pupae. The number of dead leaves and seedlings in each container were recorded. RESULTS AND DISCUSSION The results are shown in Table 36. It seems that the period of time that plants are exposed is more important than the number of insects with respect to plant injury. For example when plants were exposed to fIve pairs of insects for three days, almost all leaves on the plants were killed, but 20 pairs of insects for 1 day killed only half of the leaves (Table 36). The results confmn that high levels of Scaptomyza flava attack can kill all leaves of small plants, and hence whole plants, of Chinese cabbage. Chapter 5: Leaf miner damage assessment experiments 208 Table 36: Number leaves damaged by different number of S. flava adults Treatment Total leaves Day(s) the Mean no. Mean no. (No. pairs per plant plants were of dead of severely adult insects exposed to leaves per damaged released) insects plant leaves per plant 6 1 4 1 5 5 2 2.5 0.5 5 3 4.5 0.5 6 1 4 0 10 5 2 3.5 0 4 3 3 1 6 1 3 1 15 6 2 5 0 5 3 3.5 1 4 1 3 2 20 5 2 4.5 1 5 3 4 1 6 1 4 1 30 5 2 5 0 5 3 5 0 C h a p t e r 6 GENERAL DISCUSSION In New Zealand the genus Scaptomyza occurs as a complex of four closely related known species, one of which (Scaptomyza flavella) has been recorded only from a small island locality (Mokohinau Is.). The other three species occur sympatrically but do not occupy similar feeding niches as Scaptomyza flava is considered to be a herbivore, and feeds by mining leaves whereas Scaptomyza elmoi, and Scaptomyza fuscitarsis are saprophytic. The genus Scaptomyza is placed taxonomically within the Drosopbilidae. Most other leaf mining Diptera are in the family Agromyzidae. In this study several aspects of the biology, ecology, reproductive behaviour and pest status of Scaptomyza flava were investigated. Scaptomyza flava females are polygamous and mate more than once. Multiple matings can have two effects on the fitness of female insects; they increase fertility, and also increase fecundity (Lawrence, 1 990). S. flava is unusual among phytophagous insects in that adult females make small punctures in the leaves of host plants with their toothed ovipositor from which both sexes may feed on the exuding juices. A similar habit is exhibited by some Agromyzidae. Only a small proportion of these punctures is utilised for the deposition of eggs. Flies commence making leaf punctures within 4 hours after emergence and there is a delay of approximately 24 h. before egg laying commences. This delay and the pattern of feeding suggest that Scaptomyza females require additional nutrients for oviposition and that they obtain these by feeding on leaf juices that are released by the puncturing activity of the 209 Chapter 6: General discussion 210 ovipositor. Pre-oviposition feeding therefore greatly enhances reproductive capacity. High levels of Scaptomyza flava larval attack can kill all leaves of small small plants. The period of time that plants are exposed to adult females is more important than the number of Scaptomyza flava insects with respect to plant injury. The extent of damage is linked with the number of feeding punctures and the intensity of mining by larvae in the host plant' s leaves. My results show that such mining activities reduce considerably the lifespan of primary cabbage leaves. In the laboratory quite often the less heavily attacked plants survive. Pre-oviposition feeding by adults can thus be extensive and damaging to plants- both hosts and nearby plants. Leaf puncturing can reduce photosynthesis (Livene and Daly, 1966), growth and vigour of the whole plant (Hendrickson and Barth, 1978) and when leaf miner densities are high, host plant leaves can be completely girdled by feeding punctures that cause leaves to die and/or young plants to die (laboratory and field observations). Dehiscence of leaves in response to adult feeding occurred when adult populations reached high levels (in the laboratory). Maximum oviposition varied between different host plant species. The total fecundity of some females was as high as 320 eggs on turnip over a lifespan of about 12 days and as low as 12 eggs on cauliflower. Oviposition is dependent on the presence of a suitable host plant. Scaptomyza flava attacks living plants but also lays eggs on, and larvae can develop in, dead and decaying plant material. However, the number of emerging adults was greater when the flies fIrst laid their eggs in live leaves. The facultative saprophytic habit of Scaptomyza flava means that abundance of adults in a crop environment may not necessarily reflect a population arising from the crop itself. It would be Chapter 6: General discussion 21 1 interesting to know what proportion of a population develops saprophytically and what factor (s) determine this. The species is evidently capable of surviving in the absence of a living host if suitable rotting plant material is available. In contrast to S. flava; S. elnwi and S. fuscitarsis cannot feed, leaf mine or develop on Chinese cabbage. Also I have been unable to fmd any literature reference to other genera in the family Drosophilidae as pests of cruciferous plant species. A detailed Knowledge of an insect's host fmding and oviposition behaviour can suggest ways of modifying behaviour to man ' s advantage. Understanding the factors affecting feeding and oviposition of S. flava would be important for the development of cruciferous crop varieties that are resistant to this insect, so I discuss various factors that could be involved in host plant discrimination. S. jlava is clearly oligophagous, host plants being restricted to the Brassicaceae. Some feeding/oviposition on non- Brassicaceae plants occurred in non-choice tests but eggs failed to hatch and may have been infertile. Glucosinolates are a group of compounds found in all cruciferous plants and their principal volatile hydrolysis products are isothiocyanates, sometimes referred to as mustard oils (van Etten and Tookey, 1979). Isothiocyanates are insect attractants (Matsumoto, 1970; Read et al., 1970; Eckenrode and Am, 1 972; Free and William, 1 978) and feeding stimulants (Tanton, 1 977) for many crucifer-feeding insects. Glucosinolates are known to stimulate feeding (David and Gardiner, 1966; Nault and Styer, 1972; Tanton, 1977; Larsen et al., 1985) and oviposition (Ma and Schoonhoven, 1973; Nair and McEwen, 1976; Nair et al. , 1 976; Renwick and Radke, 1983) in a number of insect species that feed exclusively on Crucifers (Reed et al., 1989). At the same time, though, glucosinolates are feeding deterrents and toxins for many polyphagous insects. Changes in glucosinolate composition of plants might reduce the attractiveness of the crop to Cruciferous specialists (Butt and Lamb, 1990). Sang et al. , Chapter 6: General discussion ------- -- ---- --------- 212 believed that the types of glucosinolates vary in different plants and change rapidly as seedling plants develop (McGregor, 1989). As larvae of S. flava cannot move from plant to plant (or even from leaf to leaf) host selection is entirely by the egg laying female. Factor (s) responsible were not investigated in this study but for some other oligophagous insects restricted to Brassicaceae e.g., diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), oviposition is known to be regulated by plant chemicals restricted to the Brassicaceae (Reed et al., 1989). Although it seems obvious that adult female insects should select individual host-plants, or partes) of host-plants on which their larvae do best, the empirical evidence is equivocal: sometimes they do (Rausher, 1979; Rausher and Papaj , 1983; Quiring and McNeil, 1978; Damman and Feeny, 1988; Preszler and Price, 1988), but sometimes they do not (Auerbach and Simberloff, 1989). Intraspecific variation in host-plant suitability seems to be much greater for leaf­ miners than for free-living insects (Mattson et al., 1988). Adult female S. flava not only oviposit in Cruciferous plant leaves, but also host-feed, creating characteristic feeding punctures in the leaf. I cannot say whether females select plants on which to feed themselves (thereby enhancing fecundity, e.g., Minkenberg and Fredrix, 1 989) and simply stay to oviposit; or whether host­ feeding provides them with information about the suitability of plants for oviposition. Both may be involved. S. flava flies must have one or more means of recognizing Cruciferous plants. The presence of attractants/stimulants must be accompanied by the absence of deterrents. This is analogous to diamondback moth where, for example, rutin and coumarin are known to deter oviposition (Tabashnik, 1985). Host plant ranges are known to be wider in laboratory trials when plants are Chapter 6: General discussion 213 offered individually compared to the field situation with relatively unlimited supply of one or few preferred hosts. Insects will eventually become more selective given a choice but when insects exist in a habitat provided with several host species, they may prefer to feed and oviposit on a select number of hosts. On the other hand, in the absence of highly preferred host plants, what are generally nonpreferred plants may now be accepted. If we postulate that Scaptomyza flava are attracted to isothiocyanates found in Cruciferous plants, it is likely that dead plant material acceptable to S. flava for feeding and egg laying must also be from Brassica plants. Eggs laid by Scaptomyza flava on wheat in non-choice experiments did not hatch, presumably because they were unfertilized. This suggests that courtship and mating did not occur on wheat leaves. It has been hypothesized that in some insect species (e.g., Drosophila conformis) the most successful males are those that occupy the centre of leaves (Shelly, 1989). This observation has led to the suggestion (Wiley, 1978) that territory (site = leaves) position itself may serve as an important cue to females in selecting a mate. Territory selection by both males and females could depend, not only on a leaf' s position within a plant, but also on overall characteristics of the plant. Wheat leaves are narrow in contrast to wide broad leaves of Cruciferous plants and thus leaves of wheat have no distinct and facile centre as Brassica leaves have. Thus based on this hypothesis, leaf form alone, without consideration of plant chemistry, could account for S. flava choosing Cruciferous leaves for mating. In choice and non-choice tests S. flava adult flies fed and oviposited on all Cruciferous plants but showed distinct ovipositional preferences for some species. When Scaptomyza fiava were given a simultaneous choice of seven plant species for feeding and oviposition, there was a distinct hierarchical Chapter 6: General discussion 214 ordering in their ovipositional preference, with turnip and then Chinese cabbage and hedge mustard being highly preferred over all others. These results support the hypothesis that host preferences area factor in utilization of cruciferous crops by this leaf miner. The results of the non-choice tests were somewhat surprising in that wheat was more readily accepted for feeding than cauliflower. Flies did not feed or oviposit on prairie grass in choice or non-choice tests, and clearly this species is a nonhost. Numbers of feeding punctures recorded from lettuce were too low to reach fIrm conclusions. Choice tests, non-choice tests and observations of individual ovipositing females yield different insights into the ovipositional behaviour of S. flava. Choice tests permit rapid screening for effects of diverse stimuli and would thus aid the search for more resistant Cruciferous plants. Leaves of turnip, hedge mustard and Chinese cabbage gave higher fItness indices based on larval growth rate and survival and were the most preferred for egg laying while cauliflower, and radish gave the poorest performance and were the least preferred. In holometabolous insect herbivores, the main oviposition sites are not necessarily the main feeding sites for the adult. For example Scaptomyza flava flies preferred to feed on wheat compared to cauliflower but wheat was not a suitable plant for oviposition and vice versa. For some insects selection of plants for oviposition is determined both by the physical nature of their surfaces and by chemical factors which are detected only on contact (Fenemore, 1980). For potato moth (Phthorimaea operculella) apparently surface texture was the principal cue. Surface texture of substrate also Chapter 6: General discussion 215 may play a role in oviposition preference of S. flava. Heavily wax-textured surfaces e.g . , leaves of cauliflower were not suitable compared to other Brassicaceae for feeding, but were relatively well accepted for oviposition. In addition to differences in leaf surface wax, Chinese cabbage and turnip have a much softer leaf than cauliflower and may be easier to puncture with the insect's ovipositor. Such puncturing is essential in order for feeding to take place. The literature on the feeding of S. flava under field or laboratory conditions is very scarce. The effect of the non-host plants was lost if they were grown more than 0.5 m. from the brassica rows (Tukahirwa and Coaker, 1 982 cited by Nottigham, 1 988). The non-host plant might also have acted as a physical barrier to oviposition (Nottigham, 1988). Scaptomyza leaf miner development in the Manawatu area is limited by the absence of host plants in peripheral areas (by bush, mountain and river). On the other hand, the absence of other leaf miner species on Brassicaceae plants allows S. flava to exploit this niche without competition. Knowledge of larval food quality as determined by plant species and cultivar could assist in formulation of total population management strategies for S. flava. The developmental time of S. flava was significantly affected by host plant. Of the plants tested, turnip gave the best biological performance as expressed by the biological fitness ! . Insects reared on turnip required the least time and those reared on cauliflower the most time from egg to adult death. Overall survival was also better on turnip. On cauliflower only 20% of the eggs of Scaptomyza flava developed and produced adults in contrast to 77% and 80% on Chinese cabbage and turnip respectively. Unfortunately the results do not to 1 Biological fitness i.e., no. of eggs laid per female, percent of hatch of eggs, duration of larval and pupal development (day), percent pupation and weight of pupae. Chapter 6: General discussion 216 explain the mechanisms underlying these differences in growth rate or fecundity of S. flava. Oviposition by leaf mining insects is frequently non-random because ovipositing females prefer and/or avoid certain leaves or egg arrangements within leaves (Heads and Laeton, 1983; Potter, 1985; Bultman and Faeth, 1 986; Simberloff and Stiling, 1978 cited by Auerbach and Simberloff, 1989). One might expect oviposition site preference to be under strong selective control for insects such as Scaptomyza flava whose larval feeding location is determined solely by egg placement. Oviposition patterns among and within leaves should reflect enhanced probabilities of survival relative to alternative arrangements. Comparison of my results of Scaptomyza flava with those of Minkenberg et al. (1989) for Liriomyza trifolii indicate that age of leaf influences fecundity independently of nitrogen. Good to poor correspondence between oviposition preference and offspring performance on different species of plants has been observed for a variety of insect taxa (e.g., Copp and Davenport, 1 978; Valladares and Lawton, 1 991 ). A major working hypothesis on the evolution of oviposition behaviour is that females will choose plant species that maximize larval survival and growth. Most studies of Lepidoptera analysing the preference/performance hypothesis have focused on survival, growth rate, and pupal mass in the absence of natural enemies of eggs, larvae, and pupae (Thompson, 1990). Several hypotheses may explain lack of concordance between adult host­ selection behaviour and offspring performance: e.g., performance could be influenced by plant characteristics. A lack of�correlation between oviposition preference and larval performance can also result from at least five other factors: First, the preferred plant may be rare. Second, a plant commonly chosen for Chapter 6: General discussion 217 oviposition but poor for larval growth may be a recent addition to habitat. Third, a host plant may be favourable for larval growth under some conditions , but it may sometimes grow in a habitat unfavourable for flight of ovipositing females or for larval growth. Fourth, females may oviposit preferentially on plants that allow their offspring to sequester particular secondary plant compounds for defense, even if those plants result in lower growth of larvae. Fifth, in species whose larvae feed as grazers and move among several plants during development, rather than feed as parasites on an individual plant selection may not consistently favour females that oviposit on a certain plant species (Thompson and Pellmyr, 1991 ). I observed that (unrecorded data) within a plant, both sexes (but particularly females) appeared to settle preferentially on the larger leaves. The same pattern has been observed by Shelly ( 1987). He has demonstrated that two positional features of a male' s territory strongly influence the likelihood of visits of Drosophila conformis females. First females usually visited the lowest leaves within a plant. In addition, females appeared to preferentially visit territories in large leaves over those in smaller ones. This preference for larger leaves may have evolved as a behavioural mechanism to facilitate mate choice. By visiting larger leaves, females encountered larger "samples" of males and therefore may have benefited from the increased number of possible comparisons among potential mates (Alexander, 1975). Recent work on Plantago zelicaon and P. oregonius showed that oviposition preference is genetically independent of larval performance in these species, at least with respect to the physical Jinkage of loci (Thompson, 1990). Female Scaptomyza flava consistently laid more eggs on older than younger leaves in all experiments. This result is support by several pieces of evidence from work with other insects (e.g., Murai, 1 974). Leaf size could be Chapter 6: General discussion 218 a factor detennining which leaves were selected. While my results show that Scaptomyza has preference for certain leaf ages, the mechanism by which discrimination occurs is unclear. The role of nitrogen could be further investigated by manipulating plant nitrogen content. Previous larval feeding experience on turnip and Chinese cabbage influenced adult host plant oviposition preference, but adult host plant preference was not influenced by previous feeding experience as larvae on cauliflower. These results are only partly consistent with fmdings from previous experiments on the effect of adult experience in Drosophila on oviposition, where the experimenter determined the exposure time to resources. Positive effects were found in small containers (Jaenike, 1983), including experiments where apple and orange media were used (Hoffmann, 1985). However, negative or non-significant experience effects were found in other oviposition experiments in large cages (Hoffmann , 1985) that are similar to the cages I used. The reasons for these inconsistencies (non-significant effects) are unclear. One possibility is that effect of experience on oviposition is different from its effect on host attraction. Another possibility is that the resources used in the experiments differed. Hoffmann and Turelli ( 1985) reported non-significant experience effects for Drosophila females, and they also found inconsistent experience effects in releases with several fly stocks and pairs of alternative resources. The extent to which host fidelity documented in the laboratory experiments occurs in the field depends on the relevance of these experiments to field behaviours and the nature of the resources that flies encounter in the field after eclosion. On the other hand, inability to move from one food resource to another is a constraint in leaf miner larvae, so aversion learning has no relevance for them (Bernays et al. , 1992). The relative aversion of Scaptomyza flava to Chapter 6: General discussion 219 cauliflower may to be due to a nutritional deficiency rather than any toxic effect (aversion learning has been demonstrated for some insects e.g. , learned aversion of the polyphagous grasshopper Schistocerca americana to spinach [Papaj and Lewis, 1993]). Avoidance learning by fly larvae is controlled by the same genes as avoidance learning in adult flies (Aceves-Pine and Quinn, 1970). The general conclusion from these experiments is that larval or early adult experience of Scaptomyza flava to one plant species did not increase preference for that species for feeding or egg-laying with the part exception of Chinese cabbage and turnip. Effective control of pests in integrated programmes normally requires regular field samples to estimate pest population levels. Methods for estimating field densities of Scaptomyza jlava have not been thoroughly evaluated. Unfortunately, little is known about factors that might affect the variability of field samples of Drosopbilid species. In addition to time of day (Fisher et aI. , 1 982), within-field dispersion patterns of Scaptomyzajlava may be influenced by wind direction and speed, and field size. It is likely that these factors would, in turn, affect sampling variability. However, their influence on the daily or weekly pattern of Scaptomyza flava dispersion has not been quantified. Unbaited sticky traps were used for detection of adult Scaptomyza flava abundance but flies were rarely captured on such traps. Water traps were superior to sticky traps and were easy to service. I used whole-plant samples to obtain estimates of larvae and of leaf mining injury. Samples that include only a portion (e,g., certain leaves) of individual plants could reduce the effort required to reach a control or management decision (Stewart and Sears, 1 989). Chapter 6: General discussion 220 In the field adults and larvae of S. flava were present all year round with no winter donnancy. Abundance of S. flava varied considerably from month to month and year to year and it was observed that at certain times Chinese cabbage leaves abounded with mines, whereas at the same time in another year they did not (the spring and summer of 199211993 was exceptionally cool and wet). This could be a reflection of seasonal weather variability or of different stages of plant development. However, the numbers of adult flies caught showed distinct peaks during spring and early summer, and again in autumn to early winter. This pattern was reflected in the results from larval sampling. The large numbers of flies caught in early summer and early winter must be mostly progeny from the first spring and autwnn generation of larvae. Were differences in infestation levels between the two plants in field experiments (turnip and Chinese cabbage) simply a consequence of females staying. feeding and laying more eggs on turnip. From laboratory experiments turnip leaves appear more suitable for oviposition of Scaptomyza flava than Chinese cabbage leaves. Weather does seem to play a major role in determining seasonal abundance but females were present and oviposited at all times during the 2-year observation period. There remains the question of whether Scaptomyza flava is likely to be a more serious problem in warmer, i.e., more nonnal years. Although seems individual meterological parameters (e.g., rainfall) show significant correlation with catches flies. High rainfall in particular showed significant correlation with low catches of flies especially in January / February and March. Several mechanisms have been proposed to explain the effect of precipitation upon the Scaptomyzajlava populations. Eveleens (1966) suggested that the shedding of mined leaves during the rainy reason could reduce the popUlation of the leaf miner by curtailing larval development. Crowe (1964) proposed that he higher leaf miner mortality is due to larvae drowning inside Chapter 6: General discussion 221 overflowed mines in which the dead epidermis became lacerated by the physical damage provoked by rain-drops, or by the penetration of water through the pupation holes of older larvae in mines containing mixed ages of larvae. In addition, rain has been proposed as a mortality factor of leaf-miner eggs, which seem to have a greater chance of survival when the leaf surlace is dry (Nestel et at., 1 994). In this context, it should be noted that female Scaptomyzajlava, as some other leaf miner adults (Hovemeyer, 1992), may survive hidden in the litter layer for quite a long time when the weather is cold or rainy, and that they may resume oviposition activity after such adverse periods. Overall though the factors determining survival and reproductive success in Scaptomyza flava females in the field are poorly understood. For the most part, leaf-mining Drosophilidae do not appear to be economically important in New Zealand. This may be because economic injury levels are difficult to assess and data in not available. McGregor ( 1989) considered that parasitoids already present in New Zealand may restrict populations of potentially damaging Drosopbilid leaf miners but I found no evidence of parasitism in Scaptomyza jlava. As with many other species of leaf miners, the larval mine IS conspicuous, but actual damage from S. flava is often slight in terms of yield reduction. For many field crops where the damage consists of leaf mining, it is neither necessary nor really feasible to consider applying control measures. However, the effect of S. flava on some leafy vegetable brassicas such as Chinese cabbage is more serious and for a few where appearance is all important, e.g., watercress, this is particularly the case. Although my results show that S. flava can reduce the yield of both turnip and Chinese cabbage, it is apparent that plant compensation in turnip (because injury is indirect) is an important factor that would need to be Chapter 6: General discussion 222 considered when determining pest control actions. Compensation is likely to be a dynamic process which will vary throughout the growth of the plant. Furthermore adult S. flava flies are susceptible to a range of contact insecticides. In Manawatu, bras sic a leaf miner populations did not reach pest levels, so, not necessary prompted action towards control of the insect. On commercial brassica crops S. flava is probably normally controlled by insecticides applied for control of other pests such as white butterfly, diamondback moth, and aphids. This research has highlighted our limited knowledge of the biology and damage potential of Scaptomyza spp. as leaf miners of vegetable brassicas. It should also have made clear the desirability of dialogue with researchers on the behaviour and host relationships of other Drosophilidae. It is hoped that this thesis will aid in developing such dialogue. R E F E R E N C E S Aceves-Pine, E. 0.; Quinn, W. G. 1 979. Learning In nonnal and mutant Drosophila larvae. Science; 206: 93-96. Adler, P. H. 1 987. Ecology of black fly sibling species. In Blackflies : Ecology, population management, and annotated world list. Edited by K. C. Kim and Merritt. Pennsylvania State University, University Park, State College,. PA. pp. 63-76. Ahmad, S . ; Allen, W. W. 1983. Herbivorous insects. Host seeking behaviour and mechanisms. New York: Academic Press. Aiello, A. ; Vogt, G. 1 986. Tachygonus dasypus (Coleoptera: Curculionidae) observations on an unusual tropical weevil. Proc. K. Ned. Akad. Wet. c.; 89: 1 17 - 1 20. (seen in abstract only). Alder, A. 1 987. Survival of Drosophila melanogaster embryos cooled to sebzero temperatures. Cryobiol; 24: 545-546. (seen in abstract only). Ali. A.; Luttrell, R. G. ; Pitre, H. N. 1 990. Feeding site and distribution of fall armyworm (Lepidoptera: Noctuidae) larvae on cotton. Environ. Entomol. ; 19 : 1 060-67. Anwar, A. M. 1 972. Parasites of Scaptomyza (for New Zealand). In: Commonwealth Institute of Biological Control; Report of work carried out in 1 972; Project 8. (60). ------ ; Ghani, M. A. 1 970. Parasites of Phytomyza (for New Zealand). In: Commonwealth Institute of Biological Control; Report of work carried out in 1 970; Project 1 5. (75) . 223 REFERENCES 224 Askew, R R. 1 962. The distribution of galls of Neuroterus (Hym: Cynipidae) on oak. 1. Anim. Ecol.; 3 1 : 439-55. (seen in abstract only). Askew, R R 1980. The diversity of insect communities in leaf miners and plant galls. 1. Anim. Eco!. 49: 8 17-29. (seen in abstract only). Askew, R R ; Shaw, M. R. 1974. An account of the Chalcidoidea (Hymenoptera) parasiting leaf mining insects of deciduous trees in Britain. Bio!. 1. Linn. Soc. London; 6: 289-335. (seen in abstract only). Askew, R R ; Shaw, M. R 1979. Mortality factors affecting the leaf-mining stages of Phyllonorycter (Lepidoptera: Gracillariidae) in oak and birch. Zool. 1. Linn. Soc. London; 67:31-49. (seen in abstract only). Attia, R ; Mattar, B. 1939. Some notes on "The Potato Tuber Moth" (Phthorimaea opercullella, ZeIl.). In: Egypt: Ministry of Agriculture; (Bulletin Technical & Scientific Service; 216). (seen in abstract only). Auerbach, M.A. 1982. Population biology and community ecology of leaf-mining insects on native and introduced oaks. Ph.D dissertation,Florida State Univ. Auerbach, M. J.; Simberloff, D. 1984. Responses of leaf miners to typical leaf production patterns. Eco!. Entomo!. ; 9: 361-67. --------------- . 1988. Rapid leaf miner colonization of introduced trees and shifts in sources of herbivore mortality. Oikos; 52: 41-50. (seen in abstract only). ---------------- . 1989. Oviposition site preference and larval mortality in a leaf-mining moth. Ecol. Entomol. ; 14: 13 1-140. REFERENCES 225 Auerbach, M. J. ; Strong, D. R. 198 1 . Nutritional ecology of Heliconia herbivores: experiments with plant fertilization and alternative hosts. Ecological Monographs; 5 1 : 63-83. (seen in abstract only). B achi, G. B. 1 973. Faunistic and ecological studies on the Drosophila species (Diptera) of Switzerland. Mitt. Schw. Entomol. Ges. ; 46: 195-98 . (seen in abstract only). B achi, G.; Kobke, B. ; Kohler, W.; Krause, J.; Lumme, J.; Voleske, P. 1 985. On a collection of Drosophilids (Diptera) at the Edersee (Germany). Ges. Zurich; 1 26: 175-178 . (seen in abstract only). B aker, C. R. B . ; Miller G. W. 1974. Some effects of temperature and larval food on the development of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae). Bull Entomol Res; 63: 495-5 1 1 . (seen in abstract only) . Baldwin, I. T. 1 990. Herbivory simulations in ecological research. Trends in Ecol. Evo!.; 5 : 9 1 -93. Bale, J. S. 1 98 1 . Seasonal distribution and migratory behaviour of the beech leaf­ mining weevil, Rhynchaenus fagi L. Ecol. Entomol. 6: 109- 1 8 . B ale, J. S.; Luff, M. L. 1978. The food plants and feeding preferences of the beech leaf mining weevil, Rhynchaenus fagi L. Eco!. Entomol. 3: 245- 249. Bardner, R.; Fletcher, K. E. 1974. Insect infestations and their effects on the growth and yield of field crops: a review. Bull. Entomol. Res.; 64: 1 4 1 - 1 60. REFERENCES 226 Barker, G. M.; Pottinger, R. P.; Addison, P. J. Oliver, E. H. A. 1984. Pest status of Cerodontha spp. and other shoot flies in Waikato pastures. In: Proceeding of the 37th New Zealand Weed and Pest Control Conference: 96- 100. Basden, E. B. 1954. The distribution and biology of Drosophilidae in Scotland. Trans. R. ent. Soc. Edinburg; 62: 603-654. (seen in abstract only). Baust, J. G. 1982. Environmental triggers to cold hardening. Comparative Biochemistry and Physiology; 73a: 563-570. (seen in abstract only). 1982. Mechanisms of cryoprotection in freezing tolerant animal systems. Cryobiol; 10: 197-205. (seen in abstract only). ------ ; Rojas, R. R. 1985. Review of insect cold hardiness: facts and fancy. J. Insect Physiol.; 3 1 : 755-759. Beach, R. M.; Todd, J. W. 1988. Oviposition preference of the soybean looper (Lepidoptera: Noctuidae) among four soybean genotypes differing in larval resistance. 1. Econ. Entomol. ; 8 1 : 344-348. Beck, B. 1983a Insect photoperiodism. 2nd ed. Academic Press, New York. Beck, S. D. 1 965. Resistance of plants to insects. Ann. Rev. Ent. ; 10: 207-32. Beegle, C. c.; Dulmage, H. T. 198 1 . Persistence of Bacillus thuringiensis insecticidal activity on cotton foliage. Environ. Entomol.; 10: 400-401 . Beninger, C . W. 1989. Oviposition rhythm of Drosophila algonquin (Diptera: Drosophilidae). Ecological Entomology; 14: 463-466. REFERENCES 227 Berlinger, M. J.; Dahan, R; Mordechi, S. 1988. Integrated pest management of organically grown greenhouse tomatoes in Israel Applied Agricultural Research; 3: 233-38. Bernays, E. A; Bright, K. L. ; Howard, J. J. ; Champagne, D. 1992. Variety is the spice of life: the basis of dietary mixing in a polyphagous grasshopper. Animal. behav. ; Bernon, G.; Grares, R C. 1979. An outbreak: of the oil palm leaf miner beetle in Ghana with reference to a new alternative for its parasite complex. Environ. Entomol. ; 8: 108-1 12. Bethke, 1. A; Parrella, M. P. 1985. Leaf puncturing, feeding and oviposition behaviour of Liriomyza tri/olii. Entomol. Exp. Appl.; 39: 149- 154. Bigger, M. 1973. An investigation by Fourier analysis into the interaction between coffee leaf-miners and their larval parasites. J. Anim. Ecol. 42: 417-34. (seen in abstract only). Blaney, W. M. ; Simmonds, M. S. J. 1985. Food selection by locusts: the role of learning in rejection behaviour. Entomol. Exp. Appl.; 39: 273-278. Blau, P. A.; Feeny, P.; Cntardo, L. ; Robson, D. S. 1978. Allylglucosinolate and herbivorous caterpillars: a contrast in toxicity and tolerance. Science; 200: 1296- 1298. Bock, 1. R 1977. Drosophilidae of Australia. ll. Scaptomyza (Insecta: Diptera) Aust. J. Zoology; 25: 337-345. REFERENCES 228 Bock, L R 1 986. The Drosophilidae (Insecta: Diptera) of Norfolk Island. Aust. J. Zoology; 34: 305- 14. ----- ; Parsons, P. A. 1 977. Distributions of the diptera Drosophila and Scaptomyza in Australia in relation to resource utilization. J. Biogeogr. ; 4: 327-32. Bonjour, E. L. ; Fargo, W. S. 1989. Host effects on the survival and development of Anasa triStlS (Heteroptera: Coreidae). Environ. Entomol. ; 18 : 1083-85. (seen in abstract only). B orror, J. D.; Delong, D. M.; Triplehorn, C. A. 198 1 . An introduction to the study of insects. New York: The Dryden Press, 827pp. Braman, S. K. ; Sloderbeck, P. E.; Yeargan, K. V. 1 984. Effects of temperature on the development and survival of Nabis americoferus (Hemiptera: Nabidae). Ann. Entomol. Soc. Am; 77: 592-596. Buhr, H. 1937. Parasitenbefall und Pflanzenverwandtschaft. Bot. Jahrb.; 68: 14298. (seen in abstract only). B uhr, H. 1 94 1 . Minen, IV. Arch. Ver. Mecklenb.; Nova series; 15: 21 - 101 . (seen in abstract only). Bultman, T. L.; Faeth, S. H. 1 985. Patterns of intra- and interspecific association in leaf-mining insects on three oak host species. Ecol. Entomol. ; 1 0: 1 2 1 - 1 29. ------------- . 1986. Selective oviposition by a leaf miner in response to temporal variation in abscission. Oecologia; 64: 1 17-120. REFERENCES 229 ------------- . 1986a. Experimental evidence for intraspecific competition in a lepidopteran leaf miner. Ecology; 67: 442-48. ------------- . 1986b. Leaf size selection by leaf mining insects on Quercus emoryi (Fagaceae) . Oikos; 46: 3 1 1 -316. (seen in abstract only). ------------- . 1986c. Effect of within leaf density and leaf size on pupal weight of a leaf miner, Cameraria (Lepidoptera: Gracillariidae). Shout West. Nat.; 3 1 : 201-206. (seen in abstract only). ----------- . 1988. Abundance and mortality of leaf miners on artificially shaded Emory oak. Ecal. Entomol. ; 13 : 1 3 1 -42. Burnett, P. A 1984. Cereal crop pests. In: Scott, R. R. New Zealand pest and beneficial insects. Canterbury, New Zealand: Lincoln University Collage of Agriculture: 1 53-1 67. Butcher, M. R. 1 984. Vegetable crop pests. In: Scott, R. R. New Zealand pest and beneficial insects. Canterbury, New Zealand: Lincoln University College of Agriculture: 93- 1 1 8. Butts, R. A; Lamb, R. 1. 1990. Comparison of oilseed Brassica crops with high or low levels of glucosinolates and alfalfa as hosts for three species of Lygus (Hemiptera: Heteroptera: Miridae). J. Econ. Entomol.; 83: 258- 2262. Candelas, F. G.; Mensua, J. L.; Moya, A 1 990. Larval competition in Drosophila melanogaster: effects on development time. Genetica; 82: 33-44. REFERENCES 230 Capinera, J. L. 1993. host plant selection by Schistocerca americana (Orthoptera: Acrididae). Environ. Entomol. ; 22: 127- 1 33. Carolina; Herr, J. c.; Johnson, M. W. 1992. Host plant preference of Liriomyza sativa populations infesting green onion in Hawaii. Environ. Entomol. ; 2 1 : 1097- 1 102. Casas, 1. 1 989. Foraging behaviour of a leaf miner parasitoid in the field. Ecol. Entomol.; 14: 257-65. Cates, R. G. 1980. Feeding patterns of monophagous, oligophagous, and polyphagous insect herbivores: the effect of resource abundance and plant chemistry. Oecologia; 46: 22-3 1 . Chalfant, R . B . 1976. Chemical control of insect pests of the southern pea in Georgia. Ga. Agric. Exp. Res. Bull. ; 179: 3 1pp. (seen in abstract only). Chapman, R. F. 1 982. The insects: structure and function. Cambridge: Harvard University Press.: Mass. Chappel, A. V. 1929. Biological notes on New Zealand Lepidoptera. Tr. Pr. New Zeal. [nst.; 60: 259-64. Charlton, C. A. ; Allen, W. W. 198 1 . The biology of liriomyza trifolii on beansand chrysanthemums. In: Proceedings: IFAS- Industry conference on biological control of Liriomyza leaf miners; Gainesville: 42-48. (seen in abstract only). Chen, C. P.; Denberger, D. L.; Richard, E. L. JR. 1 987. Response of nondiapausing flesh flies (Diptera: Sarcophagidae) to low rearing REFERENCES 23 1 temperatures: developmental rate, cold tolerance, and glycerol concentrations. Ann. Entomol. Soc. Am.; 80: 790-796. ------; Denberger, D. L.; Lee, Jr. R E. 1987. Cold-shock injury and rapid cold hardening in the flesh fly Sarcophaga crassipalpis. Physiol. 7.001. ; 60: 297-304. (seen in abstract only). Chess, K. F.; Ringo, J. M. ; Dowse, H. B. 1990. Oviposition by two species of Drosophila (Diptera: Drosophilidae): Behavioral responses to resource distribution and competition. Ann. Entomol. Soc. Am.; 83: 7 17-24. Chew, F. S. 1977. Coevolution of Pierid butterflies and their cruciferous food plants II. The distribution of eggs on potential food plants. Evolution; 3 1 : 568-79. (seen in abstract only). Chew, F. S. 1988. Biological effects of glucosinolates, pp. 155- 1 8 1 , In: Cutler, H. G. (ed.). Biologically active natural products: Potential use in agriculture. ACS Symposium Series No. 3 80, American chemical society, Washington, D.C. (seen in abstract only). Chutter, F. M. 1970. A preliminary study of factors influencing the number of oocytes present in newly emerged blackflies (Diptera: Simuliidae) in Ontario. Can. 1. Zool.; 48: 1 389-1400. Clancy, K. M.; Price, W. P.; Sacchi, C. F. 1993. Is leaf size important for a leaf-galling sawfly (Hymenoptera: Tenthredinidae)? Environ. Entomol. ; 22: 1 16-26. Claridge, M. F. ; Wilson, M. R 1982. Insect herbivore guilds and species - area relationships: leaf miners on British trees. Ecol. Entomol. ; 7: 19-30. REFERENCES 232 Clark, L. R. 1962. The general biology of Cardiaspina albitextura (Psyliidae) and its abundance in relation to weather and parasitism. Aust.l.Zool. 1 0:537 -86 Clark, A. B. 1978. Sex ratio and local resource competition in a prosimian primate. Science; 201 : 163- 165. Cole, R. A. 1976. Isothiocyanates, nitriles and thiocyanates as products of autolysis of glucosinolates in Cruciferae. Phytochemistry; 15 : 759-762. (seen in abstract only). Cole, R. A. 1980. Volatile components produced during ontogeny of some cultivated cruciferous crops. J. Sci. Food Agric.; 3 1 : 291 -294. (seen in abstract only). Coley, P. D. 1983. Interspecific variation in herbivory on two tropical tree species. Ecology; 64: 426-433. Collin, J. E. 1953. On the British species of Scaptomyza Hardy and Parascaptomyza Duda. Entomologist; 86: 148- 15 1 . Collinge, S . K.; Louda, S . M. 1988. Herbivory by leaf miners in response to experimental shading of a native crucifer. Oecologia; 75: 559-66. ---------------- . 1988. Patterns of resource use by a Drosophilid (Diptera) leaf miner on a native crucifer. Ann. Entomol. Soc. Am.; 8 : 733-41 . ------------- . 1989. Scaptomyza nigrita Wheeler (Diptera: Drosophilidae), a leaf miner of the native crucifer, Cardamine cordifolia A. Gray (bittercress). J. Kans. Entomol. Soc. ; 62: 1 - 10. REFERENCES 233 Collins, W. E. 1956. On the biology and control of Drosophila on tomatoes for processing. 1. Econ. Ent. ; 49: 607-610. Condrashoff, S. F. 1964. Bionomics of the aspen leaf miner, Phyllocnistis populiella Cham. (Lepidoptera: Gracillariidae). Can. Entonwl. ; 96: 857-874. Connell, I. H. 1983. On the prevalence and relative importance of interspecific competition: evidence from field experiments. Amer. Natur. ; 1 22: 66 1-96. Connor, E. F. 1984. The causes of over-wintering mortality on Phyllonorycter on Quercus robur. Ecol. Entomol. ; 9: 23-28. (seen in abstract only). Connor, E. F.; Faeth, S. H.; Simberloff, D. 1983. Leaf miners on oak: the role of immigration and in situ reproductive recruitment. Ecology; 64: 191 -204. Connor, E.; Adams-Manson, R. ; Carr, T. ; Beck, W. 1994. The effects of host plant phenology on the demography and population dynamics of the leaf­ miner moth Cameraria hamadryadella. Ecological Entonwlogy. 19: 1 1 1 -20. Copeland, R. S.; Craig, Ir. G. B. 1992. Interspecific competition, parasitism and predation affect development of Aedes hendersoni and Aedes triseriatus (Dirtea: Cubicidae) in artificial tree holes. Ann. EntonwL Soc. Am; 85: 1 54- 163. Copp, N. H.; Davenport, D. 1978. Agraulis and Passiflora 1. Control of specificity. Biological Bulletin; 155: 98- 1 12. (seen in abstract only). Cornelius, S. J. ; Godfray, H. J. C. 1984. Natural parasitism of the chrysanthemum leaf-miner Chromatomyia syngenesiae (Diptera: Agromyzidae). REFERENCES 234 Entomophaga; 29 : 341-45. Craig, T. P.; Itami, J. K.; Price, P. W. 1989. A strong relationship between oviposition preference and larval performance in a shoot-galling sawfly. Ecology; 70: 1691 - 1699. Craig, T. P. ; Itami, J. K.; Price, P. W. 1990. Intraspecific competition and facilitation by a shoot-galling sawfly. 1. Anim. Ecol. ; 59: 147- 1 59. Crawley, M. J. 1983. Herbivory: the dynamics of animal-plant interactions. University of California, Berkeley. Crowe, T. J. 1964. Coffee leaf miners in Kenya Kenya Coffee, 223-23 1 . Cumber, R. A; Eyles, A C. 1961a Insects associated with the major fodder crops in the North Island N. Hymenoptera NZ 1. Agric. Res.; 4:390-408. -----------. 1961b. Insects associated with the major fodder crops in the North Island. V. Diptera NZ 1. Agric. Res. ; 4: 409-425. Damman, H.;Feeny,P. 1988.Mechanisms and consequences of selective oviposition by the zebra swallowtail butterfly Animal behaviour;36:563-573. Daoust, R. A.; Roberts, D. W.; Neves, B. D. (Eds.). 1985. Distribution, biology and control of cowpea pest in Latin America. In: Cowpea research; London; 25 1 -266. (seen in abstract only). David, W. A L.; Gardiner, B. O. C. 1966. Mustard oil glucosinolates feeding stimulants for Pieris brassicae larvae in a semi-synthetic diet. Entomol. expo appl.; 9: 247-255. REFERENCES 235 Davidson, J. 1944. On the relationship between temperature and rate of development of insects at constant temperatures. J. Anim. Eco!.; 13 : 26-38. (seen in abstract only). Day, K. R.; Watt, A. D. 1989. Population studies of the beech leaf mining weevil (Rhychaenus Jagi) in Ireland and Scotland. Ecol. Entomol.; 14: 23-30. Denno, R. F. ; McClure, M. S. 1983. Variable plants and herbivore in natural and managed systems. Academic Press, New York. (seen in abstract only). Dethier, V.G. 1954. Evolution of feeding preferences in phytophagous insects. Evolution; 8 : 33-54. Dimetry, N. Z. 197 1 . Biological studies on a leaf mining Diptera, liriomyza trifoUi (Burgess) attacking beans in Egypt Bull. Soc. Entomol. Egypt; 55: 55-69. (seen in abstract only). Dohse, L. A.; McNeil. J. N. 1988. An Intraspecific competition model for the leaf miner, Agromyza frontella (Rondani). Can. Entomol. ; 120: 779-86. Drea, 1. J. Jr. ; Hendrickson, R. M. Jr. 1986. Analysis of a successful classical biological control project: the alfalfa blotch leaf miner Agromyza frontella Rondani (Diptera: Agromyzidae) in the northeastern United States. Environ. Entomol.; 15: 448-55. DSIR. Entomology Division. fIles BC; 1/4. Duba, S. E.; Carpenter, S. E. 1980. Effect of shade on the growth, leaf morphology, and photosynthetic capacity of an American sycamore clone. Castanea; 45: 2 19-227. (seen in abstract only). REFERENCES 236 Duda, O. 1935. Drosophilidae, in Lindner: Die Fliegen der Palearktischen Region; 58g: 1 1 8pp., Tables. E. Nagele, Stuttgart Dureseau, L. Jf. ; Jeandel, D. 1977. Alfalfa blotch leaf miner (Diptera: Agromyzidae) laboratory studies of biology in Europe. Proc. Entomol. Soc. Wash.; 79: 259-65. (seen in abstract only). Dye, C. 1982. Intraspecific competition amongst larval Aedes aegypti, food exploitation or chemical interference. Ecol. Entomol.; 7: 36-46. Eckenrode, C. J.; Am, H. 1972. Trapping cabbage maggots with plant bait and allyl isothiocyanate. J. Econ. Entomol.; 65: 1 343-1345 Engelbrecht, L. U. et al. 1969. Leaf-miner caterpillars in the "green islands" of autumn leaves. Nature; 223: 3 19-32 1 . (seen in abstract only). Etten, C. H. van; Tookey, H. L. 1979. Chemistry and biological effects of glucosinolates. In: Rosenthal, G. A.; Janzen, D. H. (eds.). herbivores­ their interaction with secondary plant metabolites. Academic Press; NY: 47 1-500. (seen in abstract only). Evans, D. E. 1987. The survival of immature grain beetles at low temperatures. J. stored Prod. Res.; 23: 79-83. (seen in abstract only). Eveleens, K. G. 1966. Control biologico del minador del cafe. Revista Cafelalera; 54: 1 2- 1 6. (seen in abstract only). Ezcuyra, E.; Gomez, J. C. ; Ecerra, J. 1987. Diverging patterns of host used by phytophagous insects in relation to leaf pubescence in Arbutus xalapensis (Ericaceae). Oecologia; 72: 479-480. REFERENCES 237 Faeth, S. H. 1980. Invertebrate predation of leaf-miners at low densities. Ecol. Entomol. ; 5: 1 1 1 - 1 14. 198 1 . Experimental isolation of oak host plants: effects on mortality, survivorship and abundances of leaf-mining insects. Ecology; 62: 625-35. Faeth, S. H. 1985. Host leaf selection by leaf miners: interactions among three trophic levels. Ecology; 66: 870-75. Faeth, S. H. 1986. Indirect interactions between temporally separated herbivores mediated by the host plant. Ecology; 67: 479-494. ----- 199 1 . Effect of oak: leaf size on abundance, dispersion, and survival of the leaf miner Cameraria sp. (Lepidoptera: Gracillariidae). Environ. Entomol. ; 20: 196-204. Faeth, S. H.; Mopper, S.; Simberloff, D. 198 1 . Abundance and diversity of leaf-mining insects on three oak host species: effects of host-plant phenology and nitrogen content of leaves. Dikos; 37: 238-25 1 . (seen in abstract only). Faeth, S. H.; Simberloff, D. 198 1 . Population regulation in a leaf mining insect, Camerria sp., at increased field densities. Ecology; 62: 620-624. Fagoonee, I. ; Toory, V. 1984. Contribution to the study of the biology and ecology of the leaf-miner Liriomyza tnjolii and its control by Neem. Insect Science and Appl. ; 5 : 23-30. (seerr in abstract only). Feeny, P. P. 1970. Seasonal changes in oak leaf tannin and nutrients as a cause REFERENCES 238 of spring feeding by winter moth caterpillars. Ecology; 5 1 : 565-8 1 . Fenemore, P. G. 1977. Oviposition of potato tuber moth, fecundity in relation to mated state, age, and pupal weight. NZ 1. Zool. ; 4: 1 87- 191 . . 1978. Oviposition of potato tuber moth, Phthorimaea operculella ZeIt (Lepidoptera: Gelechiidae); the physical nature of the oviposition substrate. NZ 1. Zoo1. ; 5 : 591-99. ------- . 1979. Oviposition of potato tuber moth, Phthorimaea operculella ZeIL (Lepidoptera: Gelechiidae); the influence of adult food, pupal weight, and host-plant tissue on fecundity. NZ 1. Zoo1.; 6: 389-95 . . 1980. Oviposition of potato tuber moth, Phthorimaea operculella ZeIL (Lepidoptera: Gelechiidae); identification of host-plant factors influencing oviposition response. NZ J. Zool.; 7: 435-39. ------- . 1988. Host-plant location and selection by adult potato moth, Phthorimaea operculella (Lepidoptera: Gelechidae): a review. 1. Insect Physiol.; 34: 1 75-177. Fenwick, G. R. ; Heaney, R. K. ; Mullin, W. J. 1983. Glucosinolates and their breakdown products in food plants. CRC Crit. Rev. Food Chem Nutr. ; 1 8 : 123-201 . (seen in abstract only). Ferguson, C. S.; Linit, M. J.; Krause, G. 199 1 . Host preference of the Asiatic oak weevil (Coleoptera: Curculionidae). Environ. Entomol.; 20: 1427-32. Finch, S. 1 986. Assessing Host-plant Finding by Insects. In: Miller, 1. R.; Miller, T. A. (eds.) Insect-plant interactions. New York: Springer-verlag New REFERENCES 239 York Ine; 1986: 23-64. Fowler, S . V.; Lawton, J. H. 1982. Foliage preferences of birch herbivores: A field manipulation experiment. Oikos; 42: 238-9. (seen in abstract only). Free, J. B.; Williams, I. H. 1978. The responses of the pollen beetle, Meligethes aeneus, and the seed weevil, Ceuthorhynchus assimilis, to oil seed rape, Brassica napus, and other plants. J. Appl. Eco!. ; 15 : 76 1-774. Frey, R. 1954. Diptera Brachycera und Sciaridae von da Cunha Results Sci. Exp. Tristan da Cunha 1937-38. 6: 1-55. (seen in abstract only). Funke, W. 197 1 . Energy turnover of animal populations in terrestrial ecosystems. Verh. Dtsch. Zool. Ges.; 35: 95- 106. (seen in abstract only). Gahan, A. B. 1913. New Ichneumonoidea parasitic on leaf-mining Diptera. Can. Entomo!.; 5 : 145-154. Gibbons, D. S. 1987. The causes of seasonal changes in numbers of the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae). Eco!. Entomol.; 12: 173- 1 85. Gifford, R. M. ; Marshall, C. 1973. Photosynthesis and assimilate distribution in Lotium multijlorum Lam. following differential tiller defoliation. Aust. J. BioI. Sci.; 26: 5 17-526. (seen in abstract only). Godfray, H. C. J. 1984. Patterns in the distribution of leaf-miners on British trees. Ecol. Entomol. 9 : 163-68. Godfray, H. C. J. 1985. The absolute abundance of leaf miners on plants of REFERENCES 240 different successional stages. Oikos; 45: 17-25. (seen in abstract only). Godfray, H. C. J. 1986. Clutch size in the leaf-mining fly (Pegomya nigritarsis: Anthomyiidae) Eco!. Entomol. ; 1 1 :75-8 1 . Grimaldi, D. 1990. New distributional record of Scaptomyza (Bunostoma) australis from South Pacific island and biogeographic implications. J. New York Entomol. Soc.; 98: 484-88. (seen in abstract only). Gross, P.; Price, P. W. 1988. Plant influences on parasitism of two leaf miners: a test of enemy- free space. Ecology; 69: 1506- 16. Gunn; Gatehouse, A. G. 1985. Effects of the availability of food and water on reproduction on the African armywonn, Spodoptera exempta. Ecol. Entomol.; 10: 53-63. Guppy, J. C. 198 1 . Bionomics of the alfalfa blotch leafminer Agromyza Jrontella Rondani (Diptera: Agromyzidae), in eastern Ontario. Can. Entomol. ; 1 13: 593-600. Guppy, J. c.; Meloche, F. ; Harcourt, D. G. 1988. Host synchrony of Dacnusa dryas Nixon (Hymenoptera: Braconidae), parasiting the alfalfa blotch leaf miner Agromyza Jrontella Rondani (Diptera: Agromyzidae). Can. Entomol.; 120: 145-52. Gupta, J. P. 1970. Description of a new species of Zaprionus (Phorticella) (Diptera: Drosophilidae) from India. Proc. Indian Nat. Sci. Acad. ; 36(Ser. B): 62-70. ------ . 1975. Indian species of Drosophilidae exclusive of the genus REFERENCES 241 Drosophila. J. Entomol. (B); 43: 209-2 1 5. Gupta, P. K.; Singh, J. 198 1 . Important insect pests of cowpeas (Vigna unguiculata [L.]) in agroecosystem of eastern Uttarpradesh. Indian. J. Zoology; 22: 9 1-95. (seen in abstract only). Gwynne, D. T. 198 1 . Sexual differences theory: monnon crickets show role reversal in mate choice. Science; 2 l 3: 779-780. (seen in abstract only). Hackman, W. 1 955. On the genera Scaptomyza Hardy and Parascaptomyza Duda (Diptera: Drosophilidae). Notulae Ent.; 35: 74-91 . (seen in abstract only). Hackman, W. 1 959. On the genus Scaptomyza Hardy (Diptera: Drosophilidae) with descriptions of new species from various parts of the world. Acta Zool. Fenn.; 97: 1 -73. (seen in abstract only). ----- . 1 969. Contributions to knowledge of the fauna of Afghanistan. Acta Mus. Morav., Suppl. ; 54: 297-304. (seen in abstract only). ----- . 1 982. The relation between the genera Scaptomyza and Drosophila. Annales Entomologici Fennici; 48: 97- 1 04. (seen in abstract only). Hafez, M.; EI-Ziady, S. ; Dimetry, N. Z. 1970. Leaf-ruining Diptera of vegetables and crops in EgypL Bull. Soc. entomol. Egypt; 54: 398-4 14. (seen in abstract only). Hamilton, 1. G.; Zalucki, M. P. 199 1 . Effect of temperature on development rate, survival and fecundity of cotton tipwonn, Crocidosema plebejana Zeller (Lepidoptera: Tortricidae). Aust. J. Zoology; 39: 1 9 1 -200. (seen in abstract only). REFERENCES 242 Hanna. H. Y.; Story, R. N.; Adams, A. J. 1987. Influence of cultivar, nitrogen and frequency of insecticide application on vegetable leaf miner (Diptera: Agromyzidae) population density and dispersion on snap beans. J. Econ. Entomol.; 80: 107- 1 10. Hanula, J. L. 1988. Oviposition preference and host recognition by the black vine weevil, Otiorhynchus suicatos (F.) (Coleoptera: Curculionidae). Environ. Entomol.; 17 : 694-98. Harcourt, D. G. 1969. The development and use of life tables in the study of natural insect populations. Ann. Rev. Entomol. ; 14: 175-196. Hardy, D. E. 1965. Diptera: Cyclorrhapa II. Series Schizophora Section Acalypterae I Family Drosophilidae In: Zimmermann, E. (ed.) Insects of Hawaii; 1 2: 1 - 814. ------- 1 966. VIII. Descriptions and Notes on Hawaiian Drosophilidae (Diptera). Studies in Genetics ill. Univ. Texas PubL; 6615 : 1 95-224. (seen in abstract only). Hardy, R. J. et al. 1979. Insect pest occurrences in Tasmania. Insect pest survey, Tasmanian Department of Agriculture; 1 1 (+2): 34pp. (seen in abstract only). Harris, M. 1 994. Personal communication. Harris, M.D.; Miller, 1. R. 1 988. Host-acceptance behaviour in an herbivorous fly, Delia antiqua. 1. Insect Physiol. ; 34: 179 - 190. (seen in abstract only). REFERENCES 243 Harrison, RA. 1958. Acalypterate Diptera of New Zealand. N.Z., DSIR. Bulletin 1 28: 381pp. Hawkins, B. A. 1988. Foliar damage, parasitoids and indirect competition: a test using herbivores of birch. Eeol. Entomo!.; 13 : 301-8. Hawkins, B. A. 1990. Global patterns of parasitoid assemblage size. J. Anim. Eco!.; 59:57-72. (seen in abstract only). Heads, P. A.; Lawton, J. H. 1983. Studies on the natural enemy complex of the holly leaf-miner: the effects of scale on the detection of aggregative responses and the implications for biological controL Gikos; 40: 267-276. (seen in abstract only). Hedqvist, K. 1. 1977. A new species of Haltieoptera Spin. reared from Seaptomyza muZtispinosa Mall. in Chile (Hymenoptera, Chalcidoidea: Pteromalidae). EntomoL Seand.; 8 : 238-39. (seen in abstract only). Heinz, K. M. ; Parrella, M. P.; Newman, J. P. 1992. Time efficient use of yellow sticky traps in monitoring insect populations. J. Eeon. Entomol. ; 85: 2263-2269. Hendrickson, R M. Jr.; Barth, S. E. 1978. Biology of the alfalfa blotch leaf miner. Ann. Entomo!' Soc. Am. ; 7 1 : 495-497. Hendrickson, R M. Jr. ; Day, W. H. ; Dysart, R. J. 1983. Leaflets abscission caused by alfalfa blotch leaf miner (Diptera: Agromyzidae). J. Eeon. Entomo!.; 76: 1075-79. Hendrickson, R. M. Jr. ; Plummer, J. A. 1983. Biological control of alfalfa blotch REFERENCES 244 leaf miner in Delaware. J. Eeon. Entomol.; 76: 757-6 1 . Hendrickson, R . M. Jr. ; Day, W . H. 1986. Yield losses caused by alfalfa blotch leaf miner AgromyzaJrontella Rondani (Diptera: Agromyzidae). J. Eeon. Entomol.; 79: 988-992. Hendrickson, R. M. If.; Plummer, J. A 1990. Alfalfa blotch leaf miner Agromyza jrontella Rondani (Diptera: Agromyzidae) in Delaware. J. Eeon. Entomol. ; 83: 222-230. Hennig, W. 1952. Dipteren, ill, 628pp. Akademie Verlag, Berlin. Hering, E. M. 195 1 . Biology of the leaf miners.: Junk, W. Berlin. Herr, c.; Johnson, M. W. 1992. Host plant preference of Liriomyza sativae (Diptera: Agromyzidae) populations infesting green onion in Hawaii. Environ. Entomol.; 21 : 1097. Hespenheide, H. A. 1973. A novel mimicry complex: Beetles and flies. J. Entomol. London A; 48: 49-56. (seen in abstract only). Hespenheide, H. A. 1985. The visitor fauna of extrafloral nectaries of Byttneria aeuleata (Sterculiaceae): Relative importance and roles. Eco!. Entomol. ; 10: 191 -204. Hespenheide, H. A 1991 . Bionomics of leaf-mining insects. Annu. Rev. Entomol.; 36: 535-60. Hewett, C. G. 1917. Insects affecting garden and greenhouse plants. Rept. Agr. Dept. Canad. Dom. Entom.; 1916 : 34-35. (seen in abstract only). REFERENCES 245 Hileman, D. R.; Lieto, L. F. 198 1 . Mortality and area reduction in leaves of the bog shrub caused by the leaf miner. Am MidI. Nat.; 106: 1 80- 1 88. (seen in abstract only). Hill, D. S. 1987. Agricultural insect pests of temperate regions and their controL Cambridge: Combridge University Press; 659 pp. Hinckley, A D. 1963. Lepidopterous leaf-miners on sweet potato in Fiji. Bull. Entomol. Res. 53: 665-70. (seen in abstract only). Hinckley, A D. 1972. Comparative ecology of two leaf miners on white oak. Environ. Entomol. ; 1 : 358-61 . Hoffmann, A A. 1985. Effects o f experience on oviposition and attraction in Drosophila: comparing apple and oranges. Am Nat.; 126: 41-5 1 . (seen in abstract only). Hoffmann, A. A 1988. Early adult experience in Drosophila melanogaster. 1. Insect Physiol. ; 34: 197-204. Hoffmann, A A; Turelli, M. 1985. Distribution of Drosophila melanogaster on alternative resources: effects of experience and stravation. Am. Nat.; 126: 662-679. (seen in abstract only). Holdren, C. E.; Ehrlich, P. R. 1982. Ecological determinants of food plant choice in the checker spot butterfly Euphydryas editha in Colorado. Oecologia; 52: 417-23. (seen in abstract only). Hollingworth, M. J.; B urcom be, J. V. 1970. The nutritional requirements for longevity in Drosophila. 1. Insect Physiol.; 16: 1017- 1025. REFERENCES 246 Holloway, B. A. 1990. Personal communication. Hopkins, A. D. 1917. A discussion of C. C. Hewitt's paper on "Insect behaviour" . 1. Eeon. Entomol. ; 10: 92-93. Horton, D. R. ; Krysan, J. L. 1991 . Host acceptance behaviour of pear Psylla (Homoptera: Psyllidae) affected by plant species, host deprivation, habituation, and egg load Ann. Entomol. Soc. Am. ; 84: 6 12-27. House, H. L. 196 1 . Insect nutrition. Ann. Rev. Entomol. ; 6: 13-26. House, H. L. 1974. Physiology of insecta. Vol. V., p.26. Academic Press. New York. Houser, S. J. 1923. The wheat leafminer. Bull. Ohio. Agr. Exp. Sta. 25 1 : 79-86. (seen in abstract only). Hovemeyer, K. 1992. Population studies of Chelosia jasciata (Diptera: Syrphidae), a leaf miner of Allium ursinum. Eeol. Entomol.; 17: 331 - 337. Howarth, F. G. 1991 . Environmental impacts of classical biological control. Annu. Rev. Entomol.; 36: 483-509. Ishihara, M.; Shimada, M. 1993. Female-biased sex ratio in a wild Bruchid seed-predator, Kytrhinus sharpianus. 1. Larval competition and other factors. Eeol. Entomol.; 1 8: 54-60. Jackai, L. E. N.; Daoust, R. A. 1986. Insect pests of cowpeas. Ann. Rev. Entomol.; 3 1 : 95- 1 19. REFERENCES 247 Jaeuike, J. 1982. Environmental modification of oviposition behaviour in Drosophila. Am. Nat.; 1 19: 784-802. (seen in abstract only). Jaeuike, J. 1983. Induction of host preference in Drosophila melanogaster. Oecologia. Ber!.; 58: 320-325. (seen in abstract only). James, R. ; Pritchard, I. M. 1988. Influence of the holly leaf miner, Phytomyza ilicis (Diptera: Agromyzidae), on leaf abscission. 1. Nat. Hist.; 22: 395- 402. (seen in abstract only). Jensen, G. L.; Koehler, C. S. 1970. Seasonal and distributional abundance and parasites of leaf miners of alfalfa in California. 1. Econ. Entomol. ; 63: 1623-28. Janzen, D. H. 1973. Host plants as islands. ll. Competition in evolutionary and contemporary time. American Naturalist; 107 : 786-90. (seen in abstract only). Jermy, T. 1986. The role of experience in the host selection of phytophagous insects. In: Perspectives in chemoreception and behaviour (Ed. by Chapman, R. F.; Bernays, E. A and Stoffolano, J. G.), pp. 143- 157. New York: Springer-Verlag. Jermy, T. ; Bernays, E. A; Szentesi, A 1982. The effect of repeated exposure to feeding deterrents on their acceptability to phytophagous insects. pp. 25-32. In: J. H. Visser and A K. Minks [eds.] Proceedings, 5th International Symposium on insect-plant relationships. Wageningen, Pudoc, Netherlands. (seen in abstract only). Jenny, T.; Bernays, E. A; Szentesi, A 1988. Host plant fInding in phytophagous REFERENCES 248 insects: the case of the Colorado potato beetle. Ent. Exp. Appl.; 49: 83-98. Jenny, T.; Hanson, F. E.; Dethier, V. G. 1968. Induction of specific food preference in lepidopterous larvae. Entomol. Exp. Appl. ; 1 1 : 2 1 1-230. John, M. E.; Vaughan, J.; Evans, E. 1. 1984. Control of pests and diseases of oilseed rape. Booklet: Ministry of Agriculture, Fisheries and Food. U. K., no. 2387. 55pp; Kaneshiro, K. Y. 1969. The Drosophila crassifermur group of species in a new subgenus. Studies in Genetics V. Univ. Texas PubL; 6615 : 413-74. (seen in abstract only). Kahn, D. M.; Cornell, H. V. 1989. Leaf-miners, early leaf abscission, and parasitoids: a trophic interaction. Ecology.; 70: 1219-26. Kaneko, T. Tokumits. 1969. Drosophila survey of Hokkaido. XXVll. On Drosophilid flies from 7 localities of the Hidaka district in southern Hokkaido. J. Fac. Sci. Hokkaido Univ. ; 17 : 244-56. Kelsey, J. M. 1937. The rag wort leaf-miner Phytomyza atricomis Mg. and its parasite Dacnusa areolaris Nees. NZ J. of Sci. Tec. (A); 18 : 762-67. Ketzler, L. D.; Price J. F. 1982. Methods for growers to evaluate effects of their cultural practices on Liriomyza trifolii leaf miners in a simple laboratory. Proc. Fla. State Hortic. Soc. ; 95: 162-64. (seen in abstract only). Kircher, H. W.; Al-Azawi, B. 1985. Longevity of seven species of cactophilic Drosophila and D. melanogaster on carbohydrates. J. Insect Physiol. ; 3 1 : 165-69. REFERENCES 249 Kolodny-Hirsch, D. M.; Harrison, F. P. 1982. Comparative damage and leaf area consumption by the tobacco budwonn and corn earwonn on Maryland tobacco. J. Econ. Entomol.; 75: 168-72. Kostal, V.; Finch, S. 1994. Influence of background on host-plant selection and subsequent oviposition by the cabbage root fly (Delia radicum). Entomol. Exp. Appl.; 70: 153- 163 Krober, O. 1910. Fauna Hamburgensis. Verh. Ver. naturw. Unterh. ; 1907 : 9- 14. (seen in abstract only). Kumar, A.; Gupta, I. P. 1992. Two new and two unrecorded species of Drosophilidae from Sikkim, India (Insecta: Diptera). Senckenb. BioI.; 72: 45-5 1 . (seen in abstract only). Labeyrie, V. 1957. influence de l'alimentation sur la ponte de la teigne de la pomme de terre (Gnorimoschema operculella Z.) (Lep. Gelechiidae). Bu/. Soc. Entomol. France; 62: 64-67. (seen in abstract only). Lamb, M. I. 1964. The effects of radiation on the longevity of female Drosophila subobscura. 1. Insect Physiol. ; 10: 487-97. Lance, D. R. ; Odell, T. M.; Mastro, V. CV. ; Schwalbe, C. P. 1988. Temperature mediated programming of activity rhythms in male gypsy moth (Lepidoptera: Lymantriidae): Implications for the sterile male technique. Environ. Entomol. ; 17: 649-53. Larsen, L. M.; Nielsen I. K.; Ploger, A.; Sorensen, H. 1985. Responses of some beetle species to varieties of oil seed rape and to pure glucosinolates. In: Sorensen, H. (ed.) , Advances in the production and utilisation of REFERENCES 250 cruciferous crops (Copenhagen, 1984). Martinus Nijhoff, Dordrecht, Netherlands: 230-244. (seen in abstract only). Larsson, S. et a!. 1986. Effects of light and nutrient stress on leaf phenolic chemistry in Salix Dasyclados and susceptibility to Galerucella lineola (Coleoptera). Oikos; 47: 205- 10. (seen in abstract only). Lawrence, W. 5., 1986 b. Male choice and competition ill Tetraopes tetraophthalmus: effects of local sex ratio varation. Behv. Ecol. Sociobiol.; 1 8: 289-296. (seen in abstract only). Lawrence, W. S., 1990. Effect of body size and repeated matings on female milkweed beetle, Tetraopes Tetraophthalmus (Coleoptera: Cerambycidae) reproductive success. Ann. Entomol. Soc. Am.; 83: 1096- 1 100. Lawton, J. H.; Price, P. W. 1979. Species richness of parasites on hosts: Agromyzid flies on the British Umbelliferae. J. Anim. Eco!.; 48: 6 1 8-37. (seen in abstract only). Lawton, 1. H.; Strong, Jr. D. R. 198 1 . Community patterns and competition in folivorous insects. American Naturalist; 1 1 8: 3 17-382 Lee, E. R. Jr. ; Denlinger, D. L. 1991 . Insects at low temperature. Chapman and Hall, Ltd. pp:5 13. Lee, J. c.; Bernays, E. A. 1990. Food tastes and toxic effects: associative learning by the polyphagous grasshopper Schistocerca americana (Drury) (Orthoptera: Acrididae). Anim. Behav.; 39: 1 63- 173. Lee, R. E.; Baust, J . G. 1987. Cold-hardiness in the Antarctic tick, lxodex uriae. REFERENCES 251 Physiol. Zool. ; 60: 499-506. (seen in abstract only). Levin, R.; MacArthur, R. 1969. An hypothesis to explain the incidence of monophagy . Ecology; 50: 910- 1 1 . Lewin, R. 1985. Hawaiian Drosophila: Young islands, old flies. Science; 229: 1072-74. (seen in abstract only). Lewis, A c.; van Emden, h. F. 1986. Assays for insect feeding, pp.95- 1 19. In: Miller, J. R.; Miller, T. A [eds.] Insect-plant interactions. Springer. NY. Lincoln, E. E. ; Langenheiro, J. H. 1978. Effect of light and temperature in monoterpenoid yield and composition in Satureja douglasii. Biochem. Syst. Ecol.; 6: 2 1 -32. (seen in abstract only). Livene, A.; Daly, J. M. 1966. Translocation in healthy and rust-affected beans. Phytopathology; 56: 170- 175. (seen in abstract only). Lockwood, J. A.; Story. R. N. 1986. Adaptive functions of nymphal aggregation in the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae). Environ. Entomol. ; 15 : 739-749. Luckinbill, L. S.; Arking, R.; Clare, M. J.; Cirocco, W. C. ; Buck, S. A. 1984. Selection for delayed senescence in Drosophila melanogaster. Evolution; 38: 996- 1003. Luckinbill, L. S.; Graves, J. L.; Tomkiw, A; Srowirka, O. 1988. A qualitative analysis of some life-history correlate� of longevity in Drosophila melanogaster. Evol. Ecol.; 2: 85-94. REFERENCES 252 Ma. W. c.; Schoonhven, L. M. 1973. Tarsal contact chemonsensory hairs of the large white butterfly and their possible role in oviposition behaviour. Ento17UJl. Exp. Api.; 16: 343-357. Maca, J. 1972. Czechoslovak species of the genus Scaptomyza Hardy (Diptera: Drosophilidae) and their bionomics. Acta Entomol. Bohemoslov. ; 69: 1 19-32. (seen in abstract only). MaCek, J. 1972. Contribution to knowledge of the leaf-miners of Slovenia (Yugoslavia). Zool. Anz. ; 1 88 : 196-201 . (seen in abstract only). 1990. Hyponomological (leaf miner) fauna on cereal weeds in Yugoslavia. European Weed Research Society; 103-1 10. (seen in abstract only). Maier, C. T. 1982. Parasitism of the apple blotch leaf miner on sprayed and unsprayed apple trees in Connecticut Environ. Entomol.; 1 1 : 603-10. Maier, C. T. 1983. Effect of the apple blotch leaf mmer (Lepidoptera: Gracillariidae) on apple leaf abscission. 1. Econ. Entomoi. ; 76: 1 265-68. Maier, C. T. 1989. Accelerated abscission of cranberry leaves damaged by the leaf miner, Coptodisca negligens (Lepidoptera: Heliozelidae). Environ. Entomol.; 18 : 773-777. Malick, L. E.; Kidwell, J. F. 1966. The effect of mating status, sex and genotype on longevity in Drosophila melanogaster. Genetics; 54: 203-209. Martens, B.; Trumble, 1. T. 1987. Structural and photosynthetic compensation for leaf miner (Diptera: Agromyzidae) injury in lima beans. Environ. REFERENCES 253 Entomo!.; 1 6: 373-78. Martin, J. L. 1956. The bionomics of the aspen blotch miner, Lithocolletis salicifoliella Cham. (Lepidoptera: Gracillariidae). Canadian Entomologist; 88: 155- 1 68. (seen in abstract only). Matsumoto, Y. 1970. Volatile organic sulfur compounds as insect attractants with special reference to host selection. In: Wood, D. L.; Silverstein, R. M.; Nakajima, M. (eds.). Control of insect behaviour by natural products. Academic Press, NY: 1 33- 160 (seen in abstract only). Mattson, W. J. 1980. Herbivory in relation to plant nitrogen content. Annu. Rev. Eco!. Syst.; 1 1 : 1 19- 1 6 1 . (seen in abstract only). Mattson, W. 1. ; Laerence, R. K.; Haack, R. A. ; Herms, D. A; Charles, P. 1. 1988. Defensive strategies of wood plants against different insect-feeding guilds in relation to plant ecological strategies and intimacy of association with insects. In: Mattson, W. J.; Levieux, J.; Bernard-Dagan, C. [eds.] Mechanisms of woody plant defenses against insect. Search for pattern. pp. 3-38. Springer-Verlag, NY. (seen in abstract only). Maynard, S. J. 1958. The effects of temperature and of egg-laying on the longevity of Drosophila subobscura. J. Exp. BioL; 35: 832-42. (seen in abstract only). Mayr, E. 1963. Animal species and evolution. Cambridge Belknap Press. pp.781 . Mazanec, Z. 1985. Resistance of Eucalyptus marginata to Perthida glyphopa (Lepidoptera: Incurvariidae). J. Aust. Entomol. Soc.; 24: 209-21 . (seen in abstract only). REFERENCES 254 Mazanec, Z. 1987. Natural enemies of Perthida glyphopa Common (Lepidoptera: Incurvariidae). J. Aust. Entomo!' Soc.; 26: 303-8. (seen in abstract only). Mazur, P. 1977. The role of intracellular freezing in the death of cells cooled at supraoptimal rates. Cryobiology; 14: 25 1 -272. (seen in abstract only). Mazur, P. 1984. Freezing of living cells: mechanisms and implications. Am. J. Physiol. ; 247: 125- 142. (seen in abstract only). McClure, M. S. ; Price, P. W. 1975. Competition among sympatric Erythroneura leaf hoppers (Homoptera: Cicadellidae) on American sycamore. Ecology; 56: 1 388-97. McCreadie, J. W.; Colbo, H. 1990. The influence of temperature on the survival, development, growth, and chromosome preparation quality of the EFG/C, ACD, and AA cytotypes of the Simulium venustum-vercundum Complex (Diptera: Simuliidae). Can. 1. Zool.; 69: 1 356-65. (seen in abstract only). McCreadie, M.; Colbo, H. 1990. Penneability of Drosophila melanogaster embryos to ethylene glycoL Cryobiology; 27: 500-503. (seen in abstract only). Mc Evey, S. F. 1990. New specIes of Scaptomyza from Madagascar and Mauritius. Annals Soc. Ent. Fr. (NoS.).; 26: 5 1-64, 26 fig., 40 ref. McGregor, P. G. 1989. Agromyzidae leaf miners (Diptera). In: Cameron, P. J. ; Hill, R. L.; Bain, J.; Thomas, W. P. (eds.) A review of biological control of invertebrate pests and weeds in New Zealand 1 874 to 1987. DSIR. Entomology Division and CAB InternationaL U.K. pp. 45-49. REFERENCES 255 McLain, D. K.; Lanier, D. L.; Marsh, N. B. 1990. Effects of female size, male size, and number of copulations on fecundity, fertility, and longevity of Nezara viridula (Hemiptera: Pentatomidae). Ann. En to mo I. Soc. Am.; 83: 1 130- 1 136. McNaughton, S. J. 1979. Grazing as an optimization process: grass-ungulate relationships in the Serengeti. American Naturalist; 1 13: 691-703. McNeil, J. N.; Quiring, D. T. 1983. Evidence of an oviposition-deterring pheromone in the alfalfa blotch leaf miner Agromyza Jrontella Rondani (Diptera: Agromyzidae). Environ. En tomo 1. 12: 990-92. McNeil, S. ; Southwood, T. R. S. 1978. The role of nitrogen in the development of insect-plant relationships. pp.77-98. In: Harbome, J. [ed.]. Biochemical aspects of plant and animal co-evolution. Academic, London. (seen in abstract only). Meat, A.; Khoo, K. C. 1976. The dynamics of ovarian maturation and oocyte resorption in the Queensland fruit fly, Dacus tryoni, in daily rhythmic and constant temperature regimes. Physiol. Ent; 1 : 2 13-221 . Meats, M . 1987. Critical periods for developmental acclimation to cold in the Queensland fruit fly, Dacus tryoni. 1. Insect Physiol.; 33: 943-946. (seen in abstract only). Meisner, J. ; Ascher, K. R. S.; Lavie, D. 1974. Factors influencing the attraction to oviposition of the potato tuber moth, Gnorimoschema operculella ZeU. Z Angew. Entomol. ; 77: 1 79-89. (seen in abstract only). Mellors, W. K. ; Helgesen, R. G. 1978. Developmental rates for the alfalfa blotch REFERENCES 256 leaf miner, Agromyza frontella (Diptera: Agromyzidae), at constant temperatures. Ann. Entomol. Soc. Am.; 7 1 : 886-888. Michalska, Z. 1973. Contribution to the knowledge of the leaf- mining insects of some biotopes at Mierzwice on the Bug River, Poland. Pol. Pis. Entomologiczne; 43: 743-59. (seen in abstract only). Miller, P. F. 1973. The biology of some Phyllonorycter species (Lepidoptera: Gracilariidae) mining leaves of oak: and beech. J. Nat. Hist. ; 7: 391-409. Miller, 1. R.; Miller, T. A. 1986. Insect-plant interactions. Academic press. NY. Miller, J. R.; Strickler. K. L. 1984. Finding and accepting host plants. In: Bell, W. J.; Carde, R. T. (eds.) Chemical Ecology of Insects. second ed. New York: Chapman and Hall Ltd.; 127-157. Milliken, G. A. ; Johnson, D. E. 1984. Analysis of Messy Data, Volume 1. Designed Experiments. Van Nostrand Reinhold Co., New York. Minkenberg, O.P 1988. Life-history of the agromyzid fly Liriomyza trifolii on tomato at different temperatures. Entomol. Exp. Appl.; 48: 73-84. Minkenberg, O. P. J. M. ; Fredrix, M. J. J. 1989. Preference and performance of an herbivorous fly, Liriomyza trifolii (Diptera: Agromyzidae), on tomato plants differing in leaf nitrogen. Ann. Entomol. Soc. Am. ; 82: 350-354. Minkenberg, O. P. J. M.; Heldennan, C. A. J. 1990. Effects of temperature on the life history of Liriomyza bryoniae on tomato. J. Econ. Entomol. ; 83: 1 17- 125 REFERENCES 257 Mitchell, R. 1975. The evolution of oviposition tactics in the bean weevil Callosobruchus maculatus (F.). Ecology; 56: 696-702. Mitchell, R. 1983. Effects of host plant variability on the fitness of sedentary herbivorous insects, pp.343-370. In: R. F. Denno and M. S. McClure [eds.], Chemical ecology of insects. Montague, J. R.; Kaneshiro, D. 1982. The ecology of Hawaiian flower-breeding Drosophilids. 2. Adult dispersion and reproductive ecology. Amer. Natur. ; 133: 7 1-82. (seen in abstract only). Mopper, S.; Faeth, S. H. ; Boecklen, W. J.; Simberloff, S. D. 1984. Host-specific variation in leaf miner population dynamics: effects of density, natural enemies and behaviour of Stilbosis quadricustatella (Lepidoptera: Cosmopterigidae). EcoL Entomol. ; 9: 1 69-177. Mopper, S.; Whitham, T. G. 1992. The plant stress paradox: Effects on pinyon sawfly sex ratios and fecundity. Ecology; 73: 5 15-525. Moraes, G. J. de.; McMurtry, J. A. 1987. Physiological effect of the host plant on the suitability of Tetranychus urticae as prey for Phytoseiulus persimilis (Acari: Tetranychidae, Phytoseiidae). Entomophaga; 16: 80- 1 1 1 . Morai, M. 1974. Study on the interference among larvae of the citrus leaf miner, Phyllocnistis citrella Stainton (Lepidoptera: Phyllocnistidae). Ecology; 16: 80- 1 1 1 . Morris et al. 1987. Direct chilling injury in the effect of low temperatures on biological systems. pp. 1 20-146 Edward Arnold, London. (seen in abstract only). REFERENCES 258 Murai, M. 1974. Studies on the interference among larvae of the citrus leaf miner, Phyllocnistis citrella. Res. Popul. Ecol.; 16: 80- 1 1 L Nair, K. S. S.; McEwen, F. L. 1976. Host selection by the adult cabbage maggot: effect of glucosinolates and common nutrients on oviposition. Can. Entonwl.; 108: 102 1 - 1030. (seen in abstract only). Nair, K. S. S.; McEwen, F. L.; Snjeckus, V. 1976. The relationship between glucosinolate content of cruciferous plants and oviposition preference of Hylemya brassicae (Diptera: Anthomyiidae). Can. Entonwl. 108: 103 1- 1036. (seen in abstract only). Nault, L. R. ; Styer, W. E. 1972. Effects of sinigrin on host selection by aphids. Entonwl. Exp. Appl.; 15: 423-437. Nater, H. 1953. Vergleichend-morphologische Untersuchung des ausseren innerhalb der Gattung Drosophila. Zool. Jahrb.; 8 1 : 437-486. Nestel, D.; Diskschen, F.; Altieri, M. A. 1994. Seasonal and spatial popUlation loads of a tropical insect: the case of the coffee laef-miner in Mexico. Ecol. Entonwl. ; 19: 159- 167. New, T. R. 1 979. Biology of Labdis sp. (Lepidoptera: Cosmopterygidae), A miner in phyllodes of Acacia. Aust. J. Zoology; 27 : 529-36. Newporty, M. E. A; Gromko M. H. 1984. The effect of experimental design on female receptivity to remating and its impact on reproductive success in Drosophila melanogaster. Evolution; 38: 1 26 1-72. Nielsen, B. O. 1968. Studies on the fauna of beech foliage 2. Observations on the mortality and mortality factors of the beech weevil [Rhynchaenus REFERENCES 259 (Orchectes) fagi L.] (Coleoptera: Curculionidae). Nat. lutl. ; 14: 99- 1 25. Nielsen, B. O. 1978. Food resource partition in the beech leaf- feeding guild. Eco!. Entomol.; 3: 193-201 . Notley, F . B. 1956. The Leucoptera leaf miners of coffee on Kilamanjaro. ll. Leucoptera coffeella Ouer. Bu!. Entomol. Res.; 46: 899-912. Nottingham, S. F. 1988. Host-plant fInding or oviposition by adult cabbage root fly, Delia radicum. l. Insect Physiol.; 34: 227-34. Oatman, E. R.; Michelbacher, A. E. 1959. The melon leaf miner, Liriomyza pictella (Thomson) (Diptera: Agromyzidae). Ann. Entomol. Soc. Am. ; 52: 83-89. Okada, T. 1 956. Systematic study of Drosophilidae and allied families of Japan. 1 83pp. Oihode Co., Tokyo. (seen in abstract only). ----- 1973. Drosophilidae and Diastatidae from Mongolia (Diptera). Ann. Hist. -Nat. Mus. NatL Hung.; 65: 27 1 -79. (seen in abstract only). ----. 1 973. Four new species of Drosophila from Japan (Diptera). Kontyu; 4 1 : 434-39. (seen in abstract only). Opler, P. A. 1 974. Oaks as evolutionary islands for leaf-mining insects. Am. Sci. 62: 67-73. Osmelak, J. A. 1983. Occurrence of leaf-mining diptera in cultivated crops. Aust. Ent. Mag.; 10: 9- 10. (seen in abstract only). REFERENCES 260 Owen, D. F. 1978. The effect of a consumer Phytomyza ilicis on seasonal leaf­ fall in the holly Ilex aquifolium Oikos; 3 1 : 268-7 1 . Palaniswamy R ; lamb R. J. 1992. Host preferences of the flea beetles Phyllotreta cruciferae and P. striolata (Coleoptera: Chrysomelidae) for Crucifer seedlings. J. Econ. EntomoL; 85: 743-752. Papaj , D. R.; Alcinda, C. L. 1993. Insect learning ecological and evolutionary perspectives. 398pp. Chapman and Hall, New York. Papaj, D. R.; Prokopy, R. J. 1989. Ecological and evolutionary aspects of learning in phytophagous insects. A. Rev. Ent. ; 34: 3 15-350. (seen in abstract only). Papaj, D. R.; Rausher, M. D. 1983. Individual variation in host location by phytophagous insects. In: Herbivorous insects: Host seeking behaviour and mechanisms (ed. by Ahmed, S.), pp.77- 124. Academic Press. London. (seen in abstract only). Parker, M. A. 1984. Local food depletion and the foraging behaviour of a specialist grasshopper, Hesperotettix viridis. Ecology; 65: 89- 104. Parrella, M. P. 1984. Effect of temperature on oviposition, feeding and longevity of Liriomyza trifolii (Diptera: Agromyzidae). Can. Entomol; 1 16: 85-92. ------- . 1987. Biology of Liriomyza. Ann. Rev. Entomol; 32: 201-24. --------; Robb, K. L. ; Bethke, J. A. 1983. Influence of selected host plants on the biology of Liriomyza trifoiii (Diptera: Agromyzidae). Ann. Entomol. Soc. Am; 76: 1 12-1 15. REFERENCES 26 1 -------- ; Robb, K. L.; Bethke, J. A 1985. Effect of leaf mining and leaf stippling of Liriomyza species on photosynthetic rates of chrysanthemum. Ann. Entomol. Soc. Am.; 78: 90-93. Partridge, L.; Andrews, R. 1958. The effect of reproductive activity on the longevity of male Drosophila melanogaster is not caused by an acceleration of ageing. 1. Insect Physioi.; 3 1 : 393-95. -------; Fowler, K; Trevitt, S.; Sharp, W. 1986. An examination of the effects of males on the survival and egg-production rates of female Drosophila melanogaster. 1. Insect Physiol.; 32: 925-29. -------; Fowler, K. 1990. Non-mating costs of exposure to males in female. 1. Insect Physiol.; 36: 419-25. -------; Green, A; Fowler, K. 1987. Effects of egg- production and of exposure to males on female survival in Drosophila melanogaster. 1. Insect Physiol. ; 33: 745-749. Pearson, J. F.; Goldson, S. L. 1980. A preliminary examination of pests in fodder beet in Canterbury. In: Proceedings of the 33th New Zealand Weed and Pest Control Conference; pp. 2 1 1-2 14. Peng, C.; Williams, R. N. 199 1 . Influence of food on development, survival, fecundity, longevity, and sex ratio of Glischrochilus quadrisignatus (Coleoptera: Nitidulidae). Environ. Entomol.; 20: 205-2 10. Petitt, F. L. 1988. Temperature-dependent development and influence of larval instars of Liriomyza sativae Blanchard on parasitization by Opius dis situs Muesebeck. Entomology; l3 : 24-27. REFERENCES 262 Petitt, F. L.; Wietlisbach, D.O. 1992. Intraspecific competition among same-aged larvae of liriomyw sativae (Diptera: Agromyzidae) in Lima bean primary leaves. Entomol. Soc. Am; 2 1 : 136- 140. Phillips, W. M. 1977. Modification of feeding preference in the flea-beetle, Haltica lythri (Coleoptera: Chrysomelidae). Entomol. Exp. Appl.; 2 1 : 7 1-80. Picard, F. 19 13. Sur la parthenogenese et Ie detenninisme de la ponte chez la teigne des Pommes-de-terre (Phthorimaea operculella Z.). CRA. Sci. Paris Clvi; 1097-99. (seen in abstract only). Pitnick, S. 1991 . Male size influences mate fecundity and remating interval in Drosophila me lanogaster. Anim Behav.; 41 : 735-45. (seen in abstract only). Pittara, 1. S.; Katsoyannos, B. I. 1992. Effect of shape, size and colour on selection of oviposition site by Chaetorellia anstralis. Entomol. Exp. appl.; 63: 105- 1 13. Pivnick, K. A.; Lamb, R J. ; Reed, D. 1992. Response of flea beetles, Phyllotreta spp., to mustard oils and nitriles in field trapping experiments. J. Chem Ecol.; 18 : 863-873. Pol, J. 1974. Diptera occurring on cabbage plants. Pis. Entomol. ; 44: 381-92. (seen in abstract only). Poos, F. W. 1940. The locust leaf miner as a pest of soybean. J. Econ. Entomol. ; 33: 742-45. REFERENCES 263 Potter, D. A. 1985. Population regulation of the native holly leaf miner, Phytomyza ilicicola Loew (Diptera: Agromyzidae) on American holly. Oecologia; 66: 499-505. (seen in abstract only). Potter, D. A.; Kimmerer, T. W. 1986. Seasonal allocation of defense investment in !lex opaca Aiton and constraints on a specialist leaf miner. Oecologia; 69: 2 17-224. (seen in abstract only). Potter, D. A.; Redmond, C. T. 1989. Early spring defoliation, secondary leaf flush, and leaf miner outbreaks on American holley. Oecologia; 8 1 : 192- 197. (seen in abstract only). Powell, J. A. 1980. Evolution of larval food preferences in microlepidoptera. Annu. Rev. Entomol. ; 25: 133-59. Preszler, R. W.; Price, P. W. 1988. Host quality and sawfly populations: a new approach to life table analysis. Ecology; 69: 2012-2020. Preszler, R. W.; Price, P. W. 1993. The influence of Salix leaf abscission on leaf miner survival and life history. Ecol. Entomol. ; 1 8: 150- 154. Price, M.; Dunstan, W. R. 1983. The effect of four insecticides on leaf miner damage of cow peas in Tanzania. Trop. Grain. Legume. Bull. ; 27: 23-26. (seen in abstract only). Price, P. W. 197 1 . Toward a holistic approach to insect population studies. Ann. Entomol. Soc. Am.; 64: 1399-1406. Price, P. W. et al. 1980. Interactions among three trophic levels: Influence of plants on interactions between insect herbivores and natural enemies. Ann. REFERENCES 264 Rev. Ecol. Syst; 1 1 : 41-65. (seen in abstract only). Pritchard, I. M.; James, R. 1984. Leaf miners: Their effect on leaf longevity. Oecologia; 64: 132-9. (seen in abstract only). Prokopy, R. J.; Collier, R. H.; Finch, S. 1983. Leaf colour used by cabbage root fly to distinguish among host plants. Science; 221 : 190- 192. (seen in abstract only). Pullin, A. S. 1985. A simple life table study based on development and mortality in the beech leaf mining weevil Rhynchaenus fagi L. J. BioI. Educ.; 19: 52-56. (seen in abstract only). Quiring, D. T. ; McNeil, J. N. 1983. Exploitation and interference intraspecific larval competition in the dipteran leaf-miner, Agromyza Jrontella (Rondani). Can. J. Zaol. ; 62: 421-27. (seen in abstract only). Quiring, D. T.; McNeil, J. N. 1984. Adult-larval intra specific competition in Agromyza Jrontella (Diptera: Agromyzidae). Can. Entomologist; 1 16: 1385-91 . -------------- . 1984. Intraspecific competition between different aged larvae of Agromyza Jrontella (Rondani) (Diptera: Agromyzidae): advantages of an oviposition-deterring pheromone. Can. J. 7.001. ; 62: 2192-2196. , Quiring, D. T. ; McNeil, J. N. 1987. Foraging behaviour of a Dipteran leaf miner on exploited and unexploited hosts. Oecologia; 73: 7- 15. Rahn, R. 1977. New information on the influence of external factors (light and REFERENCES 265 temperature) on the rhythm of sexual activity in Acropelia assectella. Ann. Zool. Ecol. Anim. ; 9: 1 - 10. (seen in abstract only). Ramirez, R. 1988. Morphology and biology of Bostryx conspersus (Sowerby) (Mollusca: Bulimulidae) in the central costal slopes of Peru. Revista Brasileira de Zoologia; 5: 609- 17. (seen in abstract only). Rathke, B. J. 1976. Competition and coexistence within a guild of herbivorous insects. Ecology; 57: 76-87. Rausher, M. D. 1979. Larval habitat suitability and oviposition preference in three related butterflies. Ecology; 60: 503-5 1 1 . Rausher, M. D.; Papaj, D. R. 1987. Demographic consequences of discrimenation among conspecific host plant by Buttus phylenor butterflies. Ecology; 64: 1402- 1410. Reed, D. W.; Pivnick, K. A; Unerhill, E. W. 1989. Identification of chemical oviposition stimulants for the diamonback moth present in three species of Brassicaceae. Entonwl. Exp. Appl.; 53: 277-286. Reissig, W. H.; Weires, R. W.; Forshey, C. G. 1982. Effects of gracillariid leaf miners on apple tree growth production. Environ. Entonwl. ; 1 1 : 958-963. Renwick. J. A. A 1989. Chemical ecology of oviposition in phytophagous insects. Experientia; 45: 223-228. Renwick, J. A. A; Chew, F. S. 1994. Oviposition behaviour in Lepidoptera. Anr�u. Rev. Entonwl. ; 39: 377-400. REFERENCES 266 Ring, D. R; Harris, M. K., Olszak, R. 1985. Life tables for pecan leaves in Texas. J. Econ. Entomo!.; 78: 888-94. Risch, S. J. 1987. Agricultural ecology and insect outbreaks. Insect Outbreaks (ed. by P. Barbosa and J. Schultz), pp.2 17-238 . Academic Press, San Diego, California Rocha pite, M. T. 1979. A note on Drosophilidae collected in different provinces of Portugal. Arq. Mus. Bocage, Lsboa; 7: 67-80. (seen in abstract only). Rockwell, R F.; Grossfield, J. 1977. Courtship behaviour of Scaptomyza australis (Diptera: Drosophilidae). Pan-pac. Entomol.; 53: 305-31 1 . (seen in abstract only). Rockwood, L. L. 1974. Seasonal changes in the susceptibility of Crescentia alata leaves to the flea beetle, Oedionychus sp. Ecology; 55: 142-148. Rose, M. R 1984. Laboratory evolution of postponed senescence in Drosophila melanogaster. Evolution; 38: 1004- 1010. -----; Charlesworth, B. 198 1 . Genetics of life history in Drosophila melanogaster. II. Exploratory selection experiments. Genetics; 97: 1 87- 196. (seen in abstract only). Rossi, A. M.; Strong, D. R 1991 . Effects of host-plant nitrogen on the preference and performance of laboratory populations of Cameocephala jloridana (Homoptera: Cicadellidae). Environ. Entomol. ; 20: 1349- 1 355. Rossi, W.; Rossi, M. G. C. 1979. On some species of Stigmatomyces (Ascomycetes) parasitic on Italian Diptera Bollettino del Museo Civico REFERENCES 267 di Storia Naturale di Venezia; 30: 13-17. (seen in abstract only). Ruohomaki, K.; Haukioja, E. 1992. Interpopulation differences in pupal size and fecundity are not associated with occurrence of outbreaks in Epirrita autunmata (Lepidoptera: Geometridae). Ecol. Entomol. ; 17 : 69-75. Salmond, K. F. 1956. The insect and mite fauna of a Scottish flour milL Bul. Entomol. Res.; 47: 62 1 . (seen in abstract only). Sas Institute. 1988. Sas user' s guide: Statistics. Sas Institute, Cary, NCo Satoh, M. et at. 1977. Changes in photosynthetic activity and related processes following decapitations in mulberry trees. Physiol. Plant; 4 1 : 203-2 1 0. Saxena, K. N. 1969. Pattern of insect-plant relationships determining susceptibility or resistance of different plants to an insect Ent. Exp. Appl. ; 12: 75 1-66. Schultz, J. C. 1 983. Habitat selection and foraging tactics of caterpillars in heterogenous trees. In: Variable Plants and Herbivores in Natural and Managed Systems. New York: Academic Press; 6 1-90. Schuster, D. J. ; Taylor, J. L. 1988. Longevity and oviposition of adult liriomyza trifolii (Diptera: Agromyzidae) exposed to abamectin in the laboratory. J. Econ. Entomol. ; 8 1 : 106- 1 09. Schweitzer, D. F. 1 979. Effects of foliage age on body weight and survival in the tribe Lithophanini (Lepidoptera: Noctuidae). Oikos; 32: 403-408. REFERENCES 268 Scott, R. R. 1984. New Zealand pest and beneficial insects. Lincoln College of Agriculture, Canterbury, New Zealand. 373pp. Scriber, I. M. 1984. Host plant suitability. pp I59-202. In: Bell, W. I. ; Carde, R. T. [eds.] . Chemical ecology of insects. Chapman and Hall, Sunderland. Scriber, I. M.; Slansky, F. If. 198 1 . The nutritional ecology of immature insects. Annu. Rev. Ent. ; 26: 1 83-21 1 Sears, M. K.; Shelton, A. M.; Quick, T. c.; Wyman. I. A.; Webb, S. E. 1985. Evaluation of partial plant sampling procedures and corresponding action thresholds for management of Lepidoptera on cabbage. 1. Econ. Entomol.; 78: 9 13-916. Sekita, N.; Yamada, M. 1979. Studies on the population of the apple leaf miner Phyllonorycter ringoniella Matsumura (Lepidoptera: Lithocolletidae). ID. Some analyses of the mortality operating upon the population. Entomol. Zaol.; 14: 137-48. (seen in abstract only). Service, P. M. 1989. The effect of mating status on lifespan, egg laying, and starvation resistance in Drosophila melanogaster in relation to selection on longevity. 1. Insect Physiol.; 35: 447-52. (seen in abstract only). Sharma, H. c.; Norris, D. M. 1991 . Comparative feeding preference and food intake and utilization by cabbage looper (Lepidoptera: Noctuidae) on three legume species. Environ. Entomol.; 20: 1589-94. REFERENCES 269 Shaw, M. R. ; Askew, R. R. 1976. Ichneurnonoidea (Hymenoptera) parasitic upon leaf-mining insects of the orders Lepidoptera, Hymenoptera and Coleoptera. Ecol. Entomol.; 1 : 127- 1 33. Shelly, T. E. 1987. Lek behaviour of a Hawaiian Drosophila: male spacing, aggression, and female visitation. Anim. Behav.; 35: 1 394- 1 404. Shelly, T. E. 1989. Waiting for mates: Variation in female encounter rates within and between leks of Drosophila confonnis. Behaviour; 1 1 1 : 34-48. Silvanima, J. V. c.; Strong, D. R. 1 99 1 . Is host plant quality responsible for the populational pulses of salt-marsh plant hoppers (Homoptera: Delphacidae) in northwestern Florida? Ecol. Entomol. ; 16: 221-232. Simberloff, D., Stiling, P. 1987. Larval dispersion and survivorship in a leaf­ mining moth. Ecology; 68: 1 647-57. Simmons, A. M.; Yeargan, K. V. 1988. Development and survivorship of the green stink bug, Acrostemum hilare (Hemiptera: Pentatomidae) on soybean. Environ. Entomol. ; 17: 527-532. Singer, M. C. 197 1 . Evolution of food-plant preference in the butterfly Eurphydryas editha (Lepidoptera: Nymphalidae). Evolution; 25 : 383-89. Singh, B. B.; Merrett, P. J. 1980. leaf miner- A new pest of cowpeas. Trop. Grain Legum. Bull.; 2 1 : 15-17. (seen in abstract only). Singh, B. K.; Bhatt, M. 1988. A preliminary report on the Drosophilidae of Kumaun Region with description of two new species and three new REFERENCES 270 records. Oriental Insects; 22: 147-61 . (seen in abstract only). Singh, S. R. ; van Emden, H. F. ; Taylor, T. A. [eds.] . 1978. Pests of grain legumes: Ecology and control. LondonlNew york. Academic. 454pp. Solomon, J. D. 1988. Influence of host on larval survival, feeding habits, and adult fecundity of the carpenter worm (Lepidoptera: Cossidae). 1. Econ. Entomol.; 8 1 : 834-39. Somerfield, K. G. 1984. Greenhouse and ornamental pests. In: Scott. R. R. (ed.) New Zealand pest and beneficial insects. Canterbury, New Zealand: Lincoln University College of Agriculture; 1984. Somme, L. 1982. Supercooling and winter survival in terrestrial arthropods. Comp. Biochem. Physiol.; 73: 5 19-543. Southwood, T. R. E. 1978. Ecological methods, 2nd ed. Freeman, San Francisco. Southwood, T. R. E.; Norton, G. A. 1973. Economic aspects of pest management strategies and decisions. In: Geier, P. ; Clark, L. et al. Insects: studies in population management Sydney: Ecological Society of Australia Memoirs. (seen in abstract only). Spencer, K. A. 1973. The Agromyzidae (Diptera) of economic importance. Dr. W. Junk. The Hague. 418pp. ------- 1976. The Agromyzidae of New Zealand (Insecta: Diptera). 1. R. Soc. N Z; 6: 153-2 1 1 . Stary, B . 1930. 0 minujicim hmyzu v zemi moravskoslezske (on mining insects REFERENCES 27 1 in Moravian Silesia). Proce mor; 6: 1 25-242. (seen in abstract only). Stapel, C. 1 96 1 . Attack by mining fly larvae on rape. Rev. Appl. Ento. ; 50: 1 39. Sterling, P. H.; Gibson, C. W. D.; Brown, V. K. 1992. Leaf miner assemblies: effects of plants succession and grazing management. Ecol. Entomol.; 17: 1 67- 178. Stewart, J. G.; Sears, M. K. 1989. Quarter-plant samples to detect populations of Lepidoptera on cauliflower. J. Eeon. Entomol.; 82: 829-832. Stiling, P. D. 1980. Competition and coexistence among Eupteryx leafuoppers (Hemiptera: Cicadellidae) occurring on stinging nettles (Urtiea dioica L.). J. Anim Ecol. ; 49: 793-805. (seen in abstract only). Stiling, P. D. 1988. Density-dependent processes and key factors in insect populations. J. Anim Eco/. ; 57: 58 1-593. (seen in abstract only). -------; Brodbeck, B. V.; Strong, D. R. 1982. Foliar nitrogen and larval parasitism as determinants of leaf miner distribution patterns on Spartina alterniflora. Ecol. EntomoL; 7 : 447-52. -------; Brodbeck, B. V.; Strong, D. R. 1984. Intraspecific competition in Hydrellia valida (Diptera: Ephydridae), a leaf miner of Spartina alterniflora. Ecology; 65: 660-62. Story, R. N. ; Robinson, W. H.; Pienkowski, R. L. 1 979. The biology and immature stage of Taphrocerus schaefferi. a leaf miner of yellow nutsedge. Ann. EntomoL Soc. Am.; 72: 93-98. REFERENCES 272 Straka, F. 1979. The level of economic damage caused by leaf- gnawing insects during the fIrst half of the vegetation period of cabbage and cauliflower. Gradinarska I Lowrska Nauka; 16: 84-92. (seen in abstract only). Strong, D. R.; Lawton, 1. H.; Southwood, T. R. E. 1984. Insects on plants. Community Patterns and Mechanisms. Blackwell Scientific Publications, Oxford. (seen in abstract only). Sugimoto, T.; Ishii, M. 1979. Mortality of larvae of a Ranunculus leaf-mining fly, Phytomyza ranunculi (Diptera: Agromyzidae) due to parasitization and host-feeding by its eulophid parasite Chrysocharis pentheus (Hymenoptera: Eulophidae). Appl. Entmol. Znol.; 14: 410- 1 8. Swan, D. I. 1973. Evolution of biological control of the oak leaf miner Phyllonorycter messaniella Zell. (Lepidoptera: Gracilariidae). NZ Bul. Entomol. Res.; 63: 49-55. Szwejda, l. 1974. Flies (Diptera) occurring on cabbage plants in Poland. Pol. B Entomol. ; 44: 381-92. (seen in abstract only). Takada, H. 1970. Scaptomyza (Parascaptomyza) paliida and two related new species, S.(P.) elmoi n. sp. and S.(P. ) himalayana n. sp. (Diptera: Drosophilidae). Annot. Znol. lap.; 43: 1 42- 147. (seen in abstract only). Takasu, K. ; Hirose, Y. 1993. Host acceptance behaviour by the host- feeding egg parasitoid, Ooencyrtus nezarae (Hymenoptera: Encyrtidae): host age effects. Ann. Entomol. Soc. Am.; 86: 1 17- 1 2 1 . Taylor, B. 1984. Chinese cabbage. Booklet: Ministry of Agriculture, Fisheries and Food.U. K., no. 2336. 33pp. REFERENCES 273 Taylor, T. A. 1 968. The effects of insecticide application on insect damage and the performance of cowpea in southern Nigeria. Niger. Agric. 1.; 5: 29-37. Thanee, N. 1987. Oviposition preference, larval feeding preference and larval food quality of Heliothis armigera. Phd thesis, Massey University; pp.222 . Thomas, E. M. ; Frank:, J. R.; Vincent, H. R. 199 1 . Bionomics of leaf-mining insects. Annu. Rev. Entomol. ; 36: 535-60. Thomas, W. P.; Hill, R. L. 1989. Phyllonorycter messaniella Zeller, oak: leaf miner (Lepidoptera: gracilariidae). In: Cameron, P. J. ; Hill, R. L.; Bain, J.; Thomas, W. P. (eds.) A review of biological control of invertebrate pests and weeds in New Zealand 1 874 to 1987. DSIR Entomology Division and CAB International U.K. pp. 286-285. Thorsteinson, A. J. 1960. Host selection in phytophagous insects. Annu. Rev. Ent. ; 5: 193-2 1 8. Throckmorton, L. H. 1962. The problem of phylogeny in the genus Drosophila. Studies in Genetics II, Texas Univ. Texas PubL ; 6205: 207-343. (seen in abstract only). ---------. 1966. The relationships of the endemic Hawaiian Drosophilidae Studies in Genetics ill, Texas Univ. Texas Publ. ; 66 15: 335-396. (seen in abstract only). ---------- 1975. The phylogeny, ecology and geography of Drosophila. In: King, R. C. (ed.), Handbook of Genetics; 2: 421 -469. REFERENCES 274 Torrent J. A 1955. Outbreaks and new records. In: FAO Plant Prot. Bull. Rome; 3: 125-27 . (seen in abstract only). ------- 1955. Oak: tortrix and its control in Spain. In: FAO Plant Prot. Bull. Rome; 3: 1 17- 12 1 . (seen in abstract only). Traynier, R M. 1975. Field and laboratory experiments on the site of oviposition by the potato moth Phthorimaea operculella (ZeIL) (Lepidoptera: Gelechiidae). Bul. Entomol. Res.; 65: 39 1 -98. Tsacas, L. 1972. The genus Euscaptomyza Srguy (Diptera: Drosophila) with the description of two new African species. Studies in Genetics IT, Texas Univ. Texas PubL; 72 1 3 : 345-354. (seen in abstract only). Tuomi, J.; Niemela, P. ; Manilla, R 198 1 . Leaves as islands : interactions of Scolioneura betuleti (Hymenoptera) miners in beech leaves. Oikos; 37 : 146- 152. (seen in abstract only). Usua, E. J. 1970. Some notes on maize stem borers in Nigeria. J. Econ. Entomol.; 63: 776-8. Valentine, E. W. 1967. A list of the hosts of entomophagous insects of New Zealand. N Z J. Sci. ; 10: 1 100- 1210. -------- ; Walker, A K. 1989. Annotated catalogue of New Zealand Hymenoptera. DSIR B ulletin; 246. Valladares, G.; Lawon, J. H. 199 1 . Host-plant selection in the holly leaf miner: Does mother know best? J. Anim. Ecol.; 60: 227-240. van Lenteren, J. ; Noldus, P. 1 990. Whitefly-plant relationships: behavioural and REFERENCES 275 ecological aspects. pp.47-89. In: D. Gerling (ed.), Whiteflies: their bionomics, pest status and management. Intercept Ltd., Andover, Hants. Vaugun, TY T. ; Hoy, C. W. 1993. Effects of leaf age, injury, morphology, and cultivars on feeding behaviour of Phyllotreta cruciferae (Coleoptera: Chrysomelidae). Environ. Entomol.; 22: 41 8-424. Vimmer, A. 1 93 1 . 0 larvach musich, ktere skodi v hyponomu. Arch. vyzk.; 18 : 1 -53. (seen in abstract only). Vinson, S. B . 1 976. Host selection by insect parasitoids. Annu. Rev. Entomol. ; 2 1 : 1 09- 133. Visser, J. H. 1986. Host odour perception in phytophagous insects. Annu. Rev. Entomol. ; 3 1 : 121-44. Visser, J. H. 1988. Host-plant finding by insects: orientation, sensory input and search patterns. J. Insect Physiol. ; 34: 259-68. von Caemmere, B . ; Farquhar, A. 1984. Effects of insect injury simulation on photosynthesis of apple leaves. J. Econ. Entonwl.; 77: 245-248. Walker, G. P.; Zareh, N. 1 990. Leaf age preference for oviposition by three species of whitefly on lemon. Entonwl. Exp. Appl. ; 56: 3 1-45. Wall, R. G.; berberet, R. C. 1 979. Reduction in leaf area of Spanish peanuts by the Rednecked peanutworm. J. Econ. Entomol. ; 72: 67 1 -73. Wallace, M. M. H. 1970. The biology of the Jarrah leaf miner Penhida glyphopa (Lepidoptera: Incurvariidae). Austr. J. Zool. .. 1 8: 91 - 104. REFERENCES 276 Warren, J. H. 1980. Sex ratio adaptations to local mate competition in a parasitic wasp. Science; 208: 1 157- 1 159. Watson, P. F. 1987. Cold shock injury in animal cells. in Temperature and Animal cells. pp. 3 1 1 -340. Society for experimental biology, Cambridge. Watt, M. N. 1 923. The Leaf-mining Insects of New Zealand. pp. 465-89. Webster, F. M. ; Parks, T. H. 1913. The serpentine leaf-miner. J. Agr. Res. :59-87. Welter, S. C. 199 1 . Responses of tomato to simulated and real herbivory by tobacco hom worm (Lepidoptera: Spbingidae). Environ. Entomol; 20: 1537- 1 54 1 . West, C . 1985. Factors underlying the late seasonal appearance of the lepidopterous leaf-mining guild on oak. Ecol. Entomol. ; 1 0: 1 1 1- 1 20. Wheeler, M. R. 1952. The Drosophilidae of the nearctic region exclusive of Drosophila. Studies in the genetics of Drosophila VIT. Univ. Texas Pub!. ; 5204: 162-218. (seen in abstract only). -------- 198 1 . The Drosopbilidae: a taxonomic overview. Pages 1-97 In: Ashbumer et al. (eds.). The Genetics and Biology of Drosophila, Vol. 3a. Academic Press, London. Whitfield, G. H.; Carouthers, R. I. ; Lampert, E. P.; Haynes, D. L. 1 985. Spatial and temporal distribution of plant damage caused by the onion maggot (Diptera: Anthomyiidae). Environ. Entomol. ; 14: 262-66. Whitham, T. G. 1978. Habitat selection by Pemphigus aphids in response to resource limitation and competition. Ecology; 59: 1 164- 1 176. REFERENCES 277 -------- 1980. The theory of habitat selection: Examined and extended using Pemphigus aphids. Amer. Natur.; 1 15 : 449-466. ------- 1981 . Individual trees as heterogenous environments: Adaptation to herbivory or epigenetic noise? In: Denno, R. F.; Dingle, H. Insect life history patterns. New York: Springer-Verlag; pp. 9-27. ------- 1983. Host manipulation of parasites: within-plant variation as a defense against rapidly evolving pests. In: Denno, R. F. ; McClure, M. S. Variable plants and herbivores in natural and managed systems. New York, USA: Academic Press; pp. 15-4 1 . Wiley, R. H. 1978. The lek mating system of sage grouse. Sci. Am.;238: 1 14- 125. (seen in abstract only). William, K. M.; Robert, G. H. 1978. Developmental rate for the alfalfa blotch leafminer Agromyza jrontella Rondani (Diptera: Agromyzidae) at constant temperatures. Ann. Entomol. Soc. Am.; 7 1 : 886-88. Williams, C. E. 1989. Damage to woody plants by the locust leaf miner, Odontota dorsalis (Coleoptera: Chrysomelidae), during a local outbreak in an Appalachian oak forest. Entomol. News; 100: 1 83- 1 87. Wiren, A; Larsson, S. 1984. Preference of insects for different willow clones: a case study with Galerucella lineola (Coleoptera: Chrysomelidae). In: Perttu, K. (ed.) Ecology and management of forest biomass production systems. Swedish University of Agricultural Sciences Report: Department of Ecology and Environmental Research; 1984: 383-89. Wise, K. J. 1953. Leaf-mining pests in New Zealand. N Z J. Agri. ; 87: 75-76. REFERENCES 278 Wit, A. K. H. 1 982. The relation between artificial defoliation and yield in Brussels sprouts as a method to assess the quantitative damage induced by leaf-eating insects. Z Angew. Entonwl.; 94: 425-3 1 . -------. 1985. The relation between partial defoliation during the preheading stages of spring cabbage and yield, as a method to assess the quantitative damage induced by leaf-eating insects. Z Angew Entonwl. ; 100: 96- 100. (seen in abstract only). Wolfson, J. L. 1 982. Developmental response of Pieris rapae and Spodoptera eridania to environmentally induced variation in Brassica nigra. Environ. Entonwl. ; 1 1 : 207- 1 3. Wyatt, G. R. 1 967. The biochemistry of sugars and polysaccharides in insects. Adv. Insect. Physiol.; 4: 287-460. (seen in abstract only). Zoebisch, T. G. 1984. Oviposition and development of Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) on foliage tomato and selected weeds [M.S. thesis]. Gainesville: Dniv. of Florida (seen in abstract only). --------; Schuster, D. J. 1987. Longevity and fecundity of Liriomyza trifolii (Diptera: Agromyzidae) exposed to tomato foliage and honeydew in the laboratory. Environ. Entonwl. ; 16: 1 00 1- 1003. Zoerner, H. 197 1 . Studies of mines II. (Contribution to knowledge of the way of life of known and unknown mine-producing larvae of Diptera). Deut. Entomol. Z; 18: 233-50. (seen in abstract only). Zucker, W. V. 1 982. How aphids choose leaves: the roles of phenolics in host selection by a galling aphid. Ecology; 63 : 972-8 1 . Appendices A p p e n d i x 1 TAXONOMICAL NOTES ON THE GENERA SCAPTOMYZA HARDY (1814) AND DROSOPHILA WITHIN THE FAMILY DROSOPHILIDAE The relation between the genera Scaptomyza and Drosophila (Diptera: Drosophilidae) Family Drosophilidae Several diagnoses of the family Drosophilidae have been given by various authors. One of the most extensive is that of Duda ( 1924), after which the following is modified by Bock (1976). Head with 2 or (usually) 3 (fronto-)orbital bristles of which 1 is proclinate and remaining 1 or 2 reclinate; postvertical bristles large to minute (parallel to convergent, or absent; outer and inner vertical bristles usually present; antennae decumbent, 3rd segment more or less elliptical; arista micropubescent or plumose, if plumose usually with several short medial hairs in addition to larger dorsal and ventral rays; vibrissae usually present Mesonotum rarely bare, acrostichal hairs usually in 2- 10 more or less well defmed longitudinal rows; 1 , (usually) 2, 3 or 4 pairs of dorsocentral bristles present; prescutellar acrostichals developed or undeveloped; thorax usually with 1 pair of humeral bristles, 2 notopleurals, 2 supra-alars and 2 postalars; mesopleuron bare; stemopleuron usually with 2 or 3 bristles C stemopleurals') above and several small bristles below; disc of scutellum usually bare; scutellar margin with 4 bristles (anterior and posterior scutellars), anterior pair reduced in some genera; preapical bristles usually present on tibiae. 280 Appendices 28 1 Costa of wing with proximal and distal breaks, costa reaching end of 3rd or 4th longitudinal vein; 1 st longitudinal vein tenninating at distal costal incision; auxiliary vein obsolete apically or fused with 1st longitudinal vein; anterior and posterior crossvein present; discal and second basal cells separated by 3rd crossvein in some genera With very little loss of accuracy, the diagnosis of the family may be considerably condensed to the following essential features: Head with 1 pair of proclinate and 1 or 2 pairs of reclinate orbital bristles; postvertical bristles, when present, parallel or convergent; mesopleuron bare; costa twice broken; auxiliary vein not reaching costal margin. The separating characters Hackman (1982) has discussed characters for separating Scaptomyza and Drosophila as follows: The "external morphological characters" generally used for separating the genus Scaptomyza Hardy from Drosophila Fallen are the following: The head nearly square in proflle and the greatest eye dimension more or less oblique in Scaptomyza. In Drosophila the head is usually higher than long and the greatest eye dimension is more or less vertical. Arista with one or no ventral branch in addition to the end fork in Scaptomyza and with two or more ventral branches in Drosophila. Mesonotum usually dull in Scaptomyza, usually shiny in Drosophila. Acrostichal rows of hairs 2-4 in Scaptomyza, 6-8 in Drosophila. The Scaptomyza subgenera often have characteristic features in the male tenninalia, but no key characters have been found for separating the entire genus from Drosophila. Prominent dentate egg-guides occur in the Scaptomyza species with leaf-mining larvae. Leaf-miners are rare in Drosophila. On the other hand, sclerotized egg-guides with dense marginal dentation often occur in both genera and these structures Appendices 282 have a function in copulation (Nater, 1953). Some Scaptomyza subgenera tend to have very weakly sclerotized egg-guides (cf. Hackman, 1959). Inner anatomical characters, such as the shape of the spermatheca, testes, vasa deferentia, paragonia, ejaculatory apodemes, and Malphigian tubules, have been used as important characters by Throckmorton ( 1962, 1966) in studies of the phylogeny in the entire Drosophila complex (including related genera) and for separation of endemic Hawaiian Drosophilas and Scaptomyzas. The inner anatomy of Scaptomyza species from other parts of the world is poorly known (see further). Characters of the eggs, larvae and puparia have also been used to some extent in the taxonomy of the Drosophila complex (Throckmorton, 1962). The egg-fIlaments are usually short in Scaptomyza and long in Drosophila. Okada ( 1968b) gives much information about the developmental stages of Drosophila, but too little is known about Scaptomyza. The subgenera of Scaptomyza The origin of the Scaptomyza genus is a little more than 40 million years ago (Lewin, 1985). Sixteen subgenera have been distinguished in Scaptomyza (Hackman, 1959; Okada, 1973; Tsacas, 1972; Tsacas and Cogan, 1976). The subgenera are comparatively distinct and separated by combinations of about 10 characters of external morphology. Two endemic species from New Zealand (described by Harrison, 1959) and some Mrican species are still unplaced. Most of the subgenera are comparatively distinct from Drosophila and a general Scaptomyza type can be recognized, but there is considerable overlap of characters between the Hawaiian "Drosophiloids" and "Scaptomyzoids" (Throckmorton, 1966; Carson et ai., 1970). Before the borderline between Scaptomyza and Drosophila can be discussed further, however, there is a taxonomic and nomenclatorial matter to be cleared up. Appendices 283 The borderline between ScaptomyZll and Drosophila Several cases of adaptive radiation can be traced in the evolution of the Drosophila complex (Throckmorton, 1975), but the most impressive and unique example is provided by the Hawaiian Drosophilidae, in which nearly 500 endemic species have been described. The majority of them have been placed in Drosophila or in new endemic genera derived from Drosophila and these are all called "Drosophiloids" by Throckmorton (1966). The rest are the "Scaptomyzoids" , which comprise the Scaptomyza species and the species of the derived genus Titanochaeta Knab, in all 1 3 1 described species. A detailed investigation made by Throckmorton ( 1966), including extensive study of internal organs, showed that there is considerable overlap of characters between the Scaptomyzoids and the Drosophiloids. There are species groups, and even a subgenus, which are more or less intermediate between the genera. Throckmorton ( 1966) observes that "the simplest and most parsimonious conclusion" is that the Scaptomyzoids originated in Hawaii from the same stock as the Drosophiloids. According to him the alternative conclusion that founder Drosophilids were introduced twice into Hawaii is less likely in view of the improbable parallelism that this would involve. As a corollary of the fIrst alternative, he puts forward the theory that the entire genus Scaptomyza had its origin in Hawaii, from which it spread out all over the world, undergoing adaptive radiation as it did so. Though not incompatible with the age of the Hawaiian Islands (see further Carson et aI., 1970), the theory is rather hard to believe. Let us therefore consider the question whether Scaptomyza is a monophyletic taxon or not. Maca (1972) has described the genus Scaptomyza Hardy as follows: "The genus Scaptomyza comprises at the present time about 90 described species; it is cosmopolitan. The most conspicuous characters of the genus are as follows: Arista branching, most often with only 1 lower branch situated distally, acrostichal setae usually in 2-4 rows. The anterior sternopleural seta is longer than the medial one. Apart from the cleaning apparatus (on 1st and 3rd tibiae and metatarsi) there are no conspicuous groups of hairs on legs. The body is slender, and the wings are narrower Appendices 284 than in Drosophila Fall. (the ratio of the wing length to width is 2.4-2.6 in palaearctic species), with sensillae on the base of r ( radial vein) and with one sensilla on the posterior transverse vein. Inner organs, as far as they were studied, did not show too marked difference from the genus Drosophila" . Preimaginal stages of only a few species have been described so far. Eggs are fInely rugose, without projections or with 2-4 short fIlaments. In the mining species, the eggs are laid in pits hollowed in the leaf parenchyma with the ovipositor; saprophagous species lay them on the surface of substrate. Larvae are elongate, with several rows of tiny spines in the basal part of each segment. Above the mouth cavity there are three pairs of sensory organs. The buccal armature with mouth hooks bearing minute teeth in prevalently saprophagous larvae, in the phytophagous species these teeth are unequal and very strong. Usually there are four of them. In the fIrst instar the anterior part of buccal armature is connected with the pharyngeal sclerite and the teeth on the mouth hooks are less conspicuous. The mouth hooks of each new instar are without teeth when they are being formed. In this phase there is dark chitinous matter between the mentum and the mouth hooks, from which new sclerites are fonned. The dental sclerite of Scaptomyza, S. str. is horseshoe-shaped in the fIrst instar (Fig. 10). In the pharynx of larvae of saprophagous as well as phytophagous species there are longitudinal furrows (fanoni pharyngei - Vimmer, 193 1) ; the oesophagus is longer than the pharynx. The proventriculus bears sac-like appendages. The mesenteron and proctodaeum are broad and straight The tracheal system corresponds to that of the genus Drosophila. Anterior spiracles are lacking in the 1st instar, in the 2nd they are small and without any processes, in the 3rd instar they have 6-9 processes. In the subgenus Parascaptomyza their stem is projected. Posterior spiracles are conical, on short stems protruding from a common base; each spiracle is distally tripartite. At present the genus Scaptomyza is divided into 1 3 subgenera, two of which Parascaptomyza and Scaptomyza, S.str. occur in Central Europe. Appendices 285 A key to the species of the genus Scaptomyza according to the phallic organ (Figs. 1--4): (Maca, 1972) 1 Aedeagus not forked, only slightly emarginate distally with minute sensillae. Gonites (submedial processes of the caudal margin of hypandrium) as long as the aedeagus without apodeme or longer . . . . . . . . . . . . . . . . . . . . . . S. pal/ida (Zett) - Adeagus forked almost down to its base, gonites shorter than aedeagus . . . . . 2 2 Gonites narrow, distally more or less spiked. Submedial setae present aedeagus with sensillae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. flava (apicalis) Hardy - Gonites broad and rounded or almost lacking. Submedial setae undeveloped. aedeagus without sensillae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Gonites slightly indicated, not elongate. The length of hypandrium (from the cranial end of the ventral phragma to the outer corner of the caudal margin) less than 0.25 mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. griseola (Zett) - Gonites digitate. Hypandrium longer than 0.27 mm . . . . . . . S. graminum (Fall) For the identification of larvae, Maca suggests a key according to the shape of posterior spiracles (Figs. 7-9). (Usually they can be distinguished by their host-plants; see Hering, 1957). 1 Posterior spiracles with setae arranged in a ring on the apex. Mouth hooks narrow, usually with 4 weak teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. pal/ida (Zett) - Posterior spiracles sclerotised, without setae near the apex. Mouth hooks robust, with 4 unequal, strong teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Posterior spiracles dark, with approximately round apices (Fig. 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. graminum (Fall) Posterior spiracles light, with elongate, parallel apices (Fig. 8) . . . . . . . . . . . . . S. flava (apicalis) Hardy Appendices 286 Scaptomyza (Parascaptomyza) pa1lUla (Zetterstedt. 1 847) (Figs 1 , 9, 1 1 , 12) The analysis of the morphology of this species, supplemented by anatomical characters, was published by Okada ( 1956). Wings: See Fig. 11 . s = medium quadratic divergence ==' 'Ld2/N- l , N = number of specimens examined, d = divergence from the arithmetical mean. Depicts a wing: costal index (C-index), NB; fourth vein index (4v-index), D/C; 5x-index, FIE; 4C-index, B/C. Wing length: dd -2.49 mm (s = 0. 1 8 mm); ll ll - 2.74 (s = 0. 17 mm). C-index : de! - 3.26 (s = 0.28); II II - 3.43 (s = 0.29). 4v-index : de! - 1 .58 (s = 0. 14); II � - 1 .48 (s = 0.04). 5x-index : de! - 1 .55 (s = 0.22); � � - 1 .55 (s = 0. 17). 4C-index : de! - 0.70 (s = 0.07); II � - 0.66 (s = 0.04). Subgenus Scaptomyza, s.str. Scaptomyza graminum (Fallen, 1823) (Figs. 2, 7, 1 1 , 1 2) The principal characters of this species have been pointed out by Duda (1935) and, in particular, Okada ( 1956). According to Okada ( 1956) the legs of Japanese specimens (d II ?) are sometimes dark. The scutellar index of the central European specimens is approximately 1 .6, and that of Japanese specimens 1 .55. Wings. Wing length: d d 2.26 mm (s = 0. 15 mm); II II 2.47 mm (s = 0. 19 mm). Appendices 287 In northern Europe the wing length does not reach 2.7 mm (Hackman, 1955); in central and southern Europe individuals with longer wings are found. In a population sample from Bily Kriz (the Beskydy, Doskocil Igt.) containing 12 specimens, 9 of them have wings longer than 2.7 mm (maximum 2.92 mm in a male and 3.27 mm in a female). Identification was revised by Hackman. C-index : dd - 3.31 (s = 0.24); � � - 3.36 (s = 0.32). 4v-index : dd - 1 .47 (s = 0. 1 3); � � - 1 .48 (s = 0.09). 5x-index : e!e! - 1 .48 (s = 0.26); � � - 1 .54 (s = 0. 15). 4C-index : e!e! - 0.67 (s = 0.07); � � - 0.65 (s = 0.05). Phallic organs (Fig. 2): The average length of hypandrium is 0.29 mm. Scaptomyza no rica Hackman (1955) with genitalia resembling those of S. graminum (differing from it by a small forceps and a supernumerary orbital seta, sometimes also present in S. graminum) is probably a mere monstrosity of S. graminum. This form has also been found in Czechoslovakia. Development: Egg similar to that of S. apicalis; length 0.35 mm. The morphology of larva was described by Okada (1968). It can be distinguished from the larva of S. apicalis by the shape of posterior spiracles. Length of mouth hooks: 0.03 mm; 0.06 mm; 0.08 mm. Length of the buccal armature: 0. 14 rdm; 0.29 mm; 0.44 mm . Length of the sclerotized part of the posterior spiracle: 0.03 mm; 0.06 mm. Larval bionomics: The larvae always make mines. Specimens were collected (by Buhr, 1941) from the following families of host-plants: Silenaceae, Chenopodiaceae, AlrUJranthaceae and Viciaceae (Anthyllis vulneraria). In addition, Buhr ( 1941) recorded MesemhryanthelrUJceae, and Hering ( 1957) Portuiacaceae. Infonnation on the family Scrophuiariaceae (Hering, 1957) must be checked as well as all data given by Frost ( 1923). Artificially transferred larvae can develop on a wider range of plant families (Buhr, 1937). The occurrence on Brassicaceae mentioned by Stary ( 1930) (mines only have been preserved in a herbarium) probably concerns the grey form of S. apicalis; see Zavrel (1967). Appendices 288 Imaginal bionomics: Adults are found in habitats similar to those of S. pallida, being almost as abundant. Experiments with both pair mating and mass mating of S. graminum were made (by Buhr, 1941) . Larvae were collected on Malachium and the emerged adults (about 40 ex.) were divided into 1 It to 3 11 vessels with potted plants: Malachium, Lupinus, Phaseolus, Pisum, Trifolium, Antirrhinum, and Tussilago, respectively. The � � hollowed pits without eggs into leaves of all these plants, but only on Malachium was further development observed. Specimens removed after some time from the "sterile" plants to Malachium bred normally on the latter plant Data on the length of development (at about 18°C): 3 . V. to l O.Y. 197 1 moulting adults from the collected larvae; adults without opportunity to copulate lived till 1 . VI. Several specimens S. graminum, from larvae collected on Anthyllis, were reared on Malachium quite easily. If the leaf of Malachium is too damaged by larvae, it is best to cut it and put it on to the leaf of a sound plant and to let larvae move through. Juvenile adults are rather light in colour. The � � have light-coloured, ovipositor plates (those of older � � are dark brown); the � � could be, in the extreme cases, similar to the light fonn of S. apicalis. Graph of seasonal dynamics Fig. 12. Doskocil ( 1963) mentions 2-3 maxima of occurrence in his paper. Hering ( 1957) states 3 generations a year according to his study of larvae. Some aberrations can be brought about by quiescence which appears in a part of the population with the lack of moisture. In sheltered places larvae can develop in winter as well. Daily dynamics as in S. pallida. Larvae are rarely parasitized by a braconid, Dacnusa (Rhizarcha) faeroensis Roman (Capek det.); puparia are sometimes infected by a mould. When rearing S. graminum, Dacnusa emerged about 7 days later than the host. Appendices Scaptomyza griseola (Zetterstedt. 1 847) (Figs: 3, 5, 1 1) 289 Most of the authors considered this species to be only a form of S. graminum. B oth species are closely related and S. griseola differs mainly in the coloration of the thorax and legs and in some details of the male genitalia (Hackman, 1955). Wings: Wing length: d"d" - 2.07 mm (s = 0 . 1 8 mm); � � - 2.24 (s = 0.10 mm). C-index 4v-index 5x-index 4C-index d"d" - 3.02 (s = 0.22); � � - 3 . 1 2 (s = 0. 17). d"d" - 1 .49 (s = 0. 1 5); � � - 1 .4 1 (s = 0. 1 1 ). d"d" - 1 .36 (s = 0. 14); � � - 1 . 1 9 (s = 0. 1 2). d"d" - 0.7 1 (s = 0.07); � � - 0.68 (s = 0.05). Scaptomyza }lava (Fallen, 1 823) = Scaptomyza (s. str.) apicalis (Hardy, 1 849) (Figs. 4, 6, 8, 1 0, 1 1) Wheeler and Takada (1966) use the name S. apicalis only for palaearctic forms of this species, because they could not compare European and American specimens. Maca examined several specimens collected by Wheeler near Pasadena (California), but he did not fmd any difference from European ones. Scaptomyza ? nwntana sensu Basden, 1954 (peristomal setae remote from the margin of eye, wing length 2.7-3.6 mm, dark, narrowing lamellae of the ovipositor) also belongs, in Maca's view point. to the variability range of S. apicaiis. Maca examined several specimens, males as well as females, collected by Basden near Mortonhall (Scotland), and several similar individuals in the Czechoslovak material. The phallic organs show no difference from S. apicalis. Appendices 290 S. apicaZis displays great variability of colour, but there are no morphological differences between dark and light forms. Probably the coloration depends on the temperature at which the larva develops (similarly as in S. pallida, see Stalker, 1945, and to a lesser degree in other species as well). An analysis of the morphological characters of S. apicalis was made by Hendel (1928). Wings: Wing length: cjCcjC - 2.52 mm (s == 0.2 1 mm); � � - 3.01 (s = 0.20 mm). C-index : cjCcjC - 3. 1 8 (s = 0.27); � � - 3.33 (s = 0.25). 4v-index : cjCcjC - 1 .48 (s = 0. 1 1 ); � � - 1 .44 (s = 0.08). 5x-index : cjCcjC - 1 .60 (s == 0. 14); � � - 1 .47 (s = 0.20). 4C-index : cjCcjC - 0.69 (s = 0.05); � � - 0.65 (s == 0.05). Phallic organs (Fig. 3): The density of sensillae on the aedeagus is quite variable, irrespective of the body colour. Anatomy. dd : Bulbus ejaculatorius with a pair of long, folded appendages. Ejaculatory apodeme transparent, tetragonal, with a short stem. � �: Ovaria white, spermatheca slightly wider than long. Parovaria larger than the spermatheca, with an elliptical knob. Ventral receptacle coiled approximately five times (Fig. 5). Development: Egg (Fig. 10). Larvae: 3rd instar and puparium were described by Hendel ( 1 928). Posterior spiracles of all instars light coloured, with an elongate apex (Fig. 8). Mouth hooks: 0.04 mm; 0.07 mm; 0. 1 0 mm. Buccal armature-length:0. 1 8mm; 0.38 mm; 0.62 mm. Sclerotized part of posterior spiracle: 0.02 mm; 0.04 mm; 0.06 mm. Appendices 291 Larval bionomics: Larvae usually mine in leaves, exceptionally in the leaf-like widening fruit of Thlaspi arvense-Brassicaceae (Coll. Buhr), in the stem of Caylusea abyssinica-Resedaceae (Coll. Buhr) or in the seed-leaves of Raphanus sativus­ Brassicaceae (Maca 19t.). The families of host-plants- Brassicaceae, Resedaceae, Capparidaceae, Tropaeolaceae, Asteraceae (Rhodanthe manglesii-larvae in Coll. Buhr), Viciaceae (Pisum sativum)-given by various authors were ascertained by Maca ( 1972), too. Other data: Papaveraceae (Herling, 1957). Buhr (1937) found that artificially transferred larvae can develop on plants of certain other families as well. Most of the host-plants have a high content of thioglycosides. Imaginal bionomics: Only sporadic occurrence on non-cultivated land, more frequent in gardens and in the fields of brassicaceous monocultures. S. apicalis is easily reared in a vessel with a potted host-plant. Two couples of the yellow form reared in this way, both having emerged from puparia on Brassica rapa, produced together 43 adults of Fl generation (the progeny of one couple was reared on Brassica rapa, of the other on Pisum sativum). All Fl adults were yellow. Length of their development (at 18 °C): 1 st instar 2-3 days, 2nd instar 3-4 days, 3rd instar 8 days on the average, puparium 12 days. Oviposition about 10 days after emergence (Buhr, 1941 ). Buhr ( 1941 ) has pointed out that all adults reared from mines collected in the field (about 80 specimens) were yellow. Their development was completed at 16-18°e. 20 larvae in mines collected in July 1969 on Brassica spp. and Pisum sativum were reared at an average temperature of 12°e. All adults were yellow, a few displayed transition to brown colour. Only 1 grey-brown male emerged from the larvae in mines collected in September, 1970 on Brassica spp. and reared at a temperature ranging between Y and lYe. Appendices 292 Hering ( 1957) stated 3 generations a year. It is not always easy to determine in which generation adults belong, as at insufficient humidity (or by means of some other stimulus?) larvae and puparia enter quiescence and the puparial stage can then last up to 300 days (Buhr, unpublished). Distribution: S. apicalis occurs throughout the holarctic region. Appendices Figs. 1-4: Figs. 5-6: 293 Phallic organs of the S captomyza speCIes. 1. S. pallida, 2. S. graminum, 3 . S.griseola, 4. S. apicalis (flava) . Spennatheca, parovarium, ventral receptacle (each of the fIrst two organs is paired). 5. S. griseola, 6. S. apicalis (flava). Scale in mm. (Maca, J. 1 972). Appendices Figs. 7-10: 9 --: .: .: --.: ---:-== -- - - - - 294 Posterior spiracles of 3rd instar larvae. 7. S. graminum, 8. S. apicalis (flava) , 9. S. pallida. 10. S. apicalis (flava); Egg ( I st instar buccal armature showing through). Scales: 0.05 nun for Figs. 7-9; 0. 1 nun for Fig. 10 (Maca, J. 1 972). Appendices 2.5 2. ·1 .0 A o x x . -Q· · · · · · · · ·o, · · · · · · · · · ··Cb ·-4 C %5x . ",_.--4 '11 +_ .-.r- . + -" .,, "'" "0'" 2 mm .< -' 0 W � a: <:I ..-! I � X ... a: '" ..,; )0 x ( -fl'IOEX-1 +_._._+ -4y-OO'JEX 0----0 5x-rJomEX 0 · · · · ······-0 -4 C- JI'iDEX+ 1 is mm I I ' 3 mm " , , I I -c: !:::! Cl -' - ... -' v -' - -c: '" Cl. -CO ..,; ..,; 2.5 2 . I. 1 - 2mm 295 c x •• Q. • • . • • • · ·-·(j · · · · · · · ·- · ·TI··-·· · · ·-· · ·O� C o 0 _-5x + ,p..- ::.:""_· ..... « v _ . _._ ._._ 0-:;::: � + ----- -- - o \o.I!HG l.DlGfIT (rrrn ) , I �mm prr:rn I , I , .:: z: J -' ::;, 00( VI 0 ::t: � -' x: 00( w -' � 00( -' u a: c: "'" 0: <.:> <:> '"" "'" '" . ..; '" '" Fig. 1 1 : Wing indices of Scaptomyza and their dependence on the wing length. A : B = C - index; D : C = 4v - index; F : E = 5x - index; B : C = 4C - index (Maca, 1 972). Appendices 296 til � 0-W W 3 30 til CI 20 CI I() � 10 W 0- til 0 --l < ::l Cl > (5 ::z: � Cl IrD 0:: W CD · 30 :x: ::l ::z: I..&J ' c:l < 10 e:: W > -< 0 A 0 o S. PALLIDA +----+ S. GRAHltiUl1 IV V VI vrn 8 HOT COLLECTED N Y VI VII VIII IX � I XI HOHTHS N j 0 XI MONT H S . IV Y 7\ " \ / \ .n! \ -' , V1 VtlI Fig. 12: Frequency of Scaptomyza pallida and S. graminum during collecting periods. A: Veself n. Luz. , 1966, B: Praha-S arka, 1966, C: Veself n. Luz., 1 967, D: Praha-S arka, 1967 (Maca, 1972). I Xl Appendices 297 Duda ( 1935, p. 49) separates Parascaptomyza and Scaptomyza in his key to the subgenera of Drosophila. Hackman ( 1 982) fmds in Duda's key that the size relation of the humeral bristles (h) and the number of rows of acrostichal hairs (a.Mi) are used as the main separating characters for the two genera. The key characters for the two genera are then as follows: Acrostichals in 2 or 4 rows. One prominent humeral bristle, the upper one. The lower humeral bristle represented by a fme hair or, if a true bristle, not longer than half the upper one. Male genitalia as a rule (except in subg. Trogloscaptomyza) with conspicuous paired lobes between the anal plates (cerci) and the forcipes (see Figs. 13--17). These lobes, called paralobes by Frey (1954), are provided with one or more strong teeth or setae and are probably derived from the anal plates. The latter are usually small and not protruding below. Ovipositor usually weakly chitinized and provided with short teeth at the margin. Larvae usually feeding on vegetable debris, at least not obligate leaf-miners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parascaptomyza Duda. Acrostichals in 4 rows, rarely in two (S. subsplendens Duda). Two humeral bristles, usually of nearly the same size, or the lower one at least half as long as the upper one. Male genitalia without paralobes (sensu Frey). Forceps with a dense marginal (rarely interrupted) row of stout and usually blunt teeth. Ovipositor usually with coarse marginal dentation (see Fig. 33). Includes obligate leaf-mining species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scaptomyza Hardy. The genera Parascaptomyza and Scaptomyza are, as was already pointed out by Duda ( 1 935, p. 6 1 ), closely allied to the Jenestrarum group in the genus Drosophila. A nomenc1atorial question concerns the species which Collin (1953) records from England under the name Scaptomyza flaveola Meig. 1 830. This species is described by Hardy, 1 849 under the name Scaptomyza apicalis. Meigen ' s type specimen of flaveola is probably lost and the identity cannot be verified. There is, on the other hand, no special reason to doubt the synonymy of these two Appendices 298 names, and Hackman has used here the name flaveola Meig. for the species. Fallen names flava ( 1 823), as already pointed out by Collin (op.c.), is not available. Parascaptomyza disticha Duda is easily distinguished from the Finnish Scaptomyza species in having only 2 rows of acrostichals. For identification of Scaptomyza species the key is as follows: L Upper humeral bristle much stronger and sometimes nearly double as long as the lower one. Hind trochanters beneath with a short black spine-like bristle. Ground colour of mesonotum decidedly rufous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - Upper humeral bristle not much stronger than the lower one, or both equal in size. Trochanters beneath with hair-like bristles not contrasting in colour. Mesonotum yellow-brown or grey in ground colour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Male with a dark spot at the apex of the wing . . . . . . . . . . . . . unipunctum Zett. - Wings ( � ,d') not spotted . . . . . . . . . . . . . . . . . . . . . . . . trochanterata Collin. 3. A minute bristle, sometimes present, sometimes absent, on the frontal orbits between the upper reclinate orbital and the vertical bristles. If absent, body entirely yellow with dark anal cerci . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 No bristle between the upper reclinate orbital and vertical bristles. Greyish species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Body yellow. Male cerci dark and rounded, not drawn out to a pointflaveola Meig. - Body always grey. Male cerci drawn out to a point . . . . . . . montana Wheeler. 5. Palpus with one strong dark apical bristle, the other bristles more ha.ivhlimilis n.sp. - Palpus with two or more dark apical bristles . . . . . . . . . . . . . . . . . . . . . . . 6 6. In the male genitalia the teeth of the forceps margin are remarkably elongated in the ventral direction; the caudal margin of hypandrinm with a deep median notch. Penis apodeme stout (see Figs. 39-40). Wing length in both sexes as a rule more than 2.7 mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . teinoptera n. sp. - Marginal teeth of forceps almost equal in size, short and blunt; caudal margin of hypandrium with a narrow median split or a less deep notch (Figs. 41-44). Penis apodeme slender. Wing length in both sexes as a rule less than 2.7 mm . . . . . . . . 7 Appendices 299 7. Male cerci large with a broadly rounded free ventro-caudal margin (Fig. 42) and only partially covered with microscopically small short hairs. In both sexes the brown stripes on the mesonotum distinctly contrasting with the light grey ground colour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . graminum Fall. - Male cerci small, completely covered with microscopic hairs (Figs. 43--44). In both sexes and especially the female the brown stripes on the mesonotum are only faint, if present at all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . griseola Zett. Scaptomyza unipunctum Zett. (Figs. 1 8- 19) Scaptomyza trochanterata Collin (Figs. 20-21) . Scaptomyza flaveola Meig. (Figs. 29-30). A leaf-mining species represented in the Australianm Museum's collection. Scaptomyza montana Wheeler (Figs. 3 1-32). This species, has been reared from leaf-mines on both Pisum and Brassica. Scaptomyza consimilis n.sp. (Figs. 27-28). Scaptomyza teinoptera n.sp. (Figs. 39-40). Scaptomyza clavata Okada Scaptomyza tistai (Kumar and Gupta, 1992) Scaptomyza graminum Fall. (Figs. 41-42). The males of this species can be recognized by the large rounded cerci (visible in dried specimens even without dissecting the abdomen). The females can be separated from griseola by the distinct thorax pattern and in most cases from teinoptera by the Appendices 300 difference in wing length. According to Basden ( 1954), imagines of this species can be trapped on apple baits. The larva is leaf-mining and feeds on Caryophyllaceous plants. Some of the food plants mentioned in the literature may refer to other grey species of Scaptomyza, but there is reliable record at least for Stellaria media (Basden op. C.). Scaptomyza griseola Zett. (Figs. 43-44). Scaptomyza norica n.sp. (Fig. 34). Scaptomyza terminalis Loew (Fig. 23). Scaptomyza apieata Thomson (S. terminalis Wheeler 1952, nee Loew) (Figs. 24,26). Scaptomyza hsui n.sp. (S. terminalis Hsu 1949, nee Loew) (Figs. 22,25). Scaptomyza atlantica n.sp. (Figs. 35-36). Scaptomyza (Exalloscaptomyza) caliginosa Hardy: flower breeding Drosophilids (Montague, 1989). Scaptomyza mateola sp. nov. :from the flowers of cultivated Cucurbitaceae in Mauritius (McEvey 1990). Scaptomyza exilis sp. nov. :from Crinum sp. in Madagascar (McEvey 1990). Scaptomyza tistain n.sp. (Kumar, A. and Gupta, J.P. 1992). Scaptomyza clavata Okada (Kumar, A. and .Gupta, J.P. 1992). Appendices 301 Scaptomyza (Bunostoma) australis (Figs. 45-48) In his large monograph treating the Australian Drosophilid fauna, Bock (1977) documented numerous records of Scaptomyza australis, ranging from Western Australia to Queensland. He also mentioned that the species is an ecological generalist, and is found in most habitats. Later, he reported a large series from Norfolk Island, a possession of Australia about 500 miles south of New Caledonia and about 1000 miles northeast of Sydney (Bock, 1986). Bunostoma presently includes the following species or groups of species: bicolor Malloch (Samoa), boninensis Okada (Bonin Is.), philipensis Bock (Norfolk and nearby Philip Island), flavifacies (Malloch) (Marques as Is.), 8 species from Hawaii (Hardy, 1965) , and perhapsflavella Harrison andfuscitarsis Harrison (both from New Zealand). Grimaldi ( 1990), like Hackman, has not examined the two New Zealand species, and Hamson's descriptions are based only on the external male genitalia, not the internal ones. Wheeler ( 198 1 ) placed these two species in Scaptomyza subgenus incertae sedis, but Hackman ( 1982) indicated (on dubious morphological grounds) that they may be Bunostoma. Still, the undisputed sister species of Scaptomyza australis is S. philipensis, based on male genitalic features. The male genitalia of these species are remarkably similar to that of S. anomala from Hawaii (Grimaldi, 1990). Appendices Figs. 13· 17: Figs. 18-26: 302 Male genitalia of Parascaptomyza species. 13. Parascaptomyza disticha, ventral view. 14. Parascaptomyza substrigata. 15. Parascaptomyza impunctata 16. Parascaptomyza adusta, ventral view. 17. The same species, profile. Male genitalia of Scaptomyza species. 18. S. unipunctum, ventral view 19. The same, profile. 20. S. trochanterata. 21. Forceps of the same. 22. S. hsui n.sp . , profile. 23. S. terminalis. 24. S. apicata 25. S. hsui ventral-caudal view. 26. S. apicata, ventral view (Hackman, 1955). Figs. 27-38: 303 37 Male genitalia of Scaptomyza species. 27. S. consimilis n . sp. , ventral view. 28. The same, profile. 29. S. flaveola, ventral view. 30. The same species, profile. 31. S. montana, profile. 32. The same species, ventral view. 33. Ovipositor of the same species. 34. S. norica n.sp. Genital arch and cerci of the male. 35. S. atlantica n.sp. , ventral view. 36. The same profile. Figs. 37-38: Male genitalia of Drosophila Jorcipata ventral and side view (Hackman, 1955). Appendices 39 Figs. 39-44: 304 � \ / , : f : . : .i 4-1 Male genitalia of Scaptomyza species. 39-40. S. teinoptera n.sp. , ventral and side view. 41-42. S. graminum, ventral and side view. 43- 44. S. griseola, ventral and side view (Hackman, 1 955). Appendices Figs. 45-48: I I , ' , : .. ' \ / 45 \\Yb A j iA � � � a a i � 305 Genitalia of Scaptomyza australis from newly discovered distributions. 45. Male: hypandrium, aedeagus, and associated structures, dorsal view (Pitcairn Is.). 46. Male: epandrium, cercus, oblique terminal view (same specimen as in Fig. 45). 47. Female : sternite 8 (Pitcairn Is.). 48. Female: sternite 8 (Vanuatu) (Grimaldi, 1990). Harrison ( 1959) described New Zealand species as follows: t I Family D R 0 S O P H I L I D A E t I Arista plumose, pectinate, or pubescent. Third .antennal segment rounded or oval. Front with conspicuous bristles. Postvertical convergent. Face with distinct antennal fossae and a carina. Vibrissa present. Costal twice broken; subcosta vestigial; fIrst vein short; discal and second basal cells united; anal cell present. Distinguished and separated from other families by having two costal breaks, discal and second basal cell united, subcosta vestigial, anal cell present, arista usually plumose with ray dorsally and ventrally on main axis, and convergency postverticals. Genera occurring in New Zealand: Drosophila Fallen Scaptomyza Hardy Hutton ( 1901 ) fIrst recorded and described New Zealand representatives of the family and Harrison ( 1952) described the domestic species of the genus Drosophila in New Zealand. None of species considered up to 1952, with the possible exception of D. marmoria Hutton, is endemic. Endemic species are rec:orded here for the fIrst time. A species of Leucophenga was recorded by Miller ( 192 1 ). This is shown below to be a Drosophila and as yet no true member of Leucophenga has been found in New Zealand. Scaptomyza has been not previously recorded from New Zealand. Species additional to those recorded below are present in New Zealand but as they are represented in collections by few specimens and have not been examined in the live state, their description is postponed until further material is available. The subgenus Pholadoris and the obscura group of species appears to be represented in the undescribed material. In most New Zealand collections Drosophilidae are poorly represented. Compared with other families these flies an� rarely taken in the sweep net 306 Appendices 307 and it is only when special collecting procedures are practised, such as the use of banana-baited traps, that large numbers are obtained. Such collecting has been confmed, so far to the Auckland district When trapping can be extended in other area of New Zealand a more complete picture of the fauna will he optained. KEY TO GENERA OF DROSOPHIUDAE IN NEW ZEALAND (Harrison, 1959) Two or 4 rows of acrostichal hairs . . . . . . . . . . . . . . . . . . . . . . . . . . . Scaptomyza At least 6 rows of acrostichal hairs . . . . . . . . . . . . . . . . . . . . . . . . . . Drosophila Genus SCAPTOMYZA HA.RDY Occiput distinctly convex. 2 or 4 rows of acrostichal hairs in front of transverse suture, 2 between dorsocentral bristles; prescutallars always absent. Thorax., abdomen and wings slender. Species occurring in New Zealand: Scaptomyza jlavella sp.n. S. fuscitarsis sp.n. S. graminum (Fallen) Not previously recorded from New Zealand. S. graminum is the most widespread species in the genus and has probably been introduced to New Zealand through commerce. The other 2 species are possibly endemic. KEY TO SPECmS OF SCAPTOMYZA IN NEW ZEALAND I Entirely yellow species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . flavella Brown to black species . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Dorsal surface of scutellum almost flat . . . . . . . . . . . . . . . . . . . . graminum Dorsal surface of scutellum distinctly convex . . . . . . . . . . . . . . . . fuscitarsis Appendices Male and female Scaptomyza flavella sp.n. (Figs. 5 1 , 54 and 56) 308 Head (Fig. 56): Arista with 7 branches, two below in addition to the terminal fork; axis dark brown with basal segment light yellow. Antenna yellow; 3rd segment longer than 2nd segment, covered with [me white pile; 2nd segment with 2 strong black bristles and small black hairs. Front yellow, over half width of head at vertex; ocellar triangle small, enclosing ocelli and ocellar bristles and hairs, whitish-grey dusted; area between ocelli distinctly raised above level of front, ocelli clear; orbits light greyish-brown, pollinoses. Postverticals cruciate; raltio of length of fronto-orbitals, anterior to posterior, 3: 2: 4; anterior reclinate bristle much closer to proclinate than to posterior reclinate and lateral to it; one small hair on frontal orbit anterior to orbitals; about 8 small black hairs near anterior median margin of front. Face yellowish-white. Carina wedge shaped, broad and prominent below; not sulcate. Cheeks yellowish-white. Vibrissa strong; 2nd oral bristle equal to vibrissa; 3 prominent bristles at lower posterior angle of cheek. Occiput yellow, bunch of black hairs immediately above foramen. Eyes dark red in pinned specimens; covered with short, whitish pile. Vertical diameter of eye about 5 times width of cheek in same axis. Proboscis yellow; palpi light yellow with 2 apical [me bristles, one longer than the other, and a few fme bristles on anterior margin. Thorax: Yellowish-brown; scutellum yellowish-brown, flat disc. Acrostichal hairs in 2 rows; 2 enlarged hairs anterior to anterior- dorsocentrals; basal scutellars divergent, equal in length to apical scutellars, both pairs strong; 1 strong humeral and 1 strong hair close to it; 2 enlarged hairs medial to presutural, 2 prominent stemopleurals, 1 enlarged hair dorsal to posterior bristle; sterno-index about 0.63. Legs: Yellowish-brown; apical segments of tarsi light brown. Apical bristle on 1st and 2nd tibiae; preapicals on all three tibiae. Appendices 309 Wings: Clear; veins light brown. Costal ending at apex of 4th vein but weaken between 3rd and 4th veins; third costal section with heavy bristles on basal three-fIfths; pair of strong bristles at distal costal break. Wing indices: costal about 3.5-3.7; 4th vein about 0,6; 5x about 1 .8. Halteres yellowish-brown. Abdomen: Yellowish-white. Strong bristles on posterior margin of tergites, small black hairs elsewhere on tergites. External male genitalia: Genitalia arch lightly chitinised, parallel sided, with about 6 bristles near middle on either side; anal plate brown posteriorly, about 20 strong bristles and a cluster of fme short bristles at ventral margin; clasper with row of about 8 very strong black teeth and a subapical row of about 8 shorter stout black teeth with fme bristles between these teeth and between the row of teeth. Scapromyza graminum (Fallen). (Figs. 50, 53) A small light brown to greyish species. Body length 2.0-2.25 mm., wing length 2.0-2.75 mm. Male and female Head: Arista with about 7 branches, usually only 1 below in addition to the terminal fork; axis dark brown, basal segment light brown. Antenna light brown; 3rd segment dark on outer margin; 2nd segment darker on outer margin, with 2 bristles and smaller black hairs. Front brown posteriorly and medianly, yellowish-brown anteriorly; about half width of head at vertex; area between ocelli ailmost black in some specimens and raised above level of front; ocelli clear; frontal orbits greyish-blown about bristles, yellowish-brown anteriorly. Ratio of length of orbitals; anterior to posterior, about 7:3:9; anterior reclinate lateral to and just anterior to or level with proclinate; 1 or 2 small hairs on frontal orbit anterior to orbitals; a few minute hairs on median anterior region of front. Face yellowish-brown. Carina brown, narrow, ridge shaped, but slightly broader Appendices 3 10 and nose-like below. Cheeks light yellow. Vibrissa strong; 2nd oral bristle about half length of vibrissa; 3 or 4 prominent bristles at lower angle of cheek. Occiput grey to dark purplish-grey. Eyes dark red in pinned specimens; Covered with dense light-coloured pile. Vertical diameter of eye about 6 tUnes width of cheek in same axis. Proboscis yellowish-brown; palpi with 1 strong apical bristle and some smaller black hairs. Thorax: Light brownish-grey, dusted dorsally, sometimes lighter laterally, and yellowish-brown ventrally; broad light-coloured stripes on mesonotum extending from acrostichal rows through dorsocentral row to 1 st row of hairs outside of the dorsocentral row; scutellum greyish-brown, almost flat disc. Acrostichal hairs in 2 rows; 2 enlarged hairs anterior to anterior dorsocentrals; basal scutellars divergent, equal in length to apical, both pairs strong; 1 strong humeral; 2 prominent sternopleurals, 1 enlarged hair dorsal to posterior bristle, sterno-index about 0.5. Legs: Yellowish-brown; tarsi faintly but not distinctly darkened towards tip; preapical bristles on all tibiae; apical on 1st and 2nd only. Wings: Clear; veins light brown. Costal ending at apex of 4th vein; third costal section with heavy bristles on its basal third; pair of strong bristles at distal costal break. 3rd vein with a slight bend posteriorly near apex, thus narrowing the 1st posterior cell somewhat Wing indices: costal about 3.2; 4th vein about 1 .7; 4c about 0.75; 5x about 1.3. Halteres yellowish-greyish-brown. Abdomen: Varies from light brown to blackish-brown, shining. Lightest areas occur about median region of anterior tergites, apical tergites the darkest and often almost completely black. Sternites light yellow. External male genitalia: Genitalia arch narrow dorsally, heavily chitinised, anteriorly and posteriorly on dorsal half, ventral margin concave and produced posteriorly and anteriorly, 2 strong bristles at postero-ventral and antero-ventral regions; Appendices 3 1 1 anal plate normal and oval on dorsal half and with bristles over most of this surface, ventral half modified to a posteriorly directed auxiliary clasper with row of about 4 very strong apical teeth and a cluster of small bristles above them; clasper crescent shaped and fitting into ventral margin of arch, apical margin with strong teeth and bristles. Distribution in New Zealand: Waitakere Ranges, Auckland, Pukekohe, Christchurch, the Brothers Islands (July, August, October, December, January, March, May, June). Remarks: Separated from S. juscitarsis by having the scutellum almost flat dorsally and from S. flavella by its smaller size, darker colour, and lower costal index. Scaptomyza fuscitarsis sp.n. (Figs. 49,52 and 55) A slender shining fly, usually black but varies from brown to black. Body length 1 .75-2.25 mm., wing length 1 .75-2.5 mm. Male and female Head: Arista with 7 branches; 2 below in addition to the terminal fork; axis black, basal segment light brown. Antenna yellowish-brown, occasionally reddish-brown; 3rd segment somewhat pointed apically and about equal in length to 2nd segment; 2nd segment with 2 bristles and some minute black hairs. Front light yellowish-brown to dark brown occasionally tinged with red, dark and, in some lights, grey dusted at vertex; anterior region frequently light brown; orbits grey to dark brown, lighter anteriorly; area between ocelli dark brown to black and raised above level of front; ocelli clear. Ratio of length of orbitals, anterior to posterior, 2 : 1 : 3; anterior reclinate lateral to and level with or just posterior to proclinate; usually 1 small hair on frontal orbit anterior to orbitals; a few minute black hairs on median anterior region of front. Face yellowish brown, occasionally light yellow. Carina ridged, not sulcate, sometimes with a brown stripe on ridge. Cheeks yellowish-brow, black posteriorly. Vibrissa strong; 2nd oral Appendices 3 12 bristle usually distinct from other hairs and third to half length of vibrissa; 3 prominent bristles at lower angle of cheek. Occiput brown or greyish-black with lightly dusted bands extending from vertex, at either side of ocelli to foramen. Eyes dull red in pinned specimens; covered with dense whitish pile. Vertical diameter of eye about 6 times width of cheek in same axis. Proboscis light yellowish-brow; palpi with 1 strong apical and 2 or 3 small bristles on anterior margin of apical third. Thorax: Brown to purplish-black with much grey dusting dorsally and laterally, light ventrally, no pattern of stripes expect lighter specimen have indications of yellowish-brown area between the ventrally acrostichal and dorsocentral rows anteriorly; scutellum same colour as mesonotum, with distinctly convex disc. Acrostichal hairs in 2 rows; 2 enlarged hairs anterior to dorsocentrals; basal scutellars divergent and equal to longer than apical scutellars, both pairs strong; 1 humeral and often, 1 enlarged hair 2 sternopleurals, sterno-index about 0.5. Legs: Light yellowish-brown; anterior tarsus with apical three segments dark brown to black; other tarsi darkening gradually towards apices. Preapical on all tibiae; apical on 1st and 2nd tibiae only. Wings: Clear; veins light brown. costal ending at apex of 4th vein; but weakened between 3rd and 4th vein; third costal section with heavy bristles on its basal two-thirds; pair of strong bristles at distal costal break. Wing indices: costal about 2.5-3. 1 ; 4th vein about 1 .9; 4c about 0.9; 5x about 1.6. Halteres light yellow, darkened basally. Abdomen: Shining blackish-brown with lighter areas anteriorly. In the light­ coloured specimens the anterior tergites may be brown, or even yellowish-brown dorsally, but apical segments and lateral regions of anterior segments are always dark brown. External male genitalia: Genitalia arch broad and parallel sided, about 3 bristles near middle of posterior margin, cluster of short bristles along ventral margin; narrow Appendices 3 1 3 posteriorly directed ann arising near postero-ventral comer; anal plate ovoid, bristles over most of surface, expect at middle; shorter and thicker bristles clustered about ventral margin; clasper small with very short almost tooth-like bristles on ventral margm. Paratypes: Auckland: Browns Bay, swept off Leptospennum foliage. Palmerston North: flying around rotting swedes. Additional Specimens: Palmerston North: flying around rotting swedes, on new swede area. Distribution: Auckland, Pukekohe, Palmerston North, Christchurch, Banks Peninsula, Okarahia, Roxburgh. (All the year). Remarks: Readily separated from S. graminum and S. flavella by the distinctly convex scutellum. Appendices 3 1 4 55 Figs. 49 - 54: Wings of the Scaptomyza species. 49. S.fuscirarsis. 50. S. graminum. 51. S. flavella. Figs. 52 - 54: External male genitalia of the Scaptomyza species. 52. S.fuscitarsis. 53. S. graminum. 54. S.flavella. Figs. 55 - 56: Head of the Scaptomyza species. 55. S. juscirarsis. 56. S. flavella. Scale: Figs. 49-5 1 , 1 .0 mm.; Fig�. 52-54, 0. 1 mm.; Figs. 55-56, 0.5 mm. (Harrison, 1 959). Appendices 3 1 5 elmoi. Holloway ( 1990) believed what Harrison identified as S. graminum was in fact S. Key to Scaptomyza species occurring in New Zealand (Figs. 57-60 and Plates 1 -5) Prepared by B.A. Holloway, 1990 1 . Four longitudinal rows of acrostichal setae in front of anterior dorsocentral bristles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. flava Two longitudinal rows of acrostichal setae in front of anterior dorsocentral bristles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Scutellum convex dorsally . . . . . . . . . . . . . . . . . . . . . . . . . . . S. juscitarsis Scutellum flattened dorsally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Arista of antenna with 1 ventral ray in additional to tenninal fork . . . S. elmoi Arista of antenna with 2 ventral rays in additional to tenninal fork . S. flavella Appendices Post vertical bristles Face profile Antennal arista p v s convergent Brown vibrissa Vibrissa angle Irregular lengths Branches also on this side No spine Fig. 57: S ome characters of the family Drosophilidae (Holloway, 1 990). 3 16 Appendices 3 17 Scaptomyza flavella \ ---'7 po:S}-Q y ; o r . _ _ __ � 'Pes t s c u+<:. I \ " "1 Scaptomyza fuscitarsis Fig. 58: Profile of scutellum (from the left side) of the Scaptomyza speCles, S, juscitarsis differs from all the other Scaptomyza spp. in New Zealand in having a strongly convex, rather than flattened, dorsal surface on the scutellum (Holloway, 1990). Appendices 59. Scaptomyza spp. a: S. flava b: S. fuscitarsis po4e , cif" ----JOffO ce';y" I L,.·;'i;'� (I,' -"- J D c rS 0 ().oA.� � hv.., (;, \ " +rCC'ASvUSe . SJ--L,i.re. . _- C, .tJ,' ��. Ii �:::\" < , �� ' '* ' 5 66 � (; 7 Male genitalia of Scaptomyza and Drosophila species. Side view, ventral parts omitted. 61. Scaptomyza (Rosenwaldia) mitchelli Hackman. 62. S. (Elmomyza) recava Hardy. 63. S. (Trogloscaptomyza) brevilamellata Frey. 64. Drosophila (Lordiphosa) nigricola Strobl. 65. Scaptomyza (Bunostoma) bryanti Hackman. 66. Drosophila (Sophophora) kikawai Burla. 67. Scaptomyza (Parascaptomyza) frustulifera Frey. Redrawn figures: 6 1 and 65 from Hackman, 1959; 62 from Hardy, 1965 ; 63 and 67 from Fery, 1954; 66 from Olroyd, 1958 (Hachman, 1982). Appendices 6 8 b 9 cg .L--•• CW ,5 , 6 Figs. 68-81 : 327 ~ u;p Lf Q ~ 1 0 1 1 ,,2 1 3 i 4 CfiJ W . - . " i 7 1 8 1 9 20 21 Spennatheca of Scaptomyza and Drosophila species. 68. D. collini 69. S. anomala 70. S. pallida 71. S. taiwanica 72. S. (s. str. ) consimilis 73. S. (s. str.) sinica 74. S. (s. str.) graminum 75. D. nasalis 76. S. hsui 77. S. chylizosoma 78. S. (E.) kilemba 79. S. (E.) deemingi SO. S. horaeoptera 81. S. mauiensis. All redrawn: 68, 72 and 74 after Okada, 1956; 69, 70, 75, 76 and 8 1 after Throckmorton, 1962 and 1966; 7 1 and 73 after Lin and Ting, 197 1 ; 77-79 after Tsacas, 1972; 80 after Cogan, 1979 (Hachman, 1982). Appendices Figs. 82-85: 328 £ 2 R3 £ 5 Testes and paragonia of Drosophila fenestrarum and Scaptomyza species. 82. Drosophila (Lordiphosa) fenestrarum Fallen. 83. Scaptomyza (Parascaptomyza) pallida Zetterstedt. 84. S. (s. str.) consimilis Hackman. 85. S. (s. str.) graminum Fallen. Fig. 82 drawn after a sketch by Saura, 83-85 after Okada, 1956 (Hachm an , 1982). Appendices 329 Table 1: Comparison of characters of DrosophihI subg. Lordiphos(4 Scaptomyza subg. Bunostoma and two unplaced Scaptomyza species from New Zealand (Hachman, 1982). Lordiphosa Bunostoma S. flavella, S.juscitarsis Head not flattened not flattened not flattened Eye ± oblique ± oblique Facial carina low and restricted to usually distinct in prominent and dorsal half of face dorsal half of face nose - like below (in the type species nose-like below) proximal to end 2 - 3 ventral 1 - 2 ventral Rays of arista fork:2-3 ventral shiny without pattern shiny, brownish yellowish brown Mesonotum brownish yellow or black (l species: or purplish black blackish yellow) Humeral bristles 2 1 prominent 1 prominent Acrostichal rows of hairs 4 - 6 2 - 4 2 Dorsocentrals 1 + 3 0 + 2 (1+ 3 in one two enlarged species) hairs anterior dorsocentral Sternopleurals 3 (posterior one 2 (anterior one 2 prominent longest) longer) 1 + 3 in one species Male genitalia no secondary clasper, no secondary no secondary clasper (surstylus) clasper, clasper clasper,claspemod stout, dentate rather smaller, erately stout (usually as in Fig. usuall y dentate (cf. (S.jlaveZla) 64) Fig. 65) or small (S.juscitarsis), dentate Egg-guides heavily sclerotized, weakly sclerotized not mentioned in dentate description Distribution 9 Palaearctic Hawaii: 8 species New Zealand 2 Oriental Other Pacific 1 (2 ?) Nearctic Islands: 4 sp. species Australia: 1 sp SCAPTOMYZA DIVERSITY Hardy ( 1974) Given the large number of species and world-wide distribution of Scaptomyza, the extreme paucity of the Australia and New Zealand fauna seems remarkable on fIrst consideration; the world distribution of Scaptomyza species is, however, highly uneven. The Hawaiian islands contain a large proportion of the world total of species, most of them in the single subgenus Trogloscaptomyza 86 of 87 known species occur only in Hawaii; there has thus been as substantial a proliferation of Scaptomyza species in Hawaii as of Drosophila species. A good case can, in fact, be made for considering Hawaii the place of origin of the genus Scaptomyza (Throckmorton, 1975), with subsequent radiations into other parts of the world. Wheeler and Takada ( 1966) listed 55 species from the Nearctic and Neotropical zone; smaller numbers of species have been recorded from various Pacillc Islands. Fewer species occur in other parts of the world. Okada (1956) listed six species from Japan; a few more were subsequently added (Okada, 1973a, 1973b); several species occur in neighbouring mainland Asia. Hurla ( 1954) noted a total of four species from the Ethiopian zone; another three were added by Tsacas (1972). Harrison (1959) found three species in New Zealand, the cosmopolitan pallida and two endemic; New Zealand thus has a richer Scaptomyza fauna than Australia. Few species occur in Europe. In particular there appears to have been no radiation in south-east Asia, and area notable for several major bursts of Drosopbilid speciation from which, ultimately, Australia appears to have derived its Drosophila fauna and that of most if not all of its other Drosopbilid genera. Only one species of Scaptomyza, S. pallida, is cosmopolitan; most of the remaining species have quite limited distributions. S. australis has been collected as far north as Thursday 1; whether or not it occurs further north than this (i.e. in New Guinea) remains to be determined. Although, as mentioned above, australis has been found to be common in an orchard, the species is not generally attracted to Drosophila fruit baits and is collected by sweeping, The widespread occurrence of this species in Australia and the fact that it can be cultured in the laboratory suggest that it may be a candidate for polytene chromosomal investigations (Maca, 19782). 330 A p p e n d i x 2 SOME IMPORTANT LEAF MINER (AGROMYZIDAE) PESTS (Hill, 1987) Agromyza ambigua Fall. - (cereal leaf miner) Europe and N. America. Agromyza oryzae (Mun.) - (rice leaf miner) Japan, Java and E. Siberia. Agromyza maculosa (Mall.) - (lettuce leaf miner) USA, Hawaii and S. America. Cerodontha spp. - (cereal leaf miner) only Gramineae; worldwide. Liriomyza brassicae (Riley) - (cabbage leaf miner) Cruciferae mostly; cosmopolitan. Liriomyza bryoniae (Kalt) - (tomato leaf miner) polyphagous; Europe, W. Asia. Liriomyza cepae (Hering) - (onion leaf miner) Europe (not UK). Liriomyza chinensis (Kato) - (onion leaf miner) Japan, China and Malaysis. Liriomyza sativa Blanch. - polyphagous: Cucurbitaceae, Solanaceae, Leguminosae; USA, C. and S. America. Liriomyza trifolii (Burgess) - (American) serpentine leaf miner» polyphagous; N. and S. America and introduced to UK. Melanagromyza obtusa Mall. - (bean pod fly) India and S. E. Asia. Melanagromyza sojae (Zehn.) - (bean fly) Africa and S. E. Asia. Ophiomyia phaseoli (Tryon) - (bean fly) Africa, Asia and Australia (CIE map A.BO). Napomyza carotae Sp. - (carrot root miner) Europe (not UK). A p p e n d i x 3 ABILITY OF ADULT SCAPTOMYZA FIAVA TO SURVIVE AT LOW TEMPERATURE INTRODUCTION IT is well known that temperature has a pervasive effect on insects. Nearly every aspect of an insect's life is influenced by temperature, from direct effects on the kinetics of enzymatic reactions, to defIning the limits of physiological function and behaviour, and ultimately to shaping of evolutionary pathways. As a group, insects, more than any other eukaryotic taxon, have evolved not only to survive but to flourish in a wide variety of thermal environments (Lee, and Denlinger, 1991 ). Low temperature is not precisely defIned since it covers a wide variety of topics and temperature ranges, and includes the maintenance of normal activity at low temperature, tolerance of chilling during the summer versus survival of prolonged exposure to cold during the winter, and applied aspects including the cryopreservation of insects (Beck, 1983a). Insects are ectothermic organisms, and as such their physiological, metabolic, and developmental processes are highly responsive to ambient temperatures. Environmental temperatures undergo daily cycles (thennoperiods) in which the daytime temperature (thermophase) tends to be higher than the night-time temperature (cryophase). The daily alternation of thermophase and cryophase is, of course, approximately coincidental with the alternation of the photo phase and scotophase, respectively, of the daily photoperiod. Temperature is a key environmental factor determining the duration of survival and life stage of insects (Adler, 1987; McCreadie and Colbo, 1990). The time that an organism can survive at a temperature can be related to such factors as duration of exposure, and state of "acclimation" or "hardening" (Baust, 1982). The purpose of this study was to describe the influence of three low temperatures Appendices 333 on survival of adult Scaptomyza flava. MA TERIALS AND METHODS The ability of adult Scaptomyzajlava to survive at 0°, 5° and 12°C without food or water was detennined by placing groups of 10 newly emerged adults (5 � and 5 rT) in stoppered glass vials at these temperatures in darkness. The same procedure was followed with flies caged with plant material, at 0 and 5°C (all with a variance of ± 2°C). Five Chinese cabbage seedlings ca. 24 cm tall (plants growing in 300 ml plastic pots) were placed in small ventilated cages (in darkness) with cohorts of 100 Scaptomyza flava adults (3 days after emergence, mixed sexes). Experiments were unreplicated. Humidity was maintained at or near 35 ± 2% RH for the experiment without plant material and at or near 40% RH for the experiment where flies were confmed with Chinese cabbage plants. The number of insects alive and dead at 5 and 12°C were counted daily until all insects had died. Insects were counted twice daily at O°C. Longevity (in days) of an individual fly was taken as the mid point between two successive counts. In this way mean survival time could be calculated over all individuals for each group. RESULTS Results are presented in Table 2. The results indicate that adult S. flava is somewhat tolerant of low temperatures as there was high survival up to three days at O°C even for insects without access to food or water. This is in accordance with the fact that S. flava is active throughout the year (in the Manawatu region at least) and shows no evidence of winter diapause from field observations (see Chapter 4). Appendices 334 Table 2: Survival in days of adult S. flava at low temperatures Day Number of insects alive Without plant material With plant material ODe SDC 12DC ODe SDC 0 100 100 100 100 100 1 100 7 1 69 100 97 2 100 69 50 100 87 3 100 55 36 89 80 4 65 49 29 67 62 5 17 43 1 5 42 23 6 0 3 1 0 10 20 7 27 0 20 8 15 19 9 8 14 10 6 9 11 3 8 12 3 6 13 2 3 14 1 0 IS 0 Mean 9.45 4.84 2.99 1 1 16.95 lifespan (days) Appendices 335 The availability of live plant material at DOC did not increase survival. At this temperature insects with access to a live plant did not feed or oviposit (no punctures were detected on leaves) . Mean lifespan was reduced at 5 ° C compared to DOC in the absence of a plant even though a few individuals survived for 1 3- 14 days. This is probably because the insects were more active than at O°C (i.e. , adult Scaptomyza jZava insects were immobilized and entered a state of chill coma at OT [personal observation]). The availability of plant material at 5°C markedly prolonged lifespan. At this temperature feeding punctures on leaves were produced and a few eggs were laid but none of the eggs hatched. At 12°C (in the absence of plant material) survival was further reduced compared to 5° and O°C. An increase in temperature causes survival of adult Diptera to be reduced up to about 20T (Ballou, 1986). Lockwood and Story ( 1986) demonstrated that low relative humidity (25-50%) was detrimental to survival of some insects (e.g., Heteroptera). In my experiment, mean RH was 35% - 45%. Low relative humidity may therefore have been a factor in survival of the flies. From the results of this experiment it is likely that Scaptomyza flava can survive short periods at temperatures below 100C with no effect other than an extended development time. A p p e n d i x 4 OVIPOSITION IN SUN AND SHADE INTRODUCTION UNEQUAL shading of host-plants undoubtedly contributes to variation in the suitability of hosts for herbivorous insects (Schultz, 1983) but has received little attention as it relates to herbivory. Shading invariably reduces net photosynthetic rate and levels of foliar sugar, starch and protein, reduces leaf thickness, increases leaf area (Young and Smith, 1980; Schultz, 1983), and apparently reduces levels of some noxious secondary compounds in leaves (Lincoln, 1987). Changes in leaf chemistry with shading, if widespread, suggest phytophagous insects might prefer shade plants owing to the reduction of secondary compounds, or avoid them because of low levels of sugars and proteins compared to unshaded leaves. Similarly, physical changes in foliage that accompany variation in solar radiation also offer no general predictions concerning herbivore preference. Rather, it appears changes in leaves that accompany changes in sunlight intensity present conflicting selection pressures for herbivore insects. Over evolutionary time, insect preference for sun or shade leaves should be influenced by the balance between these opposing pressures as well as other factors like variation in predation and parasitism in sun and shade (Bultman, 1988). Collings and Louda (1988) demonstrated that total insect herbivore load on bittercress (Cardamine cordifolia) is greater on plants in the sun than on plants in the shade and that there were increases in the water associated soluble (nitrate) nitrogen concentrations in leaves (Louda, 1986); reduced plant vertical growth, leaf development, and seed reproductive success (Louda, 1984); and increases on experimentally water­ stressed plants in the shade (Louda, 1986) or on experimentally shaded plants in the sun (Collings, 1987). Collings ( 1988) tested the hypothesis that light intensity was the direct, proximal mechanism causing significantly higher vulnerability of bittercress clones in the sun to herbivory by a leaf-mining fly (Scaptomyza nigrita Wheeler). Adult densities and leaf- Appendices 337 mining damage were consistently and significantly higher on plants in sun than on those in the shade. Shading sun plants shifted their growth pattern toward that of naturally­ shaded plants. However, no information was available on the response of the leaf miner either to environmental variation or to differences in host plant quality. MATERIALS AND METHODS To study the effect of sun and shade on Scaptomyza flava an experiment was conducted under laboratory conditions during summer of 1990 at Massey University, Palmerston North. 10 two months old potted Chinese cabbage plants were selected and one pair of insects was released in gauze cages onto each of them. 5 plants were placed in a position in the laboratory so that they were directly exposed to any natural sunlight and another 5 were kept in the shade. Relative oviposition and larval survival was assessed based on the number of emerging adults of the next generation. RESULTS AND DISCUSSION Results are summarized in Table 3. From each pair of insects on Chinese cabbage kept in the sun, a mean of 125 new adults emerged after 28 days, but from each pair of insects held in the shade, a mean of only 5 adult insects emerged (Table 3). Adult flies were observed to be more active on plants in sun than on those in shade (unrecorded data). Plants in the shade were taller and had a longer fIfth leaf than those growing in the sunny area. Appendices 338 Table 3: Number of new emerged adult insects from 1 pair of Scaptomyza flava from Chinese cabbage plants in sun and shade. Days Mean number of adults Plants in sun Plants in shade 11 8 1 2 15 1 3 40 1 4 30 2 5 10 0 6 10 0 7 7 0 8 2 0 9 2 0 10 1 0 11 0 0 12 1 0 Total adults 1 25 5 1 First day of adult emergence. Appendices 339 The results show a clear pattern of greater leaf-miner success in sun compared to shade. The amount of leaf area damaged was also greater in sun (approximately 75% of leaf area) than in shade (approximately 25%). This result is consistent with those obtained for several other species of leaf miners. For example, Faeth et ai., (198 1 ), working with lepidopteran and coleopteran leaf miners on oak: trees, observed higher densities on sun-exposed leaves than on shaded leaves. This same pattern also occurred with a dipteran leaf miner on bracken fern (MacGarvin et ai. , 1986). However, other leaf-mining species are more abundant in shaded habitat (MacGarvin et al. , 1986). A p p e n d i x 5 LABORATORY INSECTICIDE EXPERIMENTS WITH SCAPTOMYZA FlAVA INTRODUCTION IN order to determine the susceptibility of Scaptomyza leaf miner to a range of insecticides, several experiments were conducted in the laboratory with adults and larvae. MA TERIALS AND METHODS To determine the susceptibility of adult S. flava flies to insecticides, two experiments were carried out . In the fIrst experiment, there were six treatments as follows, each replicated 3 times: 1 . Control, water only applied. 2. Carbaryl applied at full label rate (100 g Sevin 80 EC 1100 I water). 3. Permethrin applied at full label rate (100 ml Ambush 50 ECI 500 I water). 4. Pirimicarb applied at full label rate (125 g Pirimor 50 EC/l00 I water). 5. Diazinon applied at full label rate (60 ml Diazinon 80 ECI 100 1 water). 6. Acephate applied at full label rate ( 100 g Orthene 75 Ec/ 100 I water). The first experiment was conducted in a greenhouse commencing 3 1 October 199 1 . One-month old potted Chinese cabbage plants were sprayed with a hand mist sprayer, allowed to dry, then placed individually into cages containing 10 adult flies obtained from a colony reared on Chinese cabbage. Plants were watered as needed. After 48 hr, the number of insects remaining alive in each cage was recorded. In a second experiment, the procedure of the fIrst experiment was followed but the plants were placed in a controlled environment (Incubator Room) at 20 ± I ·C under a 1 2 L: 1 2 D photoperiod. RH was not controlled. The treatments were as follows: Appendices 1 . Control, water only applied. 341 2. Pirimicarb applied at 112 standard rate recommended (60.25 g Pirimor 50 EC / 100 1 water). 3. Diazinon applied at 112 label rate (30 ml Diazinon 80 EC / 100 I water). 4. Acephate applied at 112 label rate (50 g Orthene 75 EC / 100 1 water). RESULTS The results are summarised in Tables 4 and 5. Table 4: Mean number of live adult Scaptomyza flava in experiment one after 48 h. Treatment Mean number of live insects per cage 1- Untreated control 8.3 a 2- Carbaryl 7.3 a 3- Permethrin 3.3 b 4- Pirimicarb 0.0 c 5- Diazinon 0.0 c 6- Acephate 0.0 c Treatments accompanied by the same letter are not significantly different at P� 0.05 (ANOVA followed by LSD test for separation of means). Appendices Table 5: Mean number of live adult Scaptomyza flava in experiment two after 48 h. Treatment Mean number of live insects per cage 1 - Untreated control 9 2- Pirimicarb ( 112 rate) 0 3- Diazinon ( 112 rate ) 0 4- Acephate ( 112 rate ) 0 EVALUATION OF CONTROL 342 From Tables 4 and 5 it can be seen that pirimicarb, diazinon and acephate gave complete mortality of adult Scaptomyza flava. Carbaryl had practically no effect and permethrin was intermediate. A p p e n d i x 6 THE ABILITY OF SCAPTOMYZA ELMOI TO DEVELOP ON CHINESE CABBAGE INTRODUCTION IN order to detennine whether another species of Scaptomyza collected from the field study area is able to leaf mine on Chinese cabbage, adults of Scaptomyza elmoi were released onto plants in an experiment. MA TERIALS AND METHODS Four one-month old Chinese cabbage plants at the 3 to 4 leaf stage were caged with 5 pairs of Scaptomyza elmoi obtained from the field by sweep netting. The insects were not provided with water or honey solution. Plants were grown under natural lighting in a greenhouse in plastic pots (6.3 cm square) containing a soilless growing medium (horticultural sphagnum peat moss, venniculite and perlite). Temperature in the experimental chamber was maintained at 10 ± 2°C (night) and 1 8 ± 2°C by day and natural daylength (1Oh light: 14h dark cycle). RESULTS After 2-3 days all insects were dead. No feeding punctures were found on the plants and no eggs had been laid. The plants were kept for more than 3 weeks with no evidence of larval development The results comlnll that Scaptomyza elmoi cannot leaf mine and develop on Chinese cabbage. Table 6: Date 1 5. 1 1 . 1990 22. 1 1 . 1 990 29. 1 1 . 1990 6. 1 2. 1 990 1 3. 1 2. 1990 20. 12.1990 27. 12. 1990 3. 1 . 199 1 1 0. 1 . 1 99 1 17. 1 . 199 1 24. 1 . 1991 3 1 . 1 . 199 1 7 . 2. 199 1 14. 2. 199 1 2 1 . 2. 1 99 1 A p p e n d i x 7 SEASONAL LIFE CYCLE OF S. FLAVA Numbers of Scaptomyza flava recovered by three different sampling methods from Chinese cabbage over a two-year period Week Number of Number of Number of adult insects adult insects larvae captured by recovered from recovered from sweep netting water trap ten leaves 1 4 8 10 2 5 1 6 20 3 20 1 5 70 4 35 1 0 20 5 20 3 30 6 30 19 1 20 7 27 20 65 8 30 1 5 46 9 35 4 30 10 10 1 3 1 1 60 40 4 1 2 25 3 2 13 24 1 2 3 14 15 0 1 15 18 19 0 Appendices 345 28. 2. 1991 16 18 1 8 8 7. 3. 1 99 1 17 14 4 1 5 1 5. 3. 1 99 1 1 8 1 7 0 2 22. 3. 1 99 1 1 9 1 0 0 0 29. 3. 1 99 1 20 9 2 1 0 5. 4. 1 99 1 2 1 0 5 40 1 2. 4. 1 99 1 22 3 5 1 2 1 8. 4. 1 99 1 23 60 10 18 26. 4. 1 99 1 24 17 6 28 3. 5. 199 1 25 25 2 60 1 0. 5. 1 99 1 26 26 1 50 17. 5. 1 99 1 27 1 20 0 5 24. 5. 1 99 1 28 35 2 5 3 1 . 5. 1 99 1 29 10 1 25 6. 6. 1 99 1 30 30 3 4 13. 6. 1 99 1 3 1 50 6 0 20. 6. 1 99 1 32 24 1 0 6 27. 6. 1991 33 15 1 5 8 4. 7. 1 99 1 34 25 8 32 1 1 . 7. 1 99 1 35 20 1 25 1 8. 7. 1 99 1 36 10 0 20 25. 7. 1 99 1 37 30 1 10 Appendices 346 1 . 8. 1 99 1 38 35 1 10 8 . 8. 1 99 1 39 100 1 2 15. 8. 1991 40 78 4 9 22. 8. 1 99 1 4 1 54 7 0 30. 8. 1 99 1 42 25 10 1 0 6 . 9. 1 99 1 43 24 8 20 13. 9. 1 99 1 44 4 3 25 20. 9. 199 1 45 25 3 35 27. 9. 1991 46 50 2 60 4. 10. 1 99 1 47 60 5 60 1 1 . 10. 1 99 1 48 56 1 5 30 1 8. 1 0. 1 99 1 49 65 24 103 25. 1 0. 1991 50 75 38 83 1 . 1 1 . 1 99 1 5 1 45 20 20 8 . 1 1 . 199 1 52 1 30 1 20 1 5. 1 1 . 199 1 53 100 1 10 22. 1 1 . 199 1 54 20 24 29. 1 1 . 1991 55 160 5. 1 2. 199 1 56 160 1 2. 1 2. 199 1 57 35 19. 1 2. 1 99 1 58 40 � 26. 1 2. 1991 59 20 Appendices 347 2. 1 . 1992 60 80 9. 1 . 1992 6 1 55 16. 1 . 1992 62 1 12 23. 1 . 1992 63 1 20 30. 1 . 1992 64 45 6. 2. 1 992 65 30 13. 2 . 1992 66 45 20. 2. 1992 67 5 27. 2. 1 992 68 5 5. 3 . 1992 69 20 1 2. 3. 1992 70 1 19. 3. 1992 7 1 5 26. 3. 1992 72 8 2. 4. 1992 73 10 9. 4. 1992 74 8 17 . 4. 1 992 75 15 24. 4. 1 992 76 25 30. 4. 1 992 77 32 8. 5. 1992 78 48 15 . 5. 1992 79 1 20 22. 5. 1992 80 72 29. 5 . 1992 8 1 95 Appendices 348 5. 6. 1992 82 68 12. 6. 1992 83 300 19. 6. 1992 84 1 20 26. 6. 1992 85 49 3. 7. 1992 86 30 10. 7 . 1992 87 25 17. 7. 1992 88 14 24. 7. 1992 89 4 3 1 . 7 . 1992 90 7 7. 8 . 1992 9 1 7 15. 8 . 1992 92 29 22. 8. 1992 93 90 29. 8 . 1992 94 50 7. 9. 1992 95 10 Appendices 349 Table 7 :Numbers of Scaptomyza flava recovered by three different sampling methods from turnip over a one year period Date Week Number of Number of Number of adult insects adult insects larvae captured by recovered from recovered from sweep netting water trap ten leaves 1 5. 1 1 . 1990 1 3 16 10 22. 1 1 . 1990 2 9 8 5 29. 1 1 . 1990 3 26 25 1 2 6. 1 2. 1990 4 37 30 1 1 3 . 1 2. 1990 5 10 2 1 3 20. 12. 1990 6 1 8 1 6 30 27. 12. 19 7 60 30 0 3. 1 . 199 1 8 55 1 2 0 10. 1 . 199 1 9 30 3 0 17. 1 . 199 1 10 20 2 0 24. 1 . 199 1 1 1 30 4 2 3 1 . 1 . 199 1 1 2 6 1 3 7. 2. 199 1 1 3 6 2 4 14. 2. 199 1 1 4 1 0 0 9 2 1 . 2. 199 1 15 1 2 18 9 Appendices 350 28. 2. 1991 1 6 1 8 1 8 1 0 7. 3 . 199 1 17 14 4 4 1 5. 3. 199 1 1 8 20 1 26 2 1 . 3. 199 1 1 9 7 0 48 28. 3. 1 99 1 20 10 2 60 5. 4. 199 1 2 1 2 1 8 50 1 2. 4. 1991 22 100 5 42 1 8. 4. 199 1 23 25 10 38 26. 4. 199 1 24 1 1 6 33 3. 5. 199 1 25 60 2 30 1 0. 5. 199 1 26 80 1 40 17. 5. 199 1 27 60 0 37 24. 5. 1 99 1 28 1 10 2 30 3 1 . 5. 199 1 29 70 1 30 6. 6. 199 1 30 80 3 20 1 3. 6. 199 1 3 1 90 6 4 20. 6. 199 1 3 2 104 4 5 27. 6. 199 1 33 30 15 4 4. 7. 199 1 34 70 5 5 1 1 . 7 . 199 1 35 70 2 1 5 1 8. 7. 199 1 36 75 0 1 0 25. 7 . 199 1 37 60 1 6 Appendices 35 1 1 . 8. 199 1 38 55 1 0 8. 8. 199 1 39 100 1 4 15. 8. 199 1 40 72 4 0 22. 8. 199 1 4 1 40 4 15 30. 8. 1991 42 9 10 20 6. 9. 199 1 43 45 8 25 13. 9. 199 1 44 9 3 20 20. 9. 1991 45 39 2 1 6 27. 9. 1991 46 40 2 1 6 4. 10. 199 1 47 60 5 1 6 1 1 . 1 1 . 199 1 48 65 15 1 4 1 8. 1 1 . 199 1 49 75 24 1 1 25. 1 1 . 1991 50 75 35 10 1 . 1 1 . 199 1 5 1 60 15 13 8. 1 1 . 199 1 52 40 1 2 15. 1 1 . 1991 53 150 4 22. 1 1 . 199 1 54 99 29. 1 1 . 199 1 55 39 Appendices 352 Table 8:Number of Scaptomyza elmoi & Scaptomyza fuscitarsis captured by 10 sweep net samples from Chinese cabbage over a one year period Week Date Number Number of adult of adult S.elmoi S. fuscitarsis 1 3 1 . 10.1991 0 1 2 08. 1 1 . 1991 0 0 3 1 5. 1 1 . 199 1 2 0 4 22. 1 1 . 1991 0 0 5 29. 1 1 . 1991 1 0 6 05. 12 .1991 7 3 7 1 2. 1 2. 1991 5 0 8 19. 1 2. 199 1 0 0 9 26. 12.199 1 3 2 10 02.0 1 . 1992 0 0 1 1 09.01 . 1992 2 0 1 2 1 6.01 . 1992 30 25 1 3 23.0 1 . 1992 1 3 20 1 4 30.01 . 1992 2 2 1 5 06.02.1992 0 0 1 6 13.02. 1992 4 2 Appendices 353 17 20.02. 1992 7 2 1 8 27.02. 1992 0 0 19 05.03. 1 992 2 0 20 1 2.03 .1992 0 0 2 1 1 9.03.1992 4 0 22 26.03. 1992 2 0 23 02.04. 1992 4 0 24 09.04. 1992 1 0 25 17.04. 1992 0 0 26 24.04. 1992 0 0 27 30.04. 1992 2 0 28 08.05. 1992 0 0 29 1 5.05.1992 0 0 30 22.05.1992 0 0 3 1 29.05. 1992 0 0 32 05.06.1992 0 0 33 1 2.06. 1992 0 0 34 19.06.1992 0 0 35 26.06. 1992 3 0 36 03.07. 1992 1 3 0 37 10.07.1992 6 0 - 38 17.07 .1992 2 0 Appendices 354 39 24.07 . 1992 1 0 40 3 1.07. 1992 1 0 4 1 07.08.1992 1 0 42 15.08. 1992 1 0 43 22.08.1992 0 0 44 30.08.1992 0 0 45 07.09.1992 0 0 46 15.09. 1992 0 0 47 22.09.1992 0 0 48 29.09.1992 0 1 49 08. 10. 1992 0 1 50 1 5. 10. 1992 0 1 5 1 22. 10. 1992 0 1 Appendices 355 Table 9:Plant measurements and numbers of larvae from samples of five Chinese cabbage plants. No. of Date No. of Leaf areal Leaf Height No. of sample leaves ! plant (em2) area of plant larvae! plant mined (em) plant (%) 1 15. 1 1 .91 5 350 3 1 8 2 2 30. 1 1 .9 1 3.4 47 2.6 1 3 2.2 3 1 2. 1 2.91 6.3 177 0.05 20 0.6 4 26. 1 2.91 3.2 37 3 1 1 2 5 10. 1 .92 4 244 3.2 26 3 6 24. 1 .92 6.4 1560 5.5 22 5.6 7 6.2.92 9 973 4.4 67 1 .6 8 20.2.92 12.4 2226 0.5 39 2 9 5.3.92 9 905 7.4 30.5 8.4 10 19.3.92 7 520 1 8.5 30 4.2 1 1 2.4.92 7.6 645 6.2 3 1 3 1 2 1 6.4.92 7 796 1 1 30 3.8 13 1 .5.92 6.2 290 5 23 3 14 1 5.5.92 7 358 8.4 26 5.4 15 2 1 .5 .92 8 362 9 26 6.6 16 1 2.6.92 9 767 4 32 5 17 26.6.92 1 1 1077 1 2 3 5 5 Appendices 356 1 8 10.7.92 10 999 2.2 25 4 19 25.7.92 5 400 10 14 6 20 10.8.92 5 546 0 1 5 0 2 1 24.8.92 7 968 5 17 4 22 10.9.92 5 1 100 0 22 0 23 26.9.92 5 1050 1 2 26 10 24 15. 10.92 6 1 170 20 29 12 25 1 . 1 1 .92 5 3 10 3 . 1 1 4 1 26 15. 1 1 .92 5 200 1 5 20 6 27 30. 1 1 .92 7 600 1 8. 1 22 7.4 28 12. 1 2.92 9 1000 1 6.7 26 5.6 29 26. 12.92 5 5 1 1 2 15 3 30 10. 1 .93 6 304 15 18 5 A p p e n d i x 8 CULTURAL NOTES ON HOST PLANTS OF SCAPTOMYZA FLAVA INTRODUCTION SCAPTOMYZA flava is an oligophagous insect, with a range of host plants (cabbage, turnip, radish, cauliflower, hedge mustard, and other species) in the plant family Brassicaceae. A blotch leaf miner, ScaptomyzaJlava has been reared from a number of host plants and is considered a pest of several vegetable crops. However, some hosts appear to be more attacked than others especially Chinese cabbage and turnip (personal observations and see Chapter 3, section "Comparison of plant species as hosts for Scaptomyza flava"). CHINESE CABBAGE This vegetable sometimes called lettuce-cabbage could be grown more widely in New Zealand. Chinese cabbage is considered the most difficult brassica to consistently grow well. Being semi-tropical, it is very fast growing and capable of producing a 0.75 kg head, six weeks from planting. It is extremely sensitive to bolting at low temperatures and is susceptible to a large number of pests, diseases and physiological disorders (Anon, 1 984). There are now well over 200 varieties in commercial use. Chinese cabbage has evolved in a warm climate where days are short. They are sensitive to excessively high temperatures (over 30°C); some varieties have considerable cold tolerance and may withstand minus SOC in New Zealand, in good growing conditions. February-sown plants mature before winter; alternatively plants can be sown in spring for early summer harvest. 357 Appendix 358 The following are the main pests and diseases of Chinese cabbage: PESTS Slugs, cutwonns, leather jackets (Tipula spp.), cabbage root fly (Delia brassicaei , aphids (grey cabbage aphid Brevicoryne brassicae and peach-potato aphid Myzus persicae), Caterpillars (cabbage moth Mamestra brassicae2, and white butterfly Artogeia spp), insects with tunnelling larvae (leaf miners such as Phytomyza rufipes and Scaptomyza flava) may tunnel into leaves and stems. The cabbage stem weevil Ceuthorhynchus quadridens3 tunnels in stems, and thrips (Thrips tabaci). DISEASES Club root (Plasmodiophora brassicae), wirestem (Rhizoctonia solani), dark leaf spot (Alternaria brassicicola and brassicae), downy mildew (Peronospora parasitica) and soft rot (Erwinia carotovora). VIRUS DISEASES: Cauliflower mosaic virus and turnip mosaic virus PHYSIOLOGICAL DISORDERS: Tipbum / heart rot, boron deficiency, glassiness, nitrogen excesses and black leaf speck. TURNIP Turnips have a distinct flattened taproot, little or no neck, and hairy, coarse, yellow green leaves. There are both white - and yellow - fleshed varieties. Turnips are cool-season vegetables. Turnips can be sown over a longer period than Chinese cabbage through the spring until autumn. They mature in 30 - 80 days. 1 ,2,3 Not in New Zealand Appendix PESTS DISEASES 359 Aphids, caterpillars, grass grub (Costelytra zealandica) and wireworms. Leaf spot, rust, downy mildew and clubroot. CAULIFLOWER In most part of New Zealand, cauliflowers can be grown all year round, although some areas have a preferred season. In the past, certain winter-grown varieties were called broccoli. The various stages of cauliflower development are in many ways similar to those of the cabbage crops. They are difficult to grown in very hot, dry conditions, and their quality suffers equally under severe winter conditions. Except in mild climates, plants for setting out in early spring should be raised in very sheltered situations. RADISH Radishes are one of the quickest vegetables to raise. They grow best at moderate temperatures (lO·C - 1 8·C). Under favourable conditions, only 23 - 30 days are required from sowing to maturity. Ali A. Seraj, Plant protection Department, College of Agriculture, Shahid Chamran University, Ahwaz, Islamic Republic of mAN Tel (Home): 0098 61 23 878