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    A study of root aphid Aploneura lentisci Pass. biology and root aphid-host interactions with perennial ryegrass/endophyte associations in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Entomology at Massey University, Manawatū, New Zealand
    (Massey University, 2019) Müller, Jana Leonie
    The root aphid Aploneura lentisci Pass. is an underestimated, under-researched pasture pest likely to become more problematic in New Zealand if the environmental temperature and the frequency of water deficit stress increase, as predicted. The research presented here aimed at gaining first insights into its biology and interaction with plants and endophytes to promote future pest management research. For this purpose, root aphids were observed in model systems (in climate chambers, glasshouse or insectary; in empty microcentrifuge tubes or on diploid perennial ryegrass Lolium perenne L. plants grown on nutrient-enriched agar, with or without endophy Epichloë festucae var. lolii [Latch, M.J. Chr. & Samuels] C.W. Bacon & Schard of the AR1, AR37 or common-toxic CT strains). Apterous neonate offspring, the presumed main dispersal stage of A. lentisci, survived up to four weeks without food (median survival: 8 days). On endophyte-free, mature ryegrass kept at 17 to 21 °C, neonates developed to adults within three to four weeks and lived about two months, feeding mainly on young roots of first and second branching order. Taking into account lower outdoor temperatures, root aphids are thus likely to complete six to nine generations per year in the field. Adults produced 39 to 70 offspring over their lifetime. Presuming a similar nymphal mortality in the field as in the experiments, outdoor root aphid populations could theoretically multiply 23- to 45-fold at each generation. Root aphids raised on endophyte-infected, mature plants were shorter-lived than peers raised on endophyte-free plants. Most aphids on AR37-infected plants did not even reach reproductive maturity. The response to CT-infection was dependent on the plant genotype. Why AR1-infected plants frequently support larger root aphid populations than endophyte-free plants in the field could not be explained by the data collected, however. Root aphid feeding affected the root biomass but not the shoot biomass of perennial ryegrass in the experimental environment. This finding differed from previous reports. Furthermore, colour analyses suggested root aphid feeding could modify some leaf properties. More research will be required to confirm these findings and assess whether irrigation or fertilisation could mitigate root aphid yield losses in the field.
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    Aspects of the biology and ecology of Acyrthosiphon kondoi shinji (Homoptera: Aphididae): a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biology at Massey University
    (Massey University, 1977) Henderson, Neville Clifford
    The biology and ecology of the blue-green lucerne aphid, Acyrthosiphon kondoi Shinji, was studied in the Palmerston North area for one year. Observations on the morphology of the developmental stages and morphs of A. kondoi are presented. Winter and spring peaks in the A. kondoi numbers occurred and the aphid can survive on lucerne all year round. The aphid colonies undergo a population cycle involving a population build up, high numbers, a decline in numbers, and a period of low numbers which persists until the next population build up. The stage of the cycle is apparent from the pattern of dispersion of the aphids on the plant and the number of alates present. A. kondoi appears to be continuously viviparous and parthenogenetic. throughout the year, as no sexual forms were found. High numbers of A. kondoi migrate by flying. A distinct spring peak in flight was observed with periods of lesser flight at other times. Some synchrony between the periods of flight and the number of aphids and alates on the plants was observed. Factors controlling the A. kondoi population were studied. The predators, and an entomophthorous fungi which attacked A. kondoi were identified, but no evidence of parasitism of A. kondoi in the field was observed. The predators did not prevent the spring population peak of A. kondoi, because of the low predator numbers and their poor synchronisation with the aphid population. Predator exclusion cage studies indicated that predators, especially Nab is maoricus. prevented a summer-autumn A. kondoi population peak. N. maoricus consumed on average 11.25 A. kondoi per day in the laboratory. The state of host plant growth is important in the occurrence of population cycles, and lucerne management practices can affect this considerably. Growing lucerne appears most suitable. Flowering of lucerne is not unfavourable to A. kondoi. A decline in the plant condition is partially involved in the population decline. Cycles of the A. kondoi population occur independently of climate, though the maximum number of aphids reached in each cycle is probably dependent on climatic factors. Local, extreme weather conditions nay temporarily affect A. kondoi numbers. The population cycle involves self-regulation and can probably occur independently of extrinsic factors. It involves a rise and fall in the fecundity and reproductive rate,and the production of increasing numbers of alates as the cycle progresses. These changes could account for a considerable part of the population decline observed in a population cycle.