Interactions between Anystis baccarum (Acari: Anystidae), a generalist predatory mite, and larvae of Epiphyas postvittana (Walker (Lepidoptera: Tortricidae), a pest of apples : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science in Plant Health at Massey University

Abstract

A large numbers of Anystis baccarum (Acari: Anystidae) were discovered living alongside of Epiphyas postvittana (Lepidoptera: Tortricidae) larvae known as light brown apple moth (LBAM) in shelter belt of acacia, Acacia reva (Leguminoseae: Sub family Mimosoidae). Few questions that needed to be answered were whether the mites actually feed on the LBAM larvae and what are their interactions. The objective of my study was to investigate the general characteristics of mite feeding on LBAM larvae, and to study the age, density, webs and defence behaviour of larvae as exogenous factors, and the effect of level of starvation and experience of mites as endogenous factors on foraging behaviour of A. baccarum. Eleven experiments were conducted under laboratory conditions. At 20 c, the average daily consumption rate of A. baccarum was 11.5 ± 52.68 neonate E. postvittana larvae of 1.484 mm in lenght and 0.231 mm in width. The predator spent 1106 ± 309 seconds mean feeding time, feeding on a neonate larvae of E. postvittana. A. baccarum is cannabalistic and survived 6.1 ± 2.28 days totaly deprived of food and water. Webs of E. postvittana larvae act as a physical barrier to attack of A. baccarum. When the webs were removed larvae upto eight days of age were consumed by A. baccarum, however survival from capture by mite increased with age. When the mite was given a choice between three different age groups of larvae, a higher number of neonate faivae were taken as the first choice, but the overall results showed the choice depends on random encounters between the predator and prey and prey avoidence behaviour of larvae. Spinning was the most frequent avoidence behaviour of larvae without webs. Spinning response occured less frequently with increased age of the larvae. The most common response of larvae in webs was quick movement fonnards or backwards. Starvation for 24 hours did not significantly increase walking speed of A. baccarum over walking speed of non-starved mites, but walking speed was decreased at 48 hr and 72 hr starvation. However, starvation increased prey capture of A. baccarum compared to non starved condition. Starvation also had a significant effect on number of captures at first encounter. A. baccarum with no experience of prey on apple shoots prefered to rest on branch of apple than leaf and fruit given that area of the branch is low, preference was even greater. On their search of alternative walking and resting periods, A. baccarum spent significantly more time walking than resting. When given experience of feeding a neonate larva of LBAM on branch, leaf or fruit, A. baccarum spent significantly more time walking on the location they were fed. In conclusion, the larvae of E. postvittana includes in to the list of prey of A- baccarum. If encounterd during their dispersal phase after hatching, possibilities are high that neonate larvae of E. postvittana to be preyed by A. baccarum ocurring in large numbers in orchid ecosystems in New Zealand. Studies on this predator-prey interaction opens new venues of research on generalised predator-prey interactions.