Changes in orientation and activity behaviours of the lightbrown applemoth, Epiphyas postvittana (Walker)(Lepidoptera: Tortricidae), in response to host plant volatiles : a dissertation submitted in partial fulfilment of the requirements for a Post Graduate Diploma in Horticultural Science

Abstract

The lightbrown apple moth (Epiphyas postvittana) is a serious insect pest of New Zealand horticulture. This is particularly so in apple production, where in addition to direct crop losses caused by larval feeding, larval presence on fruit at harvest pose a serious risk to apple exports due to quarantine considerations. Management of this insect is primarily achieved through insecticide use. However, reliance on broadspectrum insecticides for insect management is increasingly seen as an unsustainable practice. An increasing number of researches are examining the interactions between insects and their host plants, in the search for more environmentally benign and ecologically sustainable insect pest management practices. In particular, the role that olfactory cues play in host plant location and feeding/oviposition, are considered to offer potential for such management. This study describes the behavioural changes of neonate E. postvittana to three host plant volatiles. Larvae were exposed to the olfactory cues provided by a range of concentrations of hexenol (a green leaf volatile) and ethyl caproate (a volatile of apple fruit), and apple fruit wax extract (a mixture of >150 volatiles). Larval behaviour in arena was recorded onto video tape and quantified by image analysis, to produce a model of larval movement. Apple wax extract was shown to have the greatest influence on larval behaviour, by significantly reducing the speed of larval locomotion (P<0.001) and stationary time (P<0.01). However, this significant effect was found only when the lid of the behavioural arena was left off, suggesting a role of the volatile concentration in the arena air space. Exposure to hexenol was also found to reduce the rate of larval locomotion, at a 1 % concentration (P<0.001) and a 10 % concentration (P<0.01). In addition, a significant (P<0.05) quadratic effect was found for three concentrations of hexenol, with speed decreasing nonlinearly as concentration increased. Ethyl caproate resulted in the least behavioural influence, with significant differences in the rate of larval locomotion (P<0.05) found only for larvae exposed to the highest concentration (10%). In another experiment, a methodology used by Suckling and Ioriatti ( 1996) to demonstrate the attractiveness of apple fruit wax extract to neonate E. postvittana, was repeated. The repeated trial was successful, with more larvae of E. postvittana caught in traps baited with apple wax than in control traps (P<0.001). The use of image analysis as a tool to describe larval behaviour is critically examined. The image analysis system used in this study required compromises in the experimental methodology that acted to limit the underlying aim of the study. However, despite these limitations it was considered that the technology can describe larval behaviour accurately and precisely, and if used with a clear understanding of system limitations, the technology can be a useful tool with which to examine insect/host plant interactions.