Factors affecting feeding site preferences of lightbrown apple moth, Epiphyas postvittana (Lepidoptera : Tortricidae), on apple trees in New Zealand

The infestation of apple (Malus domestica) trees by Epiphyas postvittana (W alker) larvae was studied over 3 years. Fresh damage to leaves increased pr ogressively during the season, although in Nelson it declined in April. Fru it damage was first detected in December and increased throughout the seaso n. The incidence of fruit damage was most strongly correlated with the surf ace area of fruit. Single leaves were the preferred feeding site for larvae on terminal shoots, although when whole branches were examined, most shelt ers occurred between two leaves. Feeding sites on fruit predominantly invol ved contact with a leaf or another apple. A field experiment examined the i nfluence of physical contact and fruit maturation on ;leafroller damage. E. postvittana larvae were offered a choice of feeding sites involving leaves and three types of "apple"; namely untreated apples, apples treated with c hlorethephon to promote ripening, and plastic balls. There was 16% more dam age on treated compared with untreated fruit, but similar levels of damage to leaves touching the three types of apple. Although riper fruit were more attractive to E. postvittana larvae, their preference for physical contact had a greater influence on the selection of feeding sites. The increase in fruit damage over time was mainly due to the increasing extent of contact between leaves and other fruit as the apples enlarged.