Behavioral responses of leafroller larvae to apple leaves and fruit

Larvae of Epiphyas postvittana and Planotortrix octo were released onto branches cut from apple trees, and allowed to colonize a range of types of artificial nests. Both species exhibited similar strong preferences for nests comprising leaf-leaf or leaf-fruitlet combinations, followed by nests comprising leaf-plastic leaf, leaf-plastic fruitlet or plastic leaf-fruitlet combinations. Nests involving fresh plant material alone (shoot, fruitlet or leaf alone) were also colonized to a lesser extent, but no larvae were found on nests consisting of plastic leaves or fruitlets alone or in combinations of the two. In another experiment, more E. postvittana larvae colonized nests with leaf and fruitlet combinations, compared to leaf and glass ball, or leaf and treated wax ball combinations, where the wax had been in contact with fresh apples or fruitlets. Choice tests, conducted using larval traps, showed that larvae were caught in traps baited with odors collected and released by wax which had been in contact with mature apples and leaves. Chloroform extracts from apple skin also caught larvae in choice tests. These results suggest that both physical and chemical cues are important to leafroller larval establishment.