Density and Time Effects on Distribution and Survival of Lightbrown Apple Moth (Lepidoptera: Tortricidae) Larvae on Granny Smith Apples

Abstract

Distribution and survival of Epiphyas postvittana (Walker) larvae on 'Granny Smith' apples (Malus domestica Bork.) were examined in a laboratory study after a range of inoculation densities and establishment periods. First instars displayed a general trend of occurrence in the following order: off fruit > calyx > stem > cheek. Their survival was poor compared with 3rd and 5th instars and declined with time. The chance of survival was greatest when 1st instars occupied the cavity beneath the sepals of the calyx or assumed an internal position inside a tunnel. No 1st instars were found in the core after the longest establishment period (14 d). Distribution of 3rd and 5th instars was strongly influenced by inoculation density. At low densities the greatest proportion of 3rd instars occupied the calyx and stem cavities, but at high densities proportions were greatest off fruit and on the cheek. Typically, once 1-2 larvae had occupied the calyx cavity beneath the sepals and the stem cavity, the remainder moved elsewhere. Although 5th instars showed a similar change in location preference with increasing inoculation density to 3rd instars, the maximum number of larvae per apple was lower, reflecting more intense interference and competition. Although 3rd and 5th instars strongly favored the apple surface over internal positions, both instars were present in the core after a 7-d establishment period.