DENSITY AND TIME EFFECTS ON DISTRIBUTION AND SURVIVAL OF LIGHTBROWN APPLE MOTH (LEPIDOPTERA, TORTRICIDAE) LARVAE ON GRANNY-SMITH APPLES

Distribution and survival of Epiphyas postvittana (Walker) larvae on ' Granny Smith' apples (Malus domestica Bork.) were examined in a labora tory study after a range of inoculation densities and establishment pe riods. First instars displayed a general trend of occurrence in the fo llowing order: off fruit > calyx > stem > cheek. Their survival was po or compared with 3rd and 5th instars and declined with time. The chanc e of survival was greatest when 1st instars occupied the cavity beneat h the sepals of the calyx or assumed an internal position inside a tun nel. No 1st instars were found in the core after the longest establish ment period (14 d). Distribution of 3rd and 5th instars was strongly i nfluenced by inoculation density. At low densities the greatest propor tion of 3rd instars occupied the calyx and stern cavities, but at high densities proportions were greatest off fruit and on the cheek. Typic ally, once 1-2 larvae had occupied the calyx cavity beneath the sepals and the stem cavity, the remainder moved elsewhere. Although 5th inst ars showed a similar change in location preference with increasing ino culation density to 3 instars, the maximum number of larvae per apple was lower, reflecting more intense interference and competition. Altho ugh 3rd and 5th instars strongly favored the apple surface over intern al positions, both instars were present in the core after a 7-d establ ishment period.