Factors Determining Variation in Fecundity of the Light Brown Apple Moth, Epiphyas Postvittana (Walker) (Tortricidae).

Abstract

The large variation in fecundity in E. postvittana was associated with temperature, larval food plant, time of year each food plant occurs, and low-density larval crowding through mutual interference. Under field conditions, moths from larvae fed on curled dock, apple, plantain, white clover and capeweed laid > 50% of their eggs by 5-7 days old and > 80% by 8-12 days old. Cool conditions produced heavier individuals which lived longer and laid more eggs over an extended laying period. The fecundity and size (pupal weight) were probably influenced by the larval food plant and the time of year of feeding, presumably through seasonal variations in nutritive quality. Low-density larval crowding, despite excess food, significantly reduced fecundity and pupal weight; it occurs under natural conditions of high population density. The combined effect of these factors was cyclic variations in fecundity and size; more fecund, heavier individuals occurred during the cool wet months (winter generation adults) and less fecund, lighter individuals during the warm dry months (summer generation adults); spring generation adults were generally intermediate. The fecundity of E. postvittana can be adequately predicted from the number of egg-laying days.