Functional Sex Ratio in the Carmine Spider Mite1,2

Abstract

Functional sex ratio (no. sexually capable males : no. available females) of T. cinnabarinus was monitored throughout a colonizing episode. The results were compared with a model constructed from life table data. Because males are sexually capable throughout their adult lives and individual females are available only briefly, the functional sex ratio becomes markedly skewed towards males, particularly during the period of maximum dispersal from the host plant. Even when males are in abundance, guarding behavior is concentrated on those female deutonymphs nearest to emergence. These factors combine to (1) increase male competition for the few available females and (2) ensure that nearly all females are fertilized at or shortly after emergence.