Some Factors Influencing Sex Ratio in Ascogaster Reticulatus Watanabe (Hymenoptera: Braconidae)

Abstract

Some candidate factors which seemed to influence the sex ratio in Ascogaster reticulatus Watanabe (Hymenoptera: Braconidae) were investigated. A. reticulatus in an arrhenotokous egg-larval parasitoid of the smaller tea tortrix, Adoxophyes sp. (Lepidoptera: Tortricidae). Females soon after mating (< 30 min) lacked the ability of sufficiently fertilize egges, so that the percentage of female progeny exceeded 50% one day after mating. This level (50-90%) was maintained throughout the rest of their life span. Neither the age (1-6 days) nor the size (91-242 egges) of host egg masses on which a mated female deposited her eggs affected the sex ratio of the progeny. In the course of oviposition (ca. 1 hr) of a mated female on an egg mass, there was no significant difference between the number of male and female progeny during the first 30 min when the rate of oviposition was relatively high, but the female progeny pre-dominated during the next 30 min when the rate was low. During the course of oviposition, the speed of deposition of female eggs was rather constant but that of male egges decreased gradually as time elapsed. These results suggest that one of the factors controlling the sex ratio of A. reticulatus is the rate of oviposition. © 1988, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.