Symposium: Insect Behavioral Ecology-'88: Clutch Size, Sex Ratio and Mating by the Polyembryonic Encyrtid Copidosoma Floridanum (Hymenoptera: Encyrtidae)

Abstract

Most parasitoids alter the clutch size and sex ratio of their progeny by facultatively controlling the number of eggs they oviposit and fertilize. However, in polyembryonic parasitoids clutch size and possibly sex ratio are also influenced by progeny development, because the eggs of these parasitoids produce multiple offspring. In this study the clutch size and sex ratio of the polyembryonic encyrtid Copidosoma floridanum (Ashmead) were examined in relation to current theory. The majority of C. floridanum broods collected from the field were comprised of males and females (i.e. mixed). No differences were found in the secondary clutch sizes of all male, all female or mixed broods. Mixed broods from the field and laboratory had median secondary sex ratios of 0.03 and 0.02 respectively. In mating experiments, 95% of females were mated when the sex ratio was @> 0.03, suggesting that only enough males to mate all females were produced in mixed broods. Laboratory studies demonstrated that C. floridanum produced a mixed brood by laying 1 female and 1 male egg. Thus, the highly female biased sex ratio of a C. floridanum mixed brood was due to an alteration of the primary sex ratio during the course of male and female egg development. Factors that might influence the sex ratio shift in mixed broods, and hypothetical conditions under which C. floridanum might preferentially produce single sex and mixed broods are discussed.