Progeny and Sex Allocation Decisions of the Polyembryonic Wasp Copidosoma floridanum

Abstract

1. The reproductive biology of the polyembryonic encyrtid wasp Copidosoma floridanum was examined in a series of laboratory experiments and related to observations from field collections. Females laid one or two eggs per host, producing broods comprised of all males, all females, or both sexes (mixed). Each egg produced multiple embryos that developed into either precocious larvae that never became adult or reproductive larvae that developed into reproductive adults. 2. The age of the host-egg when it was parasitized was found to have a substantial effect on offspring clutch sizes and sex ratios. (i) The clutch sizes and overall survivorship of female and mixed broods decreased with increasing host-egg age, whereas male clutch sizes and survivorship were relatively unaffected by host-egg age. (ii) Offspring sex ratios (proportion males) of mixed broods were higher in older hosteggs. (iii) Body sizes of males and females were negatively correlated with clutch size. Larger females had higher fecundities and larger males had greater mating abilities. 3. Host-egg age also affected competitive asymmetries between males and females. In young host-eggs, female precocious larvae were much more abundant than males and were instrumental in reducing the number of males in mixed broods. In older host-eggs, the numbers of male and female precocious larvae were much lower, and were approximately equal. As a result, sex ratios of mixed broods in older host eggs were closer to equality. 4. Ovipositing females responded to host-egg age and host encounter rates when making oviposition decisions. Females laid more female eggs in younger hosts and more mixed broods in older hosts. Females laid more mixed broods when encounter rates were low and more female broods when encounter rates were high