The size‐number trade‐off and components of fitness in clonal parasitoid broods

Body size can strongly influence the components of fitness. We investigated the role of body mass in the reproductive success of the parasitoid Copidosoma bakeri (Howard) (Hymenoptera: Encyrtidae). Copidosoma bakeri develops polyembryonically, producing thousands of genetically identical individuals from one egg. In this species, the brood size and body mass of clonal individuals developing within a host are in a trade-off relationship, which flexibly responds to the environment while maintaining female-biased sexual size dimorphism. We addressed the following questions regarding several possible effects of body mass on male and female reproductive success. (1) Is longevity positively related to body size in both sexes? (2) Is potential fecundity positively related to female body size? (3) Is mating competitiveness positively correlated with male body size? We found that body size increased with longevity of females, but not of males. Copidosoma bakeri was weakly synovigenic; a few eggs were produced after female maturation. Also, egg volume increased with age of the females. We did not detect a relationship between body size and potential fecundity, but mated females produced more eggs than unmated females. Thus, larger females may increase their opportunities to mate, find hosts, and oviposit primarily by living longer. Male mating competitiveness was not related to body mass. Mating reduced male longevity, suggesting a cost of mating that was independent of body mass. Differences between males and females in the effects of body mass on longevity suggest sex-specific selection pressures on body mass that may explain female-biased sexual size dimorphism.