Differences in larval feeding behavior correlate with altered developmental strategies in two parasitic wasps: implications for the size-fitness hypothesis

Parasitoid wasps have long been favored organisms for fundamental studies on reproductive strategies and life-history evolution. Progeny allocation models designed with parasitoids in mind assume that offspring develop by consuming most or all of the resources available from a single host, and that size is the most important factor affecting offspring fitness. Many parasitoids exhibit host usage patterns consistent with these assumptions, but our recent observations suggested that endoparasitic wasps in the family Braconidae often do not. To investigate how differences in host usage patterns might affect developmental strategies, we compared two related braconids with contrasting host usage patterns. Apanteles carpatus consumed virtually all host tissues during immature development, whereas Microplitis demolitor fed exclusively on host hemolymph and consumed a relatively small proportion of available host resources. Development time of M. demolitor was unaffected by host size, whereas development time of A. carpatus was much longer in small hosts than in large hosts. On the other hand, offspring size in M. demolitor correlated strongly with host size, but it correlated only weakly with host size in A. carpatus. Our results collectively suggest that selection has favored rapid development at the potential cost of reduced size in M. demolitor, and increased size at the potential cost of increased development time in A. carpatus. Tissue feeding appears to be more prevalent among parasitoids overall, but hemolymph feeding is the predominant pattern of host usage in several subfamilies of endoparasitic braconids. We argue that the relative importance of offspring size and development time will be influenced by host ecology and the effects of selected traits on parasitoid survival.