The developmental strategies of endoparasitoid wasps vary with host feeding ecology

Abstract

Among the most important trade-offs in life history evolution is whether to grow larger at the cost of longer development time, or to develop more rapidly at the cost of reduced size. For insect herbivores, resolution of this trade-off is thought to be strongly influenced by feeding ecology and mortality risks. In contrast, how these factors might affect the developmental strategies of third trophic level organisms, like parasitoid wasps, is less understood. To address this question, we compared the development of larval endoparasitoids in the families Ichneumonidae and Braconidae that parasitize larval stage herbivores in the order Lepidoptera. The campoplegine ichneumonid Venturia canescens parasitized concealed hosts and exhibited a developmental strategy that favored progeny size over development time. In contrast, the closely related ichneumonid Campoletis sonorensis parasitized exposed hosts and exhibited the opposite strategy of favoring rapid development time over size. The microgastrine braconid Microplitis croceipes attacks partially concealed hosts and showed evidence of a trade-off between maximizing body size and minimizing development times. These results suggested that parasitoids attacking apparent, foliar-feeding hosts may favor rapid development time over size while parasitoids that attack concealed hosts favor size over development time. A broader survey of the literature supported the trends found in our experimental studies. The braconids and ichneumonids examined in this study also exhibit distinct differences in larval feeding and pupation behavior. These developmental traits did not appear to affect the size-development time continuum. However, these traits may affect the size range of hosts that larval endoparasitoids can successfully exploit.