The evolution of host exploitation by parasitoid wasps: the timing of attack and consumption

In some parasitoid wasp species, larvae consume their host immediately after hatching (“idiobiont”), while in other species, larvae delay the consumption of the host until the maturation of the host (“koinobiont”). The delayed emergence is a life-history trait associated with numerous life-history traits including lifespan and body size. Consequently, the evolution of delayed emergence has been studied as an explanation for the diversity of life-history strategies in parasitoid wasps. Previous studies have provided support for the association between delayed emergence trait and other life-history traits such as fecundity and parasitoid-induced additional mortality. However, only poorly known is the adaptive significance of delayed emergence. As a result, we have little understanding of what the key factor in life-history diversity in parasitoid wasps is. In this study, we develop mathematical models to examine associations between delayed emergence trait and other life-history traits. Specifically, we studied the evolutionary dynamics of delayed emergence and resulting life-history characteristics of host exploitation. Our results predict that the reproductive values vary with which of the developmental stages of hosts they parasitize. Reproductive values thus determine the optimal target of attacking for parasitoids, with several empirical studies supporting the prediction. Additionally, the evolution of delayed emergence can profoundly alter the life-cycles of parasitoid wasps. For example, in species with delayed emergence, wasps attack young hosts that initially have low reproductive value for parasitoids, but only consume them after the hosts mature and their reproductive value increases. These findings suggest that delayed emergence may be a driver of the syndrome involving multiple traits related to host exploitation in parasitoid wasps. The high diversity of parasitoid wasps therefore provides a rich system for testing hypotheses about life-history syndromes. By linking delayed emergence to broader life-history strategies, this study lays a theoretical foundation for understanding life-history syndromes in parasitoid wasps.