The evolution of host utilization strategy: At what timing parasitoids attack and consume their host

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 its maturation (“koinobiont”). The timing at which wasps’ larvae start consuming the host after the attack, referred to as Parasitoid Emerging Timing (PET) in this article, is a life-history trait that is correlated to other life history traits (e.g., lifespan and body size). Consequently, the evolution of PET has been studied as an explanation for the diversity of life-history strategies in parasitoid wasps. Using statistical analyses, previous studies have provided support for the association between PET and other life history traits. However, these results lack an adaptive evolutionary explanation necessary to establish PET as a key factor in life-history diversity. In this study, we develop mathematical models to examine the evolutionary associations between PET and other life-history traits. Specifically, we studied the evolutionary dynamics of PET and resulting life history characteristics of host exploitation. Our results show that the reproductive values differ depending on the developmental stage of hosts and determine which stage parasitoids exploit. We discuss some empirical studies support that host density and reproductive value affect PET. Additionally, the evolution of PET can profoundly alter the life-cycles of parasitoid wasps. For example, in species with late PET, wasps attack young hosts that initially have low reproductive value, but only consume them after the hosts mature and their reproductive value increases. These findings suggest that PET may be a driver of the syndrome involving multiple traits related to host utilization in parasitoid wasps. The high diversity of parasitoid wasps provides a rich system for testing hypotheses about life-history syndromes. By linking PET to broader life-history strategies, this study lays a theoretical foundation for understanding life-history syndromes in parasitoid wasps.