Venom is beneficial but not essential for development and survival of Nasonia

Parasitoid wasps sting and inject venom in arthropod hosts, which alters host metabolism and development while keeping the host alive for several days, presumably to induce benefits for the parasitoid young.Here we investigate the consequences of host envenomation on development and fitness of wasp larvae in the ectoparasitoid Nasonia vitripennis, by comparing wasps reared on live unstung, previously stung, and cold-killed hosts. Developmental arrest and suppression of host response to larvae are major venom effects that occur in both stung and cold-killed hosts, but not unstung hosts; while cold-killed hosts lack venom effects that require a living host. Thus, cold-killed hosts mimic some of the effects of venom, but not others.Eggs placed on live unstung hosts have significantly higher mortality during development, however successfully developing wasps from these hosts have similar lifetime fecundity to wasps from cold-killed or stung hosts. Therefore, although venom is beneficial, it is not required for wasp survival.While wasps developing on cold-killed versus stung hosts have similar fitness, multiple generations of rearing on cold-killed hosts results in significant fitness reductions of wasps.We conclude that the largest benefits of venom are induction of host developmental arrest and suppression of host response to larva (e.g. immune responses), although more subtle benefits may accrue across generations, or under stressful conditions.