Parasitoid Increases Survival of Its Pupae by Inducing Hosts to Fight Predators

Many true parasites and parasitoids modify the behaviour of their host, and these changes are thought to be to the benefit of the parasites. However, field tests of this hypothesis are scarce, and it is often unclear whether the host or the parasite profits from the behavioural changes, or even if parasitism is a cause or consequence of the behaviour. We show that braconid parasitoids (Glyptapanteles sp.) induce their caterpillar host (Thyrinteina leucocerae) to behave as a bodyguard of the parasitoid pupae. After parasitoid larvae exit from the host to pupate, the host stops feeding, remains close to the pupae, knocks off predators with violent head-swings, and dies before reaching adulthood. Unparasitized caterpillars do not show these behaviours. In the field, the presence of bodyguard hosts resulted in a two-fold reduction in mortality of parasitoid pupae. Hence, the behaviour appears to be parasitoid-induced and confers benefits exclusively to the parasitoid

Context-dependent fitness effects of behavioral manipulation by a parasitoid

Many true parasites and parasitoids modify the behavior of their host, and most of these changes are thought to benefit the parasites. However, field tests of this hypothesis are scarce. We previously showed that braconid parasitoids (Glyptapanteles sp.) induce their caterpillar host (Thyrinteina leucocerae) to behave as a bodyguard of the parasitoid's pupae; they stand bent over the pupae and violently lash out at predators approaching them, resulting in reduced predation of parasitoid pupae on guava trees in the field. In contrast, we show here that this behavioral manipulation does not result in increased parasitoid survival on eucalyptus trees, an introduced host plant species. Hence, the effects of behavioral manipulation of the host depend on the ecological context. We hypothesize that this is due to a different species composition of the community of predators and hyperparasitoids on the 2 host plant species. Our results show that fitness effects of behavioral manipulation should be evaluated in a setting that includes all relevant components of the natural food web. Copyright 2009, Oxford University Press.