Parasitism overrides herbivore identity allowing hyperparasitoids to locate their parasitoid host using herbivore-induced plant volatiles.

Foraging success of predators profoundly depends on reliable and detectable cues indicating the presence of their often inconspicuous prey. Carnivorous insects rely on chemical cues to optimize foraging efficiency. Hyperparasitoids that lay their eggs in the larvae or pupae of parasitic wasps may find their parasitoid hosts developing in different herbivores. They can use herbivore-induced plant volatiles (HIPVs) to locate parasitized caterpillars. Because different herbivore species induce different HIPV emission from plants, hyperparasitoids may have to deal with large variation in volatile information that indicates host presence. In this study, we used an ecogenomics approach to first address whether parasitized caterpillars of two herbivore species (Pieris rapae and P. brassicae) induce similar transcriptional and metabolomic responses in wild Brassica oleracea plants and, second, whether hyperparasitoids Lysibia nana are able to discriminate between these induced plant responses to locate their parasitoid host in different herbivores under both laboratory and field conditions. Our study revealed that both herbivore identity and parasitism affect plant transcriptional and metabolic responses to herbivory. We also found that hyperparasitoids are able to respond to HIPVs released by wild B. oleracea under both laboratory and field conditions. In addition, we observed stronger attraction of hyperparasitoids to HIPVs when plants were infested with parasitized caterpillars. However, hyperparasitoids were equally attracted to plants infested by either herbivore species. Our results indicate that parasitism plays a major role in HIPV-mediated plant-hyperparasitoid interactions. Furthermore, these findings also indicate that plant trait-mediated indirect interaction networks play important roles in community-wide species interactions.