Hyperparasitoids exploit plant volatiles to locate their parasitoid host despite nonhost herbivore interference

Summary

Hyperparasitoids are ubiquitous components of terrestrial food webs. They must find their inconspicuous parasitoid host in a complex environment to generate offspring, but their foraging behaviour is poorly understood. Herbivore-induced plant volatiles (HIPVs) induced by parasitized caterpillars have been found to be exploited by hyperparasitoids in the cabbage system. However, the naturally occurring presence of nonhost organisms can interfere in HIPV production. It is unknown how hyperparasitoids respond to this source of variation in their foraging behaviour. We studied how the presence of nonhost herbivores affected foraging decisions of the hyperparasitoid Lysibia nana. In Y-tube olfactometer bioassays, we compared the preference of hyperparasitoids for volatiles from cabbage plants induced by single herbivory (host or nonhost), dual herbivory (host + nonhost) or uninfested cabbage plants. Following this, we conducted a common-garden experiment to study whether preferences observed in the laboratory are also apparent in the field. We found that L. nana preferred plants that were induced by its host, Cotesia glomerata-parasitized Pieris brassicae caterpillars. However, the volatiles of nonhost-induced plants hampered the hyperparasitoids' ability to locate host-induced plants in the Y-tube olfactometer. In particular, HIPVs induced by the nonhost caterpillar Mamestra brassicae in both single and dual herbivory hampered the hyperparasitoids' ability to locate host-induced plants. The presence of other nonhost herbivores feeding simultaneously on the same plants as host-containing herbivores did not interfere in L. nana's preference. In the field, hyperparasitoids could locate their host despite nonhost presence. Overall, these results indicate that host location errors by hyperparasitoids may occur during HIPV-guided foraging steps, which can be corrected by using more reliable cues after landing on the plant. This demonstrates the ability of higher trophic level organisms to exploit the scarce amount of available information to locate their host.