Differences in food plant species of the polyphagous herbivore Mythimna separata (Lepidoptera: Noctuidae) influence host searching behavior of its larval parasitoid, Cotesia kariyai (Hymenoptera: Braconidae)

In tri-trophic interactions among plants, herbivorous insects, and parasitoids, the food plant species of herbivores may affect parasitoid performance, such as host searching behavior and development and survival of immature parasitoids in the host body. Here, we tested the effects of food plant species of the host Mythimna separata (Lepidoptera: Noctuidae) on host searching behavior (i.e., flight responses to host-infested plant volatiles [HIPVs] and antennal responses to host feces or fecal extract) by the larval parasitoid Cotesia kariyai (Hymenoptera: Braconidae). In laboratory tests, female wasps responded differentially to HIPVs and feces produced from host caterpillars on different diets. Female wasps showed stronger responses to HIPVs from infested maize than to those from infested daikon. Similarly, wasps showed stronger contact responses to feces from caterpillars fed on maize or kidney bean than to those fed on daikon or an artificial diet. Previous studies demonstrated that maize-fed caterpillars are suitable hosts, whereas daikon-fed caterpillars are unsuitable hosts, for parasitism by C. kariyai. Therefore, our results indicate that female wasps show stronger responses to the chemicals related to suitable hosts than to those of unsuitable hosts.