Oviposition Experience of Parasitoid Wasps with Nonhost Larvae Affects their Olfactory and Contact-Behavioral Responses toward Host- and Nonhost-Infested Plants.

In nature, parasitoid wasps encounter and sometimes show oviposition behavior to nonhost species. However, little is known about the effect of such negative incidences on their subsequent host-searching behavior. We tested this effect in a tritrophic system of maize plants (Zea mays), common armyworms (hosts), tobacco cutworms (nonhosts), and parasitoid wasps, Cotesia kariyai. We used oviposition inexperienced C. kariyai and negative-experienced individuals that had expressed oviposition behavior toward nonhosts on nonhost-infested maize leaves. We first observed the olfactory behavior of C. kariyai to volatiles from host-infested plants or nonhost-infested plants in a wind tunnel. Negative-experienced wasps showed significantly lower rates of taking-off behavior (Step-1), significantly longer duration until landing (Step-2), and lower rates of landing behavior (Step-3) toward nonhost-infested plants than inexperienced wasps. However, the negative-experience did not affect these three steps toward host-infested plants. A negative experience appears to have negatively affected the olfactory responses to nonhost-infested plants. The chemical analyses suggested that the wasps associated (Z)-3-hexenyl acetate, a compound that was emitted more in nonhost-infested plants, with the negative experience, and reduced their response to nonhost-infested plants. Furthermore, we observed that the searching duration of wasps on either nonhost- or host-infested plants (Step-4) was reduced on both plant types after the negative experiences. Therefore, the negative experience in Step-4 would be nonadaptive for wasps on host-infested plants. Our study indicated that the density (i.e., possible encounters) of nonhost species as well as that of host species in the field should be considered when assessing the host-searching behavior of parasitoid wasps.