Some parasitoids oviposit in nonhosts. Parasitization of nonhosts potentially wastes gametes, risks the death of offspring, and reduces fitness. Associative learning, a strategy for efficient reproduction, has been observed in various parasitoid species. We conducted two types of experiments to reveal whether larval parasitoid wasps, Cotesia kariyai (Hymenoptera: Braconidae), learn associatively by ovipositing in nonhosts. In dissection experiments, we found wasp eggs in both host [Mythimna separata (Lepidoptera: Noctuidae)] and nonhost [Spodoptera litura (Lepidoptera: Noctuidae)] caterpillars. However, the mean number of eggs in nonhosts was significantly smaller than in hosts. In oviposition experiments, most naive C. kariyai females attacked both hosts and nonhosts. On the other hand, wasps that had previously attacked nonhosts tended to avoid them thereafter. We conclude that C. kariyai females may be able to detect and identify nonhost metabolites and/or cuticular hydrocarbons. Negative associative learning enhances C. kariyai reproductive success when hunting in complex host habitats.