Comparison of associative learning of host-related plant volatiles in two parasitoids with different degrees of host specificity, Cotesia marginiventris and Microplitis croceipes

The ability of parasitoids to learn a wide range of volatiles, including ecologically relevant and novel odors, and respond favorably to the learned stimuli has been documented for various species. Comparison of odor learning in closely related species can elucidate adaptive differences in species responses to infochemicals. The present study used a Y-tube olfactometer to compare odor learning and priming of behavioral responses of two parasitoids, Cotesia marginiventris (Cresson) and Microplitis croceipes (Cresson), to four selected host-related volatile compounds which have been previously shown to elicit behavioral response in both species; trans-2-hexanal, α-pinene, cis-3-hexenyl butyrate, and (E,E)-α-farnesene. The two parasitoid species differ in their degree of specialization at the host level with M. croceipes having a more specialized host range, but otherwise represent infochemical generalist parasitoid species at the plant level. Naïve females as well as females that had been trained to associate sugar water with the test compounds were tested. Compared to naïve females, trained females of C. marginiventris showed a significant increase in behavioral response to all four tested compounds. In contrast, trained females of M. croceipes showed a significant increase in behavioral response only to α-pinene, and (E,E)-α-farnesene. Overall, the species with a wider host range, C. marginiventris showed a greater learning-induced increase in response than the species with a relatively specialized host range, M. croceipes. The results imply that animals with different ecological constraints may show variations in learning. The adaptive significance of behavioral responses as related to dietary specializations of the parasitoids is discussed.