Host searching behavior of females of the endoparasitoid Toxoneuron nigriceps Vierick (Hymenoptera: Braconidae) was observed in the field for three tobacco herbivores, Heliothis virescens (F.), Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), and Manduca sexta L. (Lepidoptera: Sphingidae). The only developmentally suitable host for the parasitoid was H. virescens. Hovering, searching, and oviposition (for plants with herbivores) by T. nigriceps were observed for a combination of two plant types, plants with only herbivore-induced plant volatiles or damaged plants with herbivores, and three insect species. The six treatments were as follows: (1) plants with only H. virescens-induced plant volatiles, (2) plants with only H. zea-induced plant volatiles, (3) plants with only M. sexta-induced plant volatiles, (4) plants damaged by H. virescens, (5) plants damaged by H. zea, and (6) plants damaged by M. sexta. Parasitoid females readily hovered around and searched on plants of both types. However, females spent more time foraging for H. virescens than for the nonhosts, H. zea and M. sexta. For plants with only herbivore-induced plant volatiles, T. nigriceps females spent more time searching on H. virescens plants than on H. zea and M. sexta plants. For damaged plants, parasitoid females visited more H. virescens plants than M. sexta plants and spent more time searching for H. virescens larvae than for M. sexta and H. zea larvae. Even though T. nigriceps females laid eggs in M. sexta and H. zea larvae, oviposition was higher for H. virescens than for the nonhosts. In conclusion, T. nigriceps females utilized more of their energy searching for and parasitizing H. virescens over the nonhosts on tobacco.

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