Behavioral responses of a specialist parasitoid, Microplitis croceipes and a generalist parasitoid, Cotesia marginiventris to host related volatiles

The use of parasitic wasps (parasitoids) as biological pest control agents is increasingly gaining acceptance as an important integrated pest management (IPM) tactic. As an indirect defense to herbivore attack, plants release many types of VOCs, which guide parasitoids to their herbivore hosts. These VOCs could be categorized as those released from i) undamaged plants (passively released volatiles), ii) freshly damaged plants and, iii) old damaged plants. Despite the intense interest in the mechanisms of host-parasitoid interactions, only a few studies have compared behavioral responses of specialist (species with a narrow host range) and generalist (species with a broader host range) parasitoids to different categories of host related VOCs. We used as models, two parasitoids with different degree of host specificity, Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), to address the evolutionary and mechanistic question of whether specialist and generalist parasitoids differ in their use of VOCs for host location. Both species belong to the same family (Hymenoptera: Braconidae) and are important parasitoids of caterpillar pests of cotton. Specifically, we hypothesized that the specialist will show greater attraction to VOCs released by old damaged plants, while the generalist will show greater attraction to VOCs released by freshly damaged plants and those released passively by undamaged plants. To test this hypothesis, the responses of both parasitoid species to different categories of VOCs were compared in four-choice olfactometer bioassays. The ecological significance and practical implications of the results are discussed