Duration of plant damage by Heliothis virescens caterpillars affects attraction of two parasitoids with varying degree of host specificity (Microplitis croceipes and Cotesia marginiventris) to cotton

Herbivore-damaged plants release many types of volatile organic compounds (VOCs), which guide parasitoids to their herbivore hosts.  The quantity and quality of VOC blends may be affected by the duration of plant damage. We used as models Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), to address the evolutionary and mechanistic question of whether the degree of host specificity affects parasitoids’ use of plant VOCs for host location. Both species are larval endoparasitoids of Heliothis virescens, an important pest of cotton. Attraction of the parasitoids to VOCs emitted by undamaged (UD), fresh (6 hr infestation) damage (FD), and old (24 hr infestation) damage (OD) cotton plants infested by H. virescens larvae was investigated using a headspace volatile collection system coupled with four-choice olfactometer bioassay. The specialist showed a preference for host-damaged (FD and OD) plants over UD-plants. In contrast, the generalist could not discriminate among treatment plants. GC-MS analyses showed qualitative and quantitative differences in the VOC profiles of UD, FD and OD-plants which may explain the observed preferences of the parasitoids. These results suggest a temporal partitioning in the recruitment of specialist and generalist parasitoids to herbivore-damaged plants, and may have potential ramifications for interspecific competition between parasitoids.