Host recognition by the specialist endoparasitoid Microplitis croceipes (Hymenoptera: Braconidae): Role of host- and plant-related volatiles

The specialist parasitoid Microplitis croceipes Cresson can parasitize only noctuid larvae in the genera Helicoverpa and Heliothis. To be successful in their search for hosts, the ability to distinguish hosts from nonhosts feeding on the same plant is beneficial. In flight tunnel experiments, we found that prior to landing on the odor source M. croceipes were able to distinguish volatiles released from frass of host larvae (Helicoverpa tea Poddle) and nonhost larvae (Spodoptera exigua Hubner and Spodoptera frugiperda J. E. Smith) fed on cotton. However, an initial contact experience with frass of cotton-fed host larvae appeared to be critical for this ability. Wasps that had antennated frass of host larvae fed pinto bean diet were equally attracted to frass of host and nonhost larvae fed on pinto bean diet. In short-range walking experiments, wasps located cotton-fed host larvae faster than diet-fed larvae, regardless of their experience. Wasps that had antennated frass of cotton-fed host larvae were less attracted to cotton-fed nonhost larvae, compared to host larvae, and preferred to sting host larvae. Plant-related volatiles in host frass and larvae appear to play a major role in the successful location of host larvae.