Responses of two parasitoids of emerald ash borer, Agrilus planipennis Fairmaire, the introduced Spathius agrili Yang, and native Spathius floridanus Ashmead, to volatile host-associated cues

Two parasitoids, the introduced specialist Spathius agrili Yang (Braconidae), and the native generalist Spathius floridanus Ashmead (Braconidae), have been proposed as biological control agents of the emerald ash borer, Agrilus planipennis (Fairmaire). However, little is known about their host-location behaviors. We evaluated wasp responses to three components of this host complex, Fraxinus pennslyvanica (green ash) stem tissue, F. pennslyvanica foliage, and an A. planipennis larva within a stem. Laboratory experiments were conducted in Y-tube olfactometer bioassays, using wasps reared on A. planipennis larvae boring in F. pennslyvanica twigs at the USDA APHIS facility in Brighton, MI. Naïve S. agrili were attracted to volatiles from leaf tissue, but not from any other component, relative to blank controls. In contrast, naïve S. floridanus were attracted to a feeding larva within a stem, but not to any other component. Thus, naïve S. agrili and S. floridanus appear to employ different strategies for host-location. Because S. floridanus attack multiple Agrilus species, host-associated cues perceived during emergence from their natal hosts may improve attraction to emerald ash borer larvae. Subsequent experience may elicit attraction to plant foliage, and thereby facilitate location of host habitat. In contrast naïve S. agrili appear to only be attracted to foliage, and learning of additional host-associated cues may occur during oviposition. We are currently testing the elements of this model. Further understanding of host-location behavior may improve the utility of these parasitoids for biological control, both by suggesting strategies for pre-release conditioning, and by providing tools for accessing post-release establishment.