Movement and orientation to host-specific stimuli by the biocontrol agent, Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae) after rearing on two alternate hosts

There is an active push to diversify integrated pest management (IPM) programs for post-harvest products, and one alternative strategy is biological control. A potential post-harvest biocontrol agent is Theocolax elegans(Hymenoptera: Pteromalidae) whose host range includes the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae), and lesser grain borer, Rhyzopertha dominica (Coleoptera: Bostrichidae). In mass rearing this parasitoid, either species could possibly be used. However, the Hodgkins-Host Selection principle suggests that important foraging semiochemicals may depend on the natal host environment in which an organism is reared. In order to investigate how the behavioral response of T. elegans to potential hosts may be modulated by its natal host environment, we reared T. elegans on either S. oryzae or R. dominica for multiple generations. In a four-arm, still-air olfactometer, we evaluated the orientation and taxis of T. elegans to six treatments: damaged grain+S. oryzae, damaged grain+R. dominica, S. oryzae alone, R. dominicaalone, damaged grain+insects from the natal environment, or a control. Further, we characterized the volatiles from these treatments using dynamic headspace collection and visualized these volatiles using a nonmetric ordination procedure. Additionally, we evaluated movement (e.g. velocity and distance moved) in the presence of the odor treatments above using video tracking coupled with Ethovision software. We found that the natal host and odor source significantly affected chemotaxis of T. elegans, and our treatments emitted unique blends of semiochemicals, suggesting that careful attention should be paid to the mass rearing procedure for this parasitoid.