Alien interference: disruption of volatile-mediated interactions between plants and parasitoids by invasive insect herbivores

Plant volatiles are of key importance for the foraging behavior of predators and parasitic wasps (parasitoids) in search of prey or hosts, and the specificity of these chemically-mediated interactions results from shared evolutionary history between the interacting species. We propose that parasitoids can readily use plant-produced volatiles to distinguish between native hosts and non-hosts, but that invading insect herbivores may disrupt these finely-tuned interactions and negatively impact the foraging behavior of native parasitoids. We test this hypothesis by using Brassica rapa (wild turnip) and its complex of native herbivores and parasitoids. The effect of invasive herbivores on the foraging behavior of 4 native parasitoids will be evaluated in olfactometers by simultaneously testing parasitoid attraction to plants that are damaged by the parasitoid’s host herbivore, plants damaged by a native non-host, and plants damaged by an exotic non-host. The results will show to what extent invasive herbivores can impact chemical signaling between plants and natural enemies. Additional experiments will evaluate the relevance of these results in more natural settings and quantify the realized fitness impact of attraction to plants damaged by non-hosts on native parasitoids. The research is conducted in the context of a European-wide project that involves groups in four other countries, with the other groups studying the mechanisms of volatile emissions and evaluating the effects of invasive insects on herbivores and pollinators. The data will be used in models to predict the overall population level consequences of the disruptive impact of invasive insects on chemically-mediated interactions between plants and insects.