RAPID: Eco-evolutionary dynamics of host-parasite interactions in a novel environment

Invasive insect pests are best controlled in the long term by parasitoid natural enemies that lay their eggs inside the insect. The eggs hatch and develop into larvae, which feed on the body of the insect host from the inside. Because this is a life-and-death struggle, natural selection acts strongly on the host to evolve to escape parasitism and on the parasitoid to overcome host defenses. When insect pests invade a new region, they usually leave behind the parasitoids that are adapted to attack them. It is expected that in this new, enemy-free environment, evolution could result in an insect host with lower defenses. Host evolution in response to parasites is important because host resistance impacts biological control programs. In these programs, enemies from native ranges are introduced intentionally to control invasive insect pests. When the insect host is once again exposed to its parasitoids, natural selection will once again respond. This study investigates how defense levels of the spotted wing drosophila have changed following its invasion of North America and how those defenses may change following the release of a specialist parasitoid from the native range. In addition to broad implications for biological control, the project promises to yield specific insights into control of spotted wing drosophila, which is a major agricultural pest. Lower resistance of invasive spotted wing drosophila could help biocontrol initially, while increased or geographically variable levels of resistance could render biocontrol less successful or less predictable regionally. This project investigates eco-evolutionary dynamics of host-parasitoid interactions following the release of a classical biocontrol agent, the parasitoid wasp Ganaspis brasiliensis against the invasive spotted wing drosophila (Drosophila suzukii). Contrary to expectations, the resistance of spotted wing drosophila seems to have increased instead of decreased in the invaded range in North America and Europe. This increased resistance may stem from reduced competition and ample resources for spotted wing drosophila in the exotic range, permitting maintenance of high levels of defensive compounds. Preliminary data collected prior to the release of the biocontrol agent show that spotted wing drosophila resistance to parasitism by G. brasiliensis is relatively high but also that it is highly variable with 13-48% of parasitoid larvae being killed by the host. In this project, G. brasiliensis will be released at eight sites in Michigan where there is already baseline data about resistance levels of spotted wing drosophila. Subsequent surveys will permit assessment of any changes in resistance following this release of a co-evolved specialist natural enemy. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.