The focus of this research is to better understand the interactions between the invasive pest Drosophila suzukii and the parasitoid wasps that target it. The first chapter evaluates whether a colony of the generalist pupal parasitoid Trichopria drosophilae that had been selected in the laboratory over several generations for increased performance on D. suzukii would also show improved performance under more natural conditions than the artificial rearing environment. To assess this, adapted and non-adapted populations of T. drosophilae were used to parasitize D. suzukii in three different species of fruit. More wasps and fewer flies emerged from the adapted colony in every fruit type, which indicates that several generations of laboratory rearing did not impose an apparent cost when making the shift back to a natural environment. Subsequently, when the same adapted and non-adapted T. drosophilae were compared alongside a co-evolved larval parasitoid, Ganaspis brasiliensis, using raspberry plants, G. brasiliensis had more wasps emerge than either T. drosophilae colony, but the same number of D. suzukii emerged as the adapted population. These results show that while experimentally reared generalist parasitoids may not be able to parasitize to the same degree as a co-evolved specialist, they still have potential as a biological control agent for reducing an invasive species' population. The second chapter investigates how D. suzukii resistance to parasitism by G. brasiliensis varies with geography and time. Individuals from eight geographically distinct populations of D. suzukii across Michigan and Oregon showed different rates of parasitism and encapsulation during resistance assays. Flies collected in August from these locations also demonstrated differences in parasitism and encapsulation rates to the same populations sampled just a month later. These results demonstrate that it is possible for resistance-related traits to vary geographically and temporally which may impact the performance of G. brasiliensis as a biological agent.
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