Two Faces of Drosophila suzukii Invasion: Effects on Invaders and Communities

The spotted wing drosophila (SWD, Drosophila suzukii) has quickly spread since its introduction in 2008 to North America and Europe. Most Drosophila oviposit in rotting fruit, but SWD puncture the skin of fresh fruit to lay eggs inside, leading to premature fruit rot. I used SWD to study how new selective pressures shape invasive populations, and how invaders impact communities in their invaded ranges. I hypothesized that flies that were unable survive the winter conditions in Agassiz, BC would have quickly died out, but flies living in California would have experienced less intense selection for overwintering adaptations. I found that SWD reared at short photoperiods showed phenotypic plasticity that indirectly improved cold tolerance, and that the response was different between populations, but not in the manner predicted. To explore the impact SWD may have on communities in their invaded ranges, I conducted a sensitivity analysis of 3 parameters in an individual based model that simulated the change in fruit resources from ripe to rotten. I found that the greatest amounts of rot occurred when fruit was slow developing, many adult SWD were present, and females were adept at finding oviposition sites. Lastly, batches of cherries collected from orchard tree branches and floors both produced SWD and other species of Drosophila, suggesting that the species are not spatially separated and congener competition could be occurring on or in fruit in the field. The three data chapters presented here tested one way in which new environments could be shaping this introduced species, explored the conditions that could lead to the greatest impact of SWD on their new communities, and confirmed that the communities SWD are hypothesized to affect, do overlap. This represents a small amount of what could be learned from the SWD invasion, especially in ecology and evolution.