Survival and nutritional requirements for overwintering Drosophila suzukii (Diptera: Drosophilidae) in Kentucky

The ability to cope with novel climates is a key determinant of an invasive species' success. Drosophila suzukii (Matsumura, 1931) is an invasive fruit pest, and its seasonality varies across its range. Current evidence suggests that D. suzukii occurs year-round in warmer climates but has low overwintering survival in colder climates and relies on refuges or reinvades each spring. Here, we assessed the capacity of D. suzukii ability to overwinter in Kentucky, a temperate mid-latitude state with relatively mild but variable winters. We tracked year-round population changes for 3 yr and observed the highest populations in early winter months. Following an annual population crash in winter, small numbers of flies remained through the late winter and spring. We also conducted outdoor cage studies to determine the extent to which food resources and microhabitat impact survival and postwinter fecundity under natural conditions. Flies with no food had poor survival during the warmest periods of winter, and flies in all treatments had lower survival in the coldest month. Provisioning flies with either artificial diet or wild berries improved survival. As a follow-up, we determined whether D. suzukii could survive and reproduce after long-term exposure to a typical winter temperature on various wild berries. Drosophila suzukii had the highest survival on privet (Ligustrum sp.), but all berry types yielded higher survival than flies without food. Our results suggest that noncrop berries play an important role for overwintering D. suzukii, and as winters warm the availability of wild berries could influence early-season populations.