D3043: Evidence of spotted wing drosophila overwintering in Kentucky

Spotted wing drosophila (SWD) is an invasive pest of small fruit crops that has spread across the United States. Understanding the seasonal biology of SWD is critical for pest management, but current research indicates that seasonal dynamics and overwintering capacity vary across the continental US. Kentucky is a mid-latitude state with mild winters that are intermediate to cold Northeast and Midwest winters and warm winters of the South. We used a combination of year-round sampling and field cage experiments to test the hypothesis that SWD can overwinter in Kentucky’s relatively mild winters. Since January 2020, we have continuously sampled SWD biweekly using a combination of apple cider vinegar traps and leaf litter sampling. In 2021, SWD was present in traps through January before decreasing sharply, and no flies were caught after that point until June. However, in 2021 low numbers of SWD continued to be caught all winter and early spring, suggesting SWD remains present during the winter in some years. In the cage study, winter morph flies were buried in small cages containing one of three substrates (soil, leaf litter, or evergreen vines) in a full-factorial combination with one of three food sources (no food, artificial diet, and winter berries). Flies survived all these treatments, including during a 2021 ice storm during which temperature dropped to -4.6° C in the cages. Our results show that SWD can survive through Kentucky winters and monitoring populations of overwintering flies in Kentucky may be important for control of this invasive pest.