Overwintering Behavior of Drosophila suzukii, and Potential Springtime Diets for Egg Maturation.

Spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a serious agricultural pest, which lays eggs in ripe and ripening fruits of several cultivated and wild host plants. Here we explore several factors that may be critical to winter survival and improve D. suzukii's ability to successfully overwinter in northern climates and reestablish populations in the spring. Cold acclimation improved mobility in low-temperature laboratory mobility assays and improved survivorship in two wintertime field studies. Acclimation improved survivorship in experiments where overwintering habitats were above ground level and where habitats were at soil level by 1.9- and 13.7-fold, respectively. Soil acts to buffer changes in temperature, and the groundcovers investigated here provided microclimates that were 1-2°C warmer than bare soil during chilling events, and roughly 5°C cooler than bare soil during warm spells. Acclimated flies preferred overwintering substrates with a food source (dropped apple) over any other substrate (leaf litter, barky sticks, or bare soil). Pigeon (Columba livia L.) droppings and mushrooms (Peziza sp.) were identified as potential overwintering protein sources in laboratory feeding studies. Laboratory-simulated winter stress negatively influenced return of female reproduction, so future assays should consider biologically relevant subjects.