Drosophila suzukii infestation in ripe and ripening caneberries

Drosophila suzukii (Matsumura) is a highly invasive vinegar fly that was first detected in the continental United States in 2008. Females use their saw-like ovipositor to lay eggs in soft-skinned fruits and severely threaten the viability of raspberry, blackberry, blueberry, cherry, and strawberry production. In one recent study, females in no-choice laboratory bioassays laid eggs in ripening blueberries and blackberries. However, many of the eggs failed to develop, perhaps because the ripening process was interrupted in the prematurely-harvested fruit. We hypothesized that eggs laid in ripening fruit in the field may be able to complete development as the fruit continues to ripen on the plant. To test this hypothesis, we measured D. suzukii infestation in green-pink, pink, and ripe raspberries and in green-pink, red, purple, and ripe blackberries in Ashe County, NC, at a site with high numbers of D. suzukii. For each ripeness stage, we bagged 20 clusters with one or more berries using small mesh bags. We collected the clusters once they were ripe, and reared out and counted all of the D. suzukii present. Very few flies emerged from blackberry clusters that were bagged at the green-pink stage. In general, more flies emerged from clusters bagged at later stages of ripening (purple and red blackberries and pink raspberries) than from green-pink fruit. Knowing what ripeness stages are susceptible to D. suzukii infestation will help growers to better pinpoint when to begin applying management tools.