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 a recent study, females in no-choice laboratory bioassays laid eggs in ripening blueberries and blackberries. However, most 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 a field may be able to complete development as the fruit continues to ripen. To test this hypothesis, we used fine mesh cages to prevent later egg laying by D. suzukii in fruit at several ripeness stages: green-pink, pink, and ripe raspberries and in green-pink, red, purple, and ripe blackberries. We collected the fruit once they were ripe, and reared out and counted all D. suzukii present. This experiment was conducted at two locations during 2013 and 2014, one with very high fly populations and one with low populations. Very few flies emerged from blackberry clusters that were bagged at the green-pink stage, and 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.