Detection of fruit meals within laboratory-raised adult Drosophila suzukii guts

Spotted wing drosophila (Drosophila suzukii Matsumura) is a polyphagous pest of small fruit crops such as blackberries and blueberries. It first entered the Southeastern United States more than a decade ago yet continues to pose economic damage to berries. We developed molecular methods to study adult fly gut content in order to understand fly feeding habits. We verified two primers specific to each blueberries and blackberries and used a qPCR meltcurve analysis to determine whether we can detect presence or absence of berry feeding by adult flies. To validate these methods, we conducted a metabolism assay to determine how long we could detect fruit feeding after a single berry feeding event at both the colony-maintenance temperature of 20°C and a temperature ramping regime typical of fruit ripening dates for North Carolina research stations. We found that the blueberry fly meal can be detected for longer than the blackberry meal. Generally, female meals are detected for longer than male meals. We also tested recently emerged flies who were not fed as adults but developed as larvae in either blueberries or blackberries. Some adult flies from each fruit had detectable fruit DNA in their gut, which could be due to meconium feeding after emerging. Together, these data provide context to interpret future studies of adult feeding from the field.