Risk of spotted-wing drosophila injury and associated increases in acetic acid in Minnesota winegrapes

Spotted-wing drosophila, Drosophila suzukii (Matsumura), is an invasive species to Minnesota that was first recorded in 2012. Since its arrival it has become a major pest of stone fruit and berry crops, including winegrapes. High fecundity and short generation times have allowed D. suzukii to flourish and spread throughout North America and Europe in a relatively short period of time. Laboratory and field trials were conducted between 2017 and 2019 to determine the risk of injury from D. suzukii in Minnesota winegrape varieties and to assess acetic acid (AA) levels in wine and juice samples from cold-hardy winegrape varieties in Minnesota. Results from risk of injury studies in 2017 and 2018 demonstrated a low risk of direct injury to intact grape berries. Winemakers, however, are concerned about the potential risk of D. suzukii infestations increasing AA-producing bacteria (e.g., Acetobacter spp.), known to expedite the development of sour rot in grapes. AA trials in 2017 and 2019 demonstrated significant increases in AA for select grape varieties as fly density increased. However, the 2018 AA trials with modified infestation protocols did not result in significant differences in AA. Our results are discussed within the context of improving integrated pest management programs for D. suzukii.