Drosophila suzukii (Diptera: Drosophilidae) and its Potential Impact to Wine Grapes During Harvest in Two Cool Climate Wine Grape Production Regions.

Drosophila suzukii (Matsumura) is a global pest attacking various berry crops. Drosophila suzukii lays eggs in damaged and in intact wine grape berries of the most soft-skinned varieties. Here, we describe the relative host utilization of different wine grape cultivars grown in Northern Italy and Oregon. Assessments of host berry utilization were performed in both field and laboratory settings. Results were correlated to physiological changes occurring during grape berry development starting at veraison and concluding during harvest. We found that oviposition increased with an increase in sugar content and a decrease of acidity levels. Oviposition increased with a decrease of penetration force. Penetration force, as a measure of skin hardness, is a critical component of host selection among the Drosophila suzukii-exposed cultivars. We demonstrated that incised berries are more favorable for Drosophila suzukii oviposition and as a nutrient substrate. Increased presence on wine grapes, as indicated by egg laying and increased longevity, was observed for flies that were exposed to incised berries as opposed to fully intact berries. Drosophila suzukii flies can be found feeding on damaged wine grapes during the harvest period, especially when the skins of berries are negatively impacted due to cracking, disease, hail injury, and bird damage. Such an increase of feeding and oviposition may increase the likelihood of spoilage bacteria vectoring due to Drosophila suzukii.