Drosophila suzukii (Diptera: Drosophilidae) oviposition and adult emergence in six wine grape varieties grown in Virginia

Drosophila suzukii (Matsumura) is a pest of small fruits and grapes in the United States and in its home range of Japan. Physiological and morphological laboratory testing was performed on six commonly grown wine grape varieties in Virginia. Skin thickness, penetration force, and ºBrix were analyzed to determine ovipositional preferences. Experiments were performed for three consecutive years from grapes collected at one Virginia vineyard. More eggs were laid in intact Viognier grapes than any other variety. Oviposition into intact grapes was not affected by skin thickness or ºBrix; however, oviposition increased when penetration force decreased. An ovipositional choice test determined no varietal preferences. Survivorship from egg to adulthood using uninjured and injured grapes was also assessed to determine varietal suitability as D. suzukii hosts, with more flies emerging from injured grapes than uninjured. However, D. suzukii adults did emerge from intact grapes and at higher percentages than previously recorded in other wine grape studies. All varieties had eggs oviposited into them when injured. Determining the time at which each grape variety became susceptible to oviposition was determined using a D. suzukii bioassay spanning 12 wk using grapes from the green pea stage until ripe. Susceptibility to D. suzukii oviposition was based upon ripening period and penetration force. Early ripening varieties may be more susceptible to D. suzukii oviposition in the field with later maturing, harder fleshed-varieties which may escape D. suzukii oviposition.