Relationships between Drosophila Suzukii and grapevine in North-Western Italy: Seasonal presence and cultivar susceptibility

Drosophila suzukii (Matsumura) is an Asian species, and is now widespread also in America and Europe. While it is acknowl-edged as a serious pest to many soft fruits, its impact on viticulture needs further investigation. This study focused on the relationships between D. suzukii and grapevine in Piedmont (North-western Italy), and was conducted for three seasons in 10 vineyards of six different grape varieties, surrounded by different crops and/or vegetation. Flies were collected using food traps, and grape berries were sampled to assess oviposition. The susceptibility of grape cultivars was analysed in the laboratory by exposing intact berries with a known skin hardness (i.e. skin break force mechanical property) and injured berries to female flies. A choice test was also performed to investigate the preference of D. suzukii for grape juice of different cultivars. Capture of adults in vineyards depended on sampling dates, surrounding vegetation, and years, but few eggs were observed in field-collected berries. Overall, in laboratory experiments, cultivars with soft-skinned berries were more exploited for egg-laying. However, among cultivars, the susceptibility changed depending on whether the berries were intact or injured. Concerning the latter, the most infested cultivars were also the most attractive to flies in the choice test. At present, D. suzukii may not be considered a threat to viticulture in Piedmont. However, considering the influence of grape skin hardness on oviposition and the attractiveness of some grape culti-vars, further studies are needed to better understand the relationship between D. suzukii and grapevine.