Susceptibility of various grape cultivars to Drosophila suzukii and other vinegar flies

Abstract: In 2011, the spotted-wing drosophila Drosophila suzukii native to Asia has been identified for the first time in Switzerland. Since then, this vinegar fly has established itself all over the country and it has also been observed in many vineyards. It has been reported that D. suzukii is able with its long, sharp, serrated ovipositor to attack healthy grapes just before harvest and that the level of infestation depends on the grape cultivar. It is assumed that in particular red and thin-skinned cultivars are of higher susceptibility. Our laboratory studies confirmed that D. suzukii was able to lay eggs within grape berries. However, almost none of the eggs laid at the beginning of grape ripening allowed the development of adults. In subsequent tests, oviposition was highest on the red and thin-skinned cultivars Bondoletta and Gamay followed by the red cultivars Pinot Noir and Divico, and the two white cultivars Müller-Thurgau and Chasselas. Yet, the development of adults remained very low and did not exceed 9% of eggs deposited, which is considerably less than on an artificial diet. These results, as well as field observations, confirm the lesser attractiveness of white compared to red grape cultivars and the importance of the thickness of the skin. Moreover, observations in the field and preliminary laboratory experiments indicate that grape infestation by D. suzukii does neither considerably favor the development of other Drosophilidae nor rot diseases within grapes. Overall, our various observations confirm that grapes can be damaged by D. suzukii, but they are probably not very suitable for larval development and the buildup of large pest populations. Nonetheless, it cannot definitely be excluded that D. suzukii favors the infestation of grapes by native vinegar flies and pathogens and its development in vineyards should therefore be followed carefully.