Maturity indicators to predict grape skin strength for controlling Drosophila suzukii

Abstract: Drosophila suzukii has become a pest of economic importance ever since it has spread around the world through the soft fruit trade. In vineyards, it is thought that the risk of infestation is correlated with the strength of the grape’s skin. There is an idea that there might be a common threshold in skin strength when a grape passes from being safe from infestation to being susceptible to infestation. The relationships between D. suzukii infestation rate and grape properties were explored. Also, the relationships with grape skin strength (= penetration force) and other grape properties related to total soluble solids, acidity, nitrogen content, and grape seed color were compared at a single site and across different sites. Cultivars were found to be infested by D. suzukii across a wide range of penetration forces. Therefore, the idea of a common threshold is not supported by our study. Factors relating to grape maturity were overall more successful in predicting risk of infestation. Penetration force was not able to be successfully correlated with any single tested grape property or with a statistical combination of them. Moreover, cultivars behaved quite differently depending on their location. Thus, the study was not able to discover any general relationships that might be used to indicate a grapevine’s susceptibility to D. suzukii infestation.