Comparative evaluation of insecticide efficacy tests against Drosophila suzukii on grape berries in laboratory, semi-field and field trials

As the period for field trials on grapevine is limited, we designed a laboratory test system to evaluate the effectiveness of selected insecticides against spotted-wing Drosophila (SWD), Drosophila suzukii, on different types of grape berries all year round. Tests were undertaken during winter and early spring with table grapes of different purchased varieties according to their seasonal availability and with wine grapes from experimental field plots in autumn. In preliminary experiments, we defined parameters for a standard laboratory test system for screening the effectiveness of several formulated insecticides in two different experimental set-ups: i) application before confining adults with berries and ii) application after confining adult D. suzukii with berries. These approaches allowed us to determine the contact activity of the products on adult D. suzukii or the impact on the larval development until the emergence of adult flies. The developed test system is suitable for screening substances with diverse types of activity on different grape types. In a second step, we combined laboratory bioassays with field applications in a semi-field persistence study and lastly we installed a randomized field plot in order to compare the effectiveness of selected insecticides in the laboratory and under field conditions. In all cases, the products Karate Zeon and SpinTor proved most efficacious in their contact mortality or as oviposition deterrents, while Mospilan SG and Coragen exhibited a good larvicidal activity. However, important disagreements occurred for the efficacy of currently authorized insecticides among laboratory, semi-field and practical field applications. The transferability of laboratory results into the field is discussed.