Efficacy of lime treatments against Drosophila suzukii in Swiss berries

Abstract: Drosophila suzukii is an invasive pest that lays eggs in healthy fruits with a serrated ovipositor, resulting in considerable economic losses, mainly in berry crops. It was first recorded in Switzerland in 2011, causing considerable damage in all small fruit crops, especially in late-developing crops (autumn raspberries, blackberries, blueberries and elderberries). Control methods have been implemented to minimize the use of insecticides. Greenhouse trials were conducted in 2015 to test lime (calcium hydroxide) treatments efficiency as a substitute or complement to insecticide treatments. Fourteen blueberry bushes were individually placed in insect-proof cages: seven of them were treated weekly with a solution of lime, while seven others did not receive any treatment. In each cage, 10 D. suzukii were released per week. Ten blueberry fruits per bush were harvested each week, and the number of larvae and eggs per fruit was determined for each cage. The pH, strongly suspected to contribute to the efficiency of lime against D. suzukii, has been measured in 2015 on the treated and non-treated strawberry epidermis during three days. The semi-field test on blueberry showed that after several treatments, lime significantly reduced the number of D. suzukii eggs in fruits. The pH was consistently higher in treated strawberries than in non-treated strawberries. Our greenhouse trials showed the potential efficiency of lime treatments. However, they need to be repeated on-farm in order to provide producers with an efficient management strategy (treatments, mass trapping, nets, hygiene), ensuring a high quality and residue-free Swiss berry production.