Bait Sprays Combined With Insecticides Targeted at Drosophila suzukii Have Negligible Impacts on Non-Target Insects Compared to Full Foliar Spray Applications

Abstract

Current control of the invasive pest Drosophila suzukii relies primarily on insecticides, including the incorporation of phagostimulant baits. The impact of insecticidal bait sprays on beneficial insects in crops is largely unknown. In a laboratory and field trial, we exposed non-target insects to insecticides with or without bait and compared these to non-insecticide controls. In laboratory arena tests, we assessed the impact on mortality. In the subsequent commercial raspberry field trial, 1 m width spray bands of bait were applied weekly, using alternating 25% or 50% field rates of spinosad and cyantraniliprole respectively. Results from the laboratory assays separated the insects into three categories: (1) adult Eupeodes corollae, Forficula auricularia, and Orius laevigatus, (2) adult Drosophila melanogaster and (3) larval Chrysopa sp. and Adalia bipunctata. In the first group, bait + spinosad or spinosad alone were equally detrimental to the life expectancy of insects. For D. melanogaster, bait + spinosad was faster acting than spinosad without bait. No detrimental impact of the treatments was observed on the third group of larval predators. Baits alone did not increase insect mortality. In the raspberry crop, there were no observed impacts of baits with insecticides on the abundance of insect pollinators or natural enemies compared to the full foliar applications of insecticides. This study is the first to test a range of non-target insects for toxicity to low dose insecticides combined with baits. Further field testing in commercial crops should explore the placement of bait droplets for optimal D. suzukii control, whilst minimising further impacts on non-target insecticides.