Efficacy of field-aged insecticide residues for control of Drosophila suzukii

Drosophila suzukii (Matsumura) is a recognized economic threat to high-value specialty crops where there is little tolerance for insect damage. To control D. suzukii, pesticides are applied in timed intervals every 7-10 days once fruit is susceptible. Some insecticide residues may be more persistent than others, warranting a tailored spraying schedule to best protect fruit, minimize inputs, and avoid exceeding Maximum Residue Levels. We tested field-aged residues of four insecticide classes (spinosyns, pyrethroids, diamides, and insect growth regulators (IGRs)) for mortality and fruit protection efficacy. Treated leaves and cherries were collected from a sprayed orchard 1, 3, 7, 14, and 21 days after treatment (DAT). Ten female D. suzukii were released into plastic container arenas lined with treated leaves and cherries suspended from lids. Cherries were evaluated for damage after 16 hours of exposure, moved into a new container, and monitored for adult emergence. Female D. suzukii mortality was evaluated after 24 hours. DoubleTake, a combination IGR-pyrethroid, had the highest level of mortality and best fruit protection, with over 94% mortality and less than 0.8 ovipositions per fruit, throughout the 21-day test. Pyrethroids also provided excellent fruit protection, although the mortality caused by Danitol dropped from 98% to 82% at 7 DAT, and continued to decrease thereafter. Spinosyns killed approximately 100% SWD until 14 DAT, and Entrust provided high levels of fruit protection, below 2 ovipositions per fruit. Our results suggest pyrethroids and spinosyns are candidate insecticides for long-term fruit protection from D. suzukii damage.