Ethyl formate fumigation and ethyl formate plus cold treatment combination as potential phytosanitary quarantine treatments of Drosophila suzukii in blueberries

Abstract Spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae), is a serious invasive pest of berries and cherries in the U.S. and Europe and has become a major phytosanitary trade barrier. In this pilot study, we explored the potential of using stand-alone ethyl formate (EF) treatment and combinatory treatment of EF and cold as postharvest control options for D. suzukii in imported blueberries. Stand-alone EF fumigations were effective against D. suzukii with LCt99% of 207.7 and 168.5 g·h·m-3 for eggs, the most tolerant life stage, at 5 and 21°C, respectively. In a scale-up (10 m3) trial conducted at 5°C, complete control of D. suzukii eggs placed inside and outside of blueberry boxes was achieved using 70 g·m-3 EF for 4 h with 5% blueberry loading ratio without deleterious impact on blueberry appearance such as soft spot or berry shrivel. In small scale pilot studies, 9-d stand-alone cold treatment at 5°C was sufficient for complete control of D. suzukii eggs and larvae tested, but not pupae. The efficacy of this cold treatment appeared to be improved when D. suzukii eggs were first treated with low-dose EF (LCt50% level) prior to the cold treatment. The combination treatment resulted in complete mortality of D. suzukii eggs, larvae, and pupae tested after 7, 5, and 9 d of cold treatment, respectively. Together, these results suggest that stand-alone EF treatment, or the combination treatment of low-dose EF and cold as a systems approach may have a potential as postharvest treatments for D. suzukii in blueberries.