High-throughput screening of natural benzyl esters for potential spotted-wing drosophila repellents

Drosophila suzukii, commonly known as the spotted-wing drosophila (SWD), is an invasive species native to southeast Asia and introduced to North America in 2008. SWD lays eggs in thin-skinned, ripening fruits causing significant economic loss in the produce industry. The synthetic pesticides applied to suppress SWD populations have detrimental off-target effects, so the use of a more environmentally friendly alternative is desired. In this study we used a high-throughput screening method to assess the repellent properties of a group of naturally occurring volatile organic compounds called benzyl esters, some of which are toxic to SWD, but safe for human consumption We adapted a laboratory assay designed for mosquitos to test repellency against SWD. We tested five benzyl esters, all of which are FDA-approved food additives, at five concentrations ranging from 40-80 µg/cm². Dose-response models were used to compare RD50s, the dose required to repel 50% of the test subjects, at 15, 30, and 60 min. The most potent repellent compound was methyl 2-methoxy benzoate, which was about 4-fold more repellent than the next best compound. We also compared the amount of knockdown, referring to how many flies are unable to move towards/away from a compound due to partial paralysis. Our findings will be used to inform field trials in blueberry orchards where SWD are serious pests.