Biology And Pesticide Resistance Management Of Drosophila Suzukii In Coastal California Berries

Unlike common drosophilids that develop in rotten or decaying fruit, Drosophila suzukii (Matsumura) prefer to oviposit in ripe or ripening fruit. Native to Southeast Asia, D. suzukii has become an important pest of berries and small fruits throughout North America and Europe since its initial detection in Santa Cruz County, CA in 2008. Management guidelines established shortly after the emergence of D. suzukii as a serious pest included monitoring recommendations, but these were made with little information on trap design and potential lures for use in raspberries. To address this issue, we trapped adult D. suzukii weekly for two years (including both spring and fall harvests) in multiple raspberry varieties, using apple cider vinegar and a yeast-sugar-water mixture as liquid lures, measuring fruit infestation when commercially ripe fruit were available. The yeast lure captured significantly more D. suzukii during the fall harvest than the apple cider vinegar, and while both lures tended to capture more females than males, this varied by month of the year and was more pronounced for the yeast lure. Because yeasts are believed to be an important source of nutrients for many species of Drosophila, and Drosophila spp. have preferences for specific species of yeast, it is unsurprising that yeast fermentations are highly attractive. To discover candidate yeast species for association with D. suzukii, yeasts were isolated from larval frass, adult midguts, and fruit hosts of D. suzukii. A total of 126 independent isolates of yeasts were cultivated from frass, midguts, and fruit hosts of D. suzukii, representing 28 species of yeasts. Hanseniaspora uvarum was predominant in all locations, and accounted for 46.8% of all strains. This suggests a potential association between D. suzukii and H. uvarum that could be utilized for development of a more attractive and specific lure. Since current D. suzukii management strategies rely heavily on insecticide usage, and insecticide detoxification gene expression is under circadian regulation in the closely related Drosophila melanogaster, we also set out to determine if integrative analysis of daily activity patterns and detoxification gene expression can predict chronotoxicity of D. suzukii to insecticides. Five of the genes tested exhibited rhythmic expression, with the majority showing peak expression at dawn (ZT0, 6am). We also observed significant differences in the chronotoxicity of D. suzukii towards malathion, with highest susceptibility at ZT0 (6am), corresponding to peak expression of cytochrome P450s that may be involved in bioactivation of malathion. The chronobiology and chronotoxicity of D. suzukii provide valuable insights for monitoring and control efforts, because insect activity as well as insecticide timing and efficacy are crucial considerations for pest management. When coupled with or work on yeast associations and lures for monitoring D. suzukii, we have gained information necessary for the development of effective D. suzukii monitoring and control strategies.