Deterrent Effects of Essential Oils on Spotted-Wing Drosophila (Drosophila suzukii): Implications for Organic Management in Berry Crops

SIMPLE SUMMARY: Spotted-wing drosophila (Drosophila suzukii Matsumura; SWD) poses a significant threat to small fruit production world-wide. Though frequent applications of insecticides is the dominant strategy to manage this pest, insecticide resistance is a concern. Resistance has already been reported for one of the only consistently effective insecticides labeled for organic production systems, spinosad, underscoring the need to diversify management strategies. Botanical products, such as essential oils, contain volatile organic compounds (VOCs) which could interfere with SWD preference for or ability to locate host fruit. We conducted laboratory and field studies to determine the efficacy of botanical products (lavender oil, catnip oil, KeyPlex Ecotrol(®) PLUS, and KeyPlex Sporan(®) EC(2)) on preventing SWD infestation in raspberry and blueberry crops. Under laboratory conditions lavender oil, Ecotrol, and Sporan deterred SWD from diet. In the field trials, Ecotrol deterred SWD from raspberries; however, no differences were seen in blueberry infestation. To optimize essential oil deterrents for SWD, such as how to maintain effective concentrations for longer periods of time, further research is needed. Botanical deterrents represent a promising alternative pest management strategy that could be implemented without additional equipment investment from growers, while decreasing the use of broad-spectrum insecticides. ABSTRACT: Due to concerns about frequent applications of spinosad and other broad spectrum insecticides for managing spotted-wing drosophila (Drosophila suzukii Matsumura, SWD), we investigated the use of essential oils as an alternative to current insecticides. Essential oils from a number of plant species have been studied for their attraction and deterrence of SWD. However, these botanical products have not been thoroughly tested in the field. We conducted laboratory and field studies to determine the efficacy of botanical products, including lavender (Lavandula angustifolia Mill.) oil, catnip (Nepeta cataria L.) oil, KeyPlex Ecotrol(®) PLUS, and KeyPlex Sporan(®) EC(2) on preventing SWD infestation in raspberry (Rubus idaeus L.) and blueberry (Vaccinium corymbosum L.) crops. In a two-choice laboratory bioassay, lavender oil, Ecotrol, and Sporan treatments deterred SWD from a yeast-cornmeal-sugar based fly diet. In the field trials, raspberry fruit treated with Ecotrol had lower SWD infestation (6%), compared to the control (17%), and was comparable to spinosad (6%). No differences were seen in blueberry infestation. The combination of essential oils in Ecotrol may work to decrease SWD fruit infestation under certain conditions in the field, however more research is needed on the longevity of these products.