Influence of fruit coating on Drosophila suzukii oviposition and development and implications for field use

Spotted wing drosophila, Drosophila suzu­­­kii (Matsumura), is a highly invasive vinegar fly that was first detected in the eastern United States in Florida in late 2009 and has since spread throughout the region. Females use their saw-like ovipositor to lay eggs in ripe and ripening fruit and have caused significant damage to soft-skinned fruits such as raspberries, blackberries, blueberries, cherries, strawberries, and grapes. Unmanaged D. suzukii infestations can reach 100%, particularly in later fruiting crops. Insecticides are the primary tool currently used against D. suzukii. However, only a few insecticides are both effective against D. suzukii and can be applied to ripe and ripening fruit (i.e., have sufficiently short preharvest intervals). Therefore, other tools are desperately needed to help manage D. suzukii infestations. Several food grade coatings containing carnuba wax are used to protect fruit post harvest and enhance shelf life, and kaolin clay and calcium carbonate are used to prevent sunscald and insect damage in the field. We tested three coatings to determine if D. suzukii females lay fewer eggs in coated fruit. In no-choice laboratory bioassays in 0.30 m³ collapsible mesh cages, we compared egg laying and larval survival in 20 gram samples of ripe blueberries and raspberries. We compared four potential field dilution rates for each coating and found that some of the coatings reduced the number of eggs laid, but did not prevent oviposition altogether. Additional experiments were conducted to determine if coatings can be applied to fruit preharvest and if field applications of fruit coatings reduce D. suzukii infestation under field conditions.