Spotted wing drosophila (SWD), Drosophila suzukii, is a fruit fly first found in 2008 damaging fruit in many California counties. It infests ripening cherries and raspberry, blackberry, blueberry, and strawberries, especially in coastal areas. It has been a great disappointment to gardeners and farmers locally to not be able to enjoy the fruit trees and vines they have spent so much time developing into bearing plants. Some farmers have cut down their cherry trees altogether. We are also seeing the maggots in raspberries, blueberries and blackberries; truly a great disappointment.
Adult flies and maggots closely resemble the common vinegar fly and other species that attack primarily rotting or fermenting fruit. Spotted wing drosophila, however, readily attacks undamaged fruit. This fact makes it important to monitor and use sprays at effective times. The most distinguishable trait of male flies is a black spot towards the tip of each wing. The females do not have spots on wings but have a very prominent, saw-like ovipositor for laying eggs in fruit. The insecticide spinosad (e.g., Monterey Garden Insect Spray) is effective and has the least negative environmental effects of currently available products. Some spinosad products are sold to be applied with a hose-end sprayer, but a compressed-air sprayer will give more reliable coverage. They are sold as 1 and 2 gallon sprayers. If you have a lot of plants, you may want to invest in a backpack sprayer. Timing can be determined by watching the color of the fruit, as it slightly changes to it’s ripening color.
Traps are used for monitoring the presence of the adult flies. Commercial fruit fly traps are available or you can make traps out of 1-quart plastic yogurt (or similar) containers that have a lid. Drill 10 to 16 holes that are 3 /16-inch in diameter around the upper side of the container for fly entry. Bait the trap with 1 to 2 inches of pure apple cider vinegar. Add a drop of unscented liquid dishwashing soap to break the surface tension so the flies will drown. Hang the trap in the shade in your cherry tree or near your berries in early May or well before fruit begins to ripen. Check the trap weekly for small flies with dark spots at the tip of their wings floating in the fluid. These are male spotted wing drosophila and will confirm that you have the pest. Put fresh apple cider vinegar and a drop of soap in each week.
For more detailed information go to this publication. The ipm.ucdavis.edu website has many more topics to help you prevent and solve pest problems in the home garden and small farm.