Insect alert: Spotted Wing Drosophila in Spokane!

Spotted Wing Drosophila: Photos courtesy of Beverly Gerdeman, PhD, WSU Research Associate and WSU Whatcom County Extension.

Even if you can’t pronounce the name of this dreaded insect, you need to know about this. And especially if you grow fruit trees or berry plants. The Spotted Wing Drosophila (or SWD), Drosophila suzukii, has been found in Spokane. It is very damaging to all sorts of fruit crops.

This small fruit fly is a major threat to tree fruit crops such as cherries, peaches and plums; grapes. They also are a problem with berry crops like strawberries, blueberries, blackberries and raspberries. SWD lays its eggs into both ripening and rotting fruit. Once the maggots hatch, they ruin the fruit as they tunnel through it and feed on the fruit.

According to information I’ve received as a WSU/Spokane County Master Gardener, SWD’s are fairly easy to identify. You’ll need a 15X magnifying hand lens because the flies are very small (less than 1/8″ long). My source states “Both males and females have red eyes, clear wings and yellow-brown body color. The male has one black spot on the end of his wings, and two black ‘combs’ on his front legs. The female does not have these black spots or combs, so is more difficult to identify. A female SWD is equipped with a unique saw-like ovipositor. It allows her to ‘sting’ soft-skinned fruit and insert her eggs.

“There may be two visible hair-like filaments sticking out of the sting site. These filaments are attached to the egg and allow the egg to breathe. The larvae, or maggots, that hatch from the eggs are creamy white or transparent. They grow to a maximum size of 1/8″ long. These maggots are legless and lack a head. The mouth hooks in the front and ‘tailpipes’ in the back that they stick through the fruit surface to breathe….”

You can monitor for the adult flies by making simple traps that contain apple cider vinegar and dish detergent. Here is a link to information on how to make and position the traps. There’s also more in-depth information about the SWD: http://cru.cahe.wsu.edu/CEPublications/FS049E/FS049E.pdf.

The most important thing you can do as you tidy up your garden this fall is to eliminate any rotten or fallen fruit on or around your berry vines or fruit trees. Do not place any of this material into your compost pile! It’s much safer to dispose of the potentially-infested fruit through your garbage pick-up although you can also crush the fruit to destroy any potential eggs or you can bury the fruit 18″ deep. I fully intend to be diligent about disposing any rotten berries or fruits from my vines and fruit trees.

Next year, it will be helpful to set several of the above-mentioned traps to trap as many as possible. If you find any fruit flies that you suspect are Spotted Wing Drosophila in your garden/orchard/berry patch, I would recommend capturing them, placing them in the freezer until they’re dead, and then taking them to the Spokane County Master Gardener Plant Clinic, 222 N. Havana St., for positive identification. This will also enable us to determine the magnitude of the problem.

And last but not least, let’s all hope for a cold winter because SWD’s aren’t able to survive those conditions!