DIY contraption catches fruit flies

Question: Last summer, I had a lot of fruit flies around my blueberries and raspberries as they ripened. Is there something I can do now to discourage or prevent them from coming back with a vengeance this summer?

Answer: Fruit flies, including the spotted wing fruit fly (drosophila), also known as the vinegar fly, can be a problem as backyard fruit ripens. This Asian fly is a newer pest in Oregon; it was first identified here in 2009.

Spring is the time to start looking for fruit flies by trapping them. Oregon State University entomologists describe the tiny spotted wing drosophila as similar to other small fruit flies “but is distinctive for its yellowish-brown body, red eyes and dark unbroken bands encircling its abdomen.”

Trapping lets you know you have a potential problem while also killing the adults who lay eggs in ripe fruit. Here are instructions from OSU entomologists on how to make your own trap at home.

Find a red 18-ounce plastic cup with a lid, the kind often used at tailgating parties for beer. The fruit flies are especially attracted to the color red. Drill several holes, each about 3/16 inch wide, around the side of the upper third of the cup. Another option is to glue a rectangular piece of plastic canvas mesh to the side of an open area cut into the cup measuring about 1.5 inches by 4 inches.

Then, fill the cup with 1.5 inches of pure apple cider vinegar and a drop of non-scented liquid soap. Adult flies also are drawn to a yeast solution. So, rather than vinegar, you could make a solution with 1 tablespoon active dry baker’s yeast, 4 tablespoons sugar and 12 ounces of water.

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Attach a heavy-coated wire, strap or durable twist tie to the top of the cup. Hang it from the shady (usually north side), cooler side of your raspberry canes or blueberry bushes near the level of the fruit to capture fruit flies. Since fruit flies also infest stone fruits such as peaches, plums and cherries, you can hang traps on your trees as well. Refresh the bait once per week.

To detect fruit fly larvae (maggots) in your fruit, first prepare the following solution. Dissolve one cup salt or 2.5 cups brown sugar per one gallon of warm water. Put several ounces of ripe fruit into a ziplock bag and crush the fruit with your hands. Then add a few ounces of the solution to the fruity ziplock. Close the bag and shake lightly and observe in good light. Small, white legless larvae (maggots) should float to the top if your fruit is infested.

But, if you are like me, maybe you don’t want to know your fruit has maggots. Maybe you just want to enjoy the fruit. Maybe your eyesight is bad without glasses, as mine is. So let’s leave our glasses off. As far as I’m concerned, ignorance is bliss in the case of maggots in my fruit. I’ll stick to monitoring and trapping adult flies, thank you very much.

Trapping adult fruit flies from now into fall (the big season) is a good way to help keep populations from ruining your summer fruit. Good garden sanitation helps as well, including these simple tasks:

• Do not add maggot-infested fruit to your compost pile. Instead, dig a hole and bury it. Cover the spot with clear plastic, and the heat of the sun will kill the maggots in the fruit before they emerge as adults.
• Pick your fruit often, as soon as it ripens. Then put it into the refrigerator immediately. Chilling slows or kills developing larvae.
• Pick up overripe or spoiled fruit left on the plant as well as fruit and berries that have fallen to the ground.

For the latest updates and resources, check out OSU’s website at spottedwing.org or the photo-illustrated OSU guide, “A New Pest Attacking Healthy Ripening Fruit in Oregon” at catalog.extension.oregonstate.edu.

Carol Savonen is a naturalist and writer. She is an associate professor emeritus at OSU and tends a large garden in the Coast Range Hills west of Philomath with her husband and dogs. She can be reached at Carol.Savonen@oregonstate.edu or c/o: EESC, 422 Kerr Admin. Bldg., OSU, Corvallis, OR 97331.

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