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Spotted wing drosophila attacks stone fruits and berries

This space is generally devoted to talk of delicious foods, but today we need to address something far less appetizing: insect-infested fruits — yuck!

It’s been brought to my attention that we are experiencing more than a casual outbreak of fruit flies.

by: SUBMITTED PHOTO:  ERIC LAGASSA, WASHINGTON STATE DEPARTMENT OF AGRICULTURE - Adult spotted wing drosophila female, left, and male,  right, flies. Females have a saw-like ovipositor on their hind end (circled).

My friend Carol Peterson sounded the alarm. She discovered the dastardly spotted wing drosophila on the berries she had brought home from an area farm stand. As is her routine, she washed the perfect-looking blackberries in a solution of water and white vinegar and then noticed little white worms crawling out of them. An Internet search of white worms in berries led her to the conclusion that they were probably spotted wing drosophila (SWD or Drosophila suzukii), a relatively new-to-us invasive pest that attacks stone fruits and berries.

Jordis Yost, Master Gardener coordinator at the Clackamas County OSU Extension Service, concurred with Carol’s finding. She said this tiny fruit fly is native to Japan and has been established in Hawaii since the 1980s. SWD was first noticed on the mainland U.S. in fall 2008 and made its debut in Oregon in 2009. SWD has been confirmed in 17 Oregon counties and OSU Extension says is reasonable to suspect the pest is most likely present in additional counties and states.

Of course fruit flies are nothing new; they seem to show up wherever there is fruit or other sweet things beyond their prime. These foods are usually no longer appealing to us to consume so we don’t mind throwing them away. What is unique about SWD is that they attack perfect fruits. The females have a saw-like attachment on their abdomens (an ovipositor) that allows them to open unripe fruit and deposit their eggs. After the eggs are laid, the larvae feed inside the fruit for five to seven days before the pupae would begin to emerge, making it difficult to detect infestation, as Carol discovered.

Yost points out that insect-infested fruit is not toxic, just unpleasant to eat. If this makes you a little squeamish about eating fresh fruit, don’t be. Our friends at OSU suggest these methods to separate larvae from fruit:

Salt extraction method: Place no more than two pounds of fruit in a shallow, white pan. Add 1 tablespoon salt to 1 cup warm water. Allow the salt to dissolve, and then pour the solution over the fruit. The salt will cause the larvae to exit the fruit and move to the top layer of the salt solution. Within minutes — if larvae is present — you should see small white moving larvae on the top layer of the liquid. (The experts at OSU caution that the larvae will eventually die and sink to the bottom of the pan, so work quickly to remove them.)

Fruit dunk flotation method: Lightly crush the collected fruit and place it in plastic sandwich bag. Prepare a sugar solution of 1 tablespoon sugar to 1 cup water; allow the sugar to dissolve and then pour the solution into the bag. If the fruit is infested, you will generally see the white SWD larvae floating in the bag. As the fruit settles to the bottom some larvae will float to the top. Depending on their weight and sugar content, some fruit may float. It may take up to an hour for the larvae and fruit to separate. Hold the bag up to the light to better see the larvae floating among the fruit. If the larvae are small, a hand lens may be useful.

OSU is researching many methods to control SWD infestation, including promoting good farming practices that will prevent or reduce the probability of infestation, such as managing irrigation to avoid fruit splitting, harvesting fruit in a timely manner, solarization (using heat from the sun to kill pests) and more. Physical controls, such as netting, and biological controls, such as naturally occurring predators, parasitoids or pathogens, are all being researched. OSU experts say that chemical sprays will not prevent SWD from visiting gardens and instead will result in needless application that may negatively affect biological controls and the environment.

Much of the information shared here came from OSU’s publication “Protecting Garden Fruits From Spotted Wing Drosophila.” You can read the document online at ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/20883/em9026.pdf.

The talk in our office leads me to believe that we’ve all eaten “a little extra protein” with our fruit before and lived to tell the tale.

Still have an appetite? I hope so, because hundreds of Oregon fruit producers are counting on us to eat what they grow.

The methods described above and certainly baking should take care of any infestation problems. But as in all food-related things, follow the adage: When in doubt, throw it out.

Bon appetite eat something wonderful!

Summer Berry Crisp

Juicy berries are marvelous nestled under a crispy top. This dessert is easy enough for a beginning baker to make and serve with pride.

2 cups blueberries

2 cups blackberries

2 cups raspberries

1/4 cup sugar

1/4 cup all-purpose flour

1/4 teaspoon cinnamon

Crisp topping

1 cup rolled oats

1/2 cup all-purpose flour

1/2 cup brown sugar

1/2 cup sugar

Pinch of salt

1/2 cup (1 stick) cold unsalted butter, cut into small pieces

Whipped cream or vanilla ice cream, for serving

Preheat the oven to 350°F. Butter a 9-inch Pyrex pie plate.

Gently combine the berries with the sugar, flour and cinnamon; place in the prepared pie plate.

Prepare the topping: Combine the oats, flour, both sugars and salt in a bowl. Use a pastry blender or two knives to work in the butter until topping resembles coarse meal. Sprinkle evenly over the berries.

Place the pie plate on a baking sheet. Bake in the center of the oven until the fruit is bubbling and the topping is golden brown, about 1 hour. Remove the crisp to a rack to cool slightly. Serve in dessert bowls with whipped cream or ice cream.

Adapted from Parade, July 2007

Randall welcomes your food questions and research suggestions. She can be reached at 503-636-1281, ext. 100, or by email at This email address is being protected from spambots. You need JavaScript enabled to view it..

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