CORVALLIS, Ore. – Oregon gardeners can reduce the spread of the invasive spotted wing drosophila with the help of a new Oregon State University Extension publication EM 9026, Protecting Garden Fruits from Spotted Wing Drosophila.
"The fly is minute (2 to 3 millimeters in length), infests a variety of fruits and could have a considerable negative effect on Oregon's fruit industry," said Amy Dreves, entomologist in the OSU crop and soil science department. "Although commercial monitoring and management tools are being developed, gardeners also have an important role to play in protecting Oregon's fruit producers."
Evidence of the drosophila, which attacks stone fruits and berries, has been confirmed in 17 Oregon counties, primarily in the Willamette Valley, home to several commercial fruit producers as well as many gardeners who tend backyard berries and fruits.
"Given the rapid spread of spotted wing drosophila in Oregon and across the United States, we suspect that the fly is widespread, well-established and most likely present in additional counties and states,"
The OSU Extension publication has a list of documented host plants – including stone fruits such as cherries, mulberries and peaches, or berries such as strawberries, raspberries and blueberries. It also shows how to recognize infected fruit and monitor adults and larvae.
In addition, videos on how to identify and trap the flies are available on YouTube. For help in recognizing damage, see the online publication EM 9021, Recognize Fruit Damage from Spotted Wing Drosophila.
Careful examination is needed to prevent confusing spotted wing drosophila with common vinegar flies. OSU Master Gardener coordinator Gail Langellotto-Rhodaback advises using a magnifying glass, small hand lens or head-mounted magnifier to more easily see key characteristics.
"Spotted wing drosophila flies are slightly more robust than most vinegar flies," she said. "That includes Drosophila melanogastor, which is commonly used in biology classes."
Both spotted wing drosophila and the common vinegar fly have red eyes and an amber-colored body, but two key characteristics distinguish the spotted wing drosophila: Adult male flies have a black spot near the leading edge of each wing tip, and females have a prominent, serrated and sawlike egg-laying device on their hind end that inserts eggs into ripe fruit. Males also have two sets of black combs, which appear as bands on their front legs.
Spotted wing drosophila flies can infest a variety of stone fruits and berries. They prefer hosts that have soft, thin skin. Some fruits, such as figs, apples, tomatoes and grapes, are subject to infestation if they are damaged or have split skin. Susceptible fruits appear to be most vulnerable when ripe or slightly overripe.
A combination of cultural, physical, biological and chemical methods can be used to control the spotted wing drosophila, and the OSU Extension publication tells how to use them with fewer negative effects.
To share findings with OSU researchers on weekly backyard fly counts or samples of infested fruit, download the sample form found online.