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Rhonda Ferree's ILRiverHort

Rhonda Ferree's Horticulture Blog

Alert on new pest of fruits – Spotted Wing Drosophila

Everyone growing blueberries, blackberries, and raspberries should be monitoring for spotted wing Drosophila, a new invasive pest that infests thin-skinned fruits as they ripen. University of Illinois Extension Entomology Dr. Rick Weinzierl says, "This invasive insect is known to be present in much of Illinois and will damage these crops severely, making the fruits unmarketable."

On June 28th Dr. Weinzierl's traps in raspberries at the research farm at Urbana picked up spotted wing Drosophila for the first time this season. He also received a call on infested fruit south of Springfield and had reports in the Peoria area last fall. "It likely is present in most, if not all, of the counties in Illinois." Dr. Weinzierl emphasizes that this WILL be an issue for home gardeners as well as commercial growers. If you are seeing gross little white maggots in your garden raspberries right now, this may be the critter.

According to the Home, Yard, & garden Pest Newsletter (, Spotted Wing Drosophila (SWD) is a destructive pest of thin-skinned fruits because unlike other fruit flies, it lays eggs into ripening fruit before fruit is ready for harvest. Infested fruits "melt down" from larval feeding and fungal rots in just a few days. Adult flies are tan with red eyes and a tiny 2-3 millimeters long (up to one-eighth inch long). Males have characteristic dark spots on their wings that can easily be seen with a magnifying glass. Adults live for up to 2 weeks, and females can lay up to 300 eggs. Development from egg to adult can occur in as little as 8 days, and 10 or more generations may occur within a season.

The highest risk fruits include raspberries, blackberries, strawberries, cherries, nectarines and blueberries. At moderate risk are peaches, grapes, pears, apples and tomatoes. SWD can also build up populations on wild and cultivated plants with berries such as snowberry, elderberry, pokeweed and dogwood.

So what can you do now? To minimize build-up of populations remove and destroy overripe fruit and keep fruit harvested. Since SWD can also attack fruits of weedy plants such as pokeweed, remove these plants and/or their fruits. The tiny white maggot larvae will be feeding in the fruit even before harvest.

To monitor presence of the adults a simple trap can be made out of a clear plastic cup with numerous small holes and a lid and hung in the shade near raspberries. Apple cider vinegar is used as bait in the bottom of the cup and yellow sticky traps keep the flies trapped until they can be identified.

For more information about Spotted Wing Drosophila and constructing monitoring traps, Dr. Weinzierl recommends a Michigan State University web stie devoted to it ere is lots of useful information on this insect on a Michigan State University web site devoted to it

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