The Homeowners Column

The Homeowners Column

Alert on new pest of fruits – Spotted Wing Drosophila

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator

Okay we are all used to fruit flies annoyingly fluttering around our kitchens this time of year. Their existence can be quickly traced back to the rotting tomatoes or bananas you've ignored in a bowl or on the windowsill. Once the rotting fruit is gone and any white pupa stuck to bowls or containers are squished and removed, then our native fruit flies have no place to reproduce and eventually die out. Unfortunately there is a new fruit fly native to East Asia that goes well beyond being just an annoyance since it does not need damaged or rotting fruit to lay eggs.

According to the recent University of Illinois Extension Home, Yard and Garden Pest Newsletter over the summer and especially the last few weeks, detections of adult Spotted Wing Drosophila (Drosophila suzukii) and reports of larval damage to fruit have been increasing in Illinois and nearby states including Iowa, Wisconsin, and Minnesota. Infestations have posed problems in Michigan since 2010 and in the Pacific Northwest since 2008. In Illinois, the list of counties where this insect has been collected include Pope, Union, and Marion in the southern part of the state, Champaign, Tazewell, and Adams in the central part of the state, and Ogle County in the north. It likely is present in most, if not all, of the counties in Illinois. If you are seeing gross little white maggots in your garden raspberries right now, this may be the critter.

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. Right now the SWD fruit flies are showing up in fall raspberries. 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.

In future years growers may have to consider insecticide spray programs to keep this insect in check. For more information about Spotted Wing Drosophila and constructing monitoring traps or contact UI Extension for information.

Now for some good news join us Tuesday October 2 at noon for Master Gardener Ann Tice's program on "Beautiful Bulb-O-Mania" held at UI Extension auditorium 801 North Country Fair Drive in Champaign. Program is free. No registration required. Bring your lunch at 11:30 am and stay for the 45 minute program at noon. Ann has a wealth of practical experience, pearls of wisdom and inside tips on how to grow bulbs successfully!

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