News release: Spotted Wing Drosophila

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640

Release date: Sept. 5, 2013

Title: Spotted Wing Drosophila

Earlier this year, I spoke to a group in Trenton about several invasive pests that are either here, or on their way to Missouri. Examples included the Emerald Ash Borer, the Brown Marmorated Stink Bug, and Thousand Canker Disease of black walnut.

Well, now there’s another one:  the Spotted Wing Drosophila (SWD). This is a small fruit fly, about 2-3mm long.  We have known for the last couple of years that they could invade Missouri at any time.  Unfortunately, this seems to be the year, with reports coming in from all parts of Missouri.

SWD was first observed in Asia and Europe in the 1900’s, but it wasn’t found in North America until 2008. It was initially seen on the west coast, but quickly spread to parts of Canada and Florida. Later infestations were found all along the east coast, and finally the Midwest.

Fruit flies, sometimes known as vinegar files, are commonly seen around damaged or fermenting fruit. But most fruit flies cannot attack good, undamaged, healthy fruit.  SWD is different.  The female SWD has a serrated ovipositor, which allows it to penetrate the unbroken skin of good fruit to lay its eggs. This allows the larvae to develop inside the fruit.

Preferred fruit include raspberries, blackberries, blueberries, grapes, and cherries. They are also seen in peaches, nectarines, and elderberries. They can also affect tomatoes if they have cracks or bruises.  Wild fruits subject to SWD infestations include persimmon, mulberry, pokeweed, autumn olive, crabapple, nightshade, Amur honeysuckle, and wild grapes, just to mention a few.

SWD can be controlled with insecticides.  There are even some insecticides that are approved for organic growers. These should be rotated frequently, to avoid resistance problems.

Most large orchards and vineyards are probably already on a spray schedule that will keep SWD under control. But small fruits such as brambles and blueberries typically did not require as much insecticide use since insect pests were generally not as severe. SWD, however, has changed that picture.  All fruit growers will need to be on the outlook for this new insect.

To tell if you have SWD in your fruits, the easiest way is to construct a trap.  My web site has links to plans to make these traps and instructions on how to bait them. Once you start collecting fruit flies, you will need to correctly identify them. A guide to identification is also on my web site. Once you know that you have SWD in your orchard, vineyard, or berry patch, you will need to start your spray program to keep them under control.

I am aware of two infestations of SWD in the Northwest Extension Region. One was in a large blackberry planting, and the other in some raspberries under a high tunnel.  I saw the latter infestation in person. Almost every raspberry contained tiny larvae, which the grower obviously could not sell. A third location with a small blackberry patch may have also had them earlier this summer.

Spotted Wing Drosophila is a serious issue. If you have plantings of fruits that are subject to these pests, you’ll want to watch out for them.  I have created a web page to show you what this insect looks like.  The page also links to other resources which will help. You can find my web page at: