Wednesday, July 31, 2013

Monitoring for Spotted Wing Drosophila: An Insect Pest of Berries and Other Fruits in Missouri

Male SWD
2 black spots on wings

A Spotted Wing Drosophila (SWD) is a small vinegar or “fruit” fly that is about 2-3mm in length. For the past two years, it has been a problem in several areas of the U.S., including the Midwest.

The Spotted Wing Drosophila (SWD) (pronounced Dros-o-fill-ah) has caused economic damage to berries, grapes and soft-fleshed fruits, such as peaches. The SWD is also able to attack some vegetables, including tomatoes and peppers. Unlike most other vinegar flies that lay eggs on damaged or fermenting fruits, SWD females can cut into healthy fruit. They do this by using their serrated (saw-toothed) ovipositor (organ for depositing eggs) to inject eggs under the skin of the fruit. The adult SWD lives for about two weeks; during this time, each female can lay more than 300 eggs. The larvae hatch and feed inside the fruits, causing them to rot. This insect reproduces so quickly that a few adults can become thousands of flies in just a few months.
Female SWD
Lacks 2 black spots on wings

It is very important that farmers learn how to monitor for this invasive pest. A simple trap can help you determine whether the SWD is present. The most effective and economical trap can be prepared using a clear plastic cup with a fitted lid. Bait this trap with a mixture of water, dry active yeast and sugar, as shown below. Note that there are small holes in the sides of the trap that allow the flies to enter.

A small yellow sticky card can be placed inside the cup. In that way, flies that are attracted by the bait will enter the trap and be retained by the card. This allows for easier fly identification, which is the purpose of this trap. For small acreage (or in a high tunnel), researchers suggest setting one trap for plots up to one acre. However, for larger farms, a minimum of three traps per five acres should be used. These monitoring traps need to be placed inside the vegetation, in the shade.

It is also a good idea to put a trap in adjacent woods, where activity can occur earlier if there are plants bearing wild berries. Set traps just before the fruit starts to ripen. Check traps and replace yeast and sugar bait each week.

If you are interested in monitoring for this pest and need materials at no cost, please contact Dr. Jaime Piñero at or (573) 681-5522.

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