By KEVIN WALKER
Michigan Correspondent

VAN BUREN COUNTY, Mich. — A pest that could pose a threat to fruit crops has been detected for the first time in southwestern Michigan.
Spotted wing drosophila (SWD), a fruit fly never before detected in Michigan or anywhere in the Midwest, has been found in plastic traps set out for this purpose. The insect was found only after harvest; officials believe no harvested fruit could have been infested with the flies.

Extension specialists have been setting out traps for the fruit fly since early this year and none were found during the growing season, according to state officials and Michigan State University extension personnel. (A link to the SWD website set up by extension is provided at the end of this article.)

The MSU SWD website provides a link to another website in Oregon, where SWD was already known to exist. It has existed in Hawaii since the early 1980s, according to Robin Rosenbaum, plant industry section manager at the Michigan Department of Agriculture (MDA). It was discovered in California in 2008.

“I know there have been 10 positive detections in 10 counties,” Rosenbaum said. “It’s not in the northwest part of the state. Spotted wing drosophila is in Michigan. We knew it was going to make its way here.

“Farmers will have to manage for this pest. They’ll have to be on the lookout for it.”

Rosenbaum said farmers who grow blueberries and other fruits may have to treat their crops more frequently to avoid an infestation of SWD; however, the same kind of insecticides used to treat for other insects can be used effectively for SWD. SWD may end up posing more of a threat than some other pests because it has the ability to cut into healthy fruit and lay eggs, rather than just infest fruit that’s already damaged.

On the other hand, it’s not yet known if the fly can survive the winter in Michigan. Rosenbaum said most likely, the insect was inadvertently transported to Michigan from Florida, where it was discovered early in 2010. SWD is unable to fly very far on its own.
It’s also been detected in the Carolinas. It was detected most recently in Flint, Mich., in the southeastern part of the state.
“We will go under the assumption that it will survive the winter,” Rosenbaum said. “Nobody likes the idea of having to control yet another pest, but we’re pretty well prepared for it. We’re confident that Michigan growers are well versed in IPM (integrated pest management).”

Mark Longstroth, extension district fruit educator for southwestern Michigan, said SWD has been trapped in Van Buren, Berrien, Allegan, Ottawa and Kent counties.

“We trapped them in blueberry and raspberry,” he said. “I believe other people have trapped them in grapes. I expect to see them in grapes next year.”

He said Ohio, Indiana and Illinois put traps out, but not enough to catch any flies. He believes those states will detect them next year.
Since fruit crops are so significant in Michigan, more monitoring has been done. People in Michigan put out about 200 traps, which are simple contraptions – basically, a plastic cup with a little bit of vinegar in it to attract the fly, with a small hole to allow the tiny insect through but not other, larger insects. A yellow sticky piece of paper is put in to trap the fly.

Longstroth thinks the flies will probably survive the winter. “They can handle several freeze-frost cycles,” he said. “I would not want to guess that they can’t over-winter here. It could be a problem for anybody that grows soft fruit or vegetables.”

The upcoming fruit and vegetable show in Grand Rapids will be a focal point for educating growers about this new threat to their livelihood, Longstroth said. In the meantime, anyone wanting to learn more about SWD may find additional information at www.ipm.msu.edu/swd.htm