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Spotted wing drosophila spotted in Michigan

Spotted wing drosophila (SWD) has been found in Michigan.

Drosophila suzukii, a small vinegar fly native to Asia, had been found previously in the Pacific Northwest, California, and some other states, but it has now been trapped in September by Michigan State University (MSU) entomologists.

This is the first time it has been found in the Midwest.

SWD is a pest of berry crops, cherries, grapes and tree fruit, with a preference for softer fleshed fruit. Unlike other fruit flies that attack mostly overripe fruit, this fly invades earlier. Because of Michigan’s large acreage of vulnerable blueberries, small fruit entomologist Rufus Isaacs sought funding for a monitoring program.

No flies were trapped in Michigan through the summer months, but in late September and early October, monitoring traps in southwestern Michigan picked up adult males and females. It has not been found in any fruit, and flies were trapped only after crop harvest was complete.
A Michigan SWD response team was formed earlier this year to survey the state’s fruit industries and to develop a pre-emptive early detection-rapid response plan as part of an integrated pest management strategy, according to a university press announcement. The response team is comprised of entomologists from the MSU Departments of Entomology and Horticulture, MSU Extension staff, staff members from the Michigan Department of Agriculture, and fruit commodity leaders. The plan included setting out traps across Michigan in crops the pest was known to affect.

A page devoted to SWD was added to the MSU IPM Web site www.ipm.msu.edu/swd.htm.

Further monitoring is underway this fall to determine the distribution of this fly in Michigan. Fruit growers in the state are being asked to become aware of this pest and to plan for trapping, monitoring, and crop-specific control measures as part of their IPM program for 2011.

“We have been aware of SWD since it was first discovered in 2008 in California,” Isaacs, the chair of the response team, said. “This insect is originally from Asia but has already been found to be invasive in Hawaii, California, Oregon, Washington, Utah, Florida, the Carolinas and British Columbia. Our response team set up 300 traps in June in more than 100 fruit-growing sites and checked them regularly. The traps were monitored the entire season with no positive finds of SWD until late September in a few fruit farms. This is probably because harvest was complete in July and August, so growers were no longer actively managing pests in those fields.

Isaacs says that because the pest was found after fruit harvest, there was no threat that the pest was in harvested fruit. He also noted it was found in an area that had minimal insect management.

“This pest was found only late in the season, so this gives us an opportunity to help growers learn what they need to know to effectively address SWD in 2011,” says Isaacs. “The SWD response team is confident that Michigan growers can control this pest with proper management.”

Because SWD has not been previously found in Michigan, it is not known if it will survive the cold Michigan winter.

“If SWD is detected again next year, it is one more insect pest that Michigan fruit growers will need to add to their crop management programs. IPM strategies will be implemented next year to help monitor and control SWD.”

Educational presentations about SWD will be delivered at MSU Extension meetings for fruit growers this winter, including at the Great Lakes Expo meeting in Grand Rapids in early December.

Keith Mason, a research technician in the Isaacs entomology lab, said the finding of the fly in Florida triggered the monitoring effort in Michigan.

“Obviously, it is able to move, and we wanted to see if it would make it to Michigan,” he said. “It’s a very small insect, and it can move in fruit along highways or in somebody’s lunch bag.

“It has really caused a ruckus in Oregon, California, and Washington,” he added, noting that these arid areas traditionally have fewer insects to deal with. “We’re more used to dealing with insect pests in Michigan. A lot of insecticides are effective. We haven’t made any recommendations yet, but we see no reason to shift into panic mode.”