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Spotted Wing Drosophila Proves Formidable Fruit Foe

MSU entomologist Rufus Isaacs works with his students and staff in the laboratory.

When a tiny invasive fly — the size of a grain of rice — called spotted wing drosophila (SWD) first arrived in California from Asia in 2008, researchers weren’t overly concerned. Entomologists were confident that management programs could be developed quickly and the risk to the soft-fleshed fruit that the pest covets could be mitigated.

But that outlook changed the following year when the insect was reported more than 2,000 miles away in Florida. This revelation gave researchers, including Michigan State University (MSU) small fruit entomologist Rufus Isaacs, great pause.

“When they found SWD in Florida in 2009, that’s what really got the alarm bells ringing,” Isaacs said. “It meant that this wasn’t just a West Coast issue anymore. MSU sent me to a meeting about this pest in Oregon shortly after it was found in Florida, and when I came back it was clear we needed to get ready here in Michigan.”

MSU researchers didn’t want to take any chances, especially with a statewide fruit industry valued at more than $375 million per year. In 2010, Isaacs received his first SWD grant from Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs), a partnership among MSU AgBioResearch, MSU Extension and the Michigan Department of Agriculture and Rural Development. Project GREEEN works with commodity groups to find solutions to plant agriculture challenges in Michigan.

Isaacs, along with other fruit extension specialists and extension educators, set traps to monitor for the insect. Researchers used small plastic containers covered with holes and filled with an attractant (at first apple cider vinegar and now a mixture of sugar and yeast) and a sticky trap. In early fall 2010, a few flies were collected from a monitoring site in southwest Michigan. They were later positively identified as SWD by the MSU Diagnostics Services lab and then U.S. Department of Agriculture (USDA) taxonomists in Beltsville, Maryland. Since then, the invasive pest has been discovered across the Lower Peninsula.

Most of the SWD research led by Isaacs has been in collaboration with blueberry and raspberry growers. His early work involved testing already-registered pesticides and determining their efficacy. Other options his group has studied include physical exclusion, where growers place netting around and on top of crops as they begin to ripen.

In 2015, Isaacs and Matthew Grieshop, an organic pest management expert at MSU, were awarded a grant from the USDA’s National Institute of Food and Agriculture (NIFA) to study long-term solutions with researchers at the University of Georgia and other institutions. The goal is to develop new growing practices and test organic approaches to managing SWD.

Isaacs, as well as MSU entomologists Larry Gut and Ke Dong, is working in conjunction with North Carolina State University to study insecticides, biological controls and cultural control approaches. The group also aims to understand how this pest might develop resistance to insecticides. This project is funded by USDA’s Specialty Crop Research Initiative (SCRI), a program of NIFA.

“There is a community of natural enemy insects that attack SWD in Asia,” Isaacs said. “With the SCRI grant, one of the objectives is to look at biological controls. This pest can build up in wild areas where growers can’t manage them easily, but if biological controls can help to reduce the population pressure, it should allow control measures applied in the fields to work much better. Risk assessments are underway to determine if the Asian biological controls are a viable option here in the U.S.”

It will take a large group of researchers to tackle this problem, Isaacs says, but he is encouraged with the urgency expressed by funding agencies.

“We’ve gone from a lot of people getting small, local funding for research to now also being coordinated nationally through these two recent grants,” Isaacs said. “Since this is a national problem now, we need to address it with a national team of researchers.

More at the AgBioResearch website…

– Cameron Rudolf, excerpted from Futures, Fall/Winter 2016

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