Responding to invasion: MSU shields fruit industry against tiny fly with big impacts

Rufus Isaacs, MSU professor of entomology, has been leading a committed, grower-centered response to the threat of SWD in Michigan.

Rufus Isaacs, MSU professor of entomology, examines captured spotted wing drosophila in a blueberry field.

Michigan’s fruit industry boasts more than 22,000 acres devoted to small fruit production; blueberries account for a whopping 20,900 of those. Valued at $118.5 million, the blueberry industry has helped Michigan gain a reputation as a top producer of one of the world’s most popular fruits.

In 2010, researchers from Michigan State University (MSU) confirmed the presence of a pest that threatened the future of this industry: spotted wing drosophila (SWD). Since its arrival in the eastern United States, growers of most berry crops have spent millions of dollars on managing the invasive pest.

Rufus Isaacs, MSU professor of entomology, has been leading a committed, grower-centered response to the threat of SWD in Michigan.

Native to Japan, this invasive vinegar fly was discovered in the United States in fall 2008 on California raspberries and strawberries. In 2009, SWD was reported in Oregon, Washington, Florida and British Columbia, Canada, before making its way to Michigan, Utah, North Carolina, South Carolina and Louisiana a year later. SWD is a pest of small fruits (e.g., blueberries, strawberries, raspberries and blackberries) and some tree fruits (cherries, mulberries and peaches).

“Spotted wing drosophila is a problem because the pest can cut its way into fruit while it’s still intact on the bush or tree,” Isaacs said. “This creates a scenario where live larvae could be inside the fruit at harvest time, compromising fruit quality. Additionally, growers have to spend a lot more money on controlling the pest. Combine those two factors, and this pest has quickly had major economic impact.”

In partnership with several MSU AgBioResearch scientists and MSU Extension educators, Isaacs has developed an effective management program that equips Michigan growers with tools to help protect their fruit. Since 2010, he has made it a goal to understand which of the available control options are most effective to guide the recommendations that MSU makes to Michigan’s fruit industry.

Isaacs explains that this has been a team effort. He credits Steven Vantimmeren, a research technician based at the Trevor Nichols Research Center (TNRC), and John Wise, TNRC director, as well as many undergraduate students for developing the research.

“We have developed methods for testing various insecticides and sprayers and, with help from Eric Hanson of the MSU Department of Horticulture, we’ve explored cultural controls — non-chemical ways to prevent SWD infestations,” Isaacs explained. Examples of cultural controls include rapid picking, or removing fruit more frequently from the tree or bush; and netting, a physical method for limiting flies’ access to the fruit.

Over the past four years, Isaacs and his colleagues have identifi the most effective insecticides, first in a laboratory setting and then later in blueberry field tests at TNRC. Eventually, they partnered with local growers to confirm their findings.

“This allowed us to give growers combinations of programs and crop protectants they can use with confi  nce,” Isaacs said. “These have been tested on growers’ farms with success, enabling them to protect their crops and harvest marketable berries. From that perspective, I think we’ve been successful in the short term, but we also need to be thinking about what we can do in the long term to reduce the need for chemical controls.”

Isaacs also worked with the MSU Fruit Team and the Integrated Pest Management (IPM) program to use MSU Extension’s information delivery systems to quickly share vital information with growers across the state.

“Joy Landis quickly established a website from which we share IPM information and updates about this pest’s behavior and presence in the state,” he explained. “For the past three years, we’ve also held a series of hands-on workshops led by Carlos Garcia-Salazar that has brought together growers and consultants for presentations on the latest research and management techniques, as well as opportunities to take part in some hands-on demonstrations.” These activities include building SWD traps, sampling fruit for larvae and identifying the pest on fruit.

Isaacs explained that, in his next phase of research, he would like to explore a range of biological controls — use of natural predators to suppress pests.

“There’s a group in the U.S. that has gone to the native range of SWD to collect its natural enemies,” he said. “Those insects are now being put through a very rigorous screening to see if there are any promising candidates that could be released in the U.S. to reduce SWD populations.”

In addition to planning to explore biopesticides — pesticides that come from natural sources such as fl  ers, fungi, nematodes or viruses — he also expressed interest in determining the efficacy of targeting SWD controls early in the season. Isaacs speculates that there might be a way to kill the flies before they have a chance to reproduce and increase their numbers; doing so could reduce pest pressure during the growing season.

“We have gained some important insights about SWD over the past few years, as well as some results that have helped growers optimize their management of this pest,” Isaacs concluded. “It’s been so important to have the initial lines of defense that are being vigilant in an attempt to keep ahead of potential invaders. There’s still a lot to do, but we’re building on a good foundation of research and Extension eff  ts that are saving these tasty crops.”

See other articles from the AgBioResearch annual report.

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