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Entomologists Use Insects for Emerald Ash Borer Surveillance

University of Maine and state entomologists are using a novel method — using insects to track insects — in the statewide surveillance for the destructive emerald ash borer, which has devastated ash forests in 15 northeastern states, parts of Canada and now threatens Maine.

They’re using a little black ground-nesting wasp — Cerceris fumipennis — that captures, paralyzes and feeds jewel beetles and wood-boring insects related to the emerald ash borer alive to its young.

UMaine professor of entomology Eleanor Groden and School of Biology and Ecology graduate student Tawny Virgilio, working under a Maine Forest Service grant and funding from the Maine Agricultural and Forest Experiment Station (MAFES), have established several theaters for biosurveillance and volunteer training at wasp colonies, including one at the Dedham Elementary School, to monitor the behavior of the wasp. Cerceris fumipennis wasps sting only their prey – jewel beetles similar in appearance to the small metallic green emerald ash borer — but not humans.

Since discovering within the last few years that the Cerceris wasp hunts emerald ash borer beetles, the U.S. Forest Service, Maine State Forest Service and Canadian entomologists have begun volunteer-based surveillance of the Cerceris wasp. Researchers hypothesize that watching the wasps will reveal ash borer presence.

Since little is known specifically about the foraging habits of the wasp, Groden says, she and Virgilio are documenting its habits.

“We’re looking at the conditions under which the wasps are flying and collecting prey, and whether they have any preference for a particular prey type that might influence their accuracy in detecting emerald ash borers,” says Groden.

State Forest Service entomologist Colleen Teerling says eight percent of Maine’s hardwood forests are black or brown ash, which are important to Native American basketmakers, among others.

“It’s a good street tree,” she adds. “Ecologically, it’s kind of important because when the elm trees died, ash kind of moved in and filled in for the elm. If ash trees disappear, it’s not just one tree; it’s all the ash species.”

The ash borer has not yet been found in Maine, but has been reported in large numbers in Michigan, Pennsylvania, New York, Ontario and parts of Quebec. Groden says experts predict it’s a matter of when, not if, the invasive beetle arrives in Maine.

“If and when the emerald ash borer does come to Maine we want to find it as soon as possible,” Teerling says. “If we find that it’s here after a dozen years and it spreads hundreds of miles, there’s not much we can do other than watch ash trees die. If we find it early on, there are things we can do to manage it and keep the infestation smaller, keep from spreading and keep some degree of control over it.”

Virgilio has been spending warm, sunny, and also cloudy, days in the field with Groden and UMaine student Erwin Cusack, along with Lydia Horne of St. Lawrence University in New York and Orono High School student Ben Koehler, watching wasp colonies and monitoring environmental conditions and correlating it all with the wasps’ behavior.

“Emerald ash borers are very small and cryptic insects that often infest the tree canopy first, which makes spotting them difficult unless there’s a major infestation leading to a devastating ash die-back, which we want to avoid,” Virgilio says.

“These wasps are very efficient at finding them,” Groden adds. “We don’t know how they find them. That’s one of the things we’re trying to study — what they orient to, whether it’s the odors given off by the host plant that the beetle is attacking or whether it’s the odors or visual cues the beetles put out themselves.”

The research is important, Teerling says, “because there are some days we’ll go out and the wasps are flying but they’re not bringing in prey. Other days we’ll go out when we think it’s a good day for hunting and they’re just sitting down in their nests and we don’t really know why.

“Hopefully, we’ll be able to learn a little bit more about when they hunt in Maine, and under what conditions they hunt, so we can be a little more intelligent about how we do our biosurveillance,” Teerling says. “No sense sending out a volunteer on a day they may not be hunting.”

Citizen-based biosurveillance is a relatively new concept using one insect to detect the presence of another, Groden says. “In fact, if this program is successful, the USDA is very interested in the potential to use similar types of wasps to monitor for a whole variety of pest insects we want to be able to detect at very low densities,” she says.

Contact: Tawny Virgilio, (413) 347-0226; George Manlove, (207) 581-3756

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