Invasive fruit flies wreaking havoc on small, soft fruits in Androscoggin County

Invasive fruit flies wreaking havoc on small, soft fruits in Androscoggin County

After the 2023 crop season flopped for many farmers due to seemingly never-ending rains, Maine is battling another problem this year: fruit flies, more specifically the invasive spotted wing drosophila.

The spotted wing drosophila, a pest that came to the United States from Asia, can damage berries, soft fruits, and some vegetables. This year it came early and caused the failure of some strawberry farms. File photo

The flies landed in California from Asia around 2008, said Philip Fanning, assistant professor of agricultural entomology at the University of Maine.

A specialist in integrated pest management, biological pest control and applied insect ecology, he is tracking the flies in Maine, which arrived around 2011.

“It’s a small, invasive vinegar fly and (we’ve found) that some years it’s not a problem for growers, but other years it comes a little earlier and is a bigger problem,” Fanning said. “This year, it looks like our populations are going to be pretty high. They’re at least reproducing much earlier than we had hoped.”

Fanning said the pests usually appear sometime at the end or shortly after the strawberry season, but this year they have devastated many strawberry crops across the state.

Joel Gilbert of Berry Fruit Farm in Livermore Falls said his farm had to shorten the strawberry season mainly because of spoilage caused by pests.

“It’s tough after last year’s rain and we definitely want to give people the best fruit we can,” Gilbert said. “The weather has been great for berries, especially strawberries, so it’s (unfortunate) that the strawberry season had to be shortened. We’re definitely learning from it though.”

Gilbert said he is working with the University of Maine Cooperative Extension to keep the pests under control. The Extension, with Fanning and his research, has helped several farms across Maine track pest populations and implement measures tailored to each farm to limit their impact on crops and maximize yields.

David Handley, UM associate professor of horticulture and a vegetable and soft fruit specialist, specializes in pest management strategies, among many other areas of expertise. As a certified pesticide applicator and applied researcher, Handley is a driving force in helping farms combat invasive species like Drosophila.

“These flies came about three weeks earlier than expected – many were surprised by the early timing,” Handley said, adding that the damage so far provides only a small glimpse of the full potential of the pests’ impact. “(They’re) just getting started.”

Handley and researchers have helped farmers set traps for the pests, allowing researchers to track populations. The extension then helps farmers create management plans to maintain crops and keep the pests away.

While tried-and-true methods of pest control rely heavily on early and increased harvests, Handley says Fanning is trying a new method: parasitic wasps. By introducing a natural predator of the spotted wing drosophila, Fanning hopes farmers will get some relief.

“My lab bred this little parasitic wasp that was approved for release a few years ago,” Fanning said. “We’ve put a lot of time and effort into breeding this wasp and releasing it at sites here in Maine. This is the biological natural control that we hope will help contain this invasive species here in Maine.”

Fanning said he and his researchers discovered a group of wild raspberry bushes on the side of the road while traveling between sites. Curious to see how production was going outside a human-managed environment, they examined the fruit to determine the extent of damage caused by the flies.

“We actually found one of these little parasitic wasps. It’s not the one we’re releasing, but another one, Leptopilina japonica, that found its way here to Maine all on its own. It was sitting on a raspberry, probably looking for one of these fruit flies as a host. It’s really cool to find that in nature and to control these populations naturally,” Fanning said.

Walter Goss of Goss Berry Farm in Mechanic Falls said his farm participated in the trapping and tracking of the pests and the parasitic wasp experiment. He said he isn’t sure of the results, but because of basic pest control methods and these University of Maine Cooperative Extension programs and experiments, he isn’t worried about his season — the flies have made their presence felt, but his crops have not fallen victim to them.

“We’ve been fighting these fruit flies for over a decade now,” Goss said. “Other than sprays and chemicals, which we try not to use, the only way to control (the fruit flies) is to harvest the fruit.”

Goss said picking fruit when it is just beginning to ripen deprives fruit flies of a food source and forces them to look elsewhere for a source. But that’s exactly the problem, he said. The flies initially feed on wild fruits such as bird cherries, wild raspberries, blackberries and more.

“The farmers who tell you they are not a problem probably just don’t know it yet,” he said.

For more information about the University of Maine Cooperative Extension, visit

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