After a bust 2023 season for many farmers due to seemingly unending rains, Maine is dealing with a different problem this year: fruit flies, more specifically, the invasive spotted wing drosophila.

The spotted wing drosophila, a pest that came to the U.S. from Asia, can damage berries, soft fruits and some vegetables. This year, it has arrived early, shutting down some strawberry operations. File photo

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

Specializing in integrated pest management, biological control and applied insect ecology, he has been tracking the flies in Maine which arrived around 2011.

“It’s a little invasive vinegar fly and (we’ve found) some years it’s not an issue for growers and other years they can come a little bit earlier and can be more of an issue,” Fanning said. “Certainly this year, it seems like our populations are going to be pretty high. They’re at least building up much earlier than we hoped.”

Fanning said the pests usually begin showing up sometime at the end of or just after strawberry season, but this year, they have ravaged many strawberry crops throughout the state.

Joel Gilbert of Berry Fruit Farm in Livermore Falls said his farm had to cut strawberry season short mostly due to spoilage caused by the pests.

“It’s tough after last year’s rain and we definitely want to provide the best fruit possible for people,” Gilbert said. “The weather for berries, especially strawberries, has been great, so having to cut the strawberry season short is (unfortunate). We’re definitely learning from this, though.”

Gilbert said he is working with the University of Maine Cooperative Extension to manage the pests. The Extension, with Fanning and his research, has been helping several farms throughout Maine track the pests’ populations and to introduce measures tailored to each farm to limit their effects on crops and to maximize yields.

David Handley, cooperating professor of horticulture for UM and vegetable and small fruit specialist, specializes in pest management strategies among many other specialties. A certified pesticide applicator as well as an applied researcher, Handley has been one of the driving forces in helping farms combat invasive species such as drosophila.

“These flies came about three weeks sooner than people expected — many people were surprised by the earliness,” Handley said, adding that the damage, so far, is only a glimpse into the full potential of the pests’ effects. “(They’re) only just starting.”

Handley and researchers have been helping farms set traps for the pests, an exercise that allows researchers to track populations. The extension then helps farms create management plans to keep crops producing and the pests away.

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

“My lab has been rearing this little parasitic wasp which was approved for release a couple of years ago,” Fanning said. “We’ve been putting a lot of time and effort into rearing up that wasp and releasing it at sites here in Maine. That’s the biological natural control that we’re hoping will help suppress this invasive species here in Maine.”

Fanning said while traveling between sites, he and his researchers spotted a grouping of wild raspberry bushes on the side of the road. Curious to see how production was playing out outside of a human-managed environment, they examined the fruit to see the extent of any damage by the flies.

“We actually found one of those small parasitic wasps. It’s not actually the one we’re releasing, it’s a separate one, leptopilina japonica, that’s found its way here to Maine all by itself. It was on a raspberry probably looking for one of those vinegar flies as a host. It’s really cool to find that out in nature naturally controlling these populations,” Fanning said.

Walter Goss of Goss Berry Farm in Mechanic Falls said his farm has taken part in trapping and tracking the pests and in the parasitic wasp experiment. He said he isn’t sure of the results, but between fundamental methods of pest management and these University of Maine Cooperative Extension programs and experiments, he isn’t worried about his season — the flies have made themselves known, but his crops haven’t fallen victim to them.

“We’ve been managing 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 manage (the fruit flies) is to keep your fruit picked.”

Goss said picking fruit just as they’re turning ripe takes the food source away from these fruit flies and forces them to look elsewhere for a source. But therein lies the problem, he said. The flies get their start by feeding on wild fruit like chokecherry trees, wild raspberries, blackberries and more.

“Any farmers out there telling you they haven’t been a problem probably just don’t know it yet,” he said.

For more information on the University of Maine Cooperative Extension, go to extension.umaine.edu/.