Spotted wing drosophila, a pest that came to the U.S. from Asia, can cause damage to berries, soft fruits and some vegetables. New legislation proposes to fund a biocontrol to keep its numbers down. File photo

Sen. Susan Collins is co-sponsoring legislation that would fund a new program to control the spotted wing drosophila, an invasive fruit fly from Asia that has been damaging Maine fruit crops since 2011.

In Maine, the prime crop of soft fruits affected by the pest are blueberries, a major industry especially in Washington County, but the pest also affects raspberries, blackberries, grapes, peaches and other soft fruits that many Maine farmers and gardeners grow.

The pest arrived in North America in 2008 and is now just about everywhere soft fruit is grown – the West Coast, Midwest and down to Florida.

The legislation would provide $6.5 million a year for five years to fight the spotted wing drosophila (SWD), which has cut the state’s blueberry harvest by about 30 percent. The bill was introduced on Aug. 2 and referred to the Senate Agriculture Committee, according to Collins’ office. A hearing has not yet been scheduled.

For now, the only way growers have to fight the bug is pesticides, David T. Handley, a vegetable and small fruit specialist with the University of Maine Cooperative Extension at Highmoor Farm in Monmouth, said in a telephone interview.

But there are several problems with those pesticides, even though some are approved for use on organic crops.

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“The list of pesticides that work on this pest is pretty small,” Handley said, “and they can be used only a certain number of times, because you don’t want the flies to build up a resistance. And you can’t use them too close to the actual harvest.”

That doesn’t even touch on the price farmers must pay for the insecticides and the salary to workers who spend hours applying them.

The solution being worked on through the proposed legislation is a parasitoid, also called a biological control agent, that attacks the spotted wing drosophila. Handley described the control as a really tiny wasp. The wasp’s name is Ganaspis brasiliensis, according to Philip Fanning, assistant professor of agricultural entomology at the University of Maine.

The selection of this insect, Fanning said in a phone interview, “culminates about 12 years of research, finding the right parasite. It’s a strict process making sure the release will not impact any of our native species.”

The research then undergoes strict, peer-reviewed studies. “We are confident it will be safe to release,” he said. This particular wasp does not sting people.

Having found the right tiny wasp to attack the pesky fruit fly – also called a vinegar fly – why does it cost $6.5 million a year for five years to develop, raise and release it?

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Well, it is a difficult process. Handley described it as “sort of magical,” getting these teeny wasps to reproduce, then rearing them in a controlled environment, so that thousands can be released at the right time to control this one specific fruit fly.

Note that I said “control,” not “eliminate.” The wasps were selected because they control the drosophila in Asia, where, like their target, they are native. The damage to fruit in the pests’ home is not as bad as it has been in Maine.

The program would not be the first time such parasites have been used in Maine to control pests. A winsome fly has kept in check the Japanese beetles that used to devastate our raspberries. Parasites have also been used, with varying success, to control winter moths and lily-leaf beetles, and they are being considered for emerald ash borer.

Sometimes a pest seems to be eliminated, but then rebounds, Handley said. The good news is even when these pests rebound, they are usually less of a problem than they were before the release of the parasite, he said.

In chatting with Handley, I noted that my wife and I grow strawberries, high-bush blueberries and raspberries, and that I was surprised we haven’t had problems with spotted wing drosophila. He attributed our good fortune to the fact that our fruits are harvested by early August. SWD doesn’t do well in Maine winters. Very few survive until spring. But the ones that do survive start reproducing rapidly. The reproduction cycle is just one to two weeks, so by mid-August there are many generations of the pests, and enough to do serious damage.

Handley said many commercial blueberry growers try to take in as much of the harvest as early as they can, in order to beat the heaviest infestation. Many, however, do not have enough workers to complete the harvest that quickly, and some blueberries are not ripe by then.

Once again, I am really glad that I am a gardener, who grows food and flowers because I enjoy doing it, and not a farmer, whose livelihood depends on what he or she grows.

For the professionals’ sake, I hope the legislation is approved and this biological control works.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at: [email protected]


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