PORTLAND (AP) — Maine’s wild-blueberry growers are monitoring their fields for a harmful new fruit fly that arrived in the United States five years ago and poses a threat to the state’s crop.

With the blueberry harvest kicking into gear later this week, growers have been watching out for the tiny spotted wing drosophila, a native of Asia that caught some growers off-guard when it first appeared in Maine’s blueberry fields last summer. Growers will learn how pervasive and widespread it is as the berries ripen in the coming weeks.

The fly poses a threat because it lays its eggs in soft fruit as it ripens, damaging the fruit and making it unfit for market.

“We’ve had different insects you’ve had to control, but we haven’t had one that does all its dirty work right when you’re about to harvest,” said Ed Flanagan, president and CEO of Jasper Wyman & Son, a wild-blueberry company based in Milbridge. “We’re planning to win, but if the insect wins, we’ll have a reduced yield in our fields and we won’t have as much grade-A fruit.”

This is the time of year when mechanical harvesters and hand-pickers take to Maine’s 60,000 acres of wild-blueberry fields to harvest the sweet berries, 99 percent of which is sold as an ingredient for muffins, yogurt, jam and other food products.

Wild blueberries are native to North America and grow naturally in Maine and eastern Canada, the only places that grow them for commercial sale. Wild blueberries are different than cultivated berries, which are larger, grow on high bushes and are commercially grown in about a dozen states and British Columbia.

This year’s harvest is projected to be about average at 86 million pounds or so, down from last year’s 91 million pounds, the second-largest crop on record.

The quality of this year’s crop appears to be good, and prices could be strong because the harvest in Quebec is expected to be down after frost and disease, said David Yarborough, blueberry specialist for the University of Maine Cooperative Extension.

But it’s the spotted wing drosophila that is the biggest concern for now. A native to China, the fly was accidentally introduced in California in 2008 and has since spread across the country, damaging fruit crops in multiple states along the way.

For the past several weeks, Maine blueberry growers have been hanging thousands of fly traps on stakes or trees on the edges of their fields. The traps are nothing more than 16-ounce plastic cups filled with a sugar-and-yeast solution designed to attract and catch the flies to monitor their numbers.

If the flies show up in large numbers, the growers will have to spray insecticides on their blueberry bushes. So far, small numbers have been found in some fields in the state’s midcoast area but not enough to warrant treatment.

Still, the flies are expected to increase in number as the monthlong harvest progresses. While growers are anxious about the flies, they’re also doing what they can to monitor and control them, Yarborough said.

“It’s not a disaster in the sense we know it’s here, we’re looking for it and we can address it,” Yarborough said. “But it does mean it’s more work to monitor and more spraying, which nobody wants. But that’s the reality of it. If we want a crop, we have to protect the fruit.”