June 23, 2013

Maine Gardener: News from front lines in bug wars


Maine's bug wars are continuing. While some news is good, a lot is bad.

The updates on the spotted-wing drosophila are mixed -- good if you care more about fruits that ripen early in the year and bad if you are interested in growing late-season crops.

"Last fall is when the spotted-wing drosophila really showed up," said David Handley, a vegetable and small-fruit specialist working out of the University of Maine's Highmoor Farm in Monmouth. "We were trapping for it all year, catching a few in mid- to late summer, but it was not causing much damage. Then in the week of Sept. 10 to 14, we saw a real spike in population."

The spotted-wing drosophila is a fruit fly that, because it has the ability to saw through fruit skins, attacks ripening fruit as well as rotting fruit. Most fruit flies can eat only fruit that is at or past its prime.

"If it continues to follow this pattern," Handley said, "this may not be a problem for early-ripening fruit" such as strawberries, summer raspberries and early blueberries. "For fall raspberries and blueberries, we are going to have a challenge on our hands."

Handley said he will be talking regularly this summer with fruit specialists all around the Northeast, and because the states south and west of Maine will probably be hit first, Maine will have some warning when the drosophila is coming.

While apples are listed as a host for the spotted-wing drosophila, apples have a tougher skin and harder interior than most of its hosts, and Handley has not seen much of a problem with apples. The same is true for tomatoes, but tomatoes will be attacked if they have cracks or soft spots.

And, Handley warned, if you leave rotting apples or tomatoes on the ground, the flies will gorge on those and the population will likely increase.

WINTER MOTH has been confirmed in Cape Elizabeth in addition to Harpswell and Vinalhaven, where it had been confirmed last year.

Charlene Donahue, an entomologist with the Maine Forest Service, reported that trees in an area between the town center and Crescent Beach on Route 77 have been defoliated.

"For a mile, there aren't any leaves on the trees," she said. "If you go into some of the neighborhoods off that area, they are really the hardest hit."

While the winter moth remains in Harpswell and Vinalhaven, Donahue said, she has not seen extensive defoliation in those areas.

Male winter moths fly in late November and December and are noticeable around lights. They mate with the flightless females, who lay their eggs and die. The eggs overwinter and come out as hungry inchworm-type caterpillars in the spring. After gorging themselves, the caterpillars drop to the ground and make cocoons, from which they emerge as moths in late fall or early winter.

While one or two years of defoliation will not kill mature trees, the winter-moth caterpillar could hurt blueberries because they will eat the blueberry blossoms, meaning they will not fruit.

Donahue released parasitic flies this past spring at Two Lights State Park in Cape Elizabeth -- as she has done in Harpswell and Vinalhaven -- which she hopes will bring the pest under control. She hopes to release more flies if she gets the funding.

"This has been one of the really good biocontrol success stories," Donahue said. "The flies come from Europe and were first used in Nova Scotia back in the 1960s and British Columbia in the 1980s. In Nova Scotia it is now difficult to find winter moths, and in British Columbia they are there, but they aren't damaging trees."

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