enlarge John Ewing/Staff Photographer

A closeup of the Laricobius nigrinus, which preys on the woolly adelgid, a beetle killing hemlocks in southern Maine.

enlarge John Ewing/Staff Photographer

State entomologist Wayne Searles puts Laricobius nigrinus beetles onto an infected hemlock branch on York Water District land Wednesday. It may take years, but officials hope the beetles will stunt the spread of woolly adelgids among Maine hemlocks.

YOU CAN HELP MAINE'S HEMLOCKS

REPORTS FROM MAINE RESIDENTS are critical in the effort to find and assess infestations, says Allison Kanoti, a state entomologist.

TO REPORT the presence of woolly adelgids, contact Kanoti at 287-3147 or allison.m.kanoti@maine.gov

FOR MORE INFORMATION about identifying hemlocks and hemlock woolly adelgids, go to Maine Forest Service.

YORK — The tiny black beetles set free in a forest here Wednesday morning didn't look like much of a threat to anything.

But they have a knack for finding and eating hemlock woolly adelgids, invasive insects that have become an urgent threat to coastal Maine forests, said Allison Kanoti, an entomologist with the Maine Forest Service.

"They'll fly away and find more adelgids than we can find," Kanoti said, as she gently placed 50 Laricobius nigrinus beetles on a small hemlock tree that showed early signs of infestation.

The beetles are fresh reinforcements in a biological battle that's been quietly taking place in York County forests for several years.

Woolly adelgids have killed hemlock trees up and down the East Coast, and they are spreading north. Because pesticides are only helpful in confined areas, state officials periodically release predators, such as the Laricobius beetles.

The use of bugs to fight bugs has taken on added urgency after infestations were found in Saco and Kennebunkport this year. The Maine Forest Service is surveying forests in those areas to determine how far the adelgid has spread.

"To (find) it in Saco, that just blew us away," said Wayne Searles, a field technician with the Maine Forest Service. "Now we're saying we've got to look in Scarborough. We haven't found any there yet."

Hemlock woolly adelgids are tiny brown-and-black bugs native to Japan that have spread through the eastern United States since arriving more than 50 years ago. At this time of year, they exude a woolly substance and appear as white masses on the underside of hemlock twigs. They kill hemlocks by gradually sucking their sap and have devastated forests from Connecticut to Georgia a few years after arriving.

Woolly adelgids were found in Kittery and York in 2003 and in Eliot, South Berwick and Wells by 2005. The Saco infestation was discovered in July, and the Kennebunkport infestation was found in October.

In Maine, hemlocks provide habitat for deer and other wildlife and shade for trout streams, as well as commercially-valuable timber that's cut and sold for lumber and paper.

The threat to Maine forests is believed to be limited because of the colder winters here. Prolonged below-zero temperatures can kill or slow the spread of the insects, and the pests have indeed spread far more slowly here than in the Southeast.

But the adelgids are proving they can, gradually, multiply and spread in Maine's moderate coastal areas. "We think probably within 10 or 15 miles of the coast is pretty vulnerable," Kanoti said.

Milder winters, which are expected to become more common because of global warming, can help their spread.

The stand of trees where the beetles were released Wednesday was first found to be lightly infested in August 2006. Now, the tell-tale white masses are widespread. "A couple of warm winters and it's taken right off," Kanoti said.

The predator beetles were raised in a Virginia laboratory and paid for by the federal government. It will take years before they become established and abundant enough to make a dent in the adelgid population, Kanoti said.

Adelgids can be spread on nursery trees, which is why hemlocks cannot legally be shipped out of parts of York County and much of the eastern United States. The pests also can be spread by the wind, birds or even people who brush against them.

Hemlock woolly adelgids have been found on isolated landscape trees as far north as the coastal town of Brooklin but are not believed to have spread to forests outside of York County, said Kanoti. A South Portland resident reported infested trees in a backyard there this summer, for example. Those trees probably carried the pests when they arrived from a nursery 12 years ago, Kanoti said. Because the infestation was small and contained, it was treated with chemicals.

"We will be monitoring that area for the next...