Exotic insects pose threat to health of Maine forests

AUGUSTA – Maine forest officials bracing for the arrival of a voracious insect called the hemlock woolly adelgid are taking steps to protect hemlock stands across the state.

The effort has received much attention, but it’s not the only threat to Maine’s $2.5 billion forest products industry. Others include the Asian longhorned beetle, the emerald ash borer, the brown spruce longhorn, the citrus longhorned beetle and the “sudden oak death fungus.”

States and provinces where these pests have shown up are working frantically to contain or eradicate them. Together, the six could attack virtually every major tree species in Maine.

“You talk about forest health threats. Right now I’d say exotics pose, if not the biggest, one of the biggest threats we’re looking at at the moment,” said State Entomologist David Struble.

If a couple of these bad bugs make it to Maine, there could be a “potential disaster” on a par with chestnut blight, which killed 3.5 billion American chestnuts the last century, or Dutch elm disease, which stripped the shade from thousands of American towns, said Struble.

“The threat is real, and we have to make sure we pay a lot of attention to it,” said Thomas Doak, director of the Maine Forest Service.

Doak believes the most immediate threat is posed by the hemlock woolly adelgid, an aphid relative that munches hemlock trees and can kill a mature tree in as little as one season.

Maine forestry officials are launching a pre-emptive strike by releasing 5,000 beetles that eat the adelgids.

“We are the first state in the nation to decide that we’re not going to wait for the devastation that wipes out our hemlocks. We are putting up a shield first, before the damage is done,” said Doak.

Other insect threats include the Asian longhorned beetle, a native of China that apparently stowed away on packing material. It feeds on oaks, maples, willows and aspens – all important components of Maine forests. So far, it has been confined to areas around New York City and Chicago.

The brown spruce longhorn beetle is another threat. That pest, a native to Europe, was found in 1999 in a park in the center of Halifax, Nova Scotia. It feeds on red spruce trees.

Another worrisome pest is the emerald ash borer. A native of Russia, China, Japan and Korea, it feasts on ash trees. White, brown, and green ashes all grow in Maine. So far, the borer is limited to Michigan.

The latest arrival is the citrus longhorned beetle, which found its way from Asia to the Pacific Northwest on imported trees. Contrary to its name, the beetle doesn’t just attack lemon, lime, orange and grapefruit trees.

Struble is most concerned by a disease called “sudden oak death.” Caused by a fungus, the disease was first reported in California in 1995 and has killed tens of thousands of three types of oak trees. As of January, the disease was known to occur only in California and southwestern Oregon.

Struble notes that sudden oak death has been shown to infect rhododendrons and viburnums, widely used ornamental shrubs. “It’s possible it’s already here,” he said.

Of course, nobody really knows the cost of an infestation of one of these exotic forest pests, much less two or three simultaneously. It depends how quickly they spread, how much damage they do, and to what species.

“The key would be to somehow know ahead of time which ones would be bad players before they get here. But of course that’s difficult to do. One of the things we’re poorest at is predicting what will happen,” said Dennis Souto, an entomologist specializing in exotic forest pests at the U.S. Forest Service’s office in Durham, N.H.