Forest Service Considers Using Virus To Kill Moths Tussocks Responsible For Destroying Thousands Of Acres Of Firs In Past

The U.S. Forest Service plans to spray forests east of the Cascades against a moth that devours fir trees.

The population of tussock moths, a naturally occurring pest, explodes every decade or so, with outbreaks lasting two to four years. By the time populations peak, the moths’ furry larvae can defoliate thousands of acres of Douglas and true firs.

The worst outbreak in modern history killed 100,000 acres of trees spread throughout Eastern Washington, Eastern Oregon and Idaho in the 1970s. A 1990 outbreak in the Boise National Forest killed firs on 35,000 acres.

“In the last couple of years we’ve noticed that the population is increasing at a level that indicates there may be a widespread outbreak of epidemic proportions,” said Rex Holloway, Forest Service spokesman in Portland.

The biggest outbreak is in northeastern Oregon’s Wallowa-Whitman National Forest, where spraying likely will be necessary this spring, Holloway said. But the Forest Service’s environmental impact statement calls for spraying forests throughout Eastern Oregon and Washington, should it become necessary.

“We anticipate that in 2001 or 2002, we may have a more widespread outbreak,” including in Washington’s Umatilla and Colville national forests, he said.

At the height of an outbreak, the insects can become so abundant that forests become a mass of wriggling caterpillars. At such times, their microscopic hairs fill the air, causing allergic reactions in about a third of the people who come into contact with the creatures.

In 1992, a rare urban outbreak hit some Spokane neighborhoods. The caterpillars killed trees, then swarmed houses, worming their way through cracks and down chimneys. Residents found them on their carpets and windowsills, and in such unlikely places as inside rolled sleeping bags and refrigerators.

The Forest Service plans to attack the insects using a virus collected from the larvae in the late 1980s. When outbreaks are allowed to run their course, the virus naturally kicks in, killing off most of the larvae - after they’ve already stripped trees of needles, Holloway said.

Biologists believe the spray, called TM Biocontrol, has little effect on other organisms.

A second biological control, called Bacillus thuringiensis or BT, will be used only if the Forest Service must spray so much land that it runs out of TM Biocontrol, Holloway said. BT kills not only tussock moths, but also some other moths and butterflies.

Traditionally, the Forest Service sprayed the pesticide DDT over hundreds of thousands of acres when the moths started to gain the upper hand.

Foresters and some Northwest politicians were outraged in 1973 when the U.S. Environmental Protection Agency balked at allowing the use of DDT on a major outbreak. The agency had banned the pesticide the year before because it had caused near extinction of bald eagles, osprey and other birds of prey.

Under intense pressure, the EPA in 1974 granted emergency authority to use DDT that year only to control the caterpillar. The pesticide was sprayed over more than 400,000 acres.

Later studies showed that the spraying did little to control the moths but killed tens of thousands - some researchers said hundreds of thousands - of insect-eating songbirds.

The DDT ban led to the development of biological controls for the moths.

This sidebar appeared with the story: FAST FACTS To comment

The U.S. Forest Service is seeking comments on its plan to spray up to 560,000 acres of forests in Eastern Washington and Eastern Oregon to control tussock moths. The comment period ends Feb. 28. A copy of the agency’s draft environmental impact statement is available from the Tussock Moth Project, Forest Service Regional Office, P.O. Box 3623, Portland, OR 97208-3623. Information also is available on the Internet at www.fs.fed.us/r6/nr/fid/ eisweb/dftmeis.htm.