NEW YORK — Based in McCall, Idaho, Christy Behm has parachuted from airplanes and rappelled out of helicopters to fight forest fires in the Western United States. But her toughest foe may lie here, 30 feet above New York's Central Park.

Straddling a slender tree branch, she pauses for a safety tug on her climbing harness and backup rope. Then she swings upside down, clinging to the underside of the modest limb while city traffic whizzes by below. Her quarry: a biological terrorist that's so rarely seen, its pursuers have to scrutinize each square foot of bark for telltale holes and faint spots where eggs the size of a rice grain may have been deposited. The threat: the potential loss of every maple plus 10 other tree species across the United States.

When the Asian longhorned beetle — or ALB — was first detected in the United States nine years ago, it quickly moved onto the nation's list of most wanted bugs. But spotting the roughly 1-inch-long beetles with their gaudy black-and-white striped antennae is so difficult that normal means of detection and eradication don't work. So the U.S. Department of Agriculture has employed nearly 200 people in an intensive "bug hunt."

But even that hasn't been enough. So the USDA has called for backup from the equivalent of an insect SWAT team, whose members last month detected the beetle in Central Park on two American elms — the second such sighting in the park.

That's where Behm and her seven burly tree-climbing experts — smoke jumpers from the Western United States — come in. They usually parachute into forest fires in parched Western forests, but since 1999, some smoke-jumper volunteers have been enlisting in their off season to battle the ALB interloper.

"They've been a critical factor in turning the tide in our favor," says Joseph Gittleman, the USDA's top general in the New York area for the Asian Longhorned Beetle Cooperative Eradication Program.

Hardwood killers

Insects cause millions of dollars of damage. Here's one ranking of the top five pests for hardwood trees:

Gypsy moth: For the past quarter century, its larvae have defoliated some 1 million acres a year in the Eastern United States.

Emerald ash borer: First detected in 2002, the boring beetle kills millions of ash trees every year.

Longhorned beetles: These pests, which include the Asian longhorned variety, bore deep into trees, weakening and eventually killing the trees they infest.

Elm bark beetle: The native and European varieties spread the spores of Dutch elm fungus from infested trees to healthy ones.

Tent caterpillars: The eastern and even more destructive forest caterpillar varieties feast on wild cherry but also attack oaks, maples and other shade trees. Forest-tent caterpillars can strip all leaves from acres of forest.

Source: Steve Nix of About.com

It turns out that only the smoke jumpers can thoroughly inspect a tree's upper reaches where these beetles usually first attack. The ALB is far easier to detect after emerging in the spring thanks to the large dime-size exit holes they drill. But by the time those "bullet holes" show up, a tree is already infested.

"This needs to be seen as a national problem because it could be in other cities already," says E. Richard Hoebeke, assistant curator of the insect collection at Cornell University, who in 1996 first conclusively identified the invading beetle, which has since infested thousands of trees in urban areas including New York, Jersey City, Chicago and Toronto.

Investigators quickly discovered the invader was arriving inside green-wood pallets carrying goods from China. Such pallets are now banned.

But getting the word out to the public is key, beetle-fighters agree, since firewood carried from quarantine areas to campgrounds elsewhere could spread the menace.

"In my opinion this beetle, if it's not eradicated, is going to turn out to be the biggest economic and environmental disaster to hit American shores," says Ralph Snodsmith, host of "The Garden Hotline," a syndicated radio show. When Congress moved to cut funding for the fight against the ALB, Snodsmith says, he marshaled his listeners to lobby Congress. Funding was restored.

One reason Central Park officials are alarmed is because the beetle is an added threat to the park's beloved American elm trees. Even so, elms are considered secondary targets for the beetle. Maple trees — Norway, silver, red and sugar — top the list of the beetle's favorite dishes, with birches, poplars, horse chestnut, willow, alders and birches also among the known host species. The USDA, which has spent $213 million fighting the beetle since 1996, is taking a no-holds-barred approach. Any tree where eggs or beetle holes are found is cut down and ground up — and the sawdust burned so no egg or grub escapes. The two infested elms found in Central Park last month were eliminated, the roots ground down to six inches below sidewalk level.

Beetle battlers have tried more high-tech, less labor-intensive weapons. One early technology developed by scientists at Oak Ridge National Laboratory involved attaching sensors to trees to detect munching beetles inside. But that proved impractical in the field.

Down the road, beetle spotters might be able to use new aerial surveillance techniques involving spectral analysis of light to detect defoliation, Gittleman says. And scientists are still looking for that special mating scent that might be used to lure the beetle into a chemical trap. But unlike other beetles, the ALB hasn't been found to use powerful, long-distance scent detection to find a mate.

So far, smoke jumpers in the trees and insecticide crews on the ground are the best defense.

A cellphone virtually glued to his palm, Dan Puleo, a USDA officer, orchestrates eight crews injecting a mild insecticide into the soil around thousands of potential host trees across Central Park. About a third of its 26,000 trees are potential hosts to ALB, says the Central Park Conservancy, which manages the park.

For a few years, the USDA in New York injected trees directly with insecticide. But that proved too costly, requiring the agency to hire "tree watchers" to keep the public away for hours. A few years ago, the department began injecting insecticide into the soil around the tree.

"This insecticide injection method is really practically our only weapon, other than the smoke jumpers, for defeating the beetle," Puleo says. It makes the tree deadly to the adult beetle.

Clad in jumpsuit and green gloves, John Massing moves systematically around the base of a horse chestnut, calling out the tree's diameter and calculating the appropriate amount of insecticide. He then inserts a metal probe into the ground and pumps insecticide from a pressure bottle.

While some hope the ALB tide has turned, Hoebeke notes that this beetle battle may be a sign of things to come. Last week he identified the first female Old World wood wasp seen in the Eastern United States, discovered in a bug trap in Fulton County, N.Y. The species has wiped out up to 80 percent of pine-tree species in Australia, New Zealand, South America and South Africa, and he worries it could spread nationwide, particularly in pine forests in the Southern U.S.

"Like the Asian longhorned beetle, we don't have a lot of resources to fight invasives like the Old World wood wasp, but we just don't have any choice but to try."

That spirit has kept Behm, the smoke jumper, coming back every year for the past three years. She lowers herself from the heights, rappelling smoothly down to sidewalk level from the elm's upper reaches she's been clambering over for the past 45 minutes. Ordinarily, smoke jumpers don't like to climb trees, she explains, unless their parachutes get hung up. But this tree climbing is different.

"These are really big, old-growth trees," she says. "I've been coming back year after year. I'm just glad they called us in to help save them."