Bangor, Maine — Forest experts on both sides of the US-Canadian border are trying to outfox a tiny but obstinate caterpillar that has an apparently uncontrollable appetite. Up close, the caterpillar, choristoneura fumiferana - better known as the Eastern spruce budworm - doesn't look at all menacing, with its black head and pudgy, inch-long brown body with yellow dots.
But this particular caterpillar is Public Enemy No. 1 to forest rangers and lumber executives from Mount Katadhin to Cape Bretton Island. During the past decade budworm populations have skyrocketed in wooded tracts throughout an area extending across 150 million acres in Maine and Canada.
Armies of perpetually hungry budworms, which feed almost entirely on the new buds and needles of spruce and fir trees, are causing the gradual defoliation of millions of mature spruce and fir trees across eastern North America.
In Maine, the budworm outbreak has invaded about 7.5 million acres of forest since 1976, when forestry experts began monitoring its effects. Budworms are reported to have stripped bare about 15 million cords of spruce and fir trees - roughly the equivalent of five years' lumber harvest for the entire state of Maine, experts say.
''The budworm is a huge problem,'' says Thomas Rumpf, who heads the budworm control program for the Maine Forest Service.
But researchers and forest managers aren't giving up. Indeed, most say that in many areas the budworm population is in decline.
What scientists don't know is whether that decline is only a temporary dip or the long-awaited return to preinfestation levels of the budworm population.
The infestation has been too much for the budworm's natural predators - the black-capped chickadee and other small birds that normally feed on caterpillars - to keep in check.
And because the area of infestation is so wide and so diverse, aerial spraying of pesticides has been only partially effective, experts say. In some instances, such as on Cape Bretton Island in Nova Scotia, the infestation is so heavy that entire forests have been ravaged.
''The problem is that the acreages are so vast and the kill so complete that there is nothing left,'' says Chuck Buckner of the Canadian Forest Service. ''It will take 40 to 60 years to bring those pieces of acreage back again.
Not only is no one sure exactly what is happening in the budworm population, but no one is sure exactly what can be done to artificially control the population.
''Despite all the research done on the problem, we really don't have any silver bullets on the horizon,'' says Mr. Rumpf. ''I think we are going to have to learn to live with it.''
The budworm is nothing new. It lived in the Northeastern woods long before men did. What is new is the idea that the infestation can be sufficiently checked to prevent the destruction of mature spruce and fir stands.
In a broader ecological sense, experts say, the budworm performs a necessary service in the forest ecosystem by killing tall, mature spruce and fir trees, which inhibit sunlight from reaching the forest floor. In effect, the thinning out of the tall trees triggers a regeneration of the forest by opening up sunny areas for smaller trees and plants to start growing.
(Lumber firms have modern techniques for achieving the same result to ensure their forest stocks contain an even mix of young, middle aged, and mature trees. This guarantees a steady supply of lumber in years ahead.)
The last major budworm outbreak in the East started in 1912 and lasted approximately 10 years, until the budworms had literally eaten themselves out of house and home. The population gradually died off, and spruce trees began to grow again.
Now, 70 years later, forest experts are saying that the forest products industry - Maine's largest industrial moneymaker and employer - can't afford to let nature take its course again. Roughly 29 percent of all manufacturing jobs in Maine are related to the lumber industry, according to government statistics. The industry is dependent on a guaranteed supply of spruce and fir.
Thus, forest managers are working to prevent the complete devastation of the mature spruce and fir trees, while at the same time trying to control the budworm population.
But researchers say the two goals may not be compatible, and that could mean problems for the Maine lumber industry. According to Henry Magnuson of the Paper Industry Information Office in Augusta, if the defoliation of spruce and fir trees continues much longer, the Maine paper and lumber industry may run short of timber by the turn of the century.
That could necessitate production cutbacks, mill closures, and layoffs as early as 1995, according to some projections.
''There is more than two years' supply of standing dead timber out there,'' Mr. Magnuson says. ''We can't use it as fast as the bugs are killing it. Right now what we've got is what you might call a glut in the supply of fir.''
Magnuson notes that fir can remain harvestable for two years after it dies. Spruce, he says, can be harvested as long as six years after it dies.
Nonetheless, the problem now is that there is more dead wood in Maine forests than can be either used by industry or stored. The choice is to harvest it and have it rot in a lumber yard or just leave it in the woods and let it rot there.
''It has been a race. And, no doubt, the budworm is ahead on a lot of acreage ,'' says Paul McCann of the Great Northern Paper Company, the largest landowner in Maine, with 2.1 million acres of primarily spruce and fir forests. ''The budworm has taken the management of the forest away from us - or it did for a period of time.''
After a decade of experience with the budworm, Great Northern is embarking on a program to develop what is being termed a ''new forest.'' The company is using computer graphics to assist with a stepped-up, $6 million annual forest management strategy. The program includes a pesticide spraying program and a 12, 000-acre-a-year herbicide program designed to open up large sections of acreage to encourage faster growth of new stands of spruce and fir trees.
The younger trees have been found to be less susceptible to budworm infestation, and it is hoped that the fast-growing new stands can help reduce the projected shortfall of spruce and fir trees.
In addition, Great Northern researchers are looking into ways of increasing the utilization of hardwoods in the papermaking process to reduce the company's reliance on spruce and fir.