THE United States is facing its biggest outbreak of gypsy moths in nearly 10 years. Worse, the leaf-eating pest is steadily extending its range beyond the Northeast.
``It looks like it will be the worst since the big outbreak in '81,'' says Lawrence Abrahamson, a forest entomologist at the State University of New York at Syracuse.
``I wouldn't be surprised to see 4 million acres'' defoliated, adds Daniel Twardus, a US Forest Service entomologist in Morgantown, W.Va.
Such estimates are very preliminary, because the leaf-eating caterpillar is just now entering its final days of feeding in most of the Northeastern states, when it does its most damage.
More precise figures won't be known until states conduct aerial surveys of their forests this month.
Worse than last year
Whatever the final totals, the consensus among entomologists is that this year's infestation is worse than last year, when the pests defoliated some 3 million acres of trees (an area roughly the size of Connecticut).
Any defoliation above that total would make 1990 the worst gypsy-moth year since 1982, when the pests devoured 8.2 million acres.
In the peak year of 1981, gypsy moths stripped 12.9 million acres of trees - an area equal to Maryland, Massachusetts, and Rhode Island combined.
This year's defoliation is more spotty than in 1981 but it has spread over a much wider area. The expansion poses the most serious challenge to entomologists, because they do not know how to stop it.
In less than a decade gypsy moths have moved beyond the Northeast into Michigan, Ohio, West Virginia, Maryland, Virginia, and North Carolina.
``The problem is steadily worsening,'' says Chuck Schwalbe, director of the Otis Methods Development Center on Cape Cod, Massachusetts, part of the federal Animal and Plant Health Inspection Service. ``The opportunity is there for an outbreak of a much larger area than in 1981.''
Defoliation by the voracious gypsy moth, or Lymantria dispar, usually doesn't kill a tree the first time.
But repeated defoliations take their toll, leaving older and less vigorous trees vulnerable to drought and other pests.
Between 1969 and 1987, about 6 billion cubic feet of trees in Pennsylvania died as the result of gypsy moths.
The economic loss: more than $200 million.
Heavy infestation is a nuisance to neighborhoods, too.
Caterpillars crawl up and down walls and over lawn furniture.
They also leave behind substantial amounts of unsightly droppings and egg masses on lawns and sidewalks.
This year, Pennsylvania appears to have some of the worst gypsy-moth infestation. Some 2.5 million acres in the state may be in the process of being defoliated, says Barry Towers, chief of the Division of Forest Pest Management, part of the Pennsylvania Department of Environmental Resources.
If correct, that total would equal the 2.5 million Pennsylvania acres defoliated in the peak year of 1981.
Worse, the insects have spread.
In 1980, they infested less than half of the state; today, they have invaded the entire state except for a small area in the extreme southwest corner.
``There's no way really to control an insect,'' Mr. Towers says. ``The only thing we can do is provide some relief.''
Pennsylvania has just finished spraying 393,000 acres this season at a cost of $4 million to $5 million.
In all, about 1.6 million acres were sprayed this year under federal and state gypsy-moth programs - the highest total ever and twice last year's level.
A number of biological and chemical pesticides are available. And a fungus discovered in New England last year killed off huge numbers of caterpillars. Entomologists suspect the fungus could be an effective tool in rainy years.
Yet the prevailing wisdom is that the leaf-eating gypsy moth cannot be stopped. Not since the 1950s have entomologists tried to contain the bug with large-scale spraying.
``There are many people who believe that this thing is bigger than all of us combined - that we ought to step aside and let this thing take its course,'' Dr. Schwalbe says. But ``we have to look at what the prospects are for sustaining a [containment] program.''
At a scientific meeting on the gypsy moth planned for this winter, Schwalbe and other experts plan to debate the idea of a sustained containment program.