Counting eggs of gypsy moths gives warning

10 states plan to spend $15 million spraying 500,000 acres

March 18, 2001|By Marc Levy | Marc Levy,KNIGHT RIDDER/TRIBUNE

PHILADELPHIA - Before he begins counting the eggs, John D. Kegg stands, back straight, against a chestnut oak.

With a tape measure, he marks a circle with an 18.6-foot radius around the tree.

Then Kegg, who heads the New Jersey Bureau of Plant, Pest and Disease Control, works with his colleagues to inspect each tree within the circle - it's one-fortieth of an acre - for gypsy moth eggs laid in the hard grooves of tree bark.

They stoop to peer into bushes and underneath fallen trees. They use binoculars to look high on trunks and underneath branches.

Counting the egg masses determines, with a little extrapolation, whether the surrounding acreage is so infested that it should be sprayed in an effort to prevent the gypsy moths, while in caterpillar form, from devouring leaves in hardwood forests.

This year, Kegg and other entomologists also may need a little luck: Gypsy moths continue to spread farther than ever and the breadth of the damage they cause is somewhat unpredictable.

Spraying 500,000 acres

In May, New Jersey, Pennsylvania and eight other states plan to spend more than $15 million to spray 500,000 acres of hardwood forest to poison young caterpillars and curb the defoliation and sometimes death that the insects wreak, mostly on oak trees.

The counting job has been a doozy for Kegg and his colleagues. It lasted from August through early January and covered parts of 80 or so municipalities, mostly in North Jersey but also small chunks of counties in much of the south.

And it came on the heels of a shocking rise in the caterpillars' damage to New Jersey hardwoods last spring. The caterpillars cut through more acreage than they had in six years, devouring mostly oak leaves on 1.6 million acres in 14 states from New England south to Virginia and as far west as Wisconsin.

Pennsylvania hardest hit

Pennsylvania was the hardest hit, with damage to 842,981 acres. New Jersey was third, after West Virginia, with 132,762 acres damaged - 100 times more than in 1999.

Gypsy moth populations tend to rise and fall in cycles that usually span 10 years. This year, the U.S. Forest Service says they could damage 19 states - the farthest spread ever - as the apparent height of the cycle approaches.

It remains unclear whether this year will be the peak of the upswing. And state and federal entomologists said it is not likely that the caterpillars' damage will surpass the 1981 record of 12.9 million acres because its natural predators have since become more active.

Still, in just a month and a half of gorging on oak leaves, the Lymantria dispar regularly grows into one of the most destructive insects in North America.

The moth's life - which spans all of three months in four stages - generally begins in late April, when weather conditions are right.

The larvae emerge, one-tenth of an inch long, from their small white eggs in the bark.

They feed for six weeks, grow to 3 inches, then shrink to a dark brown, barrel-shaped cocoon about an inch long. A week to 10 days later, a moth emerges.

The females, which are about 2 inches and white, cannot fly. For several days, they mate with males and lay their fertilized eggs in tree bark and die.

The smaller males, an inch across with brown wings, are strong fliers. For two weeks, they fly around, mating with females, then die.

Sound complicated?

Began in 1869

It all began rather simply in 1869, when Etienne Leopold Trouvelot, a French naturalist living in Medford, Mass., just north of Boston, received a package of moth egg hatchlings from a friend back home.

Trouvelot kept the moths caged in his yard, part of a failed experiment to breed a silkworm strong enough to survive harsh New England winters. The moths escaped when storm winds toppled their wood-and-wire cages.

The European insect has proved strong enough to survive North American winters.

The caterpillars' main source of food was, and is, plentiful. They prefer oak leaves - they probably taste best, entomologists say - but the arthropods have been known to dine on more than 500 species of trees and bushes.

The caterpillars and their eggs have since traveled on wind, cut timber, motor vehicles, and such outdoor objects as lawn furniture throughout the Northeast and north-central and eastern United States.

There is little chance now that they will be eradicated.

"It's an essential part of the ecosystem," said Kevin Carlin, an entomologist with the Pennsylvania Department of Conservation and Natural Resources. "It's something that's here to stay. You can expect to have continued periods of low population and you have some peaks and valleys."

Since the late 1960s, Pennsylvania and New Jersey forests have experienced a roughly 10-year cycle of gypsy moth populations. The number rises as the moths first outpace their natural predators and parasites, and then falls as their enemies catch up and pull ahead.

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