Gypsy moth numbers down

March 31, 2003|by RICHARD BELISLE

They're not pretty. Their names are nearly impossible to pronounce. But they're doing the job.

One is a fungus called Entomophaga maimaiga, the other a virus named nucleopolyhedrosis. Both are wreaking havoc on gypsy moths - so much so that the Pennsylvania Bureau of Forestry won't have to spray forests this spring because gypsy moth populations are the lowest they've been in years.

Two years ago, said Bruce W. Kile, a forester at the 85,000-acre Michaux State Forest headquarters in Fayetteville, the state sprayed 169,000 acres of forests. In spring 2002, 59,000 acres were sprayed, he said.

In 2002, nearly 56,000 acres of trees were defoliated by gypsy moths in Pennsylvania, about 76 percent less than the nearly 238,000 acres stripped in 2001.


Foresters predict gypsy moth populations by counting egg masses in September after the females complete their life cycles and lay their eggs. Kile checked for egg masses in nearly 100 sites in Michaux State Forest last fall and said there weren't enough to justify spraying this year.

He said there will be pockets of moths that will defoliate trees in some areas of the forest.

The favored food of gypsy moths is oak leaves, but they will eat almost anything, including pine needles, Kile said. If their populations get so high that it's difficult to find food, they'll drop off trees and eat grass, he said.

Gypsy moths were brought to Massachusetts from Asia as an experiment to make silk in the mid-19th century. They adapted to their surroundings and began to spread south and west. They reached Pennsylvania in the 1920s, Kile said.

States started spraying by air with DDT in the 1940s. The use of the chemical was banned in the late 1950s.

Gypsy moths were thought to be eradicated in Pennsylvania in 1948, but they survived in some areas and their population exploded again in the early 1950s, Kile said.

In more recent years, Pennsylvania and neighboring states have sprayed gypsy moths with Bacillus thuringiensis, or BT, a selective biological insecticide which only kills leaf-eating caterpillars.

The Entomophaga maimaiga fungus, which came from the gypsy moths' native habitat in Asia, was introduced in the United States to control the pests in the late 1960s. Kile said. It didn't have a significant impact on the moth populations at first, he said. Scientists gave it up as a useful tool until a cool damp spring in 1990 allowed the fungus to multiply and begin destroying the gypsy moth population.

The spores of the fungus eat away at a gypsy moth's insides, much like cancer does in humans, Kile said. Moths killed by the fungus hang stiff and brittle upside down from the tree trunk and eventually fall to the ground.

Foresters at Michaux State Forest collect the fungus-ladened moth bodies and haul them to other forests to attack gypsy moths there.

"We're spreading dead caterpillars around the state," Kile said.

Michaux State Forest was one of the first places in the state to use the fungus effectively.

The fungus will continue to provide natural control over gypsy moths and prevent the epidemic levels of defoliation seen in the early 1980s, Kile said.

The virus - another natural control from Asia - while not as effective as the fungus in killing gypsy moths has met with some success when used as part of an integrated forest pest management system.

Beth Brantley, a forestry instructor at Penn State Mont Alto, said the fungus is expected to continue to build up and stay ahead of the gypsy moth populations and remain an effective control tool.

"Hopefully, the gypsy moth's day is done and the oak trees can recover," she said.

Oak trees in Pennsylvania have taken a double hit in recent years - from the gypsy moths and the drought, she said.

"They're stressed out, but the moisture from this winter should help," she said.

Gypsy moths not only denude forests and give them a winter look in mid-summer, they also have cost the state millions of dollars in loss timber revenues.

Kile said about $1 million worth of timber is sold from Michaux State Forest every year.

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