From: Susan Montova Bryan, Associated Press
Published July 13, 2005 12:00 AM

Caterpillars Invade New Mexico Forests

ALBUQUERQUE, N.M. — Some of northern New Mexico's aspen stands have been stripped of their leaves by masses of wriggling caterpillars in search of food and a place to build a home, but forest officials are confident the trees will recover in time to show off their brilliant colors.

Western tent caterpillars began to hatch in May and have since been eating their way through the aspens in the Carson National Forest, especially the Canjilon area at the southern end of the San Juan Mountains. There have also been reports of the critters in the Santa Fe National Forest.

Trees in New York, Massachusetts and Vermont have been left bare this summer because of the caterpillars.

Terry Rodgers, a forest health official with the U.S. Forest Service in Albuquerque, said officials have had numerous calls from northern New Mexico about the pests.

"Apparently the caterpillars were just extreme in their numbers and causing extreme defoliation," he said. "They have already stripped the trees."


While caterpillars were in force last summer, Rodgers said this year's invasion was likely made worse because of the mild winter.

After emerging from their eggs, the caterpillars feed indiscriminately for about a month and build tents in the tree branches before finding a place to spin their cocoons. In about two weeks, a brown moth with a stout body emerges.

Rodgers said the caterpillars are more of a nuisance than anything else. They find their way into homes and camping gear, make roads slippery and climb inside towers and other tall structures.

But they are nothing like bark beetles, which have killed millions of pinons in New Mexico over the last three years.

Rodgers said most aspens are fairly resilient to the hungry caterpillars. A single occurrence rarely kills a tree, and a healthy tree that has been invaded will usually grow new leaves by midsummer.

However, some old and young trees that are under stress can be susceptible to the caterpillars.

When an infestation is bad enough, a pesticide that specifically targets the caterpillar can be used. Otherwise, they can be picked out of the trees and destroyed.

Natural controls include birds, which eat caterpillars and moths, and a maggot that feeds off the caterpillar. A virus known as wilt also can attack the caterpillar.

Since the caterpillar population builds up and then collapses due to parasites and predators, Rodgers said forest officials are letting the insects run their course.

There can be benefits from a caterpillar invasion, such as plenty of food for some birds and more sunlight for plants that live below the defoliated trees. Also, any leaves eaten by the caterpillars end up as pellets that can break down and return nutrients to the forest floor.

Source: Associated Press

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