At first light Tuesday, the battle begins anew.

Attack helicopters armed with bacteria will launch the first assault of 1991 against gypsy moth caterpillars, insects that eat hundreds of species of plants and can literally defoliate full-grown trees.The spraying program will continue for about a month and will cover 30,000 acres in Salt Lake, Utah and Davis counties. This is the third year of the eradication program, which has reduced gypsy moth populations by more than 75 percent. Program spokesmen say they believe the pest can be eradicated by 1994.

Spokeswoman L.J. Western said the location of the first spray operation will be in Davis County. "It will be a residential area below 5,500 feet," she said.

Gypsy moth larvae hatch about the same time oak trees leaf each spring. This year's spraying program was postponed because of unseasonably cool temperatures.

Rainy conditions could further delay the spraying. "They need five hours of good weather after a spraying or otherwise it's not considered a success," Western said.

The moths live only about 10 days and spend most of their short lives reproducing. The moths winter in the egg stage and develop into caterpillars by spring.

The caterpillars are sprayed with Bacillus thuringiensis, a natural bacterium that occurs in soil and is specifically harmful to moths and butterflies.

In addition to spraying, the eradication program includes rigorous enforcement of gypsy-moth quarantine areas.

The Utah Department of Agriculture requires inspection of all recreational vehicles, outdoor furniture, brush and rocks before they are moved outside the quarantined area. Violators can be fined up to $5,000.

Agencies also set traps in affected areas to determine the size of moth populations, to gauge treatment effectiveness and to determine treatment areas.

The traps are collected in late summer or early fall, and data are studied over the winter.

The program is conducted by the Utah Department of Agriculture, the U.S. Department of Agriculture's Forest Service and Animal and Plant Health Inspection Service.

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GRAPHIC

Gypsy moth

Size: 3 inches (adult)

Male: 1-1/2 inch wingspan

Female: 2-inch wingspan

Life Span: Gypsy moth larvae hatch about the same time oak trees leaf each spring. The moths live only about 10 days and spend most of their short lives reproducing. The moths winter in the egg stage and develop into caterpillars by spring. Gypsy moth caterpillars can eat hundreds of species of plants and can defoliate full-grown trees.

History: The moths were brought to the United States in 1869 by a naturalist who attempted to cross the moths with silkworms.

Spraying program:

When: Begins Tuesday (morning) May 21.

Where: 30,000 acres in Salt Lake, Utah and Davis counties (Selected residential areas below 5,500 feet).

Pesticide: Bacillus thuringiensis, a natural bacterium that occurs in soil and is specifically harmful to moths and butterfiles. Five hour of good weather is needed for a successful spraying. After two years of spraying, the program has reduced the gypsy moth population by more than 75 percent. Total eradication is expected by 1994.