Officials in Fairfax County's gypsy moth program this week released 25,000 tiny parasitic wasps in the northern part of the county to fight the area's infestation of the leaf-eating insect.

The flea-sized wasp, which does not sting or attack people, deposits its eggs inside gypsy moth eggs. The wasp eggs hatch and feed on the inside of the gypsy moth egg, destroying it. After two weeks, an adult wasp emerges from the eggshell and repeats its cycle on other gypsy moth egg accumulations.

The parasitic wasp program is the first of its kind in Virginia. The regions treated with the wasps include Centreville, Herndon, Great Falls, McLean and Annandale.

Tom Mason, wasp program coordinator, said he expects about a 40 percent success rate in efforts to stop further hatching of the moth's foliage-eating caterpillar.

Mason and his staff collected hundreds of the parasitic wasps two months ago from ravaged moth-infested West Virginia mountains. Since then Mason has reared mass quantities of the wasps in a large test tube-lined orange wooden box in a corner of his basement office. He encourages the parasites to reproduce by periodically adding gypsy moth egg masses to their makeshift nest.

"We've raised 25,000 wasps so far," he said.

According to a report by the county's Office of Extension and Continuing Education, which sponsors the gypsy moth office, gypsy moth caterpillars were found in 302 sites in Fairfax County in 1982.

In 1983, the caterpillar sightings decreased to 275 after insect control programs were implemented by the county Board of Supervisors.

Gypsy moths were introduced into the United States in 1869 in Massachusetts and eventually spread north to Maine and then south from New York to Virginia. The caterpillar, which hatches after nine months, feeds on leaves, shade and fruit trees and shrubs. It can eventually devour entire forests.

Annandale District Supervisor Audrey Moore, a proponent of the parasite program, said the county's moth experts have been instrumental in controlling the insect's infestation in the county.

Moore said she hopes the county's infestation "never gets to the point where we have to use those horrible chemicals."

Officials hope that the use of parasitic wasps eventually could become an alternative to natural pesticides currently used to combat the moth and its infant stage in the county's stricken areas.

Natural pesticides are federal Environmental Protection Agency-approved low-toxic substances manufactured by the environment and are deadly only to insects. These natural pesticides include Bacillus Thuringiensis (BT) and Dimilin.

Raj Waghray, who organized Fairfax County's gypsy moth program, said synthetic insecticides, such as DDT, generally are used in areas with heavy infestation of gypsy moths and gypsy moth caterpillars and eggs. He said natural pesticides are used to control the moth and its offspring in low- to moderately-infested areas.

Fairfax County uses only natural insecticides because of the area's low moth population.

Mason said the wasps "are not active through the dead of winter months, but they are very cold-hearty and will survive the winter under leaves in a state of hybernation."

The wasp program's $20,000 annual operating cost is split by the Virginia Department of Agriculture and the county's Department of Extension and Continuing Education.

Waghray said the U.S. Department of Agriculture will contribute up to 40 percent of the program's expenses if the gypsy moth infestation threatens severe forest defoliation.