Aerial spraying to wipe out a colony of gypsy moths in the foothills above the city was approved Tuesday by the Centerville City Council.

Permission for the spraying effort was sought by the state's agriculture department and the U.S. Forest Service as part of an ongoing trapping and eradication program.Trapping last summer showed a population of the destructive insects in the Parrish-Centerville Canyon area in the foothills east of the city, USFS representative John Anhold told the council.

Eradication efforts on the Wasatch Front began in 1988 in the Olympus Cove area above Salt Lake City. That was expanded in 1989 and 1990 north to Mueller Park above Bountiful as further trapping showed the moth population moving north, Anhold told the council.

Although the 3,500 acres outlined for treatment is not in the city limits, the Federal Aviation Administration (FAA) requires city permission for the low-level helicopter passes involved in the spraying, Anhold said, because the area is adjacent to the city.

After raising several questions, the council approved the request unanimously.

Anhold said a helicopter will be used to spray a biological insecticide called bacillus thuringiensis, which he said has been used for 20 years to control the moth by killing it in the caterpillar stage.

Two or three applications will be needed, Anhold said, estimating the effort will kill 95 to 97 percent of the moth population. The pesticide has no harmful side effects and is not toxic to humans or pets, he said.

Anhold said the Forest Service monitors weather conditions carefully during scheduled spraying times. If weather conditions such as wind crop up that could spread the application beyond the approved boundaries, the operation is canceled, he said.

Monitoring is done in adjacent residential areas, he said, to prevent the spray from spreading.

Anhold said 1,200 acres around Olympus Cove were sprayed in 1988, an effort that increased to 20,000 acres in 1989 and now has grown to 30,000 or more acres.

Whether the moth population is growing or the trapping and eradication effort is getting more efficient in tracking the populations is difficult to say, Anhold told the council. But he is confident that within a few years the infestation will be controlled.

"We feel very comfortable that in a couple of years we'll have them eradicated," he told the council.

According to the state agriculture department, the gypsy moth feeds on the leaves of more than 500 species of trees and shrubs and presents a serious threat to watersheds and forests.