The Utah Department of Agriculture will conduct aerial spraying with a benign bacteria in the Olympus Cove area in Salt Lake County this spring to combat the voracious gypsy moth, discovered by entomologists last summer.

Gypsy moth caterpillars hatch from their eggs in mid-April and consume vegetation at an alarming rate - so fast that Salt Lake City water officials say the moths could potentially devastate city watersheds."We've never had this kind of threat before," said city Public Utilities Director LeRoy Hooton, Jr. "If it's not controlled it could affect our entire 185-square-mile watershed."

To prevent the catastrophe, the Department of Agriculture, together with the city, U.S. Forest Service and other agencies, will spray Bacillus thuringiensis, or Bt, from low-flying helicopters over a 1,190-acre area in Olympus Cove.

"Bt is a natural bacteria that, in essence, is sprayed on the foliage. When the larvae is in a feeding frenzy it ingests it into its stomach and it rots out the stomach lining of the larvae," city Forester Steve Schwab said.

Schwab stressed that Bt is not known to harm humans, has been approved for aerial use by the Environmental Protection Agency and has been subjected to an environmental impact statement.

Biologists say Bt is a parasite that colonizes gypsy moths but can't be absorbed by human beings.

Hooton said officials will embark on a major information drive to teach residents about the aerial spraying program. City water users will be told of the spraying via water bill inserts, he said.

"We feel that there has to be a great deal of education so everyone knows what's happening," he said.

The gypsy moth was discovered in the Salt Lake Valley last summer and state entomologists immediately began trapping the moths to determine where they were.

The first moths were discovered at the University of Utah, a state gypsy moth report said. In August, traps were set in Salt Lake, Davis and Utah counties.

Olympus Cove and the Mill Creek Canyon area were found to contain a high densityof the insects, the report said. In all, 1,292 moths were caught, 356 in Mill Creek.

"The main concern was that the loss of scrub oak on the steep slopes of the Wasatch would destroy the watershed," said the report, prepared by state Entomologist Edward Bianco and the Department of Agriculture's Mark Quilter.

The moth could "defoliate the entire watershed," Hooton said, exposing ground to excessive erosion. Additionally, the moths eat so voraciously that they produce huge quantities of waste that could reduce water quality.

To ensure the spraying effort will be properly timed, officials will place captured gypsy moth eggs in wire cages outside. When they hatch, aerial spraying will begin, the report said.