HARPSWELL – Scientists believe they have isolated a virus that could largely eradicate the browntail moths that have infested Casco Bay towns and sickened inhabitants for over a decade.

Testing conducted in England indicates the baculovirus will infect browntail moth larvae, but not harm humans or lobsters, according to scientists with the U.S. Forest Service.

“It is the proverbial silver bullet,” said Dr. Jim Slavicek, a scientist with the Forest Service’s Northeastern Forest Experiment Station in Delaware, Ohio.

The browntail moth made its way into the United States from Europe in 1897 and now infests sections of Cape Cod and Casco Bay, Slavicek said. The caterpillars shed toxic hairs in June and July that can cause rashes or respiratory distress in people who come into contact with them.

The project calls for the virus to be sprayed May 15 at two sites in Harpswell, the Bowdoin College Coastal Studies Center property off Route 24 and state-owned land at Merriman Cove on Harpswell Neck.

The spraying would be the first in the United States, Slavicek said. If it is successful, the virus may be introduced into other parts of Maine in a year or so.

Ellie Swanson said it would be wonderful if the spraying is successful.

“But the problem, at least for this year, is they are too late,” she said. “I don’t believe we’ve seen anything like what we are going to see this summer. I can see hundreds of [moth] webs in the trees from my window.”

Scientists hope the virus will kill at least 80 percent of the browntail moth population.

Slavicek said the virus could never completely wipe out the browntail moth, but could lead to less frequent outbreaks – one every eight or nine years instead of each year.

Over the next several weeks, Slavicek’s team will collect larvae from the sites to measure mortality rates. The team will try to determine the most effective dosage rates in the fall.

The team will also have to demonstrate to federal regulators the virus only harms the browntail moth.

Once the virus has been registered with the Environmental Protection Agency, it can be used instead of pesticides such as Dimilin, a chemical that will be sprayed this month in coastal towns such as Freeport and Brunswick. Harpswell rejected aerial spraying because of concerns about Dimilin’s effect on lobsters.

Slavicek does have some skeptics, including Dave Struble, an entomologist with the Maine Forest Service.

“I don’t think the virus can be as effective as chemicals, but the jury is still out,” Struble said. “If this works, it would be a wondrous thing because it would be very target specific. It would be like putting out rat poison. It wouldn’t hurt anything else.”