The insecticide that targets mosquitoes in an effort to combat West Nile virus in communities north of Boston also hits an unintended target: honeybees.

It’s a frustration and a concern for residential beekeepers, some of whom say they’ve lost thousands of bees.

Beekeeper Anita Deeley of Beverly, Mass., estimates that between 100,000 and 150,000 of her bees died last year — four hives — even though she covered them the night the city sprayed for mosquitoes.

This year, Deeley moved her hives prior to the spraying last week in neighboring Salem.

“I understand why they need to spray, but it is a little frustrating for beekeepers,” Deeley said. “I wish they wouldn’t spray at all, but I understand why they’re spraying.”

Mosquitoes from several towns in this part of Massachusetts, including Salem and Beverly, have tested positive for West Nile virus this summer. The disease can be fatal, but health officials estimate that fewer than 1 percent of people infected with West Nile develop severe illness.

“Against this perceived threat, we’re spraying a cloud of spray in a neighborhood,” said Salem beekeeper Richard Girard. “It’s really throwing the baby out with the bath water. … The spraying of this stuff, from a beekeeper’s perspective, is absolutely dire. You can’t protect your hives. It will kill them.”

Any resident can opt their property out of spraying by contacting the local board of health. But some beekeepers say their hives have been affected even when the spraying happens in other parts of town.

“What we’re doing is spraying for mosquitoes to reduce the risk of people becoming sick. That’s our focus, our mission,” said Jack Card, director of Northeast Massachusetts Mosquito Control, the state agency that handles mosquito issues and spraying in 32 towns across Essex County. “We have to follow all the regulations … That’s our driving force, to protect the public as best we can.”

Card’s agency sprays insecticide from trucks after dark, when the chemicals can come in direct contact with mosquitoes, he said. This summer, they’ve used an insecticide called Duet, which targets adult mosquitoes. The trucks are equipped with a GPS device, which alerts the driver to any addresses that have opted out of spraying.

Before last year’s spraying about a half-mile from her former home in Beverly, beekeeper Kim Klibansky wrapped her hives with tarps.

“I figured we’d be OK,” said Klibansky. “The next day, we went out and the front of the tarp was covered with dead bees. Our hives were so weakened that within four to five days, one hive died. About a week later, the second hive died.

“Bees are like our barometer. If there are bees, we know it’s a healthy environment,” she said. “That spray wipes out a lot of flying insects, not just mosquitoes. I just don’t think the risk is worth it.”

Bethany Bray is a reporter for The Salem (Mass.) News.