Beekeepers also complained last year that spraying is killing their bees. Even if they ask that their own property not be sprayed, they said, the chemicals can drift onto their bees.
Massachusetts health officials are concerned about mosquitoes because they are known transmitters of West Nile virus and Eastern equine encephalitis. Both are potentially fatal.
In 2012, the state tallied a record 33 human cases of West Nile virus and seven human cases of Eastern equine encephalitis, according to the Department of Public Health. Those included two West Nile cases in Essex County that resulted in the deaths of people in Georgetown and Amesbury.
Last year, the number of people diagnosed with West Nile dropped to eight, while there was only one confirmed case of EEE, which was not fatal. Health officials attributed the drop to aggressive spraying.
Mehaffey said chemicals used in the mosquito spray — including the insecticide prallethrin, used in a brand of spray called Duet — have been approved for use by state and federal environmental agencies as safe around humans, pets and other animals.
“Some people think we’re still using DDT,” he said. “There’s a lot of misconceptions out there.”
Despite assurances, state health officials note that contact with mosquito spray has been known to cause symptoms such as nausea, shortness of breath and irritation of the eyes, ears and throat. When the spraying occurs — typically by truck or helicopter at night — health officials warn residents to stay indoors, keep windows closed, turn off window fans and keep pets inside.
As mosquito-borne illnesses become widespread, health officials say regional efforts to control the insects are vital to prevent outbreaks.
Environmental groups such as the Washington D.C.-based Beyond Pesticides have pushed state and local officials to reduce reliance on what they call harmful chemicals while promoting more organic alternatives.