Residential areas of Greene, Guilford and Southhampton townships in Franklin County, Pa., were to be sprayed for mosquitos Monday and Tuesday evening, weather permitting.
The Pennsylvania Department of Environmental Protection announced the truck-mounted spraying would start late Monday night in areas where high populations of adult mosquitos have been reported.
The chemical to be used will be Biomist 3 + 15, according to a news release.
Certain mosquito species carry the West Nile virus, which, when transmitted to people, can cause West Nile encephalitis, an infection that can result in an inflammation of the brain.
There have been no confirmed human cases of West Nile virus in Pennsylvania this year.