WILLISTON (AP)- The U.S. Air Force Reserve has scheduled mosquito spraying in the Williston area for late May and mid-June, and officials are completing an environmental study to firm up details such as what chemical will be used.

Residents earlier this month voted 67 percent to 33 percent to pay another $2 a month to their mosquito control district, bringing the total assessment to $4 a month for city residents and to $2 a month for rural electric customers.

The additional money will help pay for an Ohio-based unit that uses C-130 planes to spray for mosquitoes.

"That's all part of our training for our wartime mission, which is mosquito control, and to keep troops safe from these same types of diseases that people would be concerned about here," said Mark Breidenbaugh, chief entomologist for the unit at Youngstown Air Reserve Station in Vienna, Ohio.

The unit has sprayed for mosquitoes in North Dakota before, at the Air Force bases in Grand Forks and Minot.

The environmental study for the Williston region must be approved by Williston officials, the U.S. Army Corps of Engineers, the North Dakota Game and Fish Department and the U.S. Fish and Wildlife Service.

Breidenbaugh said he expects officials to choose a mosquito larvicide that affects mosquitoes and a few other aquatic flies but does not harm people.

The Williston region has long had mosquito problems because Rocky Mountain snowmelt swells the nearby Missouri River in the spring. It can overflow its banks in low-lying areas and create thousands of acres of standing water that are ideal for mosquito breeding, said Kent Luttschwager, wildlife resource management supervisor at the Game and Fish office in Williston.

The environmental study will determine what areas will be sprayed.

"We would just as soon see every mosquito is killed," Luttschwager said. "However, we have the responsibility to make sure that the fish and wildlife resources are considered."

The U.S. Fish and Wildlife Service also is awaiting the environmental study, said Kevin Johnson, environmental contaminant specialist in Bismarck.

"Our main issue is going to be with the threatened and endangered species, which are the pallid sturgeon in the Missouri River, the least tern and piping plovers, the two birds that nest along the Missouri River and along the Yellowstone River," Johnson said.