The Associated Press

SIOUX FALLS - Many towns and cities have taken to the streets to try to control the mosquito population, and, by extension, reduce the number of West Nile virus infections.

"The (mosquito) spraying can be really effective," said Jim Wilson, pesticide education coordinator at South Dakota State University.

"We expect 90 percent or more control of the mosquitoes that are flying in the area when spraying."

Spraying or fogging kills adult mosquitoes.

"When we look at that class of chemical and class of insecticide, it tends to be one that is relatively low in toxicity," he said. "The human exposure hazard is extremely low."

Wilson said that the spraying, if needed, should be around dusk, so the impact on other insects is minimal because they are at rest during that time.

"Some people get concerned about using pesticides, but if it's done responsibly, there is minimal risk.You never say there is no risk, but there is minimal risk to humans," he said. "You have to balance that with the risk of contracting West Nile virus."

Denise Van Roekel, coordinator of the mosquito control program in Sioux Falls, said the costs of control programs can be high.

"You have to take into consideration that the chemical is one cost, the equipment that we need to get in order to apply it is another cost," Van Roekel said.

She said Scourge, the chemical used in Sioux Falls, sells for about $583 per gallon.

In the three-day process required to spray Sioux Falls, it cost about $17,000, she said.

"Getting something started up is actually a big expense," she said. "You need the kind of staffing capable of running the program. There are a ton of angles, but when you kind of put it in light of the human life, it's worth it."

Annette Bredthauer, Nebraska's public health veterinarian, said mosquito control at an early larval stage is more effective than spraying.

"It is much more efficient to find the places where (mosquitoes) are breeding," she said.

Trying to control mosquitoes at a larval stage kills them at an early stage in their lifestyle, even before they could be a threat.

"It's much more effective to try to get (mosquitoes) while they're concentrated in ponds or wet areas before they hatch than try to catch them on the wing," Wilson added.