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Helicopters out to control mosquito numbers

Helicopters are flying low over Rosemount. They're making sure mosquitoes can't do the same.

Amid concerns over West Nile virus and other dangers mosquitoes pose to the general population, the Metropolitan Mosquito Control District flies helicopters carrying natural soil bacteria over low wetlands in the metro area in order to control the mosquito larvae population.

Mosquitoes lay eggs in wetland areas that tend to be dry most of the time, according to Scott Grant, the MMCD field foreman overseeing Monday's aerial mosquito applications out of Akin Road Elementary School's parking lot in Farmington. After storms come through that drop more than an inch of water in 24 hours or less, the water allows the eggs to hatch.

"Mosquito eggs hatch fairly quickly," Grant said.

It takes seven days from the time mosquito hatch to the time they grow to pupae and then to adults. In between those seven days, mosquito larvae go through four different stages of development, called instars. The MMCD tries to catch mosquito larvae when they're in the instar stages, using helicopters for wetland areas greater than three acres. Such areas in Farmington include wetlands near Pilot Knob Road, behind Bible Baptist Church on Akin Road and south of the Dakota County Fairgrounds.

The natural soil bacteria the MMCD uses is called BTI, or Bacillus thuringiensis subgroup israelensis. They fly enough BTI for 80-acre applications every time the MMCD helicopter takes off. The BTI is coated onto ground-up corn cob that will release bacteria granules once it hits water.

Mosquito larvae feed on bacteria in the water, according to Grant. This particular type of bacteria is toxic to mosquitoes because of the chemical ph levels in their stomachs. Humans and most creatures have acidic ph levels in their stomachs. Mosquitoes have a more alkaline ph level in their digestive system.

When larvae digest BTI, the bacteria causes crystals to develop, expanding and eventually exploding the mosquito larvae within two to 48 hours. BTI is not harmful to humans and most other animals.

The Dakota County MMCD shop is located in Rosemount. They cover the county and part of Bloomington and Hennepin County. They are funded by property tax dollars, approximately $11.95 for an owner of a $250,000 home in 2008, according to the MMCD web site.

The MMCD will spray smaller wetland areas on foot, usually less than three acres of wetland with standing water. Studies have shown none of the bacteria or chemicals they use are harmful to humans.