Waiting for spring warmth? So are the mosquitoes

The prolonged spring chill is keeping mosquitoes at bay — one positive upside to the 16th-coldest April on record, and the result is that we may not be slapping and swatting until after Memorial Day.

Summer should be pleasant, too, because we won't be fending off as many of the buzzing insects searching for a meal.

"We will have fewer," said Alex Carlson with the Metropolitan Mosquito Control District (MMCD).

A number of factors are aligning to keep mosquito numbers down this year. Larvae hatch in standing water such as ponds, marshes and swamps, but when water temperatures remain low as they have this year, their development is slowed. In mid-summer, a floodwater mosquito — the most common type in Minnesota — can pass through the four stages of development and emerge as an adult in 4 to 7 days. When it's cold, that process can take weeks, Carlson said.

"There is less bacteria and food in the water for them to use to develop," Carlson said. "When it's cold, they stay in the water longer before emerging to be a nuisance."

All that buys time for the control district to fan out to 70,000 habitats in the seven-county metro area and drop granular pellets laced with a bacterium called Bacillus thuringiensis israelensis that kills off the larvae.

The district relies on seasonal staff — many college students — to survey the wetlands and drop the pellets, and many can't start until May. Average daily temperatures have remained below 40 degrees on most days this month, and that has kept waters from warming to create hatching conditions, Carlson said.

MMCD will begin its treatment program May 9. It also includes helicopters that fly over mosquito-producing areas and drop the bacteria.

Last year's drought-like weather also kept mosquito numbers suppressed, and the forecast from the National Weather Service calls for another dry June, July and August. If the forecast holds, odds are good Minnesota won't see a big burst in the mosquito population around July 4 when numbers typically peak, Carlson said.

It's not all good news. Fewer mosquitoes does not lessen the risk of contracting mosquito-borne illnesses. The state last year saw some of the lowest overall mosquito numbers in a decade but had 27 cases of West Nile virus, the most in three years, Carlson said. There also were six cases of Jamestown Canyon virus in Minnesota last year. The illness in severe forms can lead to encephalitis, according to the Centers for Disease Control and Prevention.