Mosquito populations thriving in floodwater-plagued Midwest

7/3/2008

CHICAGO - First came the floods - now the mosquitoes.

An explosion of pesky insects are pestering cleanup crews and just about anyone venturing outside in the waterlogged Midwest. In some parts of Iowa there are 20 times the normal number and in Chicago up to five times more than usual.

The good news is these are mostly floodwater mosquitoes, not the kind that usually carry West Nile virus and other diseases.

Heavy rain followed by high temperatures creates ideal conditions for these bugs, whose eggs hatch in the soil after heavy rains. Scientists call them nuisance mosquitoes.

"About 3 p.m. the bugs come out pretty bad. They're all over the place," said Bill Driscoll, a flood cleanup worker in Palo, Iowa. "We've been burning through the repellent with the volunteers."

In Lisbon, Iowa, about 20 miles east of flood-ravaged Cedar Rapids, biker Larry Crystal said mosquitoes have made his rides miserable. "Every time I stop to rest at a rest area these buggers just find a way to bite me all over my neck area between my helmet and jacket," he wrote on a bikers' blog.

Some mosquito surveillance traps in Iowa have up to 20 times more mosquitoes than in recent years, said Lyric Bartholomay, an Iowa State University insect expert.

For example, last week, 3,674 mosquitoes were counted in Ames-area traps, compared with 182 for the same week last year, Mr. Bartholomay said. Trap quantities are just a tiny snapshot of the true numbers of mosquitoes flying around.

In Iowa, the main culprit is the Aedes trivittatus, a nuisance mosquito with "a voracious appetite, and they hurt when they feed on you," she said.

A relative called Aedes vexans is doing much of the biting in Chicago's suburbs, said Mike Szyska of the Northwest Mosquito Abatement District.

Mosquito numbers in northwestern suburbs peaked last week at about five times higher than normal for this time of year, Mr. Szyska said.

Complaints and requests for insecticide spraying have the district "working day and night. We're extremely busy," he said.

There's no evidence of higher than normal numbers of Culex mosquitoes, more commonly associated with West Nile virus.

Several states have found evidence of West Nile, but only a few cases, which tend to start occurring later in July.

But health authorities say that could change with drier weather, which Culex mosquitoes prefer, so they're advising people to take precautions.

The explosion of floodwater mosquitoes has left many people feeling like mosquito magnets.

And about 10 percent of the population actually qualifies, entomologist Jerry Butler, a professor emeritus at the University of Florida, said.

These are the people who get covered in bites while others are left unscathed. Many of them get exaggerated skin reactions to the bugs - hard red welts or hives that can itch for days.

Some people have allergies to mosquitoes, developing limited but severe skin reactions that researchers call "skeeter syndrome." Some can develop potentially dangerous, widespread reactions including wheezing, and, rarely, life-threatening throat-swelling and breathing problems.