Despite dry summer, beware of mosquitoes

If it has been a while since a mosquito has buzzed by your ear, that does not mean you can expect to be free from mosquitoes or the threat of West Nile Virus this summer.

In fact, thanks to the hot, dry weather, "in principle, it does seem like it could be a pretty good year" for the vector of the virus — the culex mosquito, said University of Illinois pathobiology Professor Marilyn O'Hara Ruiz, whose research projects have zeroed in on suburban Chicago catch basins as breeding grounds for these insects.

It is the common inland floodwater mosquito, which UI Extension entomologist Phil Nixon calls the "noisy biter" (the kind that buzzes past your ear and when it bites, you feel it) which are noticeable after heavy rainfall. They are the kind of mosquitoes that can drive you inside.

But you should really beware the quiet, sneaky biters.

"People don't notice them as much. [Culex mosquitoes] are more stealthy," compared with other mosquitoes, O'Hara Ruiz said.

She and graduate student Allison Gardner have been researching the factors associated with the growth of these West Nile Virus-carrying mosquitoes.

"Those actually need stagnant water for where they put their eggs. That's why catch basins are so good for them. They want the water that's got a lot of organic matter in it," O'Hara Ruiz said.

If you want to get a sense for how much these mosquitoes like catch basins, just tap on one of them.

Then again, don't.

O'Hara Ruiz and Gardner have collected larvae and water from the basins to study how these mosquitoes respond to certain organic matter in the basins. For example, they plan to further investigate how stuff like seed pods from trees or lawn fertilizer runoff contribute to creating an environment in the basin that helps the larvae develop.

What puts the brakes on the development of these mosquitoes? Rain.

When there's a good long rain, about an inch to an inch and a half, the rainwater actually flushes out the old water where the larvae were thriving before, according to Ruiz.

"These insects like putrid water — water that's turned dark, yellowish and is smelly from debris like tree leaves. Under hotter conditions, their life cycle speeds up. And the lack of rainfall causes all those nasties in the water to concentrate, making it more putrid, which is just what they like," Nixon said.

So clean your gutters already.

Rinse out your bird bath once a week. Clean your wading pool. Don't let water sit in a tin can or a plastic toy left outside.

Unlike other kinds of mosquitoes, the cutex ones normally don't fly more than a half mile from their home so "it's a neighborhood control situation," Nixon said.

West Nile virus was first identified in Illinois in September 2001; tests results confirmed the virus in two dead crows in the Chicago area. In 2002, 100 of the 102 Illinois counties reported a positive human, bird, mosquito or horse case, and by the end of that year, Illinois reported 884 human cases of West Nile Virus, including 67 deaths.

Ruiz started looking at sites in the Chicago suburbs after the 2002 outbreak and wanted to find out why some neighborhoods seemed to be more susceptible. Early on they learned that there were more cases in neighborhoods built post-World War II, where catch basins were installed to control floodwater at the edges of streets or in backyards.

She set out to find out why some basins have a lot of larvae.

The researchers also are looking into shelter available for the mosquitoes. In the heat of the day, the mosquitoes like to find a low-lying shrub near the basins where they can take a rest, and the better the shelter available near the basin, the better for the female mosquito.

The Champaign-Urbana Public Health District treats municipal catch basins in Champaign, Urbana and Savoy, according to Jeff Blackford, the district's program coordinator. Because of the warm spring, employees started a week early putting briquettes in the catch basins. These briquettes contain a larvicide that disrupts the mosquitoes life cycle, and they should last through the summer, he said.

From mid-May to October the district monitors mosquito traps that have been placed throughout Champaign, Urbana and some outlying towns. Staff also collect dead birds and submit them to the UI College of Veterinary Medicine where they're tested for the virus.

The first time the virus was detected in Champaign County this year was on June 12. A crow and a mosquito pool tested positive for the virus. So far this summer no human cases have been reported in the state, according to the Illinois Department of Public Health.

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logicalpositivist wrote on July 10, 2012 at 1:07 pm

"for the vector of the virus — the cutex mosquito"..."People don't notice them as much. [Cutex mosquitoes] are more stealthy..."

I think the genus is spelled Culex, not Cutex.

Mike Howie wrote on July 10, 2012 at 2:07 pm
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You are correct. Thanks for catching that, although I'm sorry you had to.

Mike Howie

online editor