No West Nile virus reported as mosquito numbers rise

08/04/2013 1:35 PM

08/04/2013 1:37 PM

While the rest of us have been enjoying the unusually cool summer by the pool or at evening barbecues, Christopher Rogers has been busy counting mosquitoes.

Rogers, an invertebrate zoologist at the Kansas Biological Survey, has nine mosquito traps placed in strategic locations in the Wichita area where the bugs are likely to congregate, and where they may bother nearby humans.

He counts and categorizes the trapped mosquitoes every week, then sends the specimens off to the Kansas Department of Health and Environment, where they’re tested for West Nile virus and other diseases.

Rogers said this summer’s above-average precipitation has led to an increase in the number of mosquitoes. However, he said, relatively cool temperatures have kept those numbers from reaching historic highs.

In hotter summers, Rogers said he’s counted as many as 6,000 mosquitoes a night in some traps. During the week of July 27, Rogers’ traps caught 500 mosquitoes

“The higher the temperatures, the faster they breed,” Rogers said.

This years’ relatively dry spring may have also kept the mosquito population in check.

“We’re above average for rainfall this year, but we had a very dry period between June 1 and July 14 – only .07 of an inch of rain,” said Bob Neier, extension officer at the Sedgwick County Extension Office.

The number of Culex mosquitoes, the breed that most commonly carries the West Nile virus, has decreased over the course of the summer. During the week of June 8, Rogers’ traps caught nearly 600 Culex mosquitoes. By the week of July 27, that number had fallen to about 100.

A spokesperson for the Sedgwick County Health Department said there have been no cases of West Nile virus reported so far this year in Kansas.

Like all mosquitoes, Culex mosquitoes need water in order to breed. But Rogers said different breeds have different requirements. Culex mosquitoes lay their eggs in ponds, pools, green swimming pools or birth baths. The breed that carries malaria, on the other hand, prefers to lay eggs on the banks of rivers and streams.

Aedes Vexans, the breed of mosquito most commonly found in Sedgwick County, lays its eggs in flood plains so that the aquatic larvae can hatch once the area is underwater. Only female mosquitoes bite, Rogers said, and only when they’re about to lay eggs. The reason? Mosquito eggs do not contain a yolk, so the female “takes a blood meal,” in Rogers’ words, to get some much-needed protective protein.

Rogers said just because mosquito levels aren’t as high as they could be, that doesn’t mean people shouldn’t take adequate precautions.

The Sedgwick County Department of Health has a mnemonic for protecting yourself from West Nile: drain, dress and DEET. Drain standing water, wear clothes that cover your arms and legs, and apply bug spray that contains DEET, a chemical compound that repels mosquitoes and other insects.

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