What are your chances of contracting West Nile Virus? Pretty low, but that's no reason to let your guard down. Wisconsin has had one human case of the mosquito-borne illness so far this year. UW-Madison entomology professor Susan Paskewitz notes there's one particular species — Culex — which carries the disease. Working with other researchers, she was able to estimate that about five of every one thousand Culex mosquitoes were infected with West Nile in 2006, a rate that dropped even lower last year, to about one out every one thousand. “So, even if you are bitten by a Culex, your risk of encountering an infected mosquito is very low,” says Paskewitz.
Still, Paskewitz doesn't want people to become complacent. “We're in August now,” she notes. “This is usually a period when we see West Nile cases go up, both in Mosquitoes and in terms of our human cases. We always recommend wearing long sleeves, trying to avoid the peak biting periods at dusk and dawn, and applying a repellent.” Paskewitz has developed a website that's full of useful information on how to thwart mosquitoes.
Paskewitz and her colleagues have learned that unlike most mosquitoes, Culex prefers to deposit its eggs in the most stinking, fetid water imaginable. The scientists have developed their own special brew, to attract female Culex mosquitoes that are ready to lay eggs. Paskewitz says the potion consists of chicken manure, fresh grass, straw and brewers yeast. “We put that in a big container that we cap, and then leave that sitting in sunlight for a week or two,” Paskewitz explains, adding that it's the job of a graduate student to periodically check to see if the brew “is sufficiently smelly.”
Paskewitz's research has also led to an innovative approach to controlling mosquitoes: an inexpensive native fish that's familiar to anglers. Along with research assistant Patrick Irwin and John Hausbeck with the Madison/Dane County Department of Public Health, she's launched an experiment this summer to see if supplementing mosquito larvacide with fathead minnows can reduce Culex numbers. The idea is that if the minnows eat large numbers of larvae, larvacides could be used less often, or their use might be stopped altogether.