PEST CONTROL/City traps mosquitoes to test for West Nile
To detect the presence of the West Nile virus in its community, St. Charles, Ill., has installed two traps within its city limits that are designed to attract the type of mosquito that is the primary carrier of the infectious agent. Although no one in the city has reported contracting the virus, it has been detected in nearby jurisdictions, and city officials predict that it eventually will arrive in St. Charles.
Known as gravid traps, the devices contain a liquid mixture of water, hay and brewer’s yeast that lures female Culex mosquitoes ready to lay their eggs. In preparation for giving birth, the mosquitoes feed on the blood of an animal, such as a bird, providing a chance for the insects to contract the West Nile virus.
This spring, St. Charles approved the use of the traps after Roselle, Ill.-based Clarke Environmental Mosquito Management, the firm that the city contracts with to run its mosquito-abatement program, recommended their use. The traps, which are approximately 18 inches by 24 inches, were installed in early May. The company collects and tests samples from the traps about every five days, according to Robert Vann, building and zoning commissioner for St. Charles.
As of mid-July, none of the tests had detected the West Nile virus in the mosquitoes, Vann says. However, the virus has been making inroads into the surrounding area. Last year, a death in Kane County, the county in which St. Charles is located, was attributed to the virus. The victim lived about 15 miles from the city, Vann says. Numerous other cases of the virus were reported in the Chicago metropolitan area last year, he adds.
Given the proximity of recent West Nile cases, Vann says it is a near certainty that the virus will at some point arrive in St. Charles. “It’s just a matter of time, I believe,” he says.
In fact, he adds, it is possible there have been some cases of the virus in the city that have gone unreported. “Certainly, the unreported [cases] are something to be considered, too,” Vann says. “Everybody realizes that not everyone that gets West Nile goes in and seeks treatment.”
The two gravid traps are one component of the city’s mosquito-abatement program. The program also includes spraying retention ponds and other standing water spots with larvicide about every 10 days and placing insect growth regulator pellets, which kill mosquito larvae when they reach the pupal stage, in ditches, catch basins and subdivision drains.
