Preventing Mosquitoes and West Nile Virus - U of I Extension

News Release

Preventing Mosquitoes and West Nile Virus

This article was originally published on June 13, 2011 and expired on July 15, 2011. It is provided here for archival purposes and may contain dated information.

West Nile virus (WNV), which is carried by some mosquitoes and can be transmitted to humans, has become a common summer issue in Illinois. Recent heavy rains and accumulated spots of water are indicators of a possible high mosquito population in the coming weeks. The Illinois Department of Public Health (IDPH) and local health departments monitor WNV presence during the summer. According to IDPH, last year 35 of the state's 102 counties were found to have a West Nile positive bird, mosquito batch, or horse case. A total of 61 human cases of West Nile disease in ten counties were reported last year in Illinois, with the majority in northeastern Illinois. As of June 10 this year, there have been no reports of positive tests. However, typically, incidences increase later in the summer.

Now is a good time to reduce potential mosquito breeding sites to help control the population, especially with the recent rainy weather. "Since mosquitoes that carry west nile virus do not travel far from their hatching site, it is helpful to eliminate egg-laying sites in your own backyard," says John Church, University of Illinois Extension Educator, Natural Resources.

There are several varieties of mosquitoes in Illinois. Not all of them carry WNV. The Northern House mosquito, which carries WNV, lays eggs in standing water in places such as ditches, catch basins and other locations, such as water filled containers. Other attractive breeding sites in urbanizing areas include construction site tracks and ruts or new basement foundations that hold water. Clogged roof gutters can also provide breeding sites. Reducing the incidence of these problem sites will help reduce egg-laying and hatch.

Persons should eliminate any unnecessary water holding areas and containers, such as old tires. Sites such as wading pools, birdbaths, or pet watering dishes should be cleaned and freshened with new water often. Cutting tall grass and weeds can help reduce populations near the home, since it is a favorite hiding place during the day.

Entomologists at the University of Illinois and Purdue indicate that the entire life cycle of a mosquito can be completed in about seven to ten days. Anything that interrupts the cycle, such as reducing water availability within that time, is helpful.

The floodwater mosquito, which is one of the most common nuisance mosquitoes especially in wet years like this one, does not carry WNV. Their eggs are laid in muddy, temporary pool areas and hatch when flooded by rain or runoff water. Young mosquitoes live as larvae in water, but they are rarely found in deep water such as lakes or in flowing streams or rivers. Shallow, ponded areas are the most preferred sites. However, wetlands with a balanced diversity of wildlife can actually confine the mosquito population in that area and use it as a food source.

For individual protection, remember that dark colored clothing tends to attract mosquitoes. They are often hungriest and most active at dusk and dawn, so less outside activity at that time can reduce biting. The peak biting time for the northern house mosquito is about 8:00 pm to midnight. Also, keep pets inside during those high feeding times and out of tall grassy areas, since they can also be bitten. Apply insect repellents to exposed skin when going outside and wear long-sleeved shirts and long pants.

IDPH and the US Center for Disease Control have websites with continually updated WNV statistics at and

Pull date: July 15, 2011