Mosquito populations in Iowa are determined primarily by the frequency and amount of rain that falls during the course of the spring, summer, and early fall. Granted, we have about 50 different species of mosquitoes in Iowa that all seem to have their own preferred water sources in which they develop. However, our most abundant species and one that contributes to well over 90 per cent of the mosquito bites received in Iowa is a species known scientifically as Aedes vexans. This particular species commonly is referred to as a floodwater mosquito because it prefers to develop in temporary puddles and pools of water that form following sufficient amounts of rain. Female mosquitoes of this species actually deposit their eggs on the ground in low-lying areas. If these low-lying areas become "flooded" by rainwater the eggs hatch and the mosquito's life cycle is initiated. If temperatures are in the high 80s or above, the mosquito can complete its life cycle and emerge as an adult in 7 - 10 days. Simply stated, if we have frequent and sufficient rain throughout the spring, summer, and early fall we will have a lot of mosquitoes to contend with. If we don't have those precipitation patterns, our mosquito populations will be minimal.
While the floodwater mosquito, Aedes vexans, has the potential to be an extremely abundant and annoying pest in Iowa, it has minimal involvement in the transmission of West Nile Virus, encephalitis, or other human diseases. While West Nile Virus has garnered recent media attention and caused concern in Iowa, it must be realized that the mere presence of large numbers of floodwater mosquitoes does not equate into an increased threat of West Nile Virus.
A commonly asked question is "what can I do to eliminate mosquitoes on my property?" This is an easy question to answer, but may at times be easier said than done. To eliminate mosquitoes developing on your property all you need to do is eliminate all possible water sources that the mosquitoes could use for their development. This would include eliminating and disposing of cans, buckets, tires, and other objects that could hold water temporarily as well as filling-in, draining, or ditching any low-lying areas that could hold water following a rain. Unfortunately, while you could conceivably eliminate all mosquito development on your property you may not notice a reduction in mosquito numbers. That's because floodwater mosquitoes have no respect for property lines and easily can fly several miles from where they developed. That's why the most effective mosquito management programs are those that involve an entire community or encompass a large area.
The most effective, long-term approach to mosquito management is elimination of mosquito-breeding water sources over a large area. This would involve the mapping of all potential mosquito-breeding water sources over the entire community. Since floodwater mosquitoes develop in temporary sources that exist following rain, the ideal time and way to map these sources would be from an airplane a day or two following a sufficient rain. Once these breeding sources have been determined, efforts should be made to eliminate them through filling, ditching, draining, or other diversionary methods. Any temporary or permanent water sources that can't be eliminated should be inspected weekly for the presence of developing mosquito larvae. If mosquito larvae are found to be developing in these sources they can be safely and effectively treated with products containing the insect growth regulator methoprene or with products containing Bacillus bacteria. While these products are effective in controlling mosquitoes, they are harmless to humans, pets, fish, and other types of wildlife. While more traditional insecticides are available for application through ULV sprayers and foggers against adult mosquitoes, these applications are generally short-term in their effectiveness and are best suited for limited applications or during declared public health emergencies rather than as a routine part of a mosquito management program.
Although much media attention has been given to using propane-driven devices that emit CO 2 to attract mosquitoes, the effectiveness of these devices has centered largely on testimonials rather than research. Plus, these devices can be very expensive. You need to remember that these devices are intended to "attract" mosquitoes. As a result, if used they need to be placed well away from decks, patios, porches, etc.
Finally, you cannot overlook personal protection as a way of contending with mosquitoes. Avoiding the areas and times of day when mosquitoes are most active and wearing long, heavy-knitted clothing are recommended practices. Applying mosquito repellents that have a low concentration of DEET also will be effective in minimizing mosquito biting activity.
This article originally appeared in the 6/18/2004 issue.