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The most effective methods of mosquito control are to eliminate stagnant water where larvae can develop and applying larvicide to targeted locations. After determining that standing water is contaminated with mosquito larvae, staff uses Bacillus thuringiensis (Bti) and/or Bacillus sphaericus (Bsp) to inhibit development. Bti and Bsp are, commonly applied with ground corn or a silica-based granule that are ingested by the larvae. When that happens, the bacteria that eat away the stomach and intestines of the larvae, killing them before they further develop into pupae and adults. Although very effective on the mosquito larvae, this process causes no harm to people or other mammals, and is non-toxic to all aquatic organisms.
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The goal of the St. Charles County Division of Environmental Health and Protection's Mosquito Control Program is to decrease the number of disease-carrying pests that present a risk to the general population. We target breeding sites that harbor larvae and spray during evening hours for flying adult mosquitoes. In addition, we educate residents on the importance of eliminating potential breeding sites around their community.
There are many products that control mosquitoes, with varying levels of effectiveness and impact on the environment. The primary treatments that the Division of Environmental Health and Protection employs are Kontrol 4-4 for adult insects and Bacillus thuringiensis (Bti) and/or Bacillus sphaericus (Bsp) for larvae.
A mosquito goes through four distinct stages during its life cycle: egg, larva, pupa and adult. Kontrol 4-4 is an adulticide, which means that it affects mosquitoes in the adult life cycle only. Mosquito control programs typically apply treatment by use of an aerosol sprayer, and St. Charles County utilizes a truck-mounted method fashioned with an ultra-low volume (ULV) sprayer. We choose to apply this treatment during the late evening/night hours, when mosquitoes are most active and pollinators are most inactive. ULV sprayers dispense very fine aerosol droplets that contain small quantities of active pesticide ingredients that stay aloft and eliminate mosquitoes on contact. The application area extends almost 300 feet from the vehicle — so even though spraying may be done from the street; it is designed to reach backyard areas. St. Charles County began using Kontrol 4-4 for insect treatment in 2019.
With any pesticide or chemical application, caution must be exercised in accordance with the manufacturer's suggestions to ensure safety. St. Charles County employs public pesticide applicators that are certified by the Missouri Department of Agriculture. The chemicals we apply are carefully diluted, and our machines are calibrated daily to ensure the most effective distribution of pesticide during our control efforts. When truck drivers pass outdoor residents, they turn off the spray apparatus. While the generator may still be running, the sprayer does not disperse chemicals near people.
The best way to cut down on mosquitoes is through water management. If you have any standing water on your property, you can limit habitat and breeding areas by filling in low spots that hold water or by observing proper drainage management. Common breeding areas in many yards are buckets, unused tires, gutters, bird baths, trash piles or other objects that can hold water for a week or longer. Additionally, if you have a lake or pond on your property, a common tool to limit mosquito growth is the use of a fountain or water agitator.
Reducing the mosquito population is a team effort. If you notice potential larvae habitat or have other mosquito-related concerns, please call our office at 636-949-1800 or complete our online form to alert us to potential problems. A common question that you may be asked after this complaint is "Are the mosquitoes biting?" While this may seem to be a strange question, by asking it our staff can best determine which treatment to apply and when. Only female mosquitoes bite, and it may take up to two extra days for females to emerge versus male mosquitoes.
To protect yourself while outside, please apply a mosquito repellent containing DEET, picaridin, IR 3535 or oil of lemon eucalyptus.