Adulticides are materials used to reduce adult mosquito populations. At San Mateo County Mosquito and Vector Control District, EPA-registered adulticides are applied by licensed applicators and only in areas where high numbers of adult mosquitoes or adult mosquitoes carrying disease exist.
The main material currently used to control adult mosquitoes in San Mateo County is called Zenivex E4. This product contains 4% etofenprox, the same active ingredient found in many topical flea and tick treatments for pets. It is applied at an ultra-low volume (ULV) from either hand-held or truck mounted equipment. Hand-held equipment is used to treat very small contained areas. Such cases usually occur when a broken sewer pipe has caused mosquitoes to develop unnoticed under a single building. On rare occasions, it may become necessary to apply adulticides to a larger area using truck-mounted equipment. When truck-mounted adult mosquito treatments occur, they are conducted at night when mosquitoes are most active and beneficial insects, such as bees and butterflies, are inactive. Other materials may be occasionally be used as outlined in the District's Programmatic Environmental Impact Report.
The products used by the District for adult mosquito control pose very little risk to humans or the environment. They are applied at very low concentrations in a very fine mist. Because of the extremely small size of the droplets in the mist, most of the material evaporates or breaks down before settling on surfaces. When applied using the ULV method, the material is only able to kill a mosquito for approximately 15 minutes, and the material breaks down to undetectable levels within hours of exposure to sunlight. It is not necessary to take any special precautions when an adult mosquito control treatment occurs in your neighborhood.
If you have a question about the products used for adult mosquito control, you can call the District office at (650) 344-8592. You can also call the National Pesticide Information Center at (800) 858-7378.
To learn more about Zenivex E4, visit the manufacturer's website.
Page last reviewed: July 14, 2021