Control of mosquitoes in their larval stages is the backbone of most mosquito control programs in California. Larvicides are products used to reduce immature mosquito populations when they are still developing in the water. Larvicides, which can be biological or chemical, are applied directly to water sources that hold mosquito eggs and larvae. When used well, larvicides can help to reduce the overall mosquito population by limiting the number of new mosquitoes produced.

Adulticides are products that rapidly reduce adult mosquito populations. This can become necessary when larval control measures are insufficient or not feasible. Adulticiding may be initiated when there is evidence of significant West Nile Virus transmission in a region. The most common method of adulticiding is ultra-low volume (ULV) spraying. ULV spraying is the process of putting very small amounts of liquid into the air as a fine mist of droplets. These droplets float on the air currents and quickly eliminate mosquitoes that come into contact with them. ULV adulticides are applied when mosquitoes are most active-typically early evening or pre-dawn. They can be applied from hand-held sprayers, truck-mounted sprayers, or airplanes. Adulticides immediately reduce the number of adult mosquitoes in an area, with the goal of reducing the number of mosquitoes that can bite people and possibly transmit West Nile virus.

Chemical control is the use of specific chemical compounds (insecticides) that reduce adult and immature mosquitoes. It is applied when biological and physical control methods are unable to maintain mosquito numbers below a level that is considered tolerable or when emergency control measures are needed to rapidly disrupt or terminate the transmission of disease to humans. Larvicides target mosquito larvae and pupae. Adulticides are insecticides that reduce adult mosquito populations. All products are registered with the California Environmental Protection Agency (EPA) and are applied by trained and state-certified technicians.

Each state has mandated training and experience requirements that must be met before an individual can commercially apply insecticides. In California, for example, California State Health and Safety Code requires that every employee of a mosquito abatement or vector control district who handles, applies, or supervises the use of any insecticide for public health purposes be certified by the Vector-Borne Disease Section of the California Department of Public Health (CDPH) as a Certified Vector Control Technician, and upon certification, must also meet established continuing education hours. In addition, these applicators must follow the instructions and precautions that are printed on the insecticide label.

All insecticide products are required to have a label which provides information, including instructions on how to apply the insecticide and precautions to be taken to prevent health environmental effects. All labels are required to be approved by U.S. Environmental Protection Agency.

Chemical control measures are one part of a comprehensive and integrated mosquito management program. An integrated program is the most effective way to prevent and control mosquito-borne disease. An integrated mosquito management program should include several components: surveillance (monitoring levels of mosquito activity, and where virus transmission is occurring), (2) reduction of mosquito breeding sites, (3) community outreach and public education, and (4) the ability to use chemical and biological methods to control both mosquito larvae and adult mosquitoes. CDC’s Revised Guidelines for Surveillance, Prevention, and Control of West Nile Virus in the US, 2003 [254 KB, 77 pp]) provides detailed guidance about the use of control measures, including suggestions for a phased response and the actions that are possible at different levels of virus activity.

Questions concerning specific insecticides can be directed to the U.S. Environmental Protection Agency, as this agency has responsibility for registration of insecticides. Many issues are addressed on the EPA’s Mosquito Control Web site. The National Pesticide Information Center (NPIC) provides insecticide information and questions about the impact of insecticide use on human health. NPIC is cooperatively sponsored by Oregon State University and the U.S. Environmental Protection Agency.

If you are experiencing health problems for any reason it is important to see your health care provider promptly.