Spraying Frequently Asked Questions

Q. What are larvicides and adulticides?

A. 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 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.

Q. What type of insecticides are being used by the Sacramento-Yolo Mosquito and Vector Control District?

A. For larval mosquito control, the District typically utilizes Bacillus thuringensis (Bti) and B. sphaericus, bacterial products, or methoprene, an insect growth regulator which keeps the immature mosquito from becoming a flying adult.

B. For adult mosquito control two classes of insecticides, each combined with a synergist chemical, are commonly used for adult mosquito control:

Pyrethrins are the active ingredients in pyrethrum, an extract of the African flower Chrysanthemum cineriaefolium. Pyrethrins are natural insecticides that act by blocking chemical signals at nerve junctions.

Pyrethroids are the synthetic version of pyrethrins and act by blocking chemical signals at nerve junctions.

Piperonyl butoxide (PBO) is a synergist that is usually incorporated with pyrethrins. PBO enhances the effect of these insecticides by inhibiting cytochrome P450, a class of enzymes that break down the insecticides. This allows the insecticides to be effective with less active ingredient than would otherwise be required.

Organophosphate is a synthetic, organic pesticide that contains carbon, hydrodgen, and phosphorus which acts by inhibiting the blood enzyme cholinesterase.

The U.S. Environmental Protection Agency approves the use of insecticides nationally and the California Department of Pesticide Regulation (CDPR) approves their use in California. Before pesticides are registered by US EPA or CDPR, they must undergo laboratory testing for acute and chronic health effects.

Q. When does the Sacramento-Yolo Mosquito and Vector Control District use chemical mosquito control?

A. 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.

Q. What training is required for workers who apply insecticides?

A. 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 (DPH) 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.

Q. What is the Centers for Disease Control’s (CDC) position regarding the use of chemical mosquito control?

A. 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.

Q. How will these insecticides affect me and my family?

A. At the rates we apply these products (3/4 oz or less per acre), they should not pose a significant risk to you or your family, and in fact, are used at a higher rate to treat head lice in children; however, it is always a good idea to remain indoors and keep windows and doors closed during applications. For more information on insecticides and health, consult the U.S. Environmental Protection Agency, which oversees the registration of these chemicals. The National Pesticide Information Center (NPIC) can also provide information through a toll-free number, 1-800-858-7378 or online.

For treatment schedule including locations see our Spraying Update page.

Q. How will these products affect cats or dogs?

A. This is the same material used to treat cats and dogs for fleas and ticks.

Q. Will the adult mosquito treatment affect my swimming pool water, lawn furniture, play equipment, toys, etc?

A. Your swimming pool water and items found in your yard should not be affected. Applications are made in the very early morning hours or late evening hours, and pyrethrins break down rapidly in sunlight.

Q. What if I have a vegetable or fruit garden?

A. Just as you normally would, wash your vegetables and fruit before you eat them.

Q. Where can I get additional information regarding specific insecticides?

A. 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.

NPIC can be reached online or toll-free: 1-800-858-7378.

Q. What should I do if I think that I am having health problems because of insecticides used in my area?

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