Orange County Mosquito and Vector Control District
This website includes CSS elements that your browser does not support. Please upgrade your browser to a current version, then come back and try again.
The Basics

Q. What’s so dangerous about mosquitoes?
A. Mosquitoes are the most dangerous animals on the planet. The disease-causing organisms (pathogens) they transmit (vector) through their bite kills more people and wild animals than all other animals combined. Mosquitoes are found on every continent except Antarctica. Of the 3,500 species of mosquitoes worldwide, 53 occur in California, 23 in Orange County.

Q. What’s the best way to control mosquitoes?
A. The best way to control mosquitoes is to target their aquatic stages and the easiest way to do this is to deny them the water they need to develop. This is why the Orange County Mosquito and Vector Control District asks the public to eliminate any standing water around the home or workplace and to report standing water that cannot be eliminated. Anything that will hold as little as 1/4 inch of water can support mosquito reproduction and should be emptied or drained. If standing water cannot be eliminated, it must be treated. Some treatment products prevent mosquitoes in their aquatic stage from breathing. Another strategy is to introduce mosquito-eating fish into water sources. Combinations of different strategies are often required to control mosquitoes effectively. Learn about the aquatic stages of a mosquito and it’s general life cycle.

For locations where water cannot be eliminated and mosquito fish cannot be placed, larvicides are used to kill mosquitoes in their aquatic life stages. Larvicides are applied directly to water sources that hold mosquito eggs or larvae, thus limiting the number of new mosquitoes that are produced and reducing the overall mosquito population.

Mosquito Control Applications
Q. What triggers adult mosquito control applications?

A. The District's aggressive campaign against mosquito larvae is intended to minimize the need to use public health pesticides targeting adult mosquitoes. When West Nile virus is detected in the community, the District's initial response is to intensify its efforts to reduce mosquito-breeding sites and increase its levels of larviciding in those areas in which West Nile virus has been found. Reducing the population of adult mosquitoes with public health pesticides (adulticides) that are registered by the US Environmental Protection Agency (US EPA) is done if necessary to prevent human illness or to suppress a heavy nuisance infestation of mosquitoes. The decision to use adult mosquito control application either by truck-mounted, handheld, or aircraft application equipment is based on surveillance information or the documentation of West Nile virus activity at a level that indicates a threat to human health. Adulticing is concentrated in areas most at risk for disease occurrence and is conducted by certified and licensed applicators.

More information on triggers for larvicide and adulticide application can be found in the District’s Integrated Vector Management and Response Plan.  

Q. What triggers an adult mosquito control application by aircraft in Orange County?
A. The District will conduct adult mosquito control applications by aircraft based on the finding of elevated West Nile virus activity in a specific area, and when all ground-based options are ineffective. The adult mosquito control application by aircraft will reduce the population of infected adult mosquitoes, thus decreasing the risk of disease transmission to the public. To view the current map of the West Nile virus activity throughout Orange County, click here.

Q. What is the District’s primary form of mosquito control?
A. We practice Integrated Vector Management relying on larvicides, with public health pesticides reserved for situations where other methods would be ineffective to protect public health. More information about the District’s IVM policy can be found here.

Q. Where do public health pesticide applications by aircraft against adult mosquitoes take place?
A. Application of the public health pesticides by aircraft targeting adult mosquitoes will take place in areas of concern, as determined by our mosquito and disease surveillance indicators. Our trained and certified technicians use a variety of surveillance techniques and treatment criteria to ensure effective mosquito control with the least amount of risk to our residents and our environment.

Q. How can I learn about adult mosquito control application activities?
A. Announcements about adult mosquito control applications by aircraft will be posted on our District website. Click here for our weekly schedule. You may also subscribe to our mailing list to receive automatic Alerts regarding District activities. Click here to sign up!

Material Considerations

Q: What public health pesticide will you be applying by aircraft?
A: In response to a growing West Nile virus emergency, Duet ™ will be applied by aircraft to target adult mosquitoes carrying West Nile virus in Orange County. Any application will be made by Clarke/Dynamic Aviation under contract with the District. Learn more about Duet here.

See DUET’s FAQ sheet here.

Personal Considerations
Q. How do public health pesticides affect my family and me?
A: At the rates we apply these products (0.43 to 1.28 fluid ounces of DUET per acre), they do not pose a significant risk to you or your family, however, we recommend that you do whatever makes you feel most comfortable during the application. For more information on pesticides 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.

Q. What should I do if I think that I am having health problems because of pesticides used in my area?
A. If you are experiencing health problems for any reason it is important to see your health care provider promptly.

Useful Information

Q: What’s the life cycle of a mosquito and why should I care?
A: Mosquitoes have four stages in their life cycle: egg, larva, pupa, and adult. The first three stages are aquatic. The female mosquito lays eggs on or near a water surface; the eggs hatch a few hours or days later and the larvae emerge. The larvae feed on aquatic algae and bacteria. As they mature, they outgrow their skin, grow a new skin layer, and shed the old one, a process called molting. After the fourth growth-molt cycle, the mosquito enters the pupal stage. A few days later, the adult mosquito emerges from the pupal case and flies away.

The Mosquito Life Cycle

Because three (3) of the four (4) life stages of a mosquito are aquatic, the best way to control them is to target their aquatic stages.  By denying them the water they need to develop, mosquitoes cannot complete their life cycle and they die. For this reason, the Orange County Mosquito and Vector Control District asks the public to eliminate any standing water around the home or workplace and to report standing water that cannot be eliminated.

Q. What are “larvicides” and “adulticides”?
A. Larvicides are products used to kill mosquitoes in the aquatic life stages. Larvicides are applied directly to water sources that hold mosquito eggs or larvae. Larvicides help reduce the overall mosquito population by limiting the number of new mosquitoes that are produced.

Adulticides are products used to kill adult mosquitoes. Adulticides can be applied from hand-held sprayers, truck-mounted sprayers or by aircraft. Adulticides can have an immediate impact to 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.
Larvicides and adulticides used by the Orange County Mosquito and Vector Control District are regulated by the US Environmental Protection Agency.

Q. What training is required for workers who apply pesticides?
A. Each state has mandated training and experience requirements that must be met before an individual can commercially apply pesticides. 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 pesticide 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 pesticide label. All pesticide products are required to have a label, which provides information, including instructions on how to apply the pesticide and precautions to be taken to prevent health and environmental effects. All labels are required to be approved by U.S. Environmental Protection Agency.

Additional Resources

Q. Where can I get additional information regarding specific pesticides?
A: Questions concerning specific pesticides can be directed to the U.S. Environmental Protection Agency, as this agency has responsibility for registration of pesticides. Many issues are addressed on the EPA’s Mosquito Control Web site.
The National Pesticide Information Center (NPIC) provides pesticide information and questions about the impact of pesticide use on human health. NPIC is cooperatively sponsored by University and the U.S. Environmental Protection Agency.
NPIC can be reached online or toll-free: 1-800-858-7378.

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 website 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.