Adult Mosquito Spraying FAQ

 

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Q. What will trigger spraying?

A. If West Nile virus is detected in the community, the District's initial response will be 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 adult mosquito population with pesticides (adulticides) registered by the US Environmental Protection Agency (EPA) will be done if necessary to prevent human illness or to suppress a heavy nuisance infestation of mosquitoes. The decision to spray, either by truck mounted sprayers or by aircraft, will be based on surveillance information or the documentation of West Nile virus activity at a level that indicates a threat to human health. Spraying will be concentrated in areas most at risk for disease occurrence and will be conducted by certified and licensed applicators. The District's aggressive campaign against mosquito larvae is intended to minimize the need to use adulticides. 

Q. What pesticides will you use? 

A. When necessary, our District may use ground and aerial application of pesticides to kill mosquitoes that pose a health risk to the residents of Contra Costa County. In the case of adulticiding, or targeting adult mosquitoes, we would use botanical insecticides (plant derived compounds) or synthetic versions of, that include pyrethrins and synthetic pyrethroids, as well as piperonyl butoxide. In an emergency situation, we may use malathion or sumithrin. All of the products we use are registered with the Environmental Protection Agency and applied according to label directions by our trained and certified technicians. Click here for more information on pesticides used in adult mosquito control.

Q. What risks are there to the residents of Contra Costa County?

A. The risks to the public and to the environment are very low. Mosquito adulticides are applied as ultra-low volume (ULV) sprays. ULV applications involve small quantities of active ingredient in relation to the size of the area treated, typically less than 2 ounces per acre, which minimizes exposure and risk to people and the environment.

Q. Where will the spraying take place?

A. The spraying will take place in areas of concern, as determined by our mosquito and disease surveillance programs. 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 come you will not come out and spray my yard?

A. The District does not spray or fog residential yards for adult mosquitoes.

Since mosquito problems are rarely limited to a single property, fogging for adult mosquitoes is usually conducted at a neighborhood level. 

Because three of the four stages of mosquitoes live in water, it's usually more efficient and effective to control immature mosquitoes when they are still in their water source. That's why early stage mosquito control makes up the majority of the District's mosquito control program.

Providing a sample of a swatted mosquito and scheduling an inspection will help our technician to determine which of the 23 mosquito species in Contra Costa County are present and help him identify the probable source.
 
As a public health agency, the District's mission is to prevent vectors through an integrated vector management program. Vectors are insects and animals that can cause harm or spread disease. On private properties, that means:
  • We educate the public to dump or drain standing water to prevent mosquitoes before they become flying, biting adult mosquitoes.
  • We provide free mosquitofish to county residents and businesses for use in private ponds, horse troughs, rain barrels, and neglected swimming pools and spas. 
  • We provide free inspections on private properties to identify mosquito issues.
  • In some cases, District employees will treat water sources like neglected swimming pools or spas. This is a different application from spraying or fogging for adult mosquitoes. 

Q. How Can I Learn About Spraying Events?


Q. What are the risks to the environment?

A. The risks to the public and to the environment are very low. Mosquito adulticides are applied as ultra-low volume (ULV) sprays. ULV applications involve small quantities of active ingredient in relation to the size of the area treated, typically less than 2 ounces per acre, which minimizes exposure and risk to people and the environment.

Q. Will spraying pesticides hurt my vegetables, fish, or my car?

A. No. To our knowledge, there is no evidence to suggest harm to vegetables or cars. The materials we use pose little risk to people or the environment and are not applied directly to crops, weeds, or water. These materials have been used extensively and successfully throughout the country for decades.

Q. Do the products you use hurt bees and butterflies?

A. Our application methods minimize impacts to insects like bees and butterflies because treatments are made during times of the day when they are not actively foraging and are protected by their hives or resting areas. Also, the dosages/droplet sizes are designed specifically for tiny insects like mosquitoes; much higher dosages would be required to cause significant harm to bees or butterflies which have many times the body mass of a mosquito. We do not apply products to blooming crops or weeds. Finally, mosquito control districts have used EPA registered public health pesticides for decades with insignificant evidence of harm to these insects.

Q. Is spraying your last resort?

A. Fogging or spraying is the only known way to successfully control adult mosquitoes. The majority of our mosquito control is done when the mosquitoes are in the water in their larval form.

Q. I heard there are special precautions people need to take, such as rinsing off children’s toys, turning off air conditioners, staying indoors, etc. What do people need to do?

A. There is nothing that people need to do because we are spraying or fogging for mosquitoes. The products we use are registered with the Environmental Protection Agency for controlling adult mosquitoes and protecting public health.

Q. What if people are sensitive to chemicals?

A. Those individuals should consult their doctor regarding their specific concerns. A list or our spray materials can be found here. All of our products are registered with the Environmental Protection Agency and applied by our trained and certified technicians.

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.

Q. Why are some mosquito control agencies aerial spraying and some are not? If some are not spraying, is it because it DOES cause problems?

A. As part of our Integrated Vector Management (IVM) program, every effort is placed on preventing mosquito production in the first place by eliminating standing water, using mosquitofish, or larvaciding. When and if aerial spraying becomes necessary to protect public health, we will use materials registered with the Environmental Protection Agency exactly for this purpose. We will make every effort to inform residents should spraying or fogging be necessary. All mosquito control agencies share the same goal; to protect public health; however, each agency operates autonomously and has the ability to protect public health in a manner they deem appropriate. Each situation is unique and must be evaluated exclusively to determine the best course of action given the terrain, type of mosquito, weather, etc.

Q. Many Districts rely heavily on adulticiding as their primary form of control. Does your agency?

A. We do not. We practice Integrated Vector Management relying on biorational larvacides, with adulticides reserved for situations where other methods would be ineffective to protect public health.

Q. Are the insecticides exclusive to West Nile?

A. No. The pesticides we use target a variety of mosquitoes than can transmit West Nile virus as well as other diseases.

Q. Should I Take Steps to Reduce Exposure to Pesticides During Mosquito Control Spraying?

A. Generally, there is no need to relocate during mosquito control spraying. The pesticides have been evaluated for this use and found to pose minimal risks to human health and the environment when used according to label directions. All of the products we use are registered with the Environmental Protection Agency for controlling mosquitoes and protecting the public.

Although mosquito control pesticides pose very low risks, some people may prefer to avoid or even further minimize exposure. People who suffer from chemical sensitivities or feel spraying may aggravate a preexisting health condition may:

  • Consult their physician or local health department and take special measures to avoid exposure. 
  • Close windows and turn off window-unit air conditioners when spraying is taking place in the immediate area.
 
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