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FAQ - Area-Wide Mosquito Control Treatments

The Facts about Treatments

The San Gabriel Valley Mosquito and Vector Control District is a public health agency charged with managing vectors that cause human disease. We use an integrated approach that includes education, surveillance, and management. The component of our integrated program that is most commonly misunderstood is when, how, and why we use pesticides.

Area-wide treatments

When the risk for human disease reaches a specific threshold because the population of infected vectors is sufficiently high pesticides may be applied on a large scale.

These treatments can be made with a truck-mounted applicator that disperses an ultra-low volume mist into the air. All of the pesticides we use are registered with the US Environmental Protection Agency (EPA) and are chosen based on their ability to have a maximum effect on target organisms while having a minimal effect on humans, pets, and the environment.

Below are frequently asked questions related to Area-Wide Mosquito Control Treatments. 

How can I find out if mosquito control treatment applications are scheduled to take place in my area? 

A: Residents are encouraged to sign up for treatment notifications to receive information on treatments occurring in their zip code:

Why is a mosquito control treatment taking place? 

A: The San Gabriel Valley Mosquito and Vector Control District (SGVMVCD) is conducting an area-wide mosquito treatment from backpacks, trucks, helicopters, or airplanes based on elevated mosquito counts or elevated West Nile virus activity in a specific area. Mosquito control treatment applications effectively reduce the mosquito population and the number of infected adult mosquitoes, thereby decreasing the risk of disease transmission to the public. To view the current treatment schedule in the San Gabriel Valley, visit:

When do treatment email notifications go out? 

A: Email notifications are sent prior to scheduled mosquito treatment events. For treatments conducted on the weekend, notifications will be sent on Friday, outlining the work that will be performed throughout the weekend. Emails are sent to residents subscribed to the eAlerts in the affected area ( Notifications are also posted online. Treatment events can be cancelled or rescheduled due to weather conditions or other unforeseen circumstances.

What are larvicides and adulticides? 

A: Control of mosquitoes while in the larval stage 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-based, are applied directly to water sources that hold immature mosquitoes, including eggs, larvae, and pupae. Larvicides reduce the overall mosquito population by limiting the number of biting adult mosquitoes produced from a water source.

Adulticides are products that rapidly reduce adult mosquito populations. This can become necessary when larval control measures no longer reduce the presence of biting-adult mosquitoes, or there is significant threat of disease transmission in an area. The most common method of adulticiding is ultra-low volume (ULV) spraying. ULV 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 the droplets. Treatments can be applied from backpacks, trucks, helicopters, 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 disease.

When does the San Gabriel Valley Mosquito and Vector Control District use chemical mosquito control (pesticide)? 

A: Chemical control is used for immature mosquitoes in water when biological control (mosquitofish) and source reduction is not plausible or effective.

Chemical control for adult mosquitoes is necessary 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 and reduce the transmission of disease to humans.

All products are registered with the California Environmental Protection Agency (EPA) and are applied by trained and state-certified San Gabriel Valley Mosquito and Vector Control District technicians.

How will these pesticides affect me and my family? 

A: At the rates these products are applied (2 tablespoons or less per acre), they do not pose a risk to you or your family, and in fact, some head lice control products, that are applied directly to a person’s head, contain an active ingredient that is often used in adult mosquito control products but the lice products are applied at a much higher rate. For more information on insecticides and public health, consult the U.S. Environmental Protection Agency, which oversees the registration of these chemicals. The National Pesticide Information Center (NPIC) and the Centers for Disease Control and Prevention also post their mosquito control resources online.

For treatment schedule including locations see our Area-wide Mosquito Treatments, click here:

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.

Do I have to go indoors during a treatment? 

A: The District uses public health pesticides approved by the US EPA for treatments on and over outdoor residential and recreational areas. It is not necessary to close doors or windows. The treatment will dissipate from the treated area and degrade quickly in sunlight. In some instances, mosquito control backpack treatments may leave wet surfaces and should not be contacted until dry.

Can pets go outside during treatments? 

A: The materials used for controlling mosquitoes, when used in accordance with the label, are not harmful to pets. Many times, it is the same materials used to treat cats and dogs for fleas and ticks. However, if you choose to reduce your pet’s exposure, keep them inside during treatment applications.

Should I close my windows when a treatment is scheduled in my area? 

A: It is not necessary to close doors or windows. The treatment will dissipate from the treated area and degrade quickly in sunlight. However, residents may take additional measures to achieve personal comfort during the application.

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

A: Your swimming pool water and items found in your yard will not be affected.

What if I have a vegetable or fruit garden? 

As you normally would, wash your vegetables and fruit before you eat them.

Will the adult mosquito treatment affect bees? 

A: When adult mosquito control treatment is conducted using ULV applications at the label rates at night, there should be no impacts to bees. In some instances, the SGVMVCD may apply adult mosquito control products during the day to either control resting mosquitoes infected with West Nile virus; or to control invasive Aedes mosquitoes. If a daytime application is necessary, applicators are trained to avoid blooming plants, beehives, or other areas where bees may congregate.

I have an air conditioner. Should I turn it off if a treatment is scheduled in my area? 

A: It is not required to turn off air conditioning units during or after mosquito control treatment events. However, if you have a window or wall air-conditioning unit that is running on the fan setting, you may turn it off so that air is not brought in from the outside. Window and wall units running on cooling settings do not draw air from outside of the home, so there is no need to turn your air conditioning unit off. Central air-conditioning units cool recirculated air in your house. Since a central air-conditioning unit does not pull in outside air, there is no need to turn it off

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 the 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. The Center for Disease Control and Prevention have also posted guidance and planning resources online.