CA Dept. of Public Health UC Davis Arbovirus Research and Training Mosquito and Vector Control Assoc. of CA

Case Counts by County

CountyDead birds
Contra Costa1
Del Norte-
El Dorado-
Los Angeles45
San Benito-
San Bernardino4
San Diego2
San Francisco-
San Joaquin5
San Luis Obispo-
San Mateo-
Santa Barbara-
Santa Clara8
Santa Cruz-

WNV Activity by County
Printable Version
2018 | 2017 | 2016 | 2015 | 2014
2013 | 2012 | 2011
2010 | 2009 | 2008

Mosquito Control

This document was prepared by the Vector-Borne Disease Section, California Department of Public Health, (916) 552-9730 , June 2005.

Last Updated: Oct 13, 2014


  • What is "mosquito control"?
  • Mosquito control is the process of actively reducing the number of mosquitoes. Comprehensive mosquito control can use one or more approaches that target different environments and life stages of the mosquito.

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  • Why should mosquitoes be controlled?
  • The most important reason to control mosquitoes is to reduce the likelihood of diseases such as West Nile virus being transmitted to people through mosquito bites. Throughout history, no insect has been a more significant contributor to human discomfort, disease, and death than the mosquito.

    Even mosquitoes that do not transmit disease can be bothersome in their biting behavior. In severe instances nuisance mosquitoes can be economically detrimental to businesses, and reduce the quality of life for residents.

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  • How is mosquito control accomplished?
  • Most mosquito control programs reduce mosquito populations through a multi-faceted approach known as Integrated Pest Management (IPM). A mosquito has four life stages - egg, larva, pupa, and adult. In the life cycle of the mosquito, only the adult stage does not require standing water. An IPM program targets each life stage of the mosquito, but is intended to eliminate as many mosquitoes as possible before they emerge as biting adults.

    More than 70 mosquito and vector control agencies have been established in California since 1915. Together, these agencies cover approximately 60,000 square miles and protect more than 85% of California residents.

    These agencies engage in larval and adult mosquito population monitoring and control, monitor activity of vector mosquitoes and disease agents, and provide information to the communities they serve. The scope and range of activities within each program vary according to their location, climate, and available resources. Some areas in California are not within the jurisdiction of an established mosquito control program.

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  • Can we eliminate mosquitoes?
  • No, mosquitoes live in many different habitats, and it is impossible to find and treat all of the places that they breed. Furthermore, mosquito control is not intended to eliminate mosquitoes. The goal of a mosquito control program is to reduce adult mosquito populations to a level that minimizes the possibility of people and animals getting sick from diseases associated with mosquitoes, and reduces biting to a level that most people find tolerable.

    Limiting mosquito populations through active mosquito control is an essential public health function in California.

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  • Am I producing mosquitoes in my yard?
  • Mosquitoes require water for the immature stages to develop. Any source of standing water, big or small, can produce mosquitoes. To reduce the number of mosquitoes in your neighborhood, it is important to eliminate any standing water (from rain or irrigation) from your home and yard. Cleaning rain gutters, turning over buckets, and draining wading pools are important actions, but there are other, less obvious places that mosquito larvae can develop. Flower pots (especially if plants are being rooted), aquariums on porches, covered and uncovered boats, trash and recycle bins, and irrigation control boxes are all commonly overlooked as potential larval mosquito habitat in people's yards.

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  • Why are mosquitoes in my grass, shrubs, and garden?
  • Mosquitoes go to these cooler, humid, shady areas in your yard during the daytime to rest and escape hot dry air that will quickly kill them. Thinning shrubs and cutting down tall grass and weeds will reduce the harborage areas and number of mosquitoes in your yard.

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  • Why am I getting mosquito bites during the daytime?
  • Some species of mosquitoes actively seek a blood meal during the daytime; others will bite during the daytime if you disturb them. It is important to remember that the mosquitoes that transmit disease in California are much more active and aggressive around dawn and dusk, especially the two hours immediately following sunset.

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  • How far do mosquitoes fly?
  • Mosquitoes typically fly a few hundred yards up to two miles from the place they emerge, depending on species and environmental factors. Some common mosquitoes in California are known to fly 10 miles or more.

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  • Do all mosquitoes bite?
  • Only adult female mosquitoes bite. Female mosquitoes need the protein in the blood to produce eggs. Not all species of mosquitoes bite humans - some species prefer birds, large mammals, or even snakes. During the aquatic stages of its life a mosquito feeds on algae and other small organic matter.

    It is also important to remember that mosquitoes are not the only small flying insect that bites! Other small and biting insects are commonly mistaken for mosquitoes, including midges, no-see-ums, and black flies.

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  • What is the most important thing I can do to reduce the chance of myself or my family getting West Nile virus or another mosquito transmitted disease?
  • Avoid getting bitten by mosquitoes! No amount of mosquito control can completely prevent diseases associated with mosquitoes. Taking simple precautions makes a big difference in the likelihood of getting WNV.
    • Eliminate all sources of standing water on your property because standing water provides a place for mosquitoes to develop.
    • Avoid spending time outside when mosquitoes are most active, especially at dawn and dusk.
    • If you go out, apply insect repellent containing an EPA approved active ingredient. A list of approved active ingredients is available from the US Center for Disease Control and Prevention (CDC) at: DEET is the most common active ingredient.
    • Make sure window screens are well maintained.

    These simple actions will help keep you and your family from getting bitten by mosquitoes that may be carrying WNV.

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  • Who do I contact if I have a mosquito problem?
  • Local mosquito and vector control agencies are the best place for most California residents to get help with a mosquito problem. To find out the name and phone number of the local agency serving your region, go to and click on the tab "Find your local mosquito control agency." In addition, the Mosquito and Vector Control Association of California (MVCAC) maintains a web site with links to many member agencies at:

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  • Where can I get additional information about mosquitoes, mosquito control, and West Nile virus?
  • Additional information about mosquitoes and mosquito-transmitted diseases can be obtained by contacting your local mosquito and vector control agency, local health department, or by visiting the California West Nile virus web site at:

    Information on mosquito control products is available on the Environmental Protection Agency (EPA) Web site:

    This document was reviewed by the Mosquito and Vector Control Association of California (MVCAC). DHS thanks MVCAC for their comments and suggestions.

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Compared to previous year and previous five-year average to date

As of Nov 15, 2019201920185Y AVG
Human cases194182480
Dead birds2144981217
Mosquito samples328319603096
Sentinel chickens136161337
YTD - Year to date corresponds to the same time last year or last five years.

- view all 2019 YTD activity -

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