General Information - Napa County Mosquito Abatement District


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General Information Napa County Mosquito Abatement District Mosquito abatement districts are formed pursuant to the laws found in the California Health and Safety Code-Division 3, Chapter 1, Section 2000 et seq. These laws, also known as the Mosquito Abatement Act of 1915, allow for local municipalities or counties to form these Districts. The broad powers that a District has under these laws are granted to a governing Board that consists of five or more members who may be appointed (District Boards of Trustees) or elected (County Boards of Supervisors and City Councils). The Board members represent all of the citizens that reside within the area served by the District and may or may not be mosquito and vector control experts. The Board employs a Manager to whom it delegates the authority to conduct the business of the agency in accordance with the policies of the Board. Napa County Mosquito Abatement District (Napa County MAD) was formed in 1925 to minimize the effects of the County’s most numerous resident, the mosquito. Citizens residing near the marshes and along the Napa River and its tributaries were plagued by marsh, malaria and encephalitis mosquitoes. Napa County MAD currently services the entire County, which is an area of approximately 797 square miles. The District has a staff of seven full time employees and one half time employee and is funded by both ad valorem property tax and benefit assessment revenues. Napa County MAD makes every effort to use the safest materials and methods available to control the mosquitoes and other vectors found within its service area. There are four essential methods utilized in the District's Integrated Pests Management Program. They are: biological control (mosquitofish, bacteria and natural enemies), chemical control (pesticides and insect growth regulators), physical control (source reduction), and community education (prevention). It is the goal of this District to minimize environmental impacts by using Best Management Practices, (e.g. targeting the immature stages of mosquitoes rather than the adults thereby reducing the total area treated for these pests.) An effective Integrated Pest Management Program requires intensive monitoring with timely and effective applications of the safest materials and techniques. Biological control can provide either short-term or long-term control depending on the agent used. Napa County MAD utilizes the following biological control agents: the spores of the bacterium Bacillus thuringiensis var. israelensis (Bti), the live bacterium Bacillus sphaericus (Bs) and the mosquitofish, Gambusia affinis. The spores of Bti and Bs only affect the larval or immature stages of the mosquito. These pesticides only provide short-term control with Bti persisting in the environment for about 36-48 hours and Bs lasting about three weeks. Factors that affect their usefulness include temperature, pH, salinity, organic content of the water, and the density of both vegetative cover and immature mosquito population at the breeding site. These materials also require proper timing of their application in order to be effective. Late stage, non-feeding immature mosquitoes, pupae and adults are unaffected by Bti and Bs. Use of mosquitofish is a long-term control strategy that works well in permanent water bodies such as stock ponds, back yard ponds, water gardens and rainwater barrels. Salinity, pH, density of vegetative cover, presence of game fish such as Bluegill or Bass, persistent water temperatures above 80° F, and organic content of the water are the limiting factors for the usefulness of this control strategy. Chemical control, a short-term strategy, involves the application of insecticides either by hand (hand cans, granular spreaders, ATV’s, or truck mounted spray rigs), or by aircraft. The chemicals used by this District are: pyrethrin, an insecticide derived from chrysanthemum flower heads and used to control adult mosquitoes and yellowjackets; methoprene, an insect growth regulator that specifically effects mosquitoes by preventing adult emergence; and Golden Bear 1111, a surfactant that effects all immature stages of mosquitoes including pupae. None of these materials has any significant residual activity (pyrethrin degrading within four to six hours, methoprene persisting for about three days, and Golden Bear 1111 lasting less than two days). Pyrethrin is used to control yellowjackets and the Western Treehole Mosquito, a vector of Dog Heartworm. Use of this insecticide would also occur when the District, in conjunction with County public health authorities or the State, has declared a public health emergency. This pesticide comes in both powdered and liquid formulations and is applied with a bulb duster or the use of a truck mounted ultra low volume (ULV) machine that applies 0.87 ounces of liquid per acre by creating an extremely fine mist. Applications with a ULV machine can only occur when the wind is less than five miles per hour and an atmospheric temperature inversion exists at the site of the application. Methoprene is routinely used and is applied to those water sites that contain the larval or immature stages of mosquitoes. This material does not affect the pupal or adult stages and thus requires proper timing of the application in order to be effective. Golden Bear 1111 is a petroleum-based surfactant that is also used to prevent adult emergence. This material changes the surface tension of the water causing the immature stages of mosquitoes to drown. Chemical control can provide emergency relief from mosquitoes and other vectors but does not provide any long-term control. The chemical control strategy can be quite costly both in time and materials. Physical control, also known as source reduction, is a long-term control strategy that is very cost effective for mosquito and vector control programs. This strategy requires the manipulation of the habitat where mosquitoes and other vectors develop to prevent future breeding. Improving water circulation at a site so that there is little if any stagnation of the water or removal of rubbish and food sources are all examples of habitat management. Vegetation control may also be employed to reduce the wind protected cover that is created by plants for both adult and immature vectors. This control methodology is carefully planned and coordinated with Federal and State regulatory agencies, such as the U.S. Fish and Wildlife Service, the U.S. Army Corps of Engineers, and the California Department of Fish and Game, when working in sensitive habitats or in proximity to threatened or endangered species to assure the minimization of any impact to protected species or habitats. This work may either be accomplished with hand tools or with heavy equipment, depending on the size of the project. Vegetation control can also be accomplished with the use of herbicides. These materials are used under strict guidelines that make sure they are applied properly to sites that will not impact other habitats. Herbicides are used by this District to control vegetation at the various wastewater ponds of water treatment facilities and wineries. The materials used are Karmex DF and Oust (pre-emergent for grasses and some broadleaf weeds), and RoundUp and Aquamaster (for post-emergent weed control). Community education is an excellent tool employed by this District to control organisms of public health concern. This strategy requires that the District’s personnel inform the public about the different ways to prevent mosquito and vector problems. Informational brochures, presentations to schools, clubs and associations, participation in fairs, local trade shows and local community activities, and participation on local wetlands enhancement and restoration projects all help to bring to light the many different ways that mosquitoes and vectors can be safely controlled or prevented. The thrust of community education is to prevent problems before they occur rather than react to them. Ultimately, this enhances the environment by minimizing the presence of these pests while also reducing the use of insecticides. The down side to this strategy is that it can be very costly both in materials and labor because it requires a continuous effort to prevent the citizenry from forgetting what they have learned. Due to the fact that the population dynamics of any given community is constantly changing, the need for a solid and continuous outreach program becomes more necessary. Napa County currently has 20 species of mosquitoes, ten of which are intensively monitored and controlled. Five species are known carriers of the diseases encephalitis, dog heartworm or malaria, to humans and their pets. The incidence of mosquito-borne disease in humans for Napa County has been minimal, with the last known case of malaria occurring in 1939. Dog heartworm is prevalent throughout the wooded areas in the County. The virus that causes mosquito-borne encephalitis was last detected in 1996 but this District is not aware of any confirmed human cases. West Nile Virus is a mosquito-borne disease that was introduced to North America in 1999 and detected in California in 2003. The full implications of this disease in California are unknown at this time, although its effects have been devastating to wildlife, horses and humans in other parts of the United States. Researchers are discovering that many native species of mosquitoes, including some that were not known to vector diseases before, can effectively transmit this disease to humans. In Napa County there are four very common and widespread species of mosquito (the Little House Mosquito, The Foul Water Mosquito, The Tule Mosquito and the Western Encephalitis Mosquito) that are known to be excellent carriers of this disease. Two other species (the Fish Pond Mosquito and Western Treehole Mosquito) are presumed carriers although research is still pending. All of the aforementioned species of mosquitoes are specifically targeted by this District. Ten species of ticks, three species of yellowjackets, numerous other types of wasps and bees, and of course rats and mice also enjoy the lovely environs of Napa County. Although tick-borne diseases are rare, human cases of both Lyme Disease and Rocky Mountain Spotted Fever have occurred within the last few years. At this time it is unknown if Hantavirus and other rodent-borne diseases are present within the County. The District is currently developing monitoring and control programs for yellowjackets, ticks, and rodents in response to demands for these services. A benefit assessment was passed in July of 2003 to support these new programs and enhance the mosquito control and mosquito-borne disease programs. For more information about yellowjackets, ticks, and rodents follow the links to our web pages. The yellowjacket program was started in the fall of 2003. The tick and rodent programs are still being developed and should be available in the summer of 2004. The disease surveillance programs for mosquitoes, ticks and rodents is being coordinated and developed with the California Department of Health Services. Go to our web pages for more information about mosquito, tick and rodent-borne diseases.

NAPA COUNTY MOSQUITO ABATEMENT DISTRICT

P.O. Box 10053 ~ American Canyon, CA 94503 ~ 707-553-9610

Eva Carrender Webmaster; Page last updated 04/03/2006 06:07 PM