PHONE
800-231-3236 (toll free)
707-285-2200 (office)
707-285-2210 (fax)
ADDRESS
595 Helman Lane
Cotati, California
94931-9736
HOURS
Monday through Friday
7:00am to 3:30pm
Closed
11:30am - 12:30pm
Outbreaks of insect-borne disease won't occur if the number of insects available is too small to support an epidemic. Mosquito Control Districts' surveillance and control programs aim at keeping vector insect numbers near populated areas below these critical levels. This helps explain why during recent decades, major diseases like malaria and encephalitis have mostly been limited to isolated cases in California, despite frequent reintroductions every year by migrant birds or travelers and immigrants from infested regions of the world.
Success or failure in mosquito control hinges on accurate intelligence. Activities of the Mosquito Abatement Districts are almost all based on their day-to-day knowledge of local larval breeding sources. They know that source reduction is the single most important factor in controling biting insect pests and limiting the spread of mosquito-borne disease.
Larval surveys
Most mosquito vector and pest species produce multiple broods each year. The first step in preventing the
appearance of large numbers of adult mosquitoes is locating the larval breeding sources. This is so important
that Marin / Sonoma M&VCD dedicates most of the available time of sixteen vector technicians to survey, map
and catalog more than 14,000+ permanent breeding sources in the two county area. Each technician completes a
fifteen to thirty day cycle to census, and if necessary undertake control measures, on each recorded breeding
source in his of her assigned zone of operation.
Computerized database
Every known larval source, whether a fraction of an acre or several hundred acres, is mapped and cataloged in the district's database. The database uses a custom designed software program. Additions and deletions occur daily.
Vector control technicians locate, evaluate, map and maintain accurate information on hundreds of breeding sites in their assigned zones. Every action taken to suppress a mosquito population is promptly recorded in the database. Typical actions might include introducing mosquito fish, cleaning the weeds from a slow-flowing ditch, or applying a microbial insecticide like Bacillus thuringiensis var. israeliensis (B.t.i.).
Mapping
Every source is coded based on habitat characteristics and located with page and grid numbers according to the Thomas Bros.® mapping system. Each receives a unique eight digit number made up of the zone number, the map page and grid numbers, and a source number along with Latitude and Longitude within each grid. This allows tracking of up to 99 sources in each quarter square mile grid in the two county district.
This system has been used for more than ten years, and makes available a detailed picture of the type, extent and location of mosquito breeding sources in Marin and Sonoma counties. It gives an overview of mosquito production, the success of different control techniques, and makes possible a cost-effective review of the personnel and resources required for each task
Adult surveillance
Nearly all mosquito abatement districts use traps like the "New Jersey light trap" (see photo) to help keep track of adult mosquito populations. The Marin / Sonoma district keeps 32 New Jersey traps scattered throughout the two county area.
New Jersey traps work because adults of some mosquitoes are attracted to light. The trap operates on 110 volt current, with a 40 watt bulb and a fan that blows attracted insects into a killing jar at the bottom. A photocell turns the trap on at sunset and off during the day.
Every week, the jar's contents are identified in the laboratory, and recorded on a weekly trap collection form. With years of data now at hand, the districts can make experienced decisions based on known population trends according to current season, weather, and environmental conditions.
Three examples from weekly trap records show seasonal changes in adult mosquito numbers. Culiseta inornata [green] develops huge numbers following the winter rains; Ochlerotatus sierrensis [blue], the "treehole mosquito", is only present in the spring and early summer; Culex tarsalis [red], the "encephalitis mosquito", occurs year-around, becoming frequent through the summer and fall.
Not all mosquitoes are attracted to light traps. A variety of other traps are used to help survey adult populations. Some work well only with a single species. Several rely on attractants: carbon dioxide is useful to attract treehole mosquitoes looking for a host to take a blood meal (vertebrates exhale carbon dioxide when they breathe); and a broth made from wet hay attracts female mosquitoes looking for a place to lay eggs.