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Programs -> Mosquitoes -> Integrated Pest Management -> Marsh Program
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| Bair Island Salt Marsh |
Marsh Program:
Mosquitoes are found in both fresh and saltwater marshes in San Mateo County. However, not all marshes produce mosquitoes. Mosquito larvae are not strong swimmers and they cannot survive in flowing water, deep open water, or in the presence of significant populations of insect predators or fish. The District works with property owners on new wetland restoration projects to encourage design elements that will reduce mosquito development. For existing marshes, the District encourages property owners to maintain as much open water as possible and remove obstructions that hinder water flow. For design guidance to minimize mosquito production in fresh and salt water marshes, contact the District at (650)344-8592 or Online Service Request.
Saltwater Marshes:
San Mateo County contains approximately 5,000 acres of salt marsh along the shores of San Francisco Bay and the coastline. The majority of these marshes are along the bay side of the county, adjacent to homes and businesses. Much of the mosquito production occurs in diked, reclaimed marshes and in low areas in the upper marsh area that retain rainwater from winter rains. Four species of mosquitoes are common in these areas: Aedes squamiger, Ae. dorsalis, Culex tarsalis, and Culiseta inornata. The first two, Ae. squamiger and Ae. dorsalis, have the greatest impact on local residents. They commonly travel great distances (up to 25 and 15 miles respectively) inland and vigorously pursue a blood meal in the cities adjacent to these marshes.
Ae. squamiger (the winter salt marsh mosquito) hatch during winter months when water becomes trapped in the marsh. Larvae of Ae. dorsalis, the summer salt marsh mosquito, develop during summer months in depressions in the high marsh which become flooded at extreme high tides. While the winter salt marsh mosquito generally produces only one generation each year, summer salt marsh mosquitoes can produce multiple broods in a single summer.
Larvae of both Aedes species can reach millions of mosquitoes per acre. Untreated salt marshes can generate billions of adult mosquitoes in a single season. Adults are strong fliers and will bite morning, noon and night, under all conditions. Once emerged, adults of this species travel inland, often following creeks, and then dispersing outward into the surrounding areas.
To prevent the emergence of adult salt marsh mosquitoes, Mosquito Control Technicians inspect marshes throughout the county on a weekly basis. When mosquito larvae are found, they are treated with biorational materials that are specific to mosquitoes and do not harm other organisms. These materials include two kinds of bacteria and a growth regulator that prevents the immature mosquitoes from completing development to the adult stage.
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Freshwater marshes:
At least six species of mosquitoes develop in freshwater marshes. Each type is specific to a season and type of habitat. Depending on the species, typical larval sources include as forest pools, grassy impounds or dense cattail marshes. Like salt marshes, freshwater marshes are inspected regularly and treated with biorational materials when mosquitoes are present.
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