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Programs -> Mosquitoes -> Integrated Pest Management -> Underground Sources
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Underground Sources:
Water that collects underneath buildings, in storm drains, vaults and other underground sites in San Mateo County are very significant sources of mosquito development. These sources are the preferred habitat of the northern house mosquito (Culex pipiens), which is an efficient vector of West Nile virus. Adults of Culex pipiens are most abundant during the summer. However, in San Mateo County, they can emerge throughout the year, particularly in sheltered underground sources. A significant amount of the District's mosquito control operations are targeted at mosquitoes developing in underground sources. These programs include treatment of storm drains during the summer and utility vaults in spring and fall.
Storm drains:
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| Treating a Catch Basin |
Storm drain systems contain "catch basins", which are the storm water inlets to the system. The basins are designed to catch sediment and have a sump area which is lower than the rest of the drainage system. During winter months, storm drain systems are flushed out regularly by winter rainstorms. However, during the summer, water collects in the basins when residents water their lawns or wash their cars. There are over 80,000 catch basins within the District and each have the potential for producing a vast numbers of mosquito larvae. Therefore the District hires seasonal mosquito control technicians to help treat catch basins during the summer months, applying a refined mineral oil in catch basins from right-hand drive trucks.
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Utility vaults:
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| Opening Vault | | |
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| Vault Lid |
Water that collects in utility vaults is another source of mosquito development. District personnel treat these vaults several times a year. The work is done on weekends in the early morning to avoid traffic. Vaults are treated with time-release briquettes that releases a hormone specific to mosquitoes over an extended duration of time. Over 3,000 vaults are treated within the county.
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Water under buildings:
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Crack under a
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Many of the buildings in San Mateo County are built on slab foundations over bay fill. Over time, the ground beneath these buildings begin to settle and large cavities are created that can collect water from rain or broken pipes. This is known as subsidence. Such cavities can produce enormous numbers of mosquito larvae that can be difficult to reach and treat. The best solution to this problem is filling the gaps around the edges of the foundation with sand and gravel. This prevents adult mosquitoes from entering the site to lay their eggs.
Water can also collect in the crawl space under buildings with perimeter foundations. In this case, the installation of a sump pump and diligent upkeep of the plumbing under the building will prevent mosquito issues from arising.
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