San Mateo County Mosquito and Vector Control District takes a preventative approach to mosquito control. Whenever possible, mosquitoes are controlled in their immature stages, before they emerge as biting adults capable of transmitting disease to humans.
Sometimes, however, adult mosquito populations become a threat to human health. When this happens, information collected through mosquito surveillance is used to make the decision to reduce adult mosquito populations.
If West Nile virus is detected in the community, the District’s initial response will be to intensify its efforts to locate and reduce mosquito breeding sites, increase its levels of larviciding in those areas in which West Nile virus has been found, and increase trapping of adult mosquitoes for disease testing. Reducing the adult mosquito population with pesticides (adulticides) registered by the US Environmental Protection Agency (EPA) will be done if necessary to prevent human illness or to suppress a heavy nuisance infestation of mosquitoes.
The District’s aggressive campaign against mosquito larvae is intended to minimize the need to use adulticides, but it is not always possible to prevent all adult mosquitoes from emerging. When adult mosquitoes infected with West Nile virus are found in an area, adult mosquito control treatments are used to quickly minimize the threat to human health.
Adult mosquito control is always done in conjunction with intensified efforts to locate and reduce mosquito breeding sites so that more adult mosquitoes cannot emerge.
Adulticides are materials used to reduce adult mosquito populations. At San Mateo County Mosquito and Vector Control District, adulticides are applied by licensed applicators and only in areas where high numbers of adult mosquitoes or adult mosquitoes carrying disease exist.
It’s important for the District to know whether the adult mosquito control treatments we conduct have the intended effect: an immediate reduction in the number of WNV-infected adult mosquitoes in an area.
To ensure that our adult mosquito control treatment was effective, we compare the number of mosquitoes trapped in the immediate area prior to treatment to the number of mosquitoes trapped in the same area after the treatment. This is reported as an overall reduction in the mosquito population.