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
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.