See also: [About Mosquitoes]
[Public Education]

Mosquito Control

Breeding Source Prevention and Reduction
Female mosquitoes lay their eggs in slow moving or standing water. The District works to eliminate or alter breeding sites by making recommendations to City and County Planning Departments, Flood Control Districts, and other relevant parties on property development and land use issues to minimize or eliminate the creation of sites capable of holding water and breeding mosquitoes.

Biological Control Methods

When breeding sources cannot be permanently abated, our staff of trained Vector Control Technicians assess the best method of mosquito control. In artificial containers such as ornamental ponds, water plant barrels, and horse troughs, mosquitofish, (Gambusia affinis), can be used to control mosquito reproduction. Mosquitofish are hardy, aggressive predators capable of eating over 100 mosquito larvae per day per fish. In order to protect threatened or endangered species and beneficial organisms in our natural environment, the District will not release mosquitofish into natural bodies of water.

BioChemical Control Methods

As mosquitofish are not released into natural systems, the District also uses a variety of environmentally safe pesticides to reduce mosquito populations at the larval stage. Larvicides which contain the active ingredients Bacillus thuringiensis israelensis (Bti) or Bacillus sphaericus (Bs), are naturally occurring bacteria which specifically target mosquito and black fly larvae. Upon ingestion, bacteria are introduced into the larvae gut causing death within 4 - 24 hours. These larvicides are highly specific and have been shown to have no harmful effects on non-target organisms.

Other pesticides contain insect growth regulators (IGR's) which control both mosquito and midge populations by interrupting normal metamorphosis. Methoprene the active ingredient, is a true analog of mosquito juvenile hormone. This pesticide artificially maintains high levels of juvenile hormone preventing the insect from developing into a normal pupa, thus preventing emergence to adulthood. This product is again highly specific to midges and mosquitoes with no harmful effects on non-target organisms.

Chemical Control Methods

In cases where the preferred biological control methods are not effective, chemical control methods may be employed. These include the use of surface film materials which break the surface tension of water making it difficult for larvae and pupa to attach and breath. Petroleum hydrocarbons kill by suffocation and are toxic to other aquatic organisms. As these chemicals are not specific to only mosquitoes and midges, they can be applied only to bodies of water that do not contain fish or other aquatic organisms, except when used just around the borders of these areas and in shallow water.  A new surface film pesticide which is significantly more specific and non-toxic to non-target aquatic life is now approved for use in California. This product will greatly reduce the need for petroleum hydrocarbon usage.