Why It's Controlled
- California is home to more than 50 species of mosquitoes. While most pose no threat, the Culex, Aedes and Anopheles species can transmit -- or vector -- disease-causing viruses such as the West Nile Virus, Saint Louis encephalitis and western equine encephalomyelitis. Their bite is uncomfortable to humans and causes an allergic reaction in some cases. Large mosquito populations can negatively affect livestock productivity and tourism by spreading disease and deterring outdoor sightseeing.
Elimination of Larval Development Sites
- California residents have helped reduce mosquito populations by eliminating larval development sites. Larvae can form where water is stagnant for five days or longer. Residents eliminate and regularly clean containers that hold water such as buckets, wading pools, ponds, flower pots, trash receptacles and boats. Through cleansing and maintenance of these sites, residents help eliminate mosquito breeding sites.
- Vector control agencies monitor mosquito-borne viruses by testing adult mosquitoes and chickens. They also track and test dead birds in connection with the spread of the West Nile Virus. Information about mosquito-borne viruses is shared by public health and agriculture agencies with vector control agencies, and the combined information is used to design action plans to reduce mosquito populations.
- Mosquito populations are also controlled by undermining the ecosystems in which these insects breed and live including wetlands, swamp lands and salt marshes. Up until the 1970s, marshes and wetlands were drained but this practice became less common as the areas became protected under environmental laws. Current practices include ditching to maintain water circulation in marshes and burning cattail, bull rush and other wetland vegetation.
- When site modification or elimination is not possible, biological control is the preferred method of vector control agencies in California. Many agencies rear and stock small fish, such as the Gambusia affinis, that eat mosquito larvae. Other animals including bats, birds and dragonflies are employed to control mosquito populations. All of these species prey upon mosquitoes but their contribution to reducing mosquito populations is limited when contrasted with other methods.