Los Angeles County West Vector & Vector-Borne Disease Control District

Mosquito Control Program

Why Do We Need to Control Mosquitoes?

    The history of mosquito control and the importance of mosquitoes are directly related to the health, comfort, and economy of humans and their use of the environment.   Financing and public support for control programs are based on the will of the public to be protected from mosquitoes.

    Where humans settle, they develop and use natural resources.  They change the environment, which may have both good and harmful results.  For example, the Great Central Valley of California was once mainly a desert, ravaged by spring floods and summer droughts so that profitable farming was uncertain.  The environment of the Valley was modified by the reservoirs and control structures which tamed the wild rivers and allowed the Valley to become the one of the most productive agricultural areas in the world.   These changes brought problems associated with ground water pollution and air pollution.  Greatly increased mosquito production occurs in the water supplied for irrigation.  The habitats for these vectors of encephalitis and malaria have been enlarged, thereby increasing the health hazard.

    There is an intimate ecological relationship between humans and mosquitoes.  By inadequately managing land and water resources, and failing to solve the problems of liquid waste management, larger, more productive habitats for mosquitoes continue to grow and to cause disease and intolerable annoyance.

    The primary objective of mosquito and vector control is to preserve or create an environment favorable to humans and animals by lessening the effect that mosquitoes and other vectors have upon our lives.

    Even mosquitoes which carry no transmissible disease but are present in sufficient numbers to produce intense annoyance and distress to humans and animals are recognized as a public health problem.  Public health, more than the mere absence of disease, includes the right to an environment free of mental and physical discomforts that destroy its positive values.  For more than two generations, the control of pest mosquitoes has been a recognized function of mosquito and vector control agencies.  Within this concept the role of mosquito abatement and vector control districts has been expanded to include other biting flies, midges, and bees.

    Discomfort is probably one of the primary motives for local public support of mosquito control programs, especially in urban areas.  Demands by the public for remedial measures result typically from:


The individuals who are hypersensitive to bites of various mosquitoes and other vector species.

The anguish and concern of mothers whose babies show numerous red swellings resulting from bites of mosquitoes and stings from other insects.
Numerous bites or stings from vectors which destroy the pleasure of patio or garden use in suburban areas.
Large numbers of biting or stinging vectors in many recreational areas, which often drastically curtail their use by sensitive individuals who help pay for such facilities.
Secondary infections which often result from the bites and stings of vectors.

    Some species of mosquitoes are involved in the transmission of important human diseases.  Encephalitis, malaria, yellow fever, dengue, and filariasis are transmitted to man and animals in various regions of the world through the bite of the mosquito.  Secondary infections can result from scratching mosquito bites even when no disease agent is transmitted.  Some people exhibit an allergic reaction to mosquito bites.



    The primary goal of the District is to control mosquitoes by preventing them from breeding.  Although this is more time consuming, more difficult to accomplish, and more costly over a short time span than other control methods, a preventative program will be more cost-effective to the District over the years.  The District is involved in reviewing and making recommendations on environmental impact reports that will prevent the breeding of mosquitoes and other vectors before they are built as permanent treatment problems.

    District staff reduce breeding sources by removing debris and vegetation and by pumping and/or filling sources.  The removal of debris and non-protected vegetation will decrease water retention, thus eliminating or reducing mosquito breeding.

    Another important aspect of prevention is education of the residents through contact with field staff.  When staff inspects an area, a notice will be left to inform the resident that a technician has been present and will list the findings and the actions taken.  District staff makes every effort to personally speak to the residents to explain the need for mosquito control activities and how to eliminate mosquito breeding sources around their home.


    Although District staff attempt to eliminate breeding sources, the need for biological and chemical control of mosquitoes is necessary.  The District has been divided into zones which are routinely inspected and treated.  Each zone has been assigned a technician who inspects known sources, answers service requests, and searches for new sources associated with the request.

    When a breeding source is found that cannot be permanently abated, the technician will determine the best method of treatment.  The preferred method of control in sources such as ponds, swimming pools, barrels, etc. is the use of biological control agents.   The main biological control agent used by the District is the mosquito fish, Gambusia affinis.  It should be noted that Gambusia affinis should never be placed in any natural habitat, such as: lakes, streams, creeks, rivers, etc.

    If the breeding source cannot support Gambusia affinis, staff will resort to the use of chemicals to control mosquitoes before they emerge as adults.  The District treats sources with either Bacillus thuringiensis var. israelensis (Bti) or methoprene (Altosid).   Bti is a microbial agent formulated as crystalline bacterial spores.  These spores are ingested by mosquito larvae and cause the cell walls of the larval digestive system to burst.  Methoprene is a synthetic insect growth regulator which mimics naturally occurring hormones in the mosquito's body.   Methoprene disrupts the mosquito's normal life cycle causing the adult mosquito to fail to emerge from the pupae.  Both of these chemicals are very safe to the environment and target specific.

    If the breeding source is active with pupae, staff will initially treat the source with Agnique MMF.  Agnique MMF is a mono molecular film which suffocates the mosquito pupae and larvae. Since pupae do not feed, they must be killed by suffocation.



Send mail to rsaviskas@lawestvector.org with questions or comments about this web site.