Vector Services & Information

Mosquitoes Are Vectors: A vector is any animal or insect that is capable of transmitting a disease or considered a public health nuisance.


Mosquito Facts

  • Mosquitoes are responsible for more human deaths than any other living creature. World-wide, nearly 4 million people die each year from various mosquito-borne diseases.
  • All mosquitoes must have water to complete their life cycle.
  • Mosquitoes do not develop in grass or shrubbery, although, flying adults frequently rest in these areas during daylight hours.
  • Only the female mosquito bites to obtain a blood meal. The male mosquito feeds only on plant juices.
  • The female mosquito may live as long as three weeks during the summer or many months over the winter in order to lay her eggs the following spring.
  • There are more than 2,500 different mosquito species worldwide, 53 species in California, and 15 species within the Greater Los Angeles County Vector Control District area.

Insects Often Mistaken for Mosquitoes

Click here to find out the differences between mosquitoes and impersonating insects.

Mosquito Lifecycle Life Cycle

  • It only takes 7-10 days to complete an entire life cycle.
  • The female lays eggs in rafts on top of stagnant water. Within a few days, the eggs hatch into larvae.
  • Larvae or wigglers come to the surface to breathe through a siphon tube. Wigglers grow and shed their skin four times. Larvae feed on organic matter.
  • Pupae called tumblers somersault through the water. They do not eat in this stage. The adult mosquito grows inside the pupae and when fully developed splits the pupal skin and emerges.

Health Risks Associated With Mosquitoes in Los Angeles County:

  • St. Louis encephalitis: humans
  • Western Equine encephalitis: humans and horses
  • West Nile virus: humans, horses, birds, and other animals
  • Malaria: humans
  • Heartworm: dogs and cats
  • Allergic reactions

Disease Transmission Cycle

Virus Transmission

  • Insect Vector: Mosquitoes

Mosquito-borne viruses are transmitted to people and animals through the bite of infected mosquitoes. Only certain species of mosquitoes carry the viruses. These mosquitoes get the viruses by feeding on infected wild birds and then passing the viruses on to their next biting victim.

  • Accidental Hosts: People and Animals

The virus in accidental or "dead-end" hosts ends the disease transmission cycle because these hosts cannot spread the disease to other species once infected.

  • Reservoir Hosts: Birds

Viruses are carried into the area by wild birds that are infected elsewhere. These birds are asymptomatic.

What You Can Do to Eliminate Mosquitoes

You can help eliminate mosquitoes by removing stagnant water from these common backyard sources:

  • Clogged rain gutter
  • Neglected or out-of-order swimming pool, hot tub, pond, or fountain
  • Swimming poolFountain
  • Containers such as rain barrels, cans, buckets, jars, flower pots, etc.
  • BucketJar
  • Old tires
  • Tires
  • Any container that can hold water for more than seven days.
  • dog bowl

How the District Prevents and Controls Mosquitoes

The District practices Integrated Mosquito Management (IMM) which is defined as a sustainable approach that combines biological, physical, and chemical control and minimizes economic, health, and environmental risks.

The IMM includes the following steps:

  • Biological control - Mosquitofish (Gambusia affinis) are placed in a variety of mosquito breeding situations where chemical treatment may be ineffective and source reduction infeasible. The District provides free mosquitofish to District residents for placement on their property only.
  • Physical control: Physically managed sources are less conducive to mosquito development. Improving these sites by employing mechanical controls, such as removing excess vegetation and debris, allows water to flow, decreasing mosquito breeding.
  • Chemical control: When feasible, non-chemical control methods are preferred and used. The application of extremely low-risk, environmentally sensitive, host specific materials are used to control mosquitoes only when necessary. The two types of materials used are larvicides, which target the aquatic immature or larval/pupal stages of these insects, and adulticides, which are aimed at killing adult mosquitoes. The District focuses on preventing adult mosquitoes and therefore mainly applies larvicides that act to suffocate, prevent growth, or interfere with molting of the larvae.

For more information, please view the presentation by the American Mosquito Control Association "Integrated Mosquito Management."

Personal Protection Against Mosquitoes

  • Don't raise your own mosquitoes. Get rid of containers that have or may hold standing water where mosquitoes can breed.
  • Make sure that doors and windows have tight fitting screens to prevent mosquitoes from entering your home.
  • Wear light-colored, long, loose clothing, such as long sleeve shirts and pants when outdoors. Keep in mind that mosquitoes can bite through thin or tight clothes.
  • Use mosquito netting when sleeping or camping outdoors.
  • Stay indoors between dusk and dawn when mosquitoes are most active.
  • Apply approved insect repellent whenever you are outdoors, even for a short period of time. Choose a repellent based on duration of activity. Remember when you are sweating, physically active, or getting wet, some repellents may not last long.

Mosquito FAQs

MosquitoWhat is a vector?
A vector is an animal or insect that can carry diseases.

What is the most dangerous vector in the world?
The mosquito!

What makes mosquitoes so dangerous?
Mosquitoes can transmit many dangerous diseases and are found virtually worldwide.

What diseases can mosquitoes transmit?
They can spread many diseases including Malaria, yellow fever, St. Louis encephalitis, West Nile virus, dog or cat heartworm, Dengue fever, and filariasis.

How are mosquitoes able to transmit diseases?
Mosquito-borne diseases are spread through the bite of an infected mosquito. Female mosquitoes first contract the disease after biting an infected animal, and then may harbor the disease and pass it on to the next victim(s) she bites.

Why does a female mosquito need blood?
Female mosquitoes need red blood as a source of protein in order to produce healthy offspring. Male mosquitoes do not need blood because they do not produce eggs. Instead, they feed on nectar or other sugar sources.

How do mosquitoes take a "blood meal"?
Mosquitoes have a piercing and sucking mouthpart called a proboscis. Female mosquitoes have six parts to their proboscis. There are two tubes in the middle surrounded by four cutting instruments known as lancets. As the mosquito pierces the skin of her victim, she injects her saliva into the wound. When she reaches a blood capillary, she uses the other tube to suck up the blood.

Why does the female inject saliva when she takes a blood meal?
Mosquito saliva contains an anesthetic to numb the wound making it where a person does not realize he/she is being bitten. The saliva also contains an anticoagulant to thin the blood allowing the female mosquito to suck up blood in a shorter period of time.

Why do mosquito bites itch and get red and swollen?
Most animals and humans are allergic to mosquito saliva.

How do mosquitoes find someone to bite?
Female mosquitoes use smell to find their victims. They are sensitive to carbon dioxide (which all red-blooded animals exhale), lactic acid and skin oils. The victim's heat also attracts them.

How do I discourage mosquitoes from living near me?
The first three stages of mosquito development occur in standing water. Reduce standing water around your house.

Cover all open containers outside. Change water in plant pots and bird baths often. Repair leaking faucets, sprinklers, and hoses. Maintain all swimming pools and spas. Clean out gutters. Repair screens on doors and windows.

How long do adult mosquitoes live?
Mosquitoes will live between one week to three months depending on the species, weather, time of year, and other variables.

Where did the name "mosquito" come from?
The Latin word musca means fly. The Latin word became mosca in Spanish and Portuguese. The word for "little fly" became mosquito or mosquita.

Mosquito Control Products Used By Greater Los Angeles County Vector Control District

Aquatic Pesticides

Toxicant Trade Name Residual Manufacted by
methoprene (IGR) Altosid 30-day briquets 30 days Wellmark International
methoprene (IGR) Altosid XR briquets 150 days Wellmark International
methoprene (IGR) Altosid SBG 5-7 days Wellmark International
methoprene (IGR) Altosid Pellet 30 days Wellmark International
methoprene (IGR) Altosid XR-G 21 days Wellmark International
methoprene (IGR) Altosid liquid larvicide (SR-5) 7-10 days Wellmark International
methoprene (IGR) Altosid liquid larvicide concentrate (SR-20) 7-10 days Wellmark International
diflubenzuron (IGR) Dimilin 25 W 24 hours Uniroyal Chemical
Oil Golden Bear 1111 24-48 hours Golden Bear Oil Specialties Inc.
Bacillus thuringiensis israelensis Vectobac CG 48-72 hours Valent Biosciences Corp.
Bacillus thuringiensis israelensis Vectobac G 48-72 hours Valent Biosciences Corp.
Bacillus thuringiensis israelensis Vectobac 12 AS 48-72 hours Valent Biosciences Corp.
Bacillus sphaericus Vectolex CG 2-8 weeks Valent Biosciences Corp.
Bacillus sphaericus Vectolex WDG 2-8 weeks Valent Biosciences Corp.

* IGR Insect Growth Regulator


Toxicant Trade Name Residual Manufacted by
Resmethrin and piperonyl butoxide Scourge 24 hours Bayer Environmental Science

Methoprene is a compound that mimics the action of an insect growth-regulating hormone and interferes with the insect's life cycle, preventing it from reaching maturity or reproducing. Altosid is the brand name of the methoprene product used in mosquito control and is applied in different formulations such as liquid, pellet, granular, or briquet(s). Methoprene used for mosquito control according to its label directions does not pose unreasonable risks to human health. It addition to posing low toxicity to mammals, there is little opportunity for human exposure, since the material is applied directly to ditches, ponds, marshes, or flooded areas that are not drinking water sources. Methoprene used in mosquito control programs does not pose unreasonable risks to wildlife or the environment. Toxicity of methoprene to birds and fish is low, and it is non toxic to bees. Methoprene is also an effective flea control agent and is the main agent used in pet collars and time release fumigants to control fleas. Methoprene breaks down quickly in water and soil and will not leach into ground water.

Dimilin was one of the first Insect Growth Regulator's (IGR) developed in the late 70's. Dimilin 25WP is an IGR that belongs to a modern class of insecticides called benzoyl urea. Dimilin contains diflubenzuron and works by disturbing the molting process of mosquito larvae. When the larvae ingest the active ingredient, it disrupts the development of the exoskeleton, resulting in death of the larvae. With increasing environmental regulations worldwide, the IGR family is a good answer to the demand for safer insect control products. Dimilin has been tested and proven to have a low toxicity on mammals, birds, fish, honeybees and most aquatic invertebrates (with the exception of micro crustaceans). However, field trials have shown no lasting adverse effects on micro-crustaceans in the natural environment. Due to the sensitivity of areas where mosquitoes breed, there are some restrictions on who can apply Dimilin 25WP. For mosquito control, Dimilin applications are restricted to "public health officials, mosquito abatement officials, and other personnel trained in public mosquito programs."

Some highly refined oils are manufactured as pesticides and used to form a thin film on top of water to drown larvae, pupae, and emerging adult mosquitoes. They are specially derived from petroleum distillates and have been used for many years in the United States. Trade names for oils used in mosquito control are Bonide, BVA2, and Golden Bear 1111, (GB-1111). Oils used according to label directions for larva and pupa control do not pose a risk to human health. In addition to low toxicity, there is little opportunity for human exposure, since the material is applied directly to ditches, ponds, marshes, or flooded areas that are not drinking water sources. Oils, if misapplied, may be toxic to fish and other aquatic organisms. For that reason, EPA has established specific precautions on the label to reduce such risks.

Microbial Larvicides
Microbial larvicides are specially processed bacteria compounds that are registered as pesticides for control of mosquito larvae in outdoor areas. The microbial larvicides used for mosquito control are Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (B. sphaericus). The microbial pesticides have undergone extensive testing prior to registration. B. sphaericus are nontoxic to humans and do not pose risks to wildlife, non-target species, or the environment when used according to label directions. Because these larvicides have a short biological half life and are very host specific, they are less likely than systemic chemical pesticides to cause field resistance in target insects.

Bacillus thuringiensis israelensis (Bti)
Bti is a naturally occurring soil bacterium registered for control of mosquito larvae. Mosquito larvae eat the Bti product that is made up of the dormant spore form of the bacterium and an associated pure toxin. The spores and crystals of Bti act as poisons in the larvae. The crystals dissolve in the intestine of the larvae and paralyze the cells in the gut, interfering with normal digestion, triggering the insect to stop feeding. The larvae stop feeding almost immediately and die within 6 to 24 hours. Bti is also effective against black flies, midge flies, and other nuisance aquatic flies.

Bacillus sphaericus
B. sphaericus is a naturally occurring bacterium that is found throughout the world. B. sphaericus spores that are eaten by mosquito larvae release toxins into the mosquitoes gut, causing the larvae to stop feeding and die. It is only effective against actively feeding larvae and does not affect mosquito pupae or adults. B. sphaericus has the unique property of being able to control mosquito larvae in water that is rich in organic matter.

Scourge is the trade name of a pesticide product used to control adult mosquitoes in outdoor residential and recreational areas. It contains resmethrin, piperonyl butoxide and a petroleum distillate. Resmethrin is a man-made pesticide, similar to a natural group of pesticides called pyrethrins which comes from plants. Piperonyl butoxide does not directly kill insects but acts to increase the ability of resmethrin to kill insects. These pesticide products are also used in pet shampoos, sprays and products used in horse stables.

The use of Scourge is part of a mosquito management program. When the risk of human exposure to West Nile virus or other mosquito-borne viruses is high, the application of Scourge, either by ground or air, may occur to reduce populations of infected adult mosquitoes. Decisions when and where to use Scourge are carefully considered.

Since Scourge is applied at very low concentration rates, it is unlikely that anyone would experience health effects as a result of contact with Scourge. The effects of exposure to any chemical depend primarily on the amount of the chemical a person is exposed to (through skin contact, ingestion, or inhalation) and the amount of time that the person is exposed to the chemical. The person's age, sex, genetics, life style and general health may also influence the possible health effects.

Scourge applied in ultra low volume amounts known as "fogging" stays in the air for a very short period of time until droplets land on surfaces. Scourge breaks down or degrades very quickly on surfaces exposed to sunlight. Rain washes away any remaining Scourge, the residual material binding with soil particles, and decomposed by bacteria.

Available information reports that Scourge is un-likely to cause cancer in humans. Resmethrin did not cause cancer in rats or mice given large doses for their entire lifetime, and so is considered unlikely to cause cancer in humans.

For more information please visit:

District Programs

There are a number of Mosquito Species and Mosquito-Borne Diseases known to occur within the Greater Los Angeles County Vector Control District.

Click here to learn more.