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
o
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.
o
All mosquitoes must
have water to complete their life cycle
o
Mosquitoes do not
develop in grass or shrubbery, although, flying adults frequently rest in these
areas during daylight hours.
o
Only the female
mosquito bites to obtain a blood meal. The male mosquito feeds only on plant
juices.
o
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.
o
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
Life Cycle
o
It only takes 7-10
days to complete an entire life cycle
o
The female lays eggs
in rafts on top of stagnant water. Within a few days, the eggs hatch into
larvae.
o
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.
o
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
o
St. Louis encephalitis: humans
o
Western Equine encephalitis: humans and horses
o
West Nile virus: humans,
horses, birds, and other animals
o
Malaria: humans
o
Heartworm: dogs and
cats
o
Allergic reactions
Disease Transmission Cycle
o
Insect Vector:
Mosquitoes-Mosquito-borne viruses are transmitted to people and animals by infected
mosquitoes. Only certain species of mosquitoes carry viruses. Infected birds
are then fed on by local mosquitoes that can pass the virus through future
bites.
o
Accidental Hosts:
People and Animals- The virus in "dead-end" carriers is not sufficient to be transmitted
back to the mosquito, thereby ending the transmission cycle.
o
Reservoir Hosts:
Birds-Viruses
are carried into the area by wild birds that are infected elsewhere. These
birds show no symptoms.
What you can do to
eliminate mosquitoes
o
You can help eliminate
mosquitoes by removing stagnant water from these common backyard sources:
o
Clogged rain gutter
o
Containers such as
rain barrels, cans, buckets, jars, flower pots, etc. 
o
Old tires
How the District prevents
and controls mosquitoes
o
The District uses Integrated
Mosquito Management (IMM):
This is a sustainable approach to managing mosquitoes by combining biological,
physical, and chemical control, which minimizes economic, health, and
environmental risks.
o
Biological control:
Mosquitofish (Gambusia affinis)
are used 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.
o
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.
o
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. Two types of materials are used: 1)
larvicides, which target the aquatic immature or larval/pupal stages of these
insects, and 2) adulticides, aimed at killing mosquito adults. 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.
Personal protection
against mosquitoes
o Don't raise your own mosquitoes. Get rid of containers (no matter how small) that have standing water.
o
Make sure that doors and windows have tight fitting screens to prevent mosquitoes from entering your home.
o
Wear light-colored, long, loose clothing, such as long sleeve shirts and pants when outdoors. Mosquitoes can bite through thin or tight clothes.
o
Use mosquito netting
when sleeping outdoors or in an unscreened structure and to protect small
babies when outdoors.
o Stay indoors when mosquitoes are most active: dawn, sunset, and early evening.
o Apply repellent whenever you are outdoors, even for a short period of time. Choose among repellents based on how long you plan to be outside and what you will be doing. When you are sweating, phycially active, or getting wet, repellents do not last long.
Mosquito Control Products Used By Greater Los Angeles County Vector Control District
Aquatic Larvicides
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 Wellamark 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 Wellamark 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 Biosciencs 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
Adulticide
Toxicant Trade Name Residual Manufactured by Resmethrin and piperonyl butoxide Scourge 24 hours Bayer Environmental Science 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 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.
Methoprene
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
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."
Oil
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.
Scourge
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: http://www.epa.gov/pesticides/health/mosquitoes/larvicides4mosquitoes.htm