Although mosquitoes are a nuisance in many populated areas and have become a health concern with the latest information regarding the spread of the West Nile Virus, they do fulfill a vital ecological function in natural settings.  Mosquitoes serve as food for fish, birds, bats, frogs and insects.   However, personal comfort and health are factors we must consider when determining when and how to control mosquito populations around our homes and recreational activities.  Please read the following information we are providing for your consideration.

COMMON MOSQUITOES

Most pest mosquitoes in the United States belong to one of three genera:  Aedes, Culex, or Anopheles.   Within these genera, 11 species have been identified as carriers of the West Nile virus.

Aedes:

Some are referred to as “floodwater mosquitoes” because they lay their eggs on damp soil or vegetation in areas that can be periodically wet.  The eggs remain dormant until they are flooded and conditions are favorable for hatching.

Other species prefer to lay their eggs in tree holes or artificial water containers.  The eggs are laid above the water line waiting to be inundated with water to hatch.

One species referred to as the Asian tiger mosquito is of particular concern because of its rapid spread within the United States since 1985.  It also breeds easily in any water-filled containers, which makes breeding sites very common.

Culex:

These species prefer to breed in quiet standing water with large amounts of organic material.  The body of water can range from small containers to large ponds.  The eggs are laid on the water surface in groups of 100 or more eggs.

Anopheles:

These species breed in permanent bodies of fresh water with abundant aquatic plants.  The eggs are laid singly on the water surface and are supported by ‘floats’ on each side.
 
 

LIFE CYCLE

Mosquitoes have four life cycles:  egg, larva, pupa, and adult.

Eggs laid on the water surfaces hatch in 1 to 3 days.  Eggs laid above the water line remain dormant until flooded.

Larvae, referred to as ‘wigglers’, that hatch must live in water (floating on the surface) to survive.  The larvae breath through an air tube and filter food through mouth brushes.  Depending upon the species and conditions, the larval stage can last from 5 days to several weeks.

Pupae, referred to as ‘tumblers’, are the third phase.  Pupae can often be seen bobbing in the water or breathing at the surface.  This stage does not feed and the adult should emerge within 2 to 3 days.

Adults emerge from the waters surface and fly away. 
 

FEEDING

Only the adult female of each species takes blood that she needs to develop and lay eggs.  Adult males feed on plant nectar. 

Most mosquitoes feed between dusk and dawn.  Their daylight hours are spent resting in dark and damp places.  However, some mosquitoes feed during the day and others both day and night.  In other words, always use caution during peak mosquito breeding seasons until their habits are identified in your area.

MOSQUITO ‘SEASONS’

Usually, mosquitoes may breed at any time from the beginning of spring until the first hard frost.  The species, the temperature, and the amount of rainfall control populations of mosquitoes.  During periods of abundant rainfall, eggs may be laid continuously and; when temperatures are high enough, development can be completed within a week.  This can result in ‘epidemic’ populations of adult mosquitoes in regional areas.

Most mosquitoes pass the winter in either the egg or the adult stage.  This often explains why thousands of mosquitoes suddenly appear following the first rainfall in spring or summer when temperatures are prime for them.

MOSQUITOES AND DISEASE

Female adult mosquitoes transmit diseases through their feeding habits.  When blood is sucked from an infected bird or mammal, the virus, complex virus or parasite is taken into the mosquito.  Once the organism multiplies within the mosquito enough to infect her saliva, the disease is transmitted when she feeds again.

Commonly known mosquito-transmitted diseases found within the United States include:  St. Louis encephalitis, LaCrosse encephalitis, Eastern equine encephalitis, Western equine encephalitis, West Nile virus, and dog heartworm.  Rare occasions of Dengue fever have also been reported.

The uncommon spread of the West Nile virus that was first noticed in Queens, New York in 1999 has been attributed to migratory birds on the east cost.  The infected birds migrate south during the winter months making a perfect overwintering receptacle for the virus.  The infected birds mingle and spread the virus to previously uninfected birds allowing the virus to spread.  In spring, the migratory birds return north and continue to spread the virus through mosquito activity.  There is no evidence to indicate the disease can spread directly from one animal to another.

To date, the West Nile virus has substantially increased the mortality rate of regional bird species and horses, but has not resulted in the human mortality rate once feared.  The experts report “exercise caution not fear”.

The following Health Risks For Humans Relating to West Nile Virus was provided by Cornell University:

• Birds are far more likely to be infected than humans.
• Birds are far more likely than humans to become ill by West Nile virus.
• Most mosquitoes are not infected with West Nile virus.
• Most mosquito bites will not result in a West Nile virus infection.
• The disease appears in humans and in August and September (in the Northeast).
• Most people who become infected do not become ill.
• Older and immuno-compromised individuals are at greater risk of becoming seriously ill.
• Children are NOT in a higher risk group.

WAYS TO REDUCE MOSQUITO SOURCES

• Remove all water-holding containers from the property, including toys, tires, cans, etc.
• Clean and drain all roof gutters of debris to prevent standing water.
• Inspect flat roofs and remove any pooled water no more than every 5 to 7 days.
• Drain and seal any tree holes so they do not collect water.
• Change water in birdbaths and wading pools every 5 to 7 days.
• Fill in any low spots in yards that retain rain or irrigation water for more than 7 days.
• Clean drainage ditches and culverts so they do not collect water.
•  Inspect flowerpots, container gardens or other receptacles around structures for mosquito larvae to be removed.
• Stock ponds or other permanent bodies of water with mosquito eating fish or treat waters with commercial larvacides to prevent mosquito populations from developing.
• Change exterior lighting fixtures to yellow bulbs or sodium vapor bulbs that are less attractive to mosquitoes.
• Use window shades or covers at night to prevent interior lighting from attracting mosquitoes.

PERSONAL PROTECTIVE MEASURES

• Avoid outdoor activities during peak mosquito activity times, usually dusk to dawn.
• Avoid possible mosquito breeding or resting sites whenever possible.
• Wear long-sleeved shirts and long pants if mosquito activity is suspected.
• Use skin mosquito repellents whenever necessary (please read the article, Insect Repellents Provide Safe Relief With Proper Use).
• Use clothing mosquito repellents whenever necessary (please read the article, Insect Repellents Provide Safe Relief With Proper Use). 

MOSQUITO TRIVIA

Q: How do mosquitoes find new hosts?

A: By sight (they observe movement); by detecting infra-red radiation emitted by warm bodies; and by chemical signals (mosquitoes are attracted to carbon dioxide and lactic acid, among other chemicals).

Q: How fast can a mosquito fly?

A: Mosquitoes are estimated to fly 1 to 1.5 miles per hour.

Q: How far do certain mosquitoes fly?

A: Many mosquitoes fly 1 to 20 miles from their hatch site; however, Saltmarsh mosquitoes can migrate 75 to 100 miles away.

Q: How far away can a mosquito smell you, or a cow or other host?

A: Mosquitoes can smell you 20 to 35 meters away.
 

There are ways to reduce the risk of mosquito bites that do not involve the use of insect repellents.  For example, some mosquitoes breed in stagnant water, so pouring out water-filled flowerpots, old tires, butters and other containers can reduce their numbers.  Mosquitoes are most active from dusk to dawn and seem to be more attracted to people wearing dark apparel.  Wear light-colored, loose fitting long sleeves and pants and stay inside when possible, especially during peak biting times.

But for those times when you must be outdoors, an insect repellent is often the best method of protection from mosquito bites.  Proper use of repellents is critical, as improper use and abuse can sometimes lead to health problems.

TYPES OF REPELLENTS:  Several types of repellents are available.  They vary in effectiveness.  Many state departments of health recommend using a repellent containing DEET.  Read the label carefully and follow directions to reduce the possibility of an adverse reaction to the active ingredient.  The following information on DEET and other repellents is from the the Annals of Internal Medicine's "Mosquitoes and Mosquito Repellents:A Clinician's Guide" and the University of Florida's "Use and Application of DEET" and "Avoiding and Repelling Mosquitoes and Other Biting Nasties."

DEET (diethyltoluamide) is widely recognized as the most broadly effective, longest-lasting repellent available.  It was developed by the U.S. Department of Agriculture in the 1940s for the U.S. Army and has been available to the general public since 1957.  It comes in formulations ranging from 5 percent to 100 percent and in many forms, including lotions, sprays and oils.  Above a certain level (about 50 percent), the increase in effectiveness with increased concentration of DEET shrinks substantially.  Depending on the situation, DEET can provide two to eight hours of protection.

For casual use, a product containing 10 percent to 35 percent DEET should be adequate.  For children, it is best to be conservative and keep the concentration of DEET at 10 percent or less.  Read the label to see how much DEET is in the repellent.  The label usually does not say "DEET".  Instead, it lists "diethyltoluamide" or "N,N-diethylmeta-toluamide" under the active ingredients.  Use the lowest concentration that works.

• High temperatures and humidity reduce the length of its effectiveness.  In such a situation, it may be necessary to apply the repellent more often or use a slightly stronger concentration.
• DEET can damage plastics, leather, synthetic fabrics (such as rayon), and painted or varnished surfaces.  Take care to avoid these materials when using repellent.  For example, a person can damage eyeglasses or a watch inadvertently by applying DEET to the hands and then touching these items.  DEET does not damage cotton, wool or nylon.
• Millions of people have used DEET since it was developed in 1946, but it can be toxic if used improperly.  Great care must be taken to ensure that it is used according to the label and EPA guidelines, especially with children because they are more likely than adults to accidentally ingest it.  Also, the low bodyweight of children means that a smaller amount of repellent could potentially have a much greater effect on a child than an adult.
• Use only DEET products made after 1993 since many older DEET products contained an additive that has raised some concern.

Permethrin, a synthetic insecticide, does not actually repel insects; it kills them on contact.  It has low toxicity in humans and is absorbed poorly by the skin.  Permethrin is also different from the other repellents in that it is applied not to the skin, but to clothing, tents or other fabrics.  It lasts on those fabrics for up to two weeks, even after washing  Fabrics treated with permethrin should dry for two to four hours before use.

Herbal or plant-derived repellents have had some success.  The oils of many plants do repel insects, but the duration of their effect is often significantly shorter than can be achieved with DEET.

Skin-So-Soft bath oil, made by Avon, and reported to have insect-repelling activity on the basis of its fragrance or formulation, has been shown in laboratory tests to be effective in repelling Aedes mosquitoes for about 40 minutes.  By comparison, a solution of 12.5 percent DEET provided protection from bites for 10 times as long.
 
 

The Environmental Protection Agency's Office of Pesticide Programs recommends following these guidelines to ensure safety when using insect repellents on adults or children:

• Read the entire product label before applying repellent to be sure you are following the directions.  Read it each time you use it.  Do not trust your memory.
• Apply repellent only to exposed skin, as indicated by the label.
• Do not go overboard with repellent.  Saturation is not necessary.  Use just enough to cover exposed skin.
• Do not use repellents on cuts or irritated skin.
• Do not spray repellent directly on the face.  Instead, spray it on your hands and apply it to the face.
• Do not apply to children's hands at all.  Use your own hands, rather than a spray, to put repellent on children.
• Do not spray repellent in enclosed areas or near food.
• Once back inside, wash treated skin with soap and water as soon as possible.  Clothing should be washed before it is worn again.

If you think you or your child might be having a reaction to a repellent, wash it off immediately, then call a local poison control center.

Health officials from Maricopa County Vector control and the Arizona Department of Health Services are requesting your help in controlling a growing mosquito problem within the community. An exotic species of mosquito known as Aedes aegypti has been found in this area.
  

Aedes Aegypti

This is why we need your help!

Here is what you can do to prevent mosquitos from breeding on your property:

• Eliminate standing water where mosquitoes breed. Remove, cover or properly store (under cover) any containers that may collect rain or sprinkler water. This includes buckets, cans, jars, coolers, open trash cans, tires, drums, watering cans, wheelbarrows, etc. Boats should be covered, or small boats can be turned over.
• Keep decorative fountains operational, or drain the water. Maintain swimming pools in working order. Unused pools should be thoroughly drained and/or covered so as to prevent water from pooling.
• Change water in flower vases, birdbaths, planters and animal watering dishes at least twice a week.
• Repair leaky pipes and outside faucets, and move air conditioner drain hoses frequently to prevent pooling.

If you have any questions regarding the Aedes aegypti problem, contact Maricopa County Environmental Services at (602) 506-6616 or the Arizona Department of Health Services - Vector-Borne Diseases Section at (602) 230-5932.