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.
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.
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.
These species breed in permanent
of fresh water with abundant aquatic plants. The eggs are laid
on the water surface and are supported by ‘floats’ on each side.
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
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.
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:
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.
REPELLENTS PROVIDE SAFE RELIEF WITH PROPER USE
With recent reports in the media about West Nile Virus, Eastern equine encephalitis and St. Louisencephalitis - which are all transmitted by mosquito bites - people are increasingly concerned with how to protect themselves and their families.
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.
Special considerations in applying
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
reported to have insect-repelling activity on the basis of its
or formulation, has been shown in laboratory tests to be effective in
Aedes mosquitoes for about 40 minutes. By comparison, a solution
of 12.5 percent DEET provided protection from bites for 10 times as
The Environmental Protection Agency's Office of Pesticide Programs recommends following these guidelines to ensure safety when using insect repellents on adults or children:
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.
|News Release: July, 2001
Health officials from Maricopa
control and the Arizona Department of Health Services are requesting
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 AegyptiThis mosquito, which is not native to Arizona, has been spreading into many populated areas of southern Arizona. Aedes aegypti is capable of transmitting diseases such as dengue fever and yellow fever. In late May, 2001, health officials initiated a local surveillance program to assess the extent of the problem. Results thus far have shown that this tropical mosquito is flourishing in Tempe neighborhoods. If the local Aedes aegypti problem is not contained and eradicated, it has the potential to spread throughout the county. Unfortunately, this particular mosquito problem cannot be contained solely through the efforts of government vector control programs. Aedes aegypti thrives in urban / suburban neighborhoods because back yard containers and clutter (ex. tires, buckets, coolers, water cans, etc.) offer ideal breeding conditions for the mosquitos in question. In order to control the problem, breeding sources need to be eliminated.
This is why we need your help!
Here is what you can do to prevent mosquitos from breeding on your property:
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.
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