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Monday, April 24, 2017

Environmental Disease Control - Mosquitoes

Habits and Characteristics of the Mosquito

All mosquitoes have four stages of development-egg, larva, pupa, and adult, and spend their larval and pupal stages in water. The females of some mosquito species deposit eggs on moist surfaces, such as mud or fallen leaves, that may be near water but dry. Later, rain or irrigation re-flood these surfaces and stimulate the eggs to hatch into larvae. The females of other species deposit their eggs directly on the surface of still water in such places as ditches, street catch basins, tire tracks, streams that are drying up, and fields or excavations that hold water for some time. This water is often stagnant and close to the home in discarded tires, ornamental pools, unused wading and swimming pools, tin cans, bird baths, plant saucers, and even gutters and flat roofs. The eggs deposited on such waters soon hatch into larvae. In the hot summer months, larvae grow rapidly, become pupae, and emerge in 4 - 7 days later as flying adult mosquitoes.

Only the Female Can Bite

After adult mosquitoes mate, the female seeks a blood meal to obtain the protein necessary for the development of her eggs. The females of a few species may produce a first batch of eggs without this first blood meal. After a blood meal is digested and the eggs are laid, the female mosquito again seeks a blood meal to produce a second batch of eggs. Depending on her stamina and the weather, she may repeat this process many times without mating again. The male mosquito does not take a blood meal, but may feed on plant nectar. He lives for only a short time after mating.

Winter Survival Is Important

Most mosquito species survive winter in the egg stage, awaiting the spring thaw, when waters warm and the eggs hatch. A few important species spend the winter as adult, mated females, resting in protected, cool locations, such as cellars, sewers, crawl spaces, and well pits. With warm spring days, these females seek a blood meal and begin the cycle again. Only a few species can over winter as larvae.

Mosquitoes Can Transmit Disease

Mosquito-borne diseases, such as malaria and yellow fever, have plagued civilization for thousands of years. Organized mosquito control in the United States has greatly reduced the incidence of these diseases. However, there are still a few diseases that mosquitoes in Arizona can transmit, including West Nile Virus, Western Equine Encephalitis and St. Louis Encephalitis. The frequency and extent of these diseases depend on a complex series of factors.

Preventing and Reducing Mosquitoes

When mosquitoes are numerous and interfere with living, recreation, and work, you can reduce their annoyance by some preventive measures.

Reduce the amount of standing water. 

The most efficient method of controlling mosquitoes is by reducing the availability of water suitable for larval and pupal growth. Large lakes, ponds, and streams that have waves, contain mosquito-eating fish, and lack aquatic vegetation around their edges usually do not contain mosquitoes; mosquitoes thrive in smaller bodies of water in protected places. Examine your home and neighborhood and take the following precautions:

  • Dispose of unwanted tin cans and tires.
  • Clean clogged roof gutters and drain flat roofs.
  • Stock ornamental pools with fish.
  • Change water in birdbaths, fountains, and troughs twice a week.
  • Clean and chlorinate swimming pools; when not regularly used, they should be emptied.
  • Turn over unused wading pools and other containers that tend to collect rainwater.
  • Cover containers tightly with window screen or plastic when storing rainwater for garden use during drought periods.
  • Ensure evaporative runoff is not creating puddles.
  • Avoid over-irrigation.

What attracts mosquitoes?

Mosquitoes are attracted by perspiration, warmth, body odor, carbon dioxide, and light. Several devices are sold that are supposed to attract, trap, and destroy mosquitoes and other flying insects. However, if these devices are attractive to mosquitoes, they probably attract more mosquitoes into the area and may, therefore, increase rather than decrease mosquito annoyance.

Repellents can offer relief.

Various repellents can be purchased as creams, lotions, or in pressurized cans and applied to the skin and clothing. Some manufacturers also offer clothing impregnated with repellents; coarse, repellent-bearing particles to be scattered on the ground; and candles whose wicks can be lit to release a repellent chemical. The effectiveness of all repellents varies from location to location, from person to person, and from mosquito to mosquito. Repellents can be especially effective in recreation areas, where mosquito control may not be conducted.

Use insect repellent containing DEET (N, N-diethyl-meta-toluamide), with concentrations of 30-35% DEET for adults and 15% for children. Do not use repellent on infants. Repellents containing concentrations of more than 35% DEET do not provide additional protection. Picaridin is a good substitute for those with sensitive skin. Note: whenever insecticide or insect repellent is used, be sure to read and follow the manufacturer’s directions for use, as printed on the product.

Other Personal Protective Measures

  • Avoid being outdoors between dusk and dawn when mosquitoes are most active and likely to bite.
  • Wear loose-fitting, long-sleeved shirts and long pants when outdoors.
  • Spray clothing with insect repellent containing DEET. Mosquitoes may bite through thin clothing.
  • Install or repair window and door screens so that mosquitoes cannot get indoors. Avoid leaving doors and windows without screens open.
  • Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites.
  • Horse owners may want to talk to their veterinarian about WNV horse vaccine.

Use insecticides safely.

Several commercially available insecticides can be effective in controlling larval and adult mosquitoes. These chemicals are considered sufficiently safe for use by the public. Select a product whose label states that the material is effective against mosquito larvae or adults. For safe and effective use, follow the instructions for applying the material. The label lists those insects that the Environmental Protection Agency (EPA) agrees are effectively controlled by the product. Read the label.

For use against adult mosquitoes, some liquid insecticides can be mixed according to direction and sprayed lightly on building foundations, hedges, low shrubbery, ground covers, and grasses. Do not overapply liquid insecticides - excess spray drips from the sprayed surfaces to the ground, where it is ineffective. The purpose of such sprays is to leave a fine deposit of insecticide on surfaces where mosquitoes rest. Such sprays are not effective for more than one or two days.

Some insecticides are available as premixed products or aerosol cans. These devices spray the insecticide as very small aerosol droplets that remain floating in the air and hit the flying mosquitoes. Apply the sprays upwind, so the droplets drift through the area here mosquito control is desired. Rather than applying too much of these aerosols initially, it is more practical to apply them briefly but periodically, thereby eliminating those mosquitoes that recently flew into the area.


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