West Nile Virus
Mosquito Control

Written by: Dr. Jay Altman

It is no secret that West Nile Virus has hit Colorado and that this summer a heavy mosquito population is anticipated, only heightening the risk of a high number of West Nile Virus cases in our area. Vaccinating your horses for the deadly West Nile Virus is one, but not the only step that can and should be taken to help prevent the spread of West Nile Virus to one horses. Because the mosquito population is the only transmitter of West Nile Virus, and the disease can be transmitted to humans, it only makes sense to practice effective mosquito control measures. It is true that all of us as horse owners apply fly and insecticide sprays or wipes of some sort to our horses, but not only do we need to increase our vigilance of our applications, but many other mosquito control measures should be considered. The following is a compilation of mosquito control measures for both you and your horse's safety.

Control of the Adult Mosquito
Repellents are substances that make a mosquito avoid biting it's target. Persons working or playing in mosquito infested areas will find repellents very helpful in preventing mosquito bites. Repellents are formulated and sold as aerosols, creams, solids (sticks), and liquids. Use repellents containing ingredients such as N, N-Diethyl-3-Methylbenzamide (DEET). For more than 40 years, DEET has been the standard in mosquito repellents. Check the label for active ingredients such as these. Repellents containing Permethrin (Permanone) are recommended for use on clothing, shoes, bed-nets and camping gear. Permethrin is highly effective as an insecticide or acaricide, and as a repellent. Clothing treated with Permethrin repels and kills ticks, mosquitoes, and other arthropods and even retains this effect after repeated laundering. Permethrin treated clothing should be safe when label directions are followed. Although Permethrin repellents do not offer any protection from mosquitoes when applied to the skin, it is often helpful to use spray repellents on outer clothing as well as the skin. When using repellents on the skin, protection may generally be expected up to 6 hours following application. Oil of citronella is another type of mosquito repellent for space repelling. Oil of citronella is the active ingredient in many of the candles, torches, or coils that may be burned to produce a smoke that repels mosquitoes. These are useful outdoors only under windless conditions. Their effectiveness is somewhat less than repellents applied to the body or clothing.

• Common sense rules when using repellents:
• Apply repellent sparingly (and only to exposed skin or clothing.) One application will last approximately 4-6 hours; Saturation does not increase efficacy.
• Wear long sleeve shirts and pants outdoors during peek mosquito activity time periods.
• Keep repellents away from eyes, nostrils and lips. Do not inhale or ingest repellents, or get them into the eyes.
• Avoid applying high-concentration (>30% DEET) products to the skin, particularly of children and horses.
• Avoid applying repellents to portions of children's hands that are likely to have contact with eyes or mouth.
• Pregnant and nursing women should minimize use of repellents.
• Never use repellents on wounds or irritated skin.
• Wash repellent-treated skin after coming indoors.
• If a suspected reaction to insect repellents occurs, wash treated skin, and call a physician.  Take the repellent container to the physician.

Mosquito traps, insect electrocutors (bug zappers) and mosquito trapping devices- are 20th century control measures. Manufacturers modernized 19th century mosquito trapping devices such as the New Jersey light trap with more "bells and whistles" to improve its appeal to the public. Insect electrocuter light traps have been extensively marketed for the past several years claiming they can provide relief from the biting mosquitoes and other pests in your back yard. Other mosquito traps are designed to mimic the heat of a mammal (horse, cattle, man, and domestic pets) by emitting a plume of carbon dioxide, heat, and moisture, which is often combined with an additional attractant (i.e. octenol) to attract not only mosquitoes, but no-see-ums, biting midges, and black flies as well.

Space sprays - Mosquitoes can be killed inside the house by using a flit gun (seldom used any longer) or a household aerosol space spray containing synergized pyrethrum or synthetic pyrethroids (allethrin, resmethrin, etc.). The major advantage of space treatment is immediate knockdown, quick application, and relatively small amounts of materials required for treatment.

Outdoor Control - Homeowners, ranchers, or businesses may find temporary relief from flying mosquitoes by using hand-held foggers, portable foggers, or fogging attachments for tractors or lawn mowers. Pyrethrins or 5% malathion can be fogged outdoors. Follow instructions on both the insecticide label and fogging attachments for application procedure.

Mechanical Barriers - Mosquitoes can be kept out of the home by keeping windows, doors, and porches tightly screened (16-18 mesh).

Vegetation Management - Because adult mosquitoes prefer to rest on weeds and other vegetation, homeowners can reduce the number of areas where adult mosquitoes can find shelter by cutting down weeds adjacent to the house foundation and in their yards. Mowing the lawn regularly contributes to this form of control. To further reduce adult mosquitoes harboring in vegetation, insecticides may be applied to the lower limbs of shade trees, shrubs, and other vegetation. Products containing allethrin, malathion, or carbaryl have proven effective.

Larval Control - The most effective way to control mosquitoes is to find and eliminate their breeding sites. Eliminating large breeding areas such as swamps and sluggishly moving streams or ditches may require community-wide effort, however individuals can take the following steps to prevent mosquito breeding on their own property:

• Destroy or dispose of tin cans, old tires, buckets, unused plastic swimming pools or other containers that collect and hold water. Do not allow water to accumulate in the saucers of flowerpots, cemetery urns, or in pet dishes for more than 2 days.
• Clean debris from rain gutters. Remove any standing water under or around structures or on flat roofs. Check around faucets and air conditioner units and repair leaks or eliminate puddles that remain for several days.
• Change the water in birdbaths and wading pools at least once a week and stock ornamental pools with top feeding predacious minnows.
• Fill or drain puddles, ditches and swampy areas, and either remove, drain or fill tree holes and stumps with mortar. These areas may be treated with Bti or methoprene products as well.
• Eliminate seepage from cisterns, cesspools, and septic tanks.
• Eliminate standing water around animal watering troughs. Flush livestock water troughs twice a week.
• Check for trapped water in plastic or canvas tarps used to cover boats, pools, etc. Arrange the tarp so that it drains the water.
• Check around construction sites or do-it-yourself improvements to ensure that proper backfilling and grading prevent drainage problems.
• Irrigate lawns and gardens carefully to prevent water from standing for several days.
• If ditches do not flow and contain stagnant water for one week or longer, they can produce large numbers of mosquitoes. Report such conditions to a Mosquito Control or Public Health Office. Do not attempt to clear these ditches because they may be protected by wetland regulations.