The Health Department uses an integrated approach to mosquito control that includes educating county residents, reducing places where mosquitoes lay their eggs, and killing immature (larvae) and adult mosquitoes.  These approaches are called “larviciding” and “adulticiding.”

Spraying uses a small amount of pesticide to kill adult mosquitoes.  About 2 tablespoons are sprayed over an area the size of a football field using a backpack or truck mounted sprayer.  All sprays used are approved by the Environmental Protection Agency (EPA) and are safe for people and pets.  Very rarely, someone who is very sensitive to ingredients in the product may have eye, skin, nose and/or throat irritation, breathing problems, or nausea.  To avoid this, stay inside and keep your pets inside while spraying is done and for about an hour afterwards.  Call your doctor if you believe that you have any symptoms that may be from exposure to the spray.

According to the EPA, when applied according to label directions, pesticides used in mosquito control programs do not pose unreasonable risks to wildlife or the environment. These chemicals are low in toxicity to mammals and are practically nontoxic to birds. However, they are toxic to fish and to bees. For this reason, EPA has established specific precautions on the label to reduce such risks, including restrictions that prohibit the direct application of products to open water. There also is language on product labels to reduce risks to pollinators.

One method of adult mosquito control is the spraying of “residual” insecticide barriers on the foliage of shrubs, hedges, ivy, other low vegetation or other areas where mosquitoes may rest. Residual means that the insecticide deposits a residue and stays effective for a period of time beyond the initial treatment. The Health Department uses backpack sprayers to apply the product as a barrier treatment. Mosquito control products are applied according to the label directions in order to minimize impacts on non-target organisms such as honeybees. When properly used, these products pose no significant risks to human health.

Another method of adult mosquito control is ultra-low volume (ULV) spraying. ULV spraying (sometimes called fogging) is the process of putting very small amounts of liquid into the air as a fine mist of droplets. These droplets float on the air currents for a relatively short time (minutes to hours) and quickly kill mosquitoes that come into contact with them. ULV adulticides are usually applied when mosquitoes are most active - typically in the evening or before dawn. ULV adulticides break down in the environment quickly after application.

Spraying is done when there is a high risk that mosquitoes may spread serious disease to people.  West Nile virus is a disease that can cause meningitis (infection of the lining of the brain and spinal cord) and encephalitis (infection of the brain).  Spraying to kill adult mosquitoes may be done when a case of West Nile virus disease has occurred, when there are very high numbers of mosquitoes carrying the West Nile virus, when mosquitoes that usually don’t spread West Nile virus are found carrying it, and when the weather conditions support further growth in the number of mosquitoes.    

All Health Department spraying will be announced ahead of time on signage in the areas to be sprayed, on information left on door-knobs, and through local media and social media.  Residents also can look at the Health Department’s website or Twitter feed @fairfaxhealth for news about mosquito control activities.

Mosquitoes lay their eggs and breed in standing water.  So empty and scrub, turn over, cover, or throw out any items that hold water like tires, buckets, planters, toys, pools, birdbaths, flowerpot saucers, or trash containers.  Tightly cover rain barrels so mosquitoes can’t get inside.  Products such as Mosquito Dunks®, can be used to kill larvae and are available at hardware stores and garden centers.  Insecticides that can control adult mosquitoes in your yard and also can be found at hardware stores and garden centers or can be applied by a pest control professional.

Decisions to spray are based on a number of factors, including numbers of mosquitoes carrying the West Nile virus, the types of mosquitoes that are found carrying the virus, reported human cases, and weather conditions that may support further growth in the number of mosquitoes. Residents can call our Disease Carrying Insects program at 703-246-8931, TTY 711 to request a yard inspection where we can provide advice and tips on how to eliminate mosquitoes.

Health Department staff who perform adult mosquito control are certified by the Virginia Department of Agriculture and Consumer Services (VDACS) in Category 8 (Public Health Pest Control).  There are no licensing requirements for individuals who wish to treat their own properties with “over-the-counter” products sold in  hardware stores and garden centers.  If you are considering applying pesticides on your property, do the following:　

• Always follow the product label instructions and focus on areas where mosquitoes rest, in dense brush, ivy and bamboo.
• Do not apply more product than recommended or reapply more often than stated on product label instructions.
• Do not apply outside directly to fruits and vegetables in your garden or inside near food.
• Do not apply to plants in bloom or to plants that bees, butterflies, and other pollinators visit.
• Keep people and pets out of the treatment area until the product has dried, usually about an hour.

Mosquito control products come in many forms. Applying an insecticide barrier spray like permethrin to your yard can provide some relief from biting mosquitoes. We would recommend you check the product label before using any product and always apply according to label instructions to minimize impact on non-target organisms. You may also wish to consult with a pest control professional on options for treating your yard and outdoor areas. The National Pest Management Association offers tips on finding a pest control professional at http://www.pestworld.org/pest-control-help/.

There are many types of mosquitoes and only a few types can spread West Nile virus. The Culex species of mosquitoes are the mosquitoes most responsible for spreading West Nile virus, but this mosquito bites birds more than people. The most common mosquito in Fairfax County, the Asian Tiger mosquito (Aedes albopictus), is a highly aggressive human biter, but is usually more of a nuisance than a transmitter of disease. However, in years where West Nile virus is widespread among birds and there are many mosquitoes, the chance for people to become infected may increase.

Most people infected with West Nile virus show no symptoms at all.  Some people develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people will recover completely, but fatigue and weakness can last for weeks or months. A small number of people who are infected develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord). If you experience any of these symptoms, contact your doctor.

Residents are encouraged to follow the Health Department’s website or Twitter feed @fairfaxhealth for news about mosquito control activities. Information on planned spray activities will also be posted in neighborhoods prior to any spray event.

For questions about mosquito control in Fairfax County, email to FightTheBite@fairfaxcounty.gov or call 703-246-8931, TTY 711.

More information on the use of pesticides for mosquito control can also be found from the following sources: 

• The U.S. Environmental Protection Agency (EPA) oversees the registration of these chemicals.
• The National Pesticide Information Center (NPIC) provides information online or through a toll-free number, 1-800-858-7376.