Mosquitoes and ticks are an annoyance for outside activities and can be a threat to human health, but commonly-used chemical treatments are contributing to declines in pollinators and essential insect populations. VCE/Master Gardeners and Master Naturalists are committed to helping our community learn how to protect themselves from these pests while protecting pollinators.
- Mosquito Facts
- What We Can Do to Protect Ourselves and Our Families Instead of Spraying Pesticides
- Mosquito Controls that Do Not Work
- Why Spraying for Mosquitoes Might Not Be Your Best Option
- Do Natural Alternatives to Insecticides Work?
- If You Have to Spray
Of the nearly 60 species of mosquitoes in Virginia, the two most commonly encountered in our area are Culex pipiens (Culex) and Aedes albopictus (Asian tiger). The small brown Culex mosquitoes are most active and more likely to bite at dawn or dusk. They prefer birds but will bite people and other mammals. Their range is a half mile to two miles. Culex mosquitoes lay eggs in stagnant water (e.g., storm drains, clogged rain gutters, and other sources of standing water).
The Asian tiger mosquitoes are the number 1 source of mosquito bites in our area and are most active and more likely to bite during the day. Their range is around 600 yards. The Asian tiger mosquito breeds in small and large containers, tree holes, and natural rock pools.
In addition to being a nuisance, these mosquitos can also carry disease. Diseases commonly carried by mosquitoes in Virginia include West Nile virus (WNV), Eastern Equine encephalitis (EEE), and La Crosse encephalitis (LAC). According to the Virginia Department of Health, a few cases of imported mosquito-borne diseases such as malaria, dengue, or chikungunya (CHIKV) are also reported each year.
Mosquitoes can live up to three months, and overwintering adult mosquitoes can live up to eight months. Hibernating females become active in late spring when temperatures reach 50 degrees, and they always lay eggs in standing water. It takes 7 – 10 days for an egg to develop into an adult. Only females bite. They need a blood meal to lay eggs, which they then lay in water, and the cycle starts again. They track down humans and animals to bite by smelling exhaled carbon dioxide, by seeing us (they can see in shades or black and white and they can see movement), or by body heat. Mosquitos are cold blooded – they generally do not bite in temperatures below 50 degrees F.
Mosquitoes require as little as a tablespoon of water to lay eggs in. They can successfully breed in any area or container that has still, shallow, standing water for more than seven days.
What We Can Do to Protect Ourselves and Our Families Instead of Spraying Pesticides
Controlling mosquito populations at the larval stage is the most effective strategy. This means eliminating mosquito breeding sites – any temporary standing water, even very small amounts. (Permanent pools attract predators that eat mosquito larvae.)
In our yards and landscapes, temporary water sources include ditches, holes in trees, leaky hoses, wagons and other toys, kiddie pools, clogged rain gutters, drains at the ends of downspouts (especially corrugated), open trash bins, upturned lids, wheelbarrows—any place where even a tablespoon of water stands for more than seven days. Empty these containers at least every 7 days.
To eliminate breeding sites, conduct a neighborhood “dump the bucket” inspection and walk-around. Look for:
- Blocked gutters, downspouts, and drainpipes. Make sure that water is flowing freely and consider replacing corrugated non-perforated pipes with smooth-walled pipes that flow freely.
- Buckets, pet water dishes, plant pot saucers, watering cans, kiddie pools, and bird baths. Do not allow water to stand undisturbed for more than 7 days and clean regularly.
- Old tires, car parts, wagons and other toys, and gardening equipment. Remove these and similar items that may collect water.
- Tarps over boats, firewood, cars, patio furniture, and other items. Tighten them down and make sure that they do not trap water or allow it to puddle.
- Use caulk to fill gaps, including around pipes, lids, vents, and holes. Make sure outflow pipes drain. Clean debris from gutters that drain into the tank. For more information, see Mosquito Control for Rainwater Harvesting Systems.
Where you can’t dump the water such as standing drains like sumps, you can use
- Bti (Bacillus thuringiensis israelensis), the active ingredient in Mosquito Dunks and Mosquito Bits, which kills mosquito larvae without harming birds, beneficial insects, or other wildlife; or
- a bubbler (for example in water features that do not have fish).
The Virginia Cooperative Extension (VCE) publishes the annual Home Grounds and Animals: Pest Management Guide. This is accessible online and can answer questions about control options for mosquito larvae and adults that are effective and rated for homeowner use.
Property managers can make sure gutters, downspouts, and drainpipes drain freely, and water doesn’t accumulate on flat roofs.
Mosquitoes can rest and breed during the day under dense ground covers that provide a moist, shady environment. Consider replacing dense ground covers like English ivy (which is nonnative and quite invasive) with native, less dense ground covers, like Pachysandra procumbens (Allegheny spurge), Eurybia divaricata (white wood aster), or other native ground covers.
2022 UPDATE: Another strategy that can help reduce the mosquito population is the community use of lethal oviposition traps—traps that attract and kill egg-laying female Aedes albopictus (Asian tiger) mosquitoes and larvae. Commercial versions of these traps are commonly called GAT traps. Researchers at Rutgers University found that a mass-trapping program in University Park, MD, that mobilized neighbors across a community to buy and use these traps experienced significantly reduced “biting pressure,” depending on how many traps were deployed. The higher the local GAT coverage, the greater the reduction in mosquitoes biting. The researchers emphasized the importance of mobilizing neighbors across the community. A pre-study survey showed that around 90% of the mosquitoes collected were Aedes albopictus, indicating Ae. albopictus traps could work. Dumping standing water regularly is still important, to maximize the likelihood that the females will lay eggs in the traps. DIY versions of these traps work in a similar way and may also help reduce mosquito populations. As the Rutgers study indicated, it is important for neighbors to work together to deploy these traps across a neighborhood, and residents should continue to dump standing water. The Audubon Society of Northern Virginia offers instructions for a DIY mosquito larva trap.
Other strategies for enjoying your yard at times when mosquitos are active include:
- using a fan on a patio or deck to keep mosquitoes at bay– mosquitos are weak flyers,
- ensuring that screens do not have holes,
- wearing long pants and a long-sleeved shirt, or
- using a mosquito repellent with DEET (25 percent to 30 percent — but do not use on infants or cut skin), Picaridin (20 percent), oil of Eucalyptus, and IR-3535 (ingredient in Avon’s Skin So Soft Bug Guard).
Mosquito Controls that Do Not Work
The following tactics do not work:
- bug zappers,
- spraying Listerine,
- wearing dryer sheets,
- VapoRub or vanilla,
- ultrasonic devices,
- plants marketed as mosquito-repellent,
- propane driven CO2 emitters, bats, or purple martins (mosquitoes make up just 1%-3% of their diets), or
- eating garlic.
Why Spraying for Mosquitoes Might Not Be Your Best Option
Pesticide sprays have only minimal and short-term effectiveness. These pesticides kill the adult mosquitoes that come into contact with the spray. Given their rapid lifecycle, mosquitoes will repopulate quickly. Hiring a mosquito control company also can be costly. Treatments typically occur every three or four weeks at an estimated cost of $40-$70 each, which can run $500 to $800 or $900 for a three-month season, depending on the size of the property and frequency of treatments.
The active ingredients in the most commonly used mosquito sprays are pyrethroids (including Permethrin, Resmethrin, Sumithrin) and organophosphates (Malathion, Naled). Organophosphates are toxic to many species of birds and to animals, and pyrethroids are highly toxic to honeybees, fish, and aquatic invertebrates (not just mosquitoes). Even though they have low toxicity to humans, birds, and animals, mosquito control companies typically recommend that children and pets stay indoors during spraying and for 30 minutes to an hour after.
A key consideration to keep in mind is that all insecticides used to target adult mosquitoes are nonselective and will kill all insects that come in contact with the chemicals, including pollinators and other beneficial insects. Insects are essential to pollinating our crops, aiding in decomposition of dead plants and animals, returning nutrients to the soil, and keeping pest insects in check. Multiple studies, however, have documented a steep decline in insects over the last several decades, driven in part by widespread use of pesticides.
Insecticide effectiveness in controlling mosquitoes is limited and short-lived, requiring repeated treatments every three weeks or so. One study found that spraying had almost no impact in controlling Culex spp. mosquitoes—one of the two most common genera of mosquitoes in Virginia—as these mosquitoes spend most of their time in the tree canopy. Depending on the species, mosquitoes generally fly a half mile up to 2 miles, so they can quickly repopulate sprayed areas unless breeding sources are eliminated. At the same time, the residual effects of these pesticides can last several weeks and will continue to harm pollinators and other insects visiting and feeding on the treated plants.
Remember—there is no insecticide targeting adult mosquitoes that will not harm pollinators or other beneficial insects.
For more information on what is happening to insects, see Insects Make My Food And… Other Reasons We Should Worry About the Decline in Bug Populations.
Do Natural Alternatives to Insecticides Work?
Many commercial pesticide applicators offer treatments with natural essential oils to eliminate or act as a repellent barrier to mosquitoes. The United States Environmental Protection Agency considers essential oils such as garlic, citronella, cedarwood, and thyme oils as minimum risk pesticides and does not require testing for effectiveness before they go on the market. There is no research on these products that shows they are effective in controlling mosquitoes in the United States.
While many of these essential oils are known to have repellent and even insecticidal properties, available research suggests that their effectiveness even as a repellent is questionable. Most essential oils are volatile when exposed to air and thus evaporate quickly. Consumer Reports’ evaluations of mosquito repellents have found that those made from various essential oils are largely ineffective after about an hour or so compared to those using DEET, picaridin or oil of lemon eucalyptus (the only essential oil with proven effectiveness as a repellent). Customers should ask to see the label of products touted as natural and not harmful to pollinators to verify that the active ingredients do not include a pesticide in addition to any essential oils.
If You Have to Spray
If you have decided that you cannot enjoy your yard without spraying for mosquitoes, here are some guidelines for hiring a pesticide applicator to minimize the harm to other pollinators:
- Use only a pest management company that has a Virginia Department of Agriculture and Consumer Services (VDACS) license.
- Ask for an integrated pest management (IPM) plan that includes strategies to identify and manage breeding sites as well as pesticide application, and whether their staff is trained on proper application.
- Compare several proposals and look for reputation for quality of service as well as price.
- Examine labels for the products to be used to know what pesticides are included and to verify claims that only essential oils or other “natural” products are being used.
- Insist that pesticides be applied at dawn and dusk when pollinators are less likely to be active and not be applied to food crops or flowering plants.
- Specify using ultra-low volume pesticides during the coolest part of the day to limit drift and request that applicators not spray on windy days or before rain is expected.
If you suspect misuse of a pesticide, contact the Virginia Department of Agriculture and Consumer Services, Office of Pesticide Services at 804-371-6560.
MGNV & VCE Resources
- Controlling Mosquitoes & Ticks in Your Yard without Pesticides – Recorded MGNV – Class
Mosquito and Tick Management: Pesticide Reduction for Pollinator Protection PowerPoint pdf
- Frequently Asked Questions from the Extension Master Gardener Help Desk about Mosquitoes pdf
- Mosquitoes and their Control – Virginia Cooperative Extension
- What to Know About Commercial Practices for Controlling Mosquitoes – MGNV
- “Bugs” & Human Health – Virginia Department of Health
- Mosquito Prevention & Information – City of Alexandria
- Mosquitoes – Arlington County Environmental Health
- Prevent Mosquito Bites – Centers for Disease Control & Prevention
- West Nile Virus – Centers for Disease Control & Prevention
- Zika Virus – Centers for Disease Control & Prevention
- Active Ingredients Eligible for Minimum Risk Pesticide Use, College of Agriculture and Life Sciences, Cornell University
- Essential Oils for Mosquito Control, Maryland Grows Blog, University of Maryland
- How to Control Mosquitoes Without Killing Pollinators and Other Important Wildlife – Arlington Regional Master Naturalists
- Insect Repellent Buying Guide, Consumer Reports, May 03, 2021
- Many Mosquito Controls Only Hammer Buyer’s Pocketbook, Texas A&M Agrilife Extension
- What is a pyrethroid insecticide? Texas A&M Agrilife Extension