See PRI’s Top-Ten List for Keeping Pests Out and Kids Safe.

Preventing and Managing Mosquito Invasions

Mosquitoes flying around your home can cause those itchy red bumps, and can potentially transmit disease. Your vector control district actively conducts large-scale mosquito management, but everyone can help prevent the spread of malaria, West Nile Virus and other mosquito-borne health threats. The goal is to remove breeding grounds and eliminate mosquito larvae to keep population levels low.

Life Cycle

The most effective control methods target the larval stage of the mosquito life cycle. In the United States there are nearly 200 species of mosquitoes, each with its own preferred habitat for laying eggs. Culex mosquitoes, a common species found in North America, will lay hundreds of eggs that stick together to form a raft on the surface of still water; some species will lay only a single egg. Floodwater mosquito species prefer moist soil where their eggs can patiently wait for water to pool, months or even years later.  Mosquito eggs will hatch in water within 48 hours, and the larvae transform into airborne adults within two weeks. Female mosquitoes need protein from mammalian blood to breed and are the ones responsible for all those painful bites. Stop the cycle and protect yourself from these bothersome feeders with the low impact approaches outlined in the following sections.

Common Mosquito Species

Low Impact Approaches

The control measures outlined below are best used in combination to disrupt the mosquito life cycle. By removing breeding sites and using window screens, you can potentially reduce the number of mosquitoes in and around your home and also limit your exposure to them.

• Keep swimming pools circulating and chlorinated at all times.

• Avoid creating small puddles with excessive irrigation. Check to make sure plants have proper drainage and maintain vegetation to reduce the number of places where adult mosquito can take shelter.

• If your home has a septic tank, test it for proper functioning and make sure that no puddles form in the drain field.

• Remove debris from rain gutters regularly and keep street gutters clear to prevent water runoff from pooling. Remember to check items stored outdoors, like plastic tarps, as well as tree stumps for standing water.

Use Natural Enemies

Consider using mosquitofish in areas where standing water cannot be drained in natural pools and ponds. Several species of birds, bats, fish, spiders and predatory insects also eat mosquitoes and will complement other control methods.

Minimize Exposure

Removing mosquito habitat from your yard may not be enough to eliminate all mosquitoes.

Mosquito Control Pesticides

Potential Consequences of Mosquito Control Pesticides

Recognize that when you use mosquito-control pesticides, you should be ready to deal with these potential consequences:

• Pesticides applied to skin may cause skin irritation. In some individuals, hypersensitivity and/or psychological effects have been noted from exposure to DEET.  Avoid frequent or heavy use of insect repellents, and wash the skin with soap and warm water after use.

• Insect repellent formulations can be irritating to some and in high concentrations can damage clothing or plastics.

• Use of aerosol sprays or foggers guarantees exposure to the pesticidal active ingredient, through inhalation of the spray droplets and contamination of exposed surfaces. See US EPA’s page on foggers.

Precautions to Take When Using Mosquito Control Products

If you determine that pesticides are necessary, take these precautionary steps to reduce the potential for adverse effects:

• Always read and follow the label instructions on the pesticide product. The label is the law.

• Use only US EPA-approved products. Check out the EPA insect repellent search tool for more information on repellents.

• Never spray repellents directly onto your face; apply first onto your hands, then apply the product lightly onto your face and head. Better yet, apply the repellent to a hat and wear the hat.

• Use repellents sparingly; applying heavier doses does not increase protection. Repellents do not kill mosquitoes; they discourage them from attacking treated areas. Effectiveness and duration of repellency vary considerably, with most lasting for four hours or less.

• Apply repellents only to clothing and exposed skin; never use underneath clothing. Do not apply on cuts or irritated skin.

• Never apply oil of lemon eucalyptus on children under three; it has not been tested on children of this age. Do not allow children to handle mosquito-control products.

Mosquito-Control Pesticides

There are many mosquito-control products sold to reduce mosquito populations at home, including liquid, granular and powder formulations. When using these chemical products, take precautions to minimize human, pet, and environmental exposure. The information below will help you understand the risks associated with the active ingredients in these products.

Aerosol Sprays, Foggers and Outdoor Misting Systems

Plugins like these put pesticides into the air, causing unnecessary inhalation exposure.

Mosquito Insecticides

In the tables below, each active ingredient found in mosquito insecticides and repellents has been assigned a Hazard Tier ranking based on the San Francisco rating system. While this system is usually used for rating formulated pesticide products that contain both active and other ingredients, PRI has adapted it to apply to active ingredients for non-acute toxicity.  The chemical Hazard Tier ranking is based on non-acute effects like cancer, developmental or reproductive toxicity, endocrine disruption or water pollution potential. Acute effects like skin and eye damage, systemic poisonings, or lethality to wildlife are a function of the concentration of the chemical in a product and are noted by the hazard signal word on the product: DANGER means very high acute toxicity, WARNING means moderate acute toxicity, and CAUTION means low acute toxicity.

Interested in finding out more about specific mosquito insecticide and repellent products? Check out PRI’s Pesticide Product Evaluator, a subscription-based online tool that allows you to look up the human and environmental toxicity of different pesticide products and find their hazard tier rankings.

Type of Active Ingredient	Representative Chemicals*	Hazards	Formulation	Hazard Tier Ranking of Active Ingredient
Bacillus thuringiensis	Bacillus thuringiensis Israelensis (Bti) Bacillus sphaericus 2362, Serotype H5a5b	Practically nontoxic to humans, pets, fish and wildlife. Both strains occur naturally in the environment and are highly selective toxins that only target mosquito larvae and that of a few related flies.	Granular, Briquette, Solution, Dust
Botanicals	Linalool Neem oil Nepeta cataria oil (catnip) Oil of cedar wood Phenylethyl propionate	Several naturally occurring substances are available in products sold for mosquito control, including neem and linalool (from mint and citrus plants). Contamination of surfaces with these common components of foods is not hazardous, but inhalation of the spray can be problematic.	Spray, Solution
Insect Growth Regulators (IGR)	Pyriproxyfen Methoprene Diflubenzuron	Very low acute and longer-term toxicity to humans. High toxicity to aquatic invertebrates. Diflubenzuron affects the hemoglobin of animals in studies. P-chloroaniline (PCA), a metabolite of diflubenzuron, is classified as a probable human carcinogen. Most products with IGRs also contain an insecticide, usually a pyrethroid.	Aerosol, Solution, Powder, Pelleted/tableted, Impregnated materials
Ketones	Dihydro-5-pentyl-2(3H)-furanone Dihydro-5-heptyl-2(3H)-furanone	Poses a low acute toxicity risk to humans and pets. Slightly toxic to freshwater invertebrates.	Granular, Solution
Polyalkyloxy Compounds	Butoxy poly propylene glycol (BPG) Poly (oxy-1,2-ethanediyl), alpha-isooctadecyl-omega-hydroxy	Low acute toxicity. BPG is never used as the sole active ingredient in a product, but is often used with pyrethrins, piperonyl butoxide, and pyrethroids.	Solution, Spray
Spinosad		Low acute toxicity for humans and pets, and not likely to cause cancer or other long-term harm. Highly toxic to bees.	Solution, Powder, Granular, Briquette
Fipronil		Moderately acutely toxic by ingestion, but not absorbed substantially through the skin. Toxic to the nervous system. Classified as a possible carcinogen by US EPA. In pure form, high acute toxicity to aquatic life and to birds; acute toxicity is less of a concern in dilute products.	Pelleted, Powder, Solutions, Granular, Impregnated materials
Avermectin		High acute toxicity in pure form, but at low concentrations it has low acute toxicity. Toxic to the nervous system and to the developing fetus at very low doses. Not absorbed through the skin to any great extent. Highly toxic to fish and aquatic invertebrates.	Ready-to-use solution
N-Methyl carbamates	Carbaryl Propoxur	High acute toxicity to humans at low concentrations. Toxic to the nervous system, especially for children. Highly toxic to aquatic life.	Aerosol, Granular, Solution, Impregnated materials
Neonicotinoids	Acetamiprid Dinotefuran Imidacloprid Thiamethoxam	Moderate acute toxicity to humans and absorbed through the skin to some extent. Toxic to the nervous system. Imidacloprid has been shown to reduce sperm counts in laboratory animals with long-term exposure. Most arer highly toxic to aquatic invertebrates and bees. Acetamiprid has a ranking of hazard tier two, it poses a low acute toxicity risk to humans and is only moderately toxic to bees.	Granular, Solution, Aerosol, Impregnated materials
Organophosphates	Chlorpyrifos DDVP Malathion Naled Propetamphos Temephos	High acute toxicity to humans at low concentrations. Toxic to the nervous system, especially for children. Highly toxic to aquatic life.	Aerosol, Solution, Granular, Impregnated materials
Pyrethroids	Allethrin Bioallethrin Cyhalothrin Cypermethrin Deltamethrin Esfenvalerate Ethofenprox Metofluthrin Permethrin Tetramethrin	Moderate acute ingestion and inhalation toxicity. Sensitizer, causing allergic reactions and asthma in some people. Toxic to the nervous system. Highly toxic to aquatic invertebrates and bees. US EPA has classified ethofenprox, metofluthrin and permethrin as likely carcinogens, and cypermethrin, tetramethrin and bioallethrin as possible carcinogens. Most products containing pyrethroids also contain a synergist that increases the insecticidal activity of the pyrethroid. Typical synergists include piperonyl butoxide (PBO) and N-octyl bicycloheptene dicarboximide. US EPA considers both of these synergists possible carcinogens.	Solution, Granular, Aerosol, Impregnated materials
*For groups of active ingredients of the same type.

Other Products

• The effectiveness of most other products marketed to repel mosquitoes differs greatly.  Burning citronella candles or mosquito coils containing allethrin are for outdoor use only and work best when there is little air movement.

• Plant oils such as pine, spearmint, geranium and neem will help deter mosquitoes.

• You can trap mosquitoes with products that release carbon dioxide, but these capture only a small proportion of the insects drawn in. Many of the insects that are killed by electric bug zappers prey on mosquitoes, making these devices counterproductive for mosquito control.

• Clip-on metofluthrin dispensers can repel mosquitoes, but like most repellents, effectiveness varies among users. Electric grids, ultrasonic emitters, electronic repellers and aromatic plants, incense coils, vitamin B1, brewer’s yeast, garlic and wristbands that contain an aromatic repellent are ineffective.

• If possible, plan your trip with a mosquito-avoidance strategy in mind. High elevations, desert and coastal areas and other places with colder night temperatures will often have fewer mosquitoes. In dry areas, mosquito activity is much higher during the rainy season, so plan accordingly.

• If you are traveling to a malaria zone, see your physician prior to travel to determine if an anti-malarial medication is required.

• Pack a mosquito net. It is essential for travel to some areas of the world when you need to sleep outdoors or in an unscreened room. Hang mosquito nets and close bug screens before dark.

• Cover up before you get bites, wear loose long sleeved shirts and long pants to reduce skin exposure. Tightly woven cotton will provide better protection than more porous synthetics.

• As much as possible, apply mosquito repellent to clothing. This is preferable to directly applying a repellent to the skin, but don’t neglect to also use repellent on exposed areas.

• Don’t spend time near waterlogged ground or other places where mosquitoes breed. Also, avoid outdoor activities at dawn and dusk, when mosquito activity is highest.

Mosquito Repellents

Type of Active Ingredient	Representative Chemicals*	Hazards	Formulation	Hazard Tier Ranking of Active Ingredient
Botanicals	Eucalyptus oil Limonene Nepeta cataria oil (catnip) Oil of citronella Oil of lemon eucalyptus p-Menthane-3,8-diol	Several naturally occurring substances are available as sprays and other formulations. Contact with these common components of foods is not a problem, but inhalation of the spray can be problematic. Oil of lemon eucalyptus is slightly toxic to the central nervous system and has very high ingestion toxicity in children if misused.	Lotion, Liquid, Spray, Impregnated materials
DEET		DEET poses a low acute toxicity risk to humans. However, there is potential for skin and eye irritation. DEET is a sensitizer, causing allergic reactions in some individuals. Moderately toxic to fish and aquatic invertebrates.	Liquid, Spray, Cream, Lotion, Foam, Solid
Ethyl butylacetylaminopropionate (Avon Skin-So-Soft)		Low acute toxicity to humans. Eye irritant.	Lotion, Cream, Liquid, Spray
Picaridin		Low acute toxicity to humans. Eye irritant. Moderately toxic to fish.	Cream, Liquid, Spray, Aerosol
Ketones	Dihydro-5-pentyl-2(3H)-furanone Dihydro-5-heptyl-2(3H)-furanone Methyl nonyl ketone	Poses a low acute toxicity risk to humans and pets. Slightly toxic to freshwater invertebrates. Methyl nonyl ketone is a weak sensitizer, causing mild allergic reactions in some individuals. It is moderately toxic to fish and highly toxic to aquatic invertebrates.	Liquid, Spray
Dipropyl isocinchomeronate (MGK Repellent 326)		Low acute toxicity to humans, but classified as a probable human carcinogen by the EPA. It is always combined with DEET when found in products intended for human use. It is used to expand the spectrum of repellency for other formulation components.	Aerosol, Lotions, Spray, Liquid
*For groups of active ingredients of the same type.

Check out the EPA insect repellent search tool for more information on repellents.

Regulatory Update on Mosquito Control Pesticides

The use of pesticides for mosquito control presents a potential risk to non-target species. On August 15, 2013, the U.S. Fish and Wildlife Service (FWS) proposed to designate critical habitat for the Florida leafwing (Anaea troglodyta floridalis) and Bartram’s scrub-hairstreak (Strymonacis bartrami) butterflies under the Endangered Species Act. Drift from mosquito control pesticide application has been identified as a threat to these species, prompting FWS to recommend the expansion of no-spray zones.

Malathion, naled, phenothrin, permethrin, and pyrethrins are all used for adult mosquito control, primarily through fogging in the early evening. Most of these applications are conducted by vector control districts. Temephos is the only organophosphate with significant larvicidal use and is labeled only for use by public health officials, personnel of mosquito abatement districts or similar agencies or personnel under contract to those agencies. When the registration review for temephos began in 2008, the registrant proposed canceling all uses.  However, due to the need for continued use for mosquito control, this use will not be canceled until December 30, 2015.

References and Additional Resources

• US Environmental Protection Agency: Mosquito Control
• University of California Davis UC IPM: Mosquito Management Guidelines
• American Mosquito Control Association: Mosquito Control Strategies
• Celebration Community Development District: Types of Mosquitoes
• National Pesticide Information Center: Pesticides Used in Mosquito Control
• Michigan Department of Community Health: Pesticide Information Resources
• Cornell University: Pesticide Active Ingredient Information and Search Tool
• Center for Disease Control:  West Nile Virus–What You Need to Know
• Agency for Toxic Substances and Disease Registry:  DEET Health Effects in Humans
• Bacillus thuringiensis subsp. israelensis:  Biological Control of Mosquito Larvae