Local governments and mosquito control programs often use integrated mosquito management (IMM), also called integrated pest management or integrated vector management.

IMM uses a combination of methods to control mosquitoes based on an understanding of mosquito biology and the mosquito life cycle. IMM uses methods that, when followed correctly, are safe and scientifically proven to reduce numbers of mosquitoes. Everyone can help control mosquitoes.

• Professionals from local government departments or mosquito control districts develop mosquito control plans, perform tasks to control larvae, pupae, and adult mosquitoes, and evaluate how well mosquito control programs are working.
• You, your neighbors, and your community can also take steps to reduce mosquitoes in and around your home and in your neighborhood.

How can I report a mosquito problem?

If you notice a high population of mosquitoes in your area, call your

• Local or state health department, or
• Local mosquito control district

You can contact your local mosquito control board or health department if you have concerns about standing water where mosquitoes lay their eggs. Mosquitoes lay eggs in places like:

• Neglected swimming pools
• Trash
• Discarded tires
• Drainage ditches with standing water

Some mosquitoes are harmful and can spread viruses like West Nile, dengue, Zika, and parasites like malaria. Other mosquitoes bother people and are considered “nuisance” mosquitoes. Nuisance mosquitoes bite people, but don’t spread germs. Of the over 200 types of mosquitoes in the United States and US territories, about 12 types spread germs.

Local government departments and mosquito control professionals track the numbers and types of mosquitoes in an area and the germs they may be spreading. When infected adult mosquitoes are spreading germs to people, acting quickly can stop further spread and prevent people from getting sick. Professionals share prevention information with the public and use multiple methods at the same time to kill mosquito larvae and adult mosquitoes.

Everyone Can Help Control Mosquitoes

• Professionals from local government departments or mosquito control districts develop mosquito control plans, perform tasks to control mosquito larvae and adult mosquitoes, and evaluate the effectiveness of actions taken.
  • Your local mosquito control program or local health department can provide information about control efforts in your area. Contact information may be found on the Internet.
• You, your neighbors, and the community can also take steps to reduce mosquitoes in and around your home and in your neighborhood.
  • Control mosquitoes outside your home.
  • Control mosquitoes inside your home.

Support Your Local Mosquito Control Programs

Mosquito control activities are most often handled at the local level, such as through county or city government. The type of mosquito control methods used by a program depends on the time of year, the type of mosquitoes to be controlled, and mosquito habitats. Methods can include eliminating mosquito larval habitats, applying larvicides to kill mosquito larvae, or spraying insecticides from trucks or aircraft to kill adult mosquitoes.

Your local mosquito control program can provide information about the type of products being used in your area. Or, check with your local health department for more information. Contact information may be found online or in the blue (government) pages of the phone book.

Local governments and mosquito control programs often use an integrated mosquito management (IMM) approach to control mosquitoes. IMM uses a combination of methods to prevent and control mosquitoes that spread viruses like West Nile, dengue, and others. Mosquito control professionals conduct mosquito surveillance, remove places where mosquitoes lay eggs, control mosquito larvae and pupae, control adult mosquitoes, and monitor control efforts.

Conduct Mosquito Surveillance

Mosquito surveillance helps professionals and local governments determine when, where, and how to control mosquitoes before people start getting sick. Mosquito control professionals want to know:

• How many mosquitoes are in the area?
• What types of mosquitoes?
• Where are sources of standing water where mosquitoes lay eggs and where mosquito larvae and pupae live?
• What germs are they spreading?
• Will Environmental Protection Agency (EPA)-registered insecticides be effective in killing local mosquitoes?
• Are current mosquito control techniques working?

Local governments and mosquito control agencies use the information gathered through mosquito surveillance to plan control activities. If professionals discover that local mosquitoes are spreading viruses (like West Nile, dengue, Zika), they intensify activities identified in their mosquito control plans.

Remove Places Where Mosquitoes Lay Eggs

Mosquitoes lay eggs on or near water because larvae need water to survive. Professionals and the public can remove standing water to reduce mosquito larvae before they become adult flying mosquitoes.

• Professionals at local government agencies and mosquito control districts may collect and dispose of illegally dumped tires, clean up and maintain public spaces like parks and greenways, and clean up illegal dumps and roadside trash.
• You, your neighbors, and your community can remove standing water. Once a week, items that hold water like tires, buckets, planters, toys, pools, birdbaths, flower pot saucers, and trash containers should be emptied and scrubbed, turned over, covered, or thrown away.
• If needed, a community cleanup event can be held to remove large items like tires that collect water.

Control Larvae and Pupae

Once mosquito eggs hatch, they become larvae and then pupae. Both larvae and pupae live in standing water. Dumping or removing standing water in and around your home is one way to control larvae. For standing water that cannot be dumped or drained, a larvicide can be used to kill larvae. Larvicides are products used to kill mosquito larvae before they become biting adults.

The public and professionals can use Environmental Protection Agency (EPA)-registered larvicides.

• Professionals treat water-holding structures and containers in public places, like storm drains or urns in cemeteries. They may also treat standing water on private property as part of a neighborhood cleanup campaign.
• People can treat standing water that cannot be dumped or drained, like rain barrels and pool covers, with larvicides. Always follow label instructions. Learn more about controlling mosquitoes outside your home.
• Controlling larvae and pupae before they become adults can minimize the need for widespread use of insecticides that kill adult mosquitoes.

Kill Adult Mosquitoes

Adult mosquitoes can spread viruses (like West Nile, dengue, or others) that make you sick. When surveillance activities show that adult mosquito populations are increasing or that they are spreading viruses, professionals may decide to apply adulticides to kill adult mosquitoes. Adulticides help reduce the number of adult mosquitoes in an area and reduce the risk that people will get sick.

The public and professionals can use Environmental Protection Agency (EPA)-registered adulticides.

• If mosquitoes are spreading viruses, professionals spray adulticides by using backpack sprayers, trucks, or airplanes.
• People can buy adulticides and use them inside and outside their homes. Always follow product label instructions. Do not apply more product than directed or reapply more often than stated on the label.

Monitor Control Programs

To make sure that mosquito control activities are working, professionals monitor the effectiveness of their efforts to control both larvae and adult mosquitoes. For example, if an insecticide did not work as well as predicted, professionals may conduct additional studies on insecticide resistance or evaluate the equipment used to apply insecticides.

Larvicides target larvae in the breeding habitat before they can mature into adult mosquitoes and disperse. Larvicide treatment of breeding habitats helps reduce the adult mosquito population in nearby areas.

Liquid larvicide products are applied directly to water using backpack sprayers and truck or aircraft-mounted sprayers. Tablet, pellet, granular, and briquet formulations of larvicides are also applied by mosquito controllers to breeding areas.

While there are a number of registered active ingredients used in larvicides, below you will find information on more commonly used larvicides. EPA’s evaluation of mosquito control product includes assuring that it does not pose risks to vulnerable populations, including children and pregnant women when used according to label directions.

Bacterial Insecticides

Insects that are exposed to the Bacillus species have trouble digesting food they eat after the exposure. They then die of starvation.

• Bacillus thuringiensis israelensis
• Bacillus sphaericus

Insect Growth Inhibitors

• Insect growth inhibitors prevent the larvae from maturing into adult mosquitoes.
• Methoprene

Organophosphate Insecticide

The organophosphate insecticides affect the nervous system of insects.

• Temephos

This pesticide is applied to standing water, shallow ponds, lakes, woodland pools, tidal waters, marshes, swamps, catch basins, and other areas where mosquitoes can breed. It 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.

Other Materials

Oils and films disperse as a thin layer on the surface of the water and cause larvae and pupae to drown.

• Mineral Oils
• Monomolecular films

Communities seek to control adult mosquitoes to combat an outbreak of mosquito-borne disease or a very heavy, nuisance infestation of mosquitoes. The pesticides we register for this use are known as adulticides. They are applied either by aircraft or on the ground employing truck-mounted sprayers. State and local agencies commonly use the organophosphate insecticides malathion and naled and the synthetic pyrethroid insecticides prallethrin, etofenprox, pyrethrins, permethrin, resmethrin and sumithrin for adult mosquito control.

Mosquito adulticides are applied as ultra-low volume (ULV) sprays. ULV sprayers dispense very fine aerosol droplets that stay aloft and kill flying mosquitoes on contact. ULV applications involve small quantities of pesticide active ingredient in relation to the size of the area treated, typically less than 3 ounces per acre, which minimizes exposure and risks to people and the environment.

Adulticides can be used for public health mosquito control programs without posing risks of concern to the general population or to the environment when applied according to the pesticide label. Our evaluation of mosquito control products includes assuring that use of such products according to label directions does not pose risks to vulnerable populations, including children and pregnant women.

Organophosphates

• Malathion
• Naled

Synthetic Pyrethroids

• Permethrin
• Resmethrin
• Sumithrin
• Prallethrin
• Etofenprox

A larvicide is a type of insecticide used to control mosquitoes indoors and outdoors around your home. They work by killing mosquito larvae before they can grow into adults. Some formulations are activated when ingested by the mosquitoes, and some formulations work when they come into contact with the larvae. When used according to product label instructions, larvicides do not harm people, pets, or the environment.

During an outbreak, local government departments and mosquito control districts take the lead for large-scale mosquito control activities. One activity is to apply larvicides. Licensed mosquito control professionals apply Environmental Protection Agency (EPA)-registered larvicides using backpack sprayers, trucks, or airplanes depending on the size of the area being affected.

Homeowners can use mosquito dunks or bits that contain larvicide and can be applied by hand to small bodies of water in the yard and community.

Forms of Larvicides

Larvicides come in many forms.

• Liquids – Liquid larvicide products are applied directly to water using backpack sprayers and truck- or aircraft-mounted sprayers.
• Dunks, tablets, bits, pellets, granules, briquettes – These forms of larvicide are also applied to areas where mosquitoes lay eggs.

Types of Larvicides

EPA-registered larvicides have been studied for the effectiveness and safety when used according to label instructions. Public health officials and mosquito control professionals use three types of larvicides: bacterial larvicides, insect growth regulators, and oils and films.

Bacterial larvicides

The following types of larvicides are made from natural substances.

• The bacterium Bacillus thuringiensis subspecies israelensis (Bti) is found in the soil and is toxic to mosquito larvae, blackflies, and fungus gnats. Bti has been used for mosquito control for more than 30 years.
• The bacterium Saccharopolyspora spinosa is found in soil and is toxic to mosquitoes, ants, fruit flies, and other insects. Spinosad is a commercial larvicide derived from this bacterium.
• The bacterium Lysinibacillus sphaericus (also known as Bacillus sphaericus) is found in soil. It works well on some mosquito species but does not work on Aedes aegypti.

Insect growth regulators

These types of larvicides prevent mosquito larvae from completing their immature stage, so they do not make it to the adult stage. Methoprene and pyriproxyfen are examples of insect growth regulators.

Oils and films

Licensed mosquito control professions use mineral oils and films to kill mosquito larvae and pupae. Mineral oils and films, when applied to water, spread in a thin layer over the surface of the water. Mosquito larvae and pupae that breathe at the water’s surface drown. Using mineral oils and films are the only effective methods for killing pupae.

During a mosquito-borne disease outbreak, local government departments and mosquito control districts take the lead for large-scale mosquito control activities. One activity is to use a toxin produced by bacteria Bacillus thuringiensis subspecies israelensis (Bti). Bti kills mosquito larvae before they can complete their life cycle. Bti does not control biting adult mosquitoes.

Bti occurs naturally in soil and has been safely used in mosquito control for more than 30 years.

How Bti works

Bti kills mosquito, black fly, and fungus gnat larvae when they eat it.

• Killing larvae that hatch from eggs reduces mosquito populations.
• Reducing mosquito populations reduces the risk of people getting infected with West Nile, chikungunya, dengue, St. Louis encephalitis, or Zika viruses.

How Bti is used

• Bti comes in many forms, including dunks, tablets, briquettes, pellets, granules, or liquid.
• Bti can be added to standing water and to containers that cannot be emptied out, covered, or turned over every week, such as rain barrels, fountains, ornamental ponds, and pools that are not in use.
• Larvicides like Bti may be applied using trucks, airplanes, handheld sprayers, or by tossing by hand.

Bti is not harmful to people, honeybees, animals, and the environment when used as directed

• Bti is not toxic to people. It has not been shown to make people sick.
• Bti will not harm people, pets and other animals, aquatic life, or other insects, including honeybees.
• Bti is an insecticide registered by the Environmental Protection Agency (EPA).
  • EPA-registered insecticides have been studied for their effectiveness and safety when used according to label instructions.
  • Existing residential and area-wide uses, like aerial or truck spraying, have been evaluated and found to be safe.
  • Bti is EPA-registered for use in residential, commercial, and agricultural settings. Organic farming operations use Bti.
• When used as directed, Bti can be applied safely to standing water where mosquitoes lay eggs without causing harm to food crops or water supplies.
• Multiple Bti products are available for use. Always follow label instructions to ensure that the product is being used correctly.
• Bti is most effective when used as part of an integrated mosquito management plan for reducing the number of mosquitoes in an area.

1. What is Bti?

Bti is a biological or a naturally occurring bacterium found in soils. (Bti is short for Bacillus thuringiensis subspecies israelensis.) It contains spores that produce toxins that specifically target and only affect the larvae of the mosquito, blackfly and fungus gnat. EPA has registered five different strains of Bti found in 48 pesticide products that are approved for use in residential, commercial and agricultural settings primarily for control of mosquito larvae.

2. Does Bti pose health risks to humans?

No. Bti has no toxicity to people and is approved for use for pest control in organic farming operations. It has been well tested by many studies on acute toxicity and pathogenicity (ability to cause disease) for Bacillus thuringiensis including studies specifically on Bti. Based on these studies, EPA has concluded that Bti does not pose a risk to humans.

3. Where has Bti been used for mosquito control?

Bti is used across the United States for mosquito control. Bti is approved for aerial spraying, which has taken place in Massachusetts, Pennsylvania, Maryland and Michigan, among other states. Bti can be sprayed over waterbodies such as ponds, lakes, rivers and streams. Bti is used to kill developing mosquito larvae by being applied to standing water where those larvae are found. Bti can be used around homes in areas and containers where water can collect, such as flower pots, tires, and bird baths. Bti can also be used to treat larger bodies of water like ponds, lakes and irrigation ditches.

4. Will Bti work to control mosquito larvae?

Yes, Bti has been shown to be effective in reducing mosquito larval populations and could be effective in controlling mosquitos carrying Zika, dengue and chikungunya in places like Puerto Rico and other areas where these diseases have been identified.

5. Are insects becoming resistant to Bti?

No. There is no documented resistance to Bti as a larvicide. A recent study (Tetreau et al. 2013) confirmed previous research showing a lack of Bti resistance in mosquito populations that had been treated for decades with Bti.

6. Are there special precautions to be taken during Bti spraying?

No special precautions are needed for applying Bti. A number of Bti products are sold as “homeowner” products and are easy and safe to use. People do not need to leave areas being treated. However, as is the case with many microbial pesticides, some commercial use Bti products may require applicators to wear a dust/mist filtering mask.

7. How will I know if aerial spraying is going to take place?

Decisions about where and when to spray will be made by local officials. Listen for announcements in your community with the dates, times and locations of upcoming sprayings on social media sites, newspapers or radios.

8. Does Bti pose risk to crops or water supplies?

No. Bti has no toxicity to people, so it can be applied safely to mosquito habitat without a detrimental impact on food crops or water supplies. In fact, Bti can be used for pest control in organic farming operations. It is important to follow the label for any Bti product to ensure that the product is being used correctly. There are multiple Bti products and some are allowed to be used on certain drinking water (e.g., cisterns) while others are not intended for that use.

9. Is Bti harmful to wildlife including honey bees?

Studies indicate Bti has minimal toxicity to honey bees. Bti produces toxins that specifically affect the larvae of only mosquitoes, black flies and fungus gnats. These toxins do not affect other types of insects including honey bees.

10. Is there a medical test to show whether I've been exposed to Bti?

Since Bti has no toxicity to humans, a medical test to show exposure to the active ingredient has not been developed.

11. What other measures should be taken to control mosquitoes besides aerial spraying?

• Eliminate any standing water (even tiny amounts) to prevent infected mosquitoes from laying their eggs (breeding) in standing water.
• Use window and door screens to block infected mosquitoes from entering your home, workplace or children’s schools.
• Use EPA-registered insect repellents to prevent getting bitten. EPA-registered means the product works and is safe when you follow the directions.
• Dress in light-colored clothing, long pants, and long sleeves and try to avoid areas where mosquitoes are present.

Adulticides are insecticides used by mosquito control programs to kill adult mosquitoes.

There are many types of mosquitoes. Some are considered a nuisance. They bite people and animals but do not spread germs. Some mosquitoes can spread viruses like West Nile, dengue, or others.

During an outbreak of mosquito-borne disease, local government departments and mosquito control districts take the lead for large-scale mosquito control activities. Depending on the size of the affected area, licensed mosquito control professionals apply Environmental Protection Agency (EPA)-registered adulticides using trucks or airplanes.

Forms of Adulticides

Local government departments and mosquito control districts use liquid adulticides. One way liquid adulticides can be applied is as an ultra-low volume (ULV) spray. ULV sprayers turn the liquid into very small droplets that float in the air and kill flying mosquitoes on contact. Only small quantities of adulticides are needed to kill adult flying mosquitoes in an area.

Liquid adulticides can also be applied as residual sprays. Liquid is sprayed onto vegetation and buildings and allowed to dry. These treatments focus on sites where mosquitoes are likely to land and rest, exposing them to the insecticide. Residual spraying is a special application that is not often used by local government departments and mosquito control districts. They are more commonly applied by pest control professionals.

Types of Adulticides

EPA-registered adulticides have been studied for effectiveness and safety when used according to label instructions. The main types of adulticides available for use in the United States are organophosphates, natural pyrethrins, and synthetic pyrethroids.

Organophosphates

Organophosphates are chemical compounds used to control mosquitoes and plant pests. Organophosphates kill mosquitoes by preventing their nervous systems from working properly. Common organophosphates used by mosquito control professionals in the United States include malathion and naled.

Natural pyrethrins and synthetic pyrethroids

Natural pyrethrins are extracted from some chrysanthemum flowers. Mosquito control professionals use natural pyrethrins, often referred to as pyrethrum, to kill adult mosquitoes using ULV spraying.

Synthetic pyrethroids are similar to natural pyrethrins. Mosquito control professionals use different types of synthetic pyrethroids to kill adult mosquitoes using ULV spraying. Examples of synthetic pyrethroids include permethrin, sumithrin (d-phenothrin), and deltamethrin.

Both natural pyrethrins and synthetic pyrethroids kill mosquitoes by preventing their nervous systems from working properly.

Malathion is an organophosphate (OP) insecticide that has been registered for use in the United States since 1956. It is used:

• in the agricultural production of a wide variety of food and feed crops to control many types of insects such as aphids, leafhoppers, and Japanese beetles;
• in the USDA’s Cotton Boll Weevil Eradication Program and Fruit Fly (Medfly) Control Program;
• by home gardeners for outdoor residential uses including vegetable gardens, fruit trees, and a variety of ornamentals; and
• in public health pest control programs for controlling mosquito-borne illnesses.

How is malathion used in mosquito control?

Malathion is part of an integrated overall strategy to control mosquitoes. In particular, malathion is an adulticide, used to kill adult mosquitoes. Most malathion mosquito adulticide applications (about 90%) are made by ground application (fogging equipment mounted on trucks). However, in situations of heavy mosquito presence across large geographic areas, aerial application is an important method of application. Less than 1% of spraying for mosquitoes is malathion aerial spray.

Do malathion products used for mosquito control pose health risks to humans?

The draft human health risk assessment raises some concerns about the use of malathion applied by air. The use of malathion by ground application (fogging equipment mounted on trucks) does not raise concerns.

How has EPA addressed the risks from aerial spraying?

Given the current importance of aerial mosquito spraying as a tool to minimize transmission of the Zika virus and other mosquito-borne diseases, EPA has provided mosquito control professionals in local governments and mosquito control districts with advice on malathion aerial spraying to reduce risks.

While EPA would normally not make risk management recommendations based on a draft risk assessment, we have provided this information to mosquito control professionals in the interim so they can be confident in the safety of malathion aerial spraying. By making slight modifications to current labeled application directions, including adjusting the height of the application and the droplet size of the spray, exposure can be reduced while maintaining efficacy and effectiveness.

Are mosquito control applicators required to follow EPA’s use recommendations for application of aerial mosquitocide products?

No. Applicators are required to follow the pesticide label at a minimum. However, these recommendations for additional precautions are intended to reduce people’s exposure to malathion. At this time, applicators are not legally required to follow the recommendations for modifying aerial application of malathion mosquito adulticide products.

EPA will continue to work with industry and applicators to ensure safe use of malathion for mosquito control while continuing the registration review process for malathion. We will seek public comment throughout its evaluation of this use, as well as all other uses of malathion, and propose any necessary risk mitigation and associated label changes. We anticipate making a decision in 2017.

Are there any special precautions to be taken during malathion spraying?

EPA is confident that aerial application is safe if mosquito control applicators follow our recommended application modifications. To reduce exposures even further, parents and caretakers may choose to keep young children inside on the day that spraying is taking place.

Some people who are especially concerned may choose to take some of these steps to help reduce exposure even more. This may include people who are sensitive to chemicals and those with pre-existing respiratory problems.

Stay indoors with the windows closed.

If you are outdoors during spraying operations and you can see the spray, avoid contact with it. If you can’t avoid contact, rinse your skin and eyes with water.

Wash fruits and vegetables from your garden before storing, cooking or eating.

Cover outside items like furniture and grills while the spraying is occurring. Bring pets and items like pet food dishes and children’s toys indoors

If you think you have had a reaction to the mosquito spray, talk to your doctor or call the regional Poison Control Center at 1-800-222-1222.

What other measures should be taken to control mosquitoes besides aerial spraying?

Aerial spraying is the one method of pest control that can rapidly reduce the number of mosquitoes that can be carrying diseases (including Zika virus, West Nile Virus, and dengue) over a large area in a relatively short period of time; however, aerial spraying is not the only method EPA and CDC are recommending to control mosquito populations.

What is naled?

Naled is an insecticide that has been registered since 1959 for use in the United States. It is used primarily for controlling adult mosquitoes but is also used on food and feed crops and in greenhouses. For mosquito control, naled is most commonly applied aerially as an ultra-low volume (ULV) spray. ULV sprayers mounted on planes or helicopters dispense very fine aerosol droplets containing small quantities of insecticide mixed with water that drift through the air and kill mosquitoes on contact. The amount of spray that reaches the ground is small, and the concentration applied is very small (only about 1-2 tablespoons of naled is applied per acre treated).

Is EPA currently evaluating the safety of naled? What is the status of registration review for naled?

EPA is currently re-evaluating naled as part of its routine registration review process. EPA expects to receive additional data by the end of 2018. Following review of these new data, the agency will develop a draft risk assessment and issue it for public comment.

This review of naled is a standard re-evaluation required by law every 15 years by law for every registered pesticide. The periodic review of pesticide registrations, or registration review, is required by the Federal Insecticide, Fungicide, and Rodenticide Act, amended by the Food Quality Protection Act of 1996 and the Pesticide Registration Improvement Act. EPA periodically reviews existing registered pesticides to ensure they can be used safely, without unreasonable risks to human health and the environment. The registration review program is intended to make sure that, as the ability to assess risk evolves and as policies and practices change, all registered pesticides continue to meet the statutory standard of no unreasonable adverse effects.

Does naled’s use for mosquito control pose health risks to people?

When applied according to label instructions, EPA does not expect the use of naled for public health mosquito control to raise a human health concern. People are unlikely to breathe in amounts large enough or touch anything with enough insecticide on it to harm them. However, anyone who is concerned because of an existing health problem should talk to their doctor. Also, people who tend to be sensitive to chemicals in general, including household chemicals, could experience short-term effects, such as skin, eye, and nose irritation. Contact your local mosquito control program to get specific information on spraying in your area.

Has EPA estimated the risks of naled to children specifically?

EPA estimates exposure and risks to both children and adults routinely, including those associated with naled. Because of the small amount of naled released (about 1-2 tablespoons of naled is applied per acre treated), exposures are below an amount that might be expected to pose a health concern to children or adults.

Where is naled being used for mosquito control?

Naled is one of the most widely used pesticides in the United States for aerial mosquito control. In recent years, naled has been applied by aerial spraying to about 16 million acres per year within the mainland United States as part of routine mosquito control. Naled has been used in highly populated major metropolitan areas as well as agricultural and more rural areas.

Does naled work on mosquitos carrying Zika?

Naled has been successfully used for many years in the mainland United States and has been effective in the ongoing effort to control mosquitoes carrying Zika, dengue, chikungunya, and other possible diseases in areas where these viruses have been identified. Laboratory tests conducted by the Centers for Disease Control and Prevention (CDC) in February and March 2016 on 14 separate populations of Aedes aegypti mosquitoes from across Puerto Rico showed that they were highly susceptible to naled. These results, combined with the success of naled’s aerial use in Florida in 2016, indicate that aerial application of naled can be effective for Zika emergency situations as part of a comprehensive Integrated Pest Management (IPM) effort. View more information about insecticide resistance testing in Puerto Rico.

Are insects becoming resistant to naled?

Resistance in Aedes aegypti mosquitoes is not a concern at this time for naled. Many acres across the United States have been sprayed with naled each year, and resistance has not been detected in Aedes aegypti mosquitoes.

Are there special precautions to be taken during naled spraying?

People may prefer to stay inside and close windows and doors when spraying takes place, but it is not necessary. Those who are especially concerned about chemicals may choose to take some of these steps to help reduce exposure.

• Contact your local health department or mosquito control program to get specific information on spraying in your area.
• Stay indoors with the windows closed during spraying.
• If you are outdoors when spraying takes place and come in contact with the chemical, rinse your skin and eyes with water.
• Wash fruits and vegetables from your garden before storing, cooking, or eating.
• Cover outside items like furniture and grills before the spraying takes place. Bring pets and items like pet food dishes and children’s toys indoors. Rinse any uncovered items left outside before using.
• If you think you have had a reaction to the spraying of naled, talk to your doctor or call the regional Poison Control Center at 1-800-222-1222.

How will I know if aerial spraying is going to take place?

Decisions about where and when to spray are made by local mosquito control or public health officials. Listen for announcements in your community or look for posts on social media with the dates, times, and locations of upcoming sprayings. They are usually announced a day or two before they are scheduled to occur, and some districts post this information to their website.

Does naled’s use for mosquito control pose risks to water supplies or to people eating fruits or vegetables grown in home gardens?

Aerial ULV sprays dispense very fine aerosol droplets containing small quantities of active ingredient that stay aloft and kill mosquitoes. The amount of pesticide that reaches the ground is small and dissipates very quickly. In addition, naled is approved by EPA for application directly to food crops at higher rates than those used for mosquito control. Drinking water is also considered in the EPA evaluation of all uses as a potential source of exposure.

Is naled harmful to wildlife?

Risks to wildlife are minimal because naled is applied at low rates and does not persist in the environment. Because naled is an insecticide, invertebrates such as insects, water fleas, and spiders could be affected. Small wildlife present in the immediate treatment area could be exposed shortly after spraying occurs but long-term effects are not expected.

How can beekeepers reduce the risk of bee exposure to naled?

Spraying naled can kill bees that are outside of their hives at the time of spraying; therefore, spraying is recommended at dawn or dusk when bees are usually inside their hives. Although we do not anticipate that bees will have significant exposure to naled, beekeepers can reduce exposure even more by covering colonies when spraying takes place, or if possible, relocating colonies to an untreated site. Providing clean sources of food (supplemental sugar water and protein diets) and clean drinking water to honey bee colonies during application can further reduce exposure.

What other measures should be taken to control mosquitoes besides aerial spraying? What can I do to control mosquitoes or prevent mosquito bites?

• Help eliminate any standing water (even small amounts) to prevent mosquitoes from laying their eggs. If water cannot be eliminated, such as in ornamental water features, use larvicides (available at many retailers) or other control measures to minimize opportunities for breeding. For example, you might be able to add fish that eat larvae to a pond, or add a fountain or aerator to keep the water moving.
• Use window and door screens to keep mosquitoes from entering your home, workplace, or children’s schools.
• Use EPA-registered insect repellents to prevent getting bitten. Products that are EPA-registered have been confirmed to be safe and effective when you follow the directions.
• Dress in light-colored clothing, long pants, and long sleeves.

Pyrethroids are synthetic chemical insecticides that act in a similar manner to pyrethrins, which are derived from chrysanthemum flowers. Pyrethroids are widely used for controlling various insects. Permethrin, resmethrin, and d-phenothrin (Sumithrin®) are synthetic pyrethroids commonly used in mosquito control programs to kill adult mosquitoes.

• Permethrin has been registered by the EPA since 1979. It is currently registered and sold in a number of products such as residential indoor and outdoor insect foggers and sprays, treated clothing, flea products for dogs, termite treatments, agricultural and livestock products, and mosquito abatement products. It is also regulated by the Food and Drug Administration as a treatment of head lice and scabies. Permethrin is the most widely used mosquito adulticide in the U.S. and is used to treat 9 to 10 million acres annually (out of 32-39 million acres treated with a mosquito adulticide). Permethrin’s widespread use can be attributed to its low cost, high effectiveness, low incidence of pest resistance, and broad labeling.

• Resmethrin has been registered by the EPA since 1967. It is currently registered for use only in public health and vector control programs to control adult mosquitos, biting and non-biting midges and blackflies. Because of its toxicity to fish, resmethrin is a Restricted Use Pesticide that is available for use only by certified pesticide applicators or persons under their direct supervision. The resmethrin registrants voluntarily canceled all of the resmethrin products. After December 31, 2015, resmethrin registrants will no longer be able to sell and distribute resmethrin products. However, user will be able to continue using any product they have purchased.

• D-phenothrin (Sumithrin®) has been registered by the EPA since 1976 for use to control adult mosquitos and other nuisance insects indoors and outdoors in residential yards and public recreational areas. Use sites include in and around residential/domestic dwellings, commercial and industrial buildings, transportation vehicles, recreation areas, animal quarters, direct animal treatment (dogs). While there are no direct applications to food crops, d-phenothrin labels allow for applications to control mosquitoes over agricultural as well as non-agricultural areas.

How are Synthetic Pyrethroids Used in Adult Mosquito Control?

Most pyrethroid mosquito control products can be applied only by public health officials and trained personnel of mosquito control districts. Mosquito control professionals apply pyrethroids as an ultra low volume (ULV) spray. ULV sprayers dispense very fine aerosol droplets that stay aloft and kill adult mosquitoes on contact. Pyrethroids used in mosquito control are typically mixed with a synergist compound, such as piperonyl butoxide, which enhances the effectiveness of the active ingredient. The product is often diluted in water or oil and applied at rates less than 1/100th of a pound of active ingredient or less than 4 fluid ounces of mixed formulation per acre.

Do Pyrethroids Pose Risks to Human Health?

We have conducted human health risk assessments for all labeled uses of pyrethroids. Based on the results of these assessments and any required label changes, pyrethroids can be used for public health mosquito control programs without posing unreasonable risks to human health when applied according to the label. At high exposure levels, such as those resulting from accidents or spills, pyrethroids can affect the nervous system.

Do Pyrethroids Pose Risks to Wildlife or the Environment?

When applied according to label directions, pyrethroids used in mosquito control programs do not pose unreasonable risks to wildlife or the environment. Pyrethroids are low in toxicity to mammals and are practically nontoxic to birds. However, pyrethroids are toxic to fish and to bees. Products for uses other than mosquito control may be subject to buffer zones to protect water bodies. There also is language on product labels to reduce risks to pollinators. Always read the product label and follow its directions carefully when using any pesticide.

What is The Current Regulatory Status of Pyrethroids?

We are currently reevaluating all pyrethrins, pyrethroids and synergists through registration review. Registration review is our program for systematically reviewing all registered pesticides every 15 years to make sure that every pesticide can still perform its intended function without unreasonable adverse effects on human health or the environment.

As a result of the Food Quality Protection Act, EPA must consider the cumulative risks of pesticides that, like the pyrethroids and pyrethrins, share a common mechanism of toxicity. In November 2011, we completed a cumulative risk assessment for the pyrethroids/pyrethrins and identified no cumulative risks of concern.

Airplanes and helicopters can be used to treat very large areas with larvicides or adulticides to kill mosquito larvae or adult mosquitoes. This process is called aerial spraying. Aerial spraying is used to:

• Control and reduce the number of mosquitoes that can spread viruses. This can reduce your chances of getting sick.
• Control and reduce the number of nuisance mosquitoes that bother people but do not spread viruses.

Mosquito control districts or local government departments track both nuisance mosquitoes and mosquitoes that can spread viruses. When large numbers of nuisance or infected mosquitoes are found or when people in a large area are getting sick, airplanes and helicopters can treat very large areas with insecticides safely, quickly, and efficiently.

What does insecticide spraying do?

Airplanes and helicopters spray products that quickly kill either adult mosquitoes or mosquito larvae to reduce the number of mosquitoes in an area.

• Spraying larvicides kills mosquito larvae that hatch from eggs.
• Spraying adulticides quickly kills flying mosquitoes.
• Both larvicides and adulticides temporarily reduce the number of mosquitoes in an area, but do not permanently get rid of them.

How does aerial spraying work?

• Aerial spraying uses very low volumes of either adulticide or larvicide in areas where mosquitoes are present.
• Aerial spraying of larvicides can occur at any time. Aerial spraying of adulticides occurs when mosquitoes are most active and when pollinating insects are not active.
• Aerial spraying is more effective and faster than truck-mounted or handheld sprayers in treating large areas of land.

How will I know aerial spraying is going to take place?

The dates and times of aerial sprayings are typically announced in the local newspaper, on district websites and social media, through public service announcements, by telephone, or through door-to-door campaigns.

Do I need to leave the area during aerial spraying?

No. You do not need to leave an area during aerial spraying. When applied by a licensed vector control professional who follows label instructions, aerial spraying poses minimal risk to people, pets, animals, and the environment.

Because aerial spraying uses very low volumes of either adulticide or larvicide, you aren’t likely to breathe or touch anything that has enough insecticide on it to harm you. There is a possibility that spraying larvicides, like Bti, or adulticides can cause eye irritation if a person is outside when spraying takes place.

Is aerial spraying safe for people with asthma?

• When aerial spraying is done correctly, it does not cause asthma attacks.
• When applied according to label instructions, EPA-registered insecticides do not pose a risk to human health or the environment.
• If people prefer to stay inside when spraying takes place they can, but it is not necessary.

Trucks fitted with special spray equipment can be used to treat areas with larvicides or adulticides to kill mosquito larvae or adult mosquitoes. This process is called truck spraying. Truck spraying is used to:

• Control and reduce the number of mosquitoes that can spread viruses. This can reduce your chances of getting sick.
• Control and reduce the number of nuisance mosquitoes that bother people but do not spread viruses.
• Treat entire neighborhoods in a short period of time compared to some other methods.

Mosquito control districts or local government departments track both nuisance mosquitoes and mosquitoes that can spread viruses. Spraying larvicides and adulticides from a truck, according to label instructions, is one way to kill mosquito larvae or adult mosquitoes in an area. This is especially important when people in the community are getting sick from mosquito bites.

What are mosquito control trucks spraying?

Adulticiding: Mosquito control trucks spray very small amounts of insecticide into the air to kill flying mosquitoes. This spray is a fine mist that acts as a fogger in the area.

Larviciding: Mosquito control trucks apply larvicides directly to the water where mosquitoes have been detected. This type of application is also useful to kill mosquito larvae living in places that are difficult to reach.

When does spraying occur?

Adulticiding: Spraying occurs when mosquitoes are most active. Generally, local government agencies or mosquito control districts announce the dates and times of spraying in the local newspaper, on district websites and social media, through public service announcements, by telephone, or through door-to-door notices.

Larviciding: Applications are typically done during the day so that the driver can easily locate bodies of water where mosquito larvae have been detected.

How often do communities spray?

After spraying, local government departments or mosquito control districts will track mosquito populations and treat an area again as necessary to reduce the chances of people getting bitten by mosquitoes.

Is the spray harmful to people, pets, animals, or the environment?

When applied by a licensed vector control professional who follows label instructions, truck spraying poses minimal risk to people, pets, animals, and the environment. There is a possibility that spraying larvicides, like Bti, or adulticides can cause eye irritation if a person is outside when spraying takes place.

What should I do during or after spraying?

Spraying is safe when applied by a licensed vector control professional who follows label instructions. If you prefer to stay inside and close windows and doors, you can, but it is not necessary. The spray does not harm pets, but you may choose to bring them inside when spraying occurs. Contact your doctor or healthcare provider if you have any concerns following spraying.

Is truck spraying safe for people with asthma?

• When truck spraying is done correctly, it does not cause asthma attacks.
• When applied according to label instructions, EPA-registered insecticides do not pose a risk to human health or the environment.
• If people prefer to stay inside when spraying takes place they can, but it is not necessary.

Emerging methods in mosquito control have been used for many years to manage other types of insects. They are now being evaluated for their effectiveness in reducing numbers of mosquitoes. Emerging methods include

• Genetically modified mosquitoes
• Irradiated mosquitoes
• Mosquitoes with Wolbachia

Emerging methods for mosquito control can be used as part of an integrated mosquito management approach. Emerging methods may be a preferred way to reduce numbers of mosquitoes in areas where use of insecticides is not possible, not supported by a community, or where insecticide-resistance has reduced the effectiveness of insecticides.

Aedes aegypti mosquitoes spread viruses including dengue, Zika, and chikungunya. Aedes mosquitoes are common throughout many areas of the United States.

Ae. aegypti mosquitoes can be genetically modified and used to control other Ae. aegypti mosquitoes in a community. In the United States, the U.S. Environmental Protection Agency (EPA) has authorized use of OX5034 GM Ae. aegypti mosquitoes for release in counties in Florida and Texas. This EPA authorization allows local mosquito control programs to evaluate how effective GM mosquitoes are in reducing Ae. aegypti mosquitoes in areas where they have been released.

How GM mosquitoes are produced and used to control Ae. aegypti mosquitoes

• Did You Know
  • Only female mosquitoes bite. They need a blood meal to produce eggs.
  • Male mosquitoes do not bite. They feed on nectar from flowers.

  GM mosquitoes are mass-produced in a laboratory to carry two types of genes:

  • A self-limiting gene that prevents female mosquito offspring from surviving to adulthood.
  • A fluorescent marker gene that glows under a special red light. This allows researchers to identify GM mosquitoes in the wild.
• GM mosquitoes produced in the laboratory lay eggs. These eggs carry the self-limiting and fluorescent marker genes.
• GM mosquito eggs that carry the self-limiting gene are released into an area. Once they have hatched and develop through to the adult stage, they are available to mate with wild females. The genes are passed on to offspring.
• The female offspring die before they become adults. The expected result is that the number of Ae. aegypti mosquitoes in the area decreases.

Effectiveness of GM mosquitoes in reducing numbers of mosquitoes

• GM mosquitoes have been successfully used in parts of Brazil, the Cayman Islands, Panama, and India to control Ae. aegypti mosquitoes. Since 2019, over 1 billion mosquitoes have been released.
• When GM mosquitoes stop being released into an area, the Ae. aegypti mosquito population will slowly return to “normal levels.”
• GM mosquitoes will only work to reduce numbers of target mosquito species (e.g., Ae. aegypti), not other types of mosquitoes. Most communities have more than one type of mosquito.

GM mosquitoes do not pose a risk to people, animals, or the environment

The EPA evaluated the potential risk of releasing GM mosquitoes into communities and determined that there is no risk to people, animals, or the environment. For more information, see EPA’s Human Health and Ecological Risk Assessment.

GM mosquitoes for disease outbreak control

Release of GM mosquitoes is not intended to stop an ongoing disease outbreak. Instead, GM mosquitoes are meant to help prevent disease outbreaks. Releasing GM mosquitoes over several months can reduce the number of a specific mosquito species, such as Ae. aegypti. Reducing numbers of mosquitoes that can spread germs can help reduce the chance of an outbreak starting. We do know that the best way to prevent disease is to control mosquitoes before an outbreak happens.

GM mosquitoes and integrated mosquito management

Using GM mosquitoes may be more effective if used along with other mosquito control methods as part of an integrated mosquito management (IMM) approach, including:

• Educating the community about how they can control mosquitoes in and around their homes
• Conducting mosquito surveillance (tracking and monitoring the number of mosquitoes, and types of mosquitoes in an area)
• Removing standing water where mosquitoes lay eggs
• Using larvicides and insecticides to control mosquito larvae, pupae, and adult mosquitoes
• Monitoring how effective mosquito programs are at reducing numbers of mosquitoes.

EPA regulates the use of GM mosquitoes in the United States

• In the United States, the use of GM mosquitoes is regulated by the EPA. Prior to release of GM mosquitoes into an area, EPA must grant an Experimental Use Permit (EUP).
• Information on EPA’s EUP is available on Regulations.gov in Docket ID EPA-HQ-OPP-2019-0274.
• In addition to EPA authorization, release of GM mosquitoes requires approval from state and local authorities.

Classical Sterile Insect Technique (SIT) uses radiation to sterilize insect pests. This technique has been used since the 1950s to control insect pests, including fruit flies and the screwworm fly.

This non-patented SIT pest control method uses radiation to sterilize male mosquitoes. Male mosquitoes are bred and sterilized using the same radiation found in X-rays. Males are then regularly released to mate with wild females. The resulting eggs will not hatch.

In the United States, SIT has been used to control Aedes aegypti mosquitoes. Aedes aegypti mosquitoes spread viruses including dengue, Zika, and chikungunya. Aedes aegypti and Aedes albopictus species of mosquitoes are common throughout many areas of the United States. SIT will not reduce numbers of all types of mosquitoes, only the type that has been irradiated and released into the wild.

Irradiated mosquitoes are not genetically modified. They are also not regulated by the U.S. Environmental Protection Agency.

How scientists irradiate mosquitoes

• Large numbers of mosquitoes are raised in a lab.
• Male mosquito pupae are separated from female pupae.
• Males are irradiated, using ionizing radiation, to make them sterile.

How irradiated mosquitoes are used in mosquito control

• Sterile, irradiated male mosquitoes are regularly released into the wild to mate with wild female mosquitoes. Male mosquitoes do not bite.
• The resulting eggs do not hatch. Over time, the number of mosquitoes being targeted in an area decrease. For example, when the target mosquito is Ae. aegypti, only this type of mosquito will be affected.
• When irradiated mosquitoes stop being released into an area, their numbers will slowly return to “normal levels.”

Effectiveness of irradiated mosquitoes in reducing the number of mosquitoes

• Using special mosquito traps, local mosquito control experts monitor the number of adult mosquitoes being targeted to determine how well release of sterile irradiated males are working to decrease numbers of mosquitoes in the area.
• Irradiated Ae. aegypti mosquitoes are currently being evaluated as a control method in communities in Florida. This technique has been used to control other types of mosquitoes in Italy.[1]
• Irradiated mosquitoes will not control all types of mosquitoes. This type of mosquito control will only work to reduce numbers of the specific mosquito species being targeted, for example Ae. aegypti. Most communities have many types of mosquitoes.

Irradiated mosquitoes for controlling outbreaks

Release of irradiated mosquitoes is not intended to stop a disease outbreak.

• Releasing irradiated mosquitoes over several months reduces the number of mosquitoes and may prevent a disease outbreak in the area where mosquitoes were released.
• The best way to prevent disease outbreaks is to start controlling mosquitoes before an outbreak happens.

Irradiated mosquitoes compliment other types of mosquito control

Irradiated mosquitoes only target a specific type of mosquito. Most communities have many types of mosquitoes. Therefore, to control other types of mosquitoes the following techniques should continue being used:

• Educating the community about how they can control mosquitoes in and around their homes
• Conducting mosquito surveillance (tracking and monitoring the number of mosquitoes, types of mosquitoes in an area)
• Removing standing water where mosquitoes lay eggs
• Using insecticides to control mosquito larvae, pupae, and adult mosquitoes

Irradiated mosquitoes do not harm animals

Irradiated mosquitoes cannot make people or animals (for example, fish, birds, pets) sick.

Wolbachia (wohl-bach-ee-uh) is a common type of bacteria found in insects. Approximately 6 in 10 of all types of insects, including butterflies, bees, and beetles, around the world have Wolbachia. Wolbachia bacteria cannot make people or animals (for example, fish, birds, pets) sick.

In the United States, the use of mosquitoes with Wolbachia is regulated by the U.S. Environmental Protection Agency (EPA). Prior to release of mosquitoes with Wolbachia into an area, EPA must grant an Experimental Use Permit (EUP).

Aedes aegypti mosquitoes spread viruses including dengue, Zika, and chikungunya. Aedes species of mosquitoes are common throughout many areas of the United States. EPA has registered mosquitoes with Wolbachia to evaluate how effective they are in reducing numbers of Ae. aegypti mosquitoes, not other types of mosquitoes.

Mosquitoes with Wolbachia are not genetically modified.

How mosquitoes with Wolbachia are used to control Ae. aegypti mosquitoes

• Wolbachia bacteria are not found in Ae. aegypti mosquitoes.
• Scientists introduced Wolbachia into Ae. aegypti mosquito eggs.
• When male Ae. aegypti mosquitoes with Wolbachia mate with wild female mosquitoes that do not have Wolbachia, the eggs will not hatch.
• Male mosquitoes with Wolbachia are released regularly into an area by mosquito control professionals.
• Male mosquitoes with Wolbachia mate with wild female mosquitoes.
• Because the eggs don’t hatch, the number of Ae. aegypti mosquitoes decreases.

Did You Know

• Only female mosquitoes bite. They need a blood meal to produce eggs.
• Male mosquitoes do not bite. They feed on nectar from flowers.

How scientists “make” mosquitoes with Wolbachia

• First, Wolbachia bacteria are introduced into male and female Ae. aegypti mosquito eggs.
• From these eggs, new mosquitoes with Wolbachia are bred.
• Mosquitoes are mass-produced in a factory.
• Male and female mosquitoes with Wolbachia are sorted. Only males are kept.
• Females are not released but may be used for breeding in the laboratory.

Effectiveness of mosquitoes with Wolbachia in reducing numbers of mosquitoes

• Communities in Texas and California that have released mosquitoes with Wolbachia report a significant drop in the number of Ae. aegypti mosquitoes. Mosquitoes with Wolbachia have been successfully used in Singapore, Thailand, Mexico, and Australia. Puerto Rico is releasing mosquitoes with Wolbachia in Ponce.
• When mosquitoes with Wolbachia stop being released into an area, the Ae. aegypti mosquito population will slowly return to “normal levels.”
• Mosquitoes with Wolbachia will only work to reduce numbers of target mosquito species, not other types of mosquitoes. Most communities have many types of mosquitoes.

Mosquitoes with Wolbachia and integrated mosquito management

Using mosquitoes with Wolbachia may be more effective if used along with other mosquito control methods as part of an integrated mosquito management (IMM) approach, including:

• Educating the community about how they can control mosquitoes in and around their homes
• Conducting mosquito surveillance (tracking and monitoring the number of mosquitoes, types of mosquitoes in an area)
• Removing standing water where mosquitoes lay eggs
• Using larvicides and insecticides to control mosquito larvae, pupae, and adult mosquitoes
• Monitoring how effective mosquito programs are at reducing numbers of mosquitoes.

Release of mosquitoes with Wolbachia is not intended to stop an outbreak. However, releasing mosquitoes with Wolbachia over several months can reduce the number of a specific mosquito species, such as Ae. aegypti. We do know that the best way to control mosquitoes is to start before an outbreak happens.

Mosquitoes with Wolbachia and the environment

• Wolbachia are very common bacteria found in insects throughout the world.
• Approximately 6 in 10 of all insects around the world have Wolbachia.
• Once an insect dies, the Wolbachia will also die.
• The type of Wolbachia used in these mosquitoes are same types of Wolbachia found throughout the world in many types of insects. Every day, insects with Wolbachia are around us. They die and decompose in the environment.
• There is no data to suggest that Wolbachia bacteria cause any harm to people or animals or the environment.
• The EPA determined that mosquitoes with Wolbachia are not likely to harm the environment.

Mosquitoes with Wolbachia do not harm animals

Wolbachia bacteria cannot make people or animals (for example, fish, birds, pets) sick.

Permits are required for release of mosquitoes with Wolbachia in a community

• Release of mosquitoes with Wolbachia requires an EUP from the EPA.
• Release of mosquitoes with Wolbachia requires approval from the EPA and local authorities.

Why it’s important to kill mosquitoes during an outbreak

When infected adult mosquitoes are spreading a virus to people, acting quickly can stop further spread and prevent more people from getting sick. By using multiple mosquito control methods at the same time, people and communities can help stop an outbreak.

Local government departments and mosquito control districts take the lead for large-scale mosquito control activities to immediately kill infected adult mosquitoes. You can also take steps to help protect yourself, your family, and your community.

What You Need to Know

• Adult mosquitoes do not generally survive high winds during a hurricane.
• Immediately following a hurricane, flooding occurs. Mosquito eggs laid in the soil by floodwater mosquitoes during previous floods hatch. This results in very large populations of floodwater mosquitoes. Most of these mosquitoes are considered nuisance mosquitoes.
• In general, nuisance mosquitoes do not spread viruses that make people sick. The types of mosquitoes that can spread viruses may increase 2 weeks after a hurricane, especially in areas that did not flood but received more rainfall than usual. However, it can take several more weeks before mosquitoes could start spreading viruses to people.
• Increased rainfall may result in increased hatching of mosquito eggs. In areas with ongoing spread of chikungunya, dengue, West Nile, or Zika viruses, you may be at increased risk of getting infected with a virus. Take steps to protect yourself and your family from mosquito bites.
• Because people spend more time outside cleaning up after a hurricane or flood, they are more likely to be bitten by nuisance mosquitoes. Though these mosquitoes generally don’t spread viruses, they can be aggressive biters. Some people may react more strongly to bites. Learn about mosquito bites and take steps to reduce swelling and itching. See a healthcare provider if symptoms worsen.
• Large numbers of floodwater mosquitoes can slow recovery efforts by making work outdoors difficult. Use of insecticides by mosquito control professionals can reduce numbers of mosquitoes in affected areas.
• Flooding caused by hurricanes can be severe, and an increase in nuisance or floodwater mosquito populations is expected in the weeks after flooding. However, because nuisance or floodwater mosquitoes don’t spread viruses to people, an increase in the number of people getting sick from diseases spread by mosquitoes is not expected after flooding.
• State and local health officials can request technical assistance from CDC to monitor the flooding situation.

Protect Yourself and Your Family from Mosquito Bites

• Wear long-sleeved shirts and long pants.
• Use Environmental Protection Agency (EPA)-registered insect repellents with one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone.
• Treat clothing and gear with 0.5% permethrin.
• Learn more about mosquito bites and how to protect yourself.

Take Steps to Control Mosquitoes Inside and Outside Your Home

After a hurricane or flood, the health department or mosquito control district will often take steps to reduce the mosquito population. Once flooding recedes, residents can take steps to help control mosquitoes in and around their homes to prevent mosquito bites.

• Remove standing water where mosquitoes could lay eggs. Once a week, empty and scrub, turn over, cover, or throw out any items that hold water like tires, tarps, buckets, planters, toys, pools, birdbaths, flowerpot saucers, or trash containers.
• Keep mosquitoes outside.
  • Install or repair and use window and door screens.
  • Do not leave doors, including garage doors, propped open.
  • Use air conditioning when possible.