West Nile Virus Prevention

The Environmental Health Division conducts a comprehensive mosquito control program which includes public education, property inspections, trapping mosquitoes across the city for identification and testing, treating stagnant water areas, and when necessary, spraying the city to reduce the number of large populations of potentially disease transmitting mosquitoes.

Mosquito Control Information & Frequently Asked Questions

I know mosquitoes can cause West Nile, but what other diseases can they cause?

Mosquito-borne diseases are diseases caused by viruses and parasites that are transmitted to people and animals by mosquitoes.

Viral Diseases - In addition to West Nile, other viral diseases transmitted by mosquitoes are Chikungunya, Zika, Dengue, yellow fever, St. Louis, Japanese, La Crosse, as well as Eastern & Western Encephalitis

Parasitic Diseases - Malaria, Filariasis, and canine heartworm

Why are we seeing diseases like West Nile and Chikungunya here in the United States that never used to be here before?

With the ease and accessibility today of worldwide travel, the risk of people being exposed to diseases that haven't been endemic in the U.S. before is increased, as well as the possibility of seeing a resurgence of endemic diseases such as malaria, dengue, and yellow fever thought to have been eliminated.

If a person becomes infected with an endemic mosquito-borne illness outside the U.S. and is then exposed to and bitten by a mosquito species in the U.S. that has the capability of transmitting that illness then the disease can become prevalent where it didn't exist or in an area where it was thought to have been eradicated.

Another factor, is the accidental introduction of an non-native invasive mosquito species to the U.S. that is capable of becoming infected with a particular virus or parasite and then having the ability to transmit it. One example is the Ades albopictus, also known as the Asian tiger mosquito. This is a small black and white daytime biting mosquito which prefers human hosts and is capable of transmitting dengue fever, yellow fever, and Chikungunya. The Ades albopictus was native to Southeast Asia, but was found in imported tires at the port of Houston and San Diego in 1985. Although a tropical species, it has adapted to cooler climates and is now found throughout the U.S.

With new and emerging mosquito-borne diseases now becoming more and more prevalent such as the Zika virus it imperative to control mosquitoes by eliminating breeding sites and take proper precautions against becoming bitten.

Why is it important to eliminate, change out, or drain all standing water?

Mosquitoes spend the first 3 life stages eggs, larvae, and pupae in water. It only takes 7 days to complete this life cycle of egg to adult mosquito. Since the immature forms are restricted to that water source, removing or eliminating it is the easiest way of ensuring they do not become adult mosquitoes.
Do mosquitoes lay eggs in creeks, rivers, or brooks?

Mosquitoes only lay eggs in non-moving, still and usually stagnant bodies of water that contain organic debris which serves as a food source for the larva, where they will also have protection from predators and direct sunlight. Moving bodies of water such as a creek or brook would not only kill the larva, which are fragile, but would not allow for the metamorphosis of the pupa into the adult mosquito. As the pupae turn into mosquitoes there can be no water or wind movement or the mosquito will fall into the water and drown. In addition to the water movement of creeks, brooks, and rivers, they usually contain predacious aquatic life such as fish, water bugs, and dragon fly nymphs which will feed on all mosquito life forms.

I see standing water on the streets and in parking lots sometimes especially after it rains. Can this water contain mosquito larva?

If the water is out in the open under direct sunlight and in the path of vehicular traffic then it will not contain mosquito larva. However, if the standing water is under a shaded area, protected from vehicles, and has organic debris in it then it could support mosquito breeding. If you see any areas of standing water notify the Environmental Health Division at 972.919.2539.

How can you tell the difference between male and female mosquitoes?

Female mosquitoes have sparse plain antennae, while male mosquitoes have a bushy feathery antennae that contain auditory receptors that can detect the characteristic whine by the female.

Male mosquito on the left / Female mosquito on the right

male and female mosquitoes.jpeg
Do both male and female mosquitoes take a blood meal?

Both male and female mosquitoes feed primarily on plant nectar, but only the female mosquito also takes a blood meal as she needs protein for the developing eggs while the male fertilizes the eggs. This cycle of obtaining a blood meal and laying eggs is repeated by the female mosquito until she dies.

Do all female mosquitoes take a blood meal?

Most female mosquitoes do take a blood meal for the protein necessary to develop eggs, however, there is one mosquito genus Toxorhynchites, with several species in this genus that does not need to take a blood meal. The mosquitoes in this genus are big and also known as the elephant mosquito because of their large size. This is a very beneficial mosquito because the larva which are also big are predatory and prey on other harmful mosquito larva. Since the larva feed on a protein fat enriched diet of aquatic life there is no need for the adult female mosquito to take a blood meal for egg production. Both male and female adult Toxorhynchites feed exclusively on carbohydrate enriched plant nectar.

Female adult Toxorhynchites genus

I am always getting bitten by mosquitoes, what attracts them to me?

Female mosquitoes can locate their preferred hosts through a number of ways. The most universal recognized attractant is carbon dioxide, a by-product given off during respiration, but research has shown that the female mosquito has scent receptors in her antennae which she uses to key in on certain odors present in sweat, fatty acids, and lactic acid given off by the skin. Visual stimulus may also be used such as being attracted to certain colors.

How long do female mosquitoes live?

From 2 to 4 weeks is most common, but some can over-winter in garages, attics or culverts and live up to 6 months.

How far can mosquitoes fly?

It varies with the species but for most mosquitoes their range is 1 to 3 miles away from a breeding site. Some such as the Ades albopictus stay very close to a breeding site about 300 feet, while saltmarsh mosquitoes can fly up to 100 miles away from a breeding site.

What are mosquito dunks and how do they kill mosquitoes?

Mosquito dunks are a biological mosquito control product that kills the mosquito larva as they feed on it because it disrupts their digestive system. The dunks are a crystal protein by-product of a bacteria species called Bacillus thuringiensis. The dunks float on top of the water, slowly releasing the long-term larvacide which gradually settles in the water where it is eaten by the larva. Mosquito dunks affect only mosquitoes and are safe for use in horse troughs, livestock ponds, fish ponds, aquatic gardens, flood control basins, bird baths and other standing bodies of water that may become stagnant and are frequented by birds, fish, wildlife, and pets. The dunks last about 30 days and then a fresh dunk should be added in its place. Alternate wetting and drying of the dunks within that 30 day period will not reduce their effectiveness.
Mosquito dunks.jpg

Where can I find mosquito dunks?

You can find the dunks at any home or garden store. The City also has made mosquito dunks available for residents and during the peak mosquito breeding season in the spring and summer you can pick them up free of charge at the main lobby at City Hall and at the Senior Center on Dennis Lane.

How do I use mosquito dunks?

Each individual dunk will last up to 30 days and cover 100 square feet of water surface. For smaller areas such as bird baths, and water filled vases dunks can be broken up into smaller pieces and suggested amounts are as follows:

1 to 5 square feet 1/4 Dunk
5 to 25 square feet 1/2 Dunk
25 to 100 square feet 1 Dunk

Note: For best results and optimum mosquito control, use the product in standing water sources before any aquatic mosquito life forms are observed. Pupae are a non-feeding stage and will not be affected by the product and can complete the transformation into adult mosquitoes once they are present.

Do ultra sonic devices, backyard misting system, bug zappers and mosquito traps control a majority of mosquitoes?

Ultra sonic devices - Research has shown that there is no scientific data that proves these devices are effective methods of mosquito control.

Backyard misting systems
- These systems use a scheduled chemical release into the environment which will affect not only mosquitoes but many beneficial and non-pest species of insects such as dragon flies, lady bugs, butterflies, bees, and spiders as well. Continued use could also lead to chemical resistance in mosquitoes.

Bug zappers
- Bug zappers can kill some mosquitoes, but research was done that showed the majority of insects killed were non-pest and beneficial insects.

Mosquito magnets - These pieces of equipment are designed with an attractant that lures female mosquitoes seeking a blood meal into a capture or killing device. They can trap and kill mosquitoes, but some important points to be considered are that these devices will need maintenance to work properly and may attract larger than normal numbers of mosquitoes into your yard. Also, since mosquitoes use a complex interconnected set of behaviors to locate a blood meal, a mosquito magnet may attract some but not all blood seeking mosquitoes into the trap.

It is important not to rely solely on one method or device for mosquito control. The most effective way of controlling mosquitoes is a organized community/neighborhood based control program through effective mosquito breeding source reduction methods, reporting standing water to the Environmental Health Division at 972.919.2539, maintaining property by keeping grass cut short, shrubs and bushes trimmed, wearing loose light colored long-sleeved shirts and pants when outdoors, and using personal protection such as an approved mosquito repellent.
Don't bats and birds especially Purple Martins eat lots of mosquitoes?

Purple Martin

Purple martin.jpg
Insectivorous bats and birds eat large numbers of insects and that can include some mosquitoes, but due to the large size and diet preference of these insect predators, mosquitoes make up only a tiny insignificant percentage of their diets. Bats tend to feed more on larger insects such as moths, beetles and caddis flies, while purple martins feed on beetles, wasps, and dragon flies. There are however, insect predators such as spiders and dragon flies which will eat larger numbers of mosquitoes.
I see lots of swarming bugs around my house that look like giant mosquitoes in the spring, do they bite?

Crane Fly

crane fly.jpg
Those insects are the adult non-feeding form of the crane fly whose only purpose is to mate and lay eggs. They may look similar to mosquitoes, but they are not giant mosquitoes, they are completely harmless and don't bite. They may be annoying in large numbers when they are swarming and enter houses because they are attracted to light.

With the recent rains I saw clouds of mosquitoes in my yard, why so many all at once?

What you were seeing were floodwater mosquitoes. These mosquitoes will lay their eggs which can stay viable for months and in some cases years in the soil till unprecedented rainfall accumulation and flooding occurs. These eggs are then triggered to hatch out all at one time thereby creating clouds or swarms of mosquitoes. Most of these mosquitoes are nuisance mosquitoes only which means they do not transmit disease, but a few species in the Ades genus fall into this category and are known disease transmitters.

What can I do to prevent being bitten by mosquitoes?

Drain or remove all standing water from your yard or property. This includes:
  • Changing water at least weekly in bird baths, and pet water bowls
  • Dumping excess water from flower pot saucers
  • Removing any containers including bottles and aluminum cans capable of holding water from your yard
  • Cleaning open gutter systems and downspouts where debris, leaves, and water can collect
  • Storing tires under a covered structure or punch holes in them to avoid collecting water
  • Treating any French drains or drainage trenches on your property with a monthly mosquito dunk to prevent breeding
  • Maintaining your swimming pool with proper chlorination and filtration
  • Draining water from wading pools, wheelbarrows, carts, children's toys and tarpaulins and storing them under a covered structure
  • Repairing all outdoor leaky faucets, A/C units, and sprinkler systems to prevent pooled up water
  • Stocking ornamental ponds with mosquito-eating fish, mosquito dunks, or aerating the water with a pump and filter mechanism
  • Cutting back overgrown bushes and shrubbery, and keeping the grass cut short to avoid providing shelter for adult mosquitoes
  • Ensuring trash and recycling receptacles have tight fitting lids to avoid water accumulation when it rains
  • Filling in low spots or ruts on your property with dirt or sand
  • Draining or using mosquito dunks on flat roofs where water can collect especially if under shade
  • Filling in any tree holes with sand and/or mortar
  • Cleaning out and covering utility vaults
  • Overturn or cover canoes and recreational boats to prevent water accumulation inside when it rains
  • Notifying the Environmental Health Division if you see standing water or stagnant swimming pools/spas so they can be checked and treated by calling 972.919.2539.

Common standing water sites around homes and yards that can breed mosquitoes if left unchecked

Dress - Weather permitting, wear loose light colored clothing such as long sleeves, pants and socks when outdoors

Defend Choose a mosquito repellent that has been registered by the Environmental Protection Agency. Registered products have been reviewed, approved, and pose minimal risk for human safety when used according to label directions. Four repellents that are approved are:

  • Use insect repellents that contain DEET (N-Diethyl-meta-tolumide) sparingly on exposed skin and clothing during daytime and nighttime activities when you will be outside during peak mosquito season months.

• Picaridin (KBR 3023)

• Oil of lemon eucalyptus (p-methane 3,8- diol, or PMD)

• IR3535

Does spraying kill all the mosquitoes?

Spraying or adulticiding will kill only active adult mosquitoes that come in contact with the chemical. Night time spraying specifically targets mosquitoes in the Culex genus, which can transmit West Nile, are nocturnal, and feed primarily on tree roosting birds. It is important to remember that although the majority of mosquitoes will be killed by the chemical there is a small percentage of mosquitoes that can survive.

Spraying in general does not affect the Ades genus, which are primarily active in the daytime preferring to draw a blood meal from people. These mosquitoes will rest during evening hours close to the ground in low lying shrubs and bushes making it hard for the spray to penetrate and kill them since the atomized spray remain suspended in the air.

Spraying does provide temporary relief from adult biting mosquitoes, but it does not leave a residual that will continue killing mosquitoes, and if there is a near-by breeding source it will not affect future emerging mosquitoes from that site, which is why mosquito control is the most effective when all potential breeding sources are eliminated.

What is in the spray and how does it kill the mosquitoes?

The chemical that is used to kill mosquitoes is permethrin, which is a safe EPA approved insecticide in the pyrethroid family. Pyrethroids are synthetically manufactured chemicals that are made to act like the natural insecticide extracts found in the chrysanthemum flower. This chemical is atomized into micro-fine droplets which stay suspended in the air so they can come in contact with active adult mosquitoes and kill them by interfering with their nervous system. The tiny droplets rapidly breakdown leaving little to no residual at ground level. For the spraying to be effective weather conditions must be ideal with no wind gusting or blowing over 10 miles an hour, air temperatures must be above 50 degrees F., and no rain or the chemical will not stay suspended in the air and will be ineffective.

How does the City determine the need for spraying?

Night time spraying specifically focuses on the mosquito species that can potentially transmit West Nile and the need for spraying is prioritized through scientific surveillance methods such as high mosquito trap counts, positive human cases, and mosquito pools that test positive for disease. The need to spray is less driven by mosquito complaints and mosquito spraying requests, although spraying can be utilized to knock down high populations of nuisance mosquitoes. It is important to remember though, that over-spraying based solely on complaints can over-expose mosquitoes to the pesticide currently in use and may result in the local mosquito population becoming pesticide resistant making spraying ineffective.

How do I find out what areas in the City will be sprayed?

Information will be added to the website and you can call a designated spraying information number that will be posted during the peak mosquito breeding season.

What precautions should I take at home when my area is sprayed?

Bring in pet dishes or cover them.
Cover aquatic ponds, fish ponds, and birdbaths.
Bring your pets inside for the night.
Do not go outside during spray times.
If you have health problems, such as asthma, take special precautions as directed by your doctor, if necessary.

What if I don't want my property sprayed?

The City will try to do everything possible to accommodate individuals who, for varying reasons prefer their property not be sprayed. For those who do not wish to have their property sprayed you can email or call the Sustainability & Public Health Department at 972.919.2539 or 972.919.2597

The following links are good resources on mosquitoes and mosquito control:

American Mosquito Control

Mosquito Safari

CDC FAQs Mosquito Control

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