Description:

Mosquitoes are insects in the order Diptera (flies), which have only a single pair of wings. The wings of mosquitoes are narrow and have a fringe of scales on the margins and veins. Mosquitoes have three pairs of long, slender legs and two long antennae. The mouthparts of mosquitoes form an elongate beak called a proboscis. Female mosquitoes use this proboscis to intake a blood meal.

Damage:

Eastern Equine Encephalitis (EEE) is caused by a virus that is transmitted by mosquitoes. It is a disease that in most years remains in bird populations and is non-fatal to native birds, although it may be fatal to horses and other animals. EEE is established in most eastern seaboard states and is usually associated with hardwood swamps. This habitat is home to numerous species of mosquitoes which feed only on birds. These species of mosquitoes maintain the virus in the wild by transmitting the virus from bird to bird. During years when mosquito populations are excessive, the numbers of infected birds and infected mosquitoes rise. This elevates the probability that other mosquito species will acquire the EEE virus. Although EEE can be fatal to humans, it is extremely rare. On average, 15 human cases are documented nationwide per year. In other countries, mosquitoes are responsible for transmitting diseases such as malaria, yellow fever, dengue fever and filarial worms. An average of 2 million people die each year from malaria, while another 400 million are infected. Mosquitoes are also responsible for transmitting canine heartworm to dogs.

Life Cycle:

Mosquitoes go through several stages of development. The egg is the first stage, laid by the adult female. Depending on the species of mosquito, eggs are either laid singly on the water, on a substrate above the water or in a large batch on the water called egg rafts. Eggs laid on solid substrates, such as mud, hatch when they are flooded with water. This is typical of saltmarsh mosquitoes (Aedes sollicitans) and the temporary pool mosquito (Aedes vexans), where these eggs can remain viable for several years until the next flooding.

The second stage of development is the larva. Unlike the egg stage, larvae must always live in the water to survive. Larvae swim at the water surface and intake air through a snorkel-like device called a siphon. Larvae will dive below the surface when disturbed, but will return to the surface in order to breath. The characteristic s-shaped motion of swimming larvae gives them their common name "wiggler." Larvae are filter feeders, eating organic matter in the water which they collect with their bristle-like mouthparts.

The third stage of development is the pupa. Pupae are comma-shaped and stay at the water surface. If disturbed, they tumble downward to escape, giving them the common name "tumblers." Pupae do not feed, and this stage lasts only two or three days. Both larvae and pupae are subject to heavy predation. Typically, the 100-400 eggs laid by a female only result in a few adults developing successfully.

In as little as seven to ten days, some mosquitoes can develop from egg to adult. Adult behaviors vary depending upon the species. Some breed and live near water, others may fly considerable distances from a breeding site to seek a blood meal. Some species are only active at dusk, while others seek blood meals during daylight hours. Some species prefer to bite birds, some prefer mammals, and others seek reptiles or amphibians. Only the females seek blood, which they need as a protein source to produce eggs. Males, as well as females, feed on flower nectar or plant juices for energy for flight.

Breeding Sites:

Mosquitoes breed in areas where there is standing water or temporary pools. Mosquitoes commonly breed in saltmarshes, swamps and areas flooded by snow melts and spring rains. However, a small collection of water around a home can breed thousands of mosquitoes. Some common sites are bird baths, roof gutters, catch basins, rain barrels, swimming pools, wading pools, cesspools, septic tanks, tires, paint buckets, tin cans, yard debris, tree holes and anywhere that holds a small collection of water.

Control:

There are three types of control strategies targeting mosquitoes. The best of these methods is source reduction. Source reduction is the elimination or manipulation of aquatic habitats known to produce mosquitoes. An example of this is eliminating small collections of water around the home. The second most common method is mosquito larviciding. This refers to applying environmentally-benign products to kill larvae (the aquatic stage). An example of this is the bacteria B.t.i, "mosquito dunks," which can be purchased in stores. Mosquito dunks are not harmful to fish, animals or humans. The third, and least preferred method of control, is mosquito adulticiding. This requires the use of broad-spectrum insecticides, which can be harmful to fish, birds and other animals.

Elimination of Breeding Sites:

One of the easiest and surest ways to control mosquitoes around the home is to eliminate standing-water breeding sites. Containers such as wading pools or bird baths should be flushed weekly with clean water. Filtering systems for swimming pools should keep a swimming pool free from immature mosquitoes. Seal openings to standing-water sources such as septic tanks or rainwater barrels. Search for and eliminate standing-water sources. Old tires or discarded containers of most any sort can collect water and attract the female mosquito for her egg laying. One tire holds enough water to breed thousands of mosquitoes. Drainage ditches, pools with lots of vegetation and sites such as roof gutters and storm drains, which occasionally hold water, can breed mosquitoes. Areas that contain fish and other natural enemies of mosquito larvae, like amphibians and insects, are not effective breeding sites because these animals eat the larvae. If waterways are clogged with vegetation, mosquitoes can survive. Check natural sites like holes in trees or stumps where water can accumulate, and fill or prevent entry by adult mosquitoes.

Bite Prevention:

Some species of mosquitoes are capable of flying long distances. An example of this is the saltmarsh mosquito Aedes sollicitans, which can be found miles away from a possible breeding site. Large populations of eggs of this species of mosquito are hatched during monthly high tides, which results in large numbers emerging all at once and searching for blood meals. If you have property close to these areas, you may not be able to effectively manage the source of the problem yourself. It may be necessary to contact your local town hall or mosquito control office to devise a community-based control strategy. However, it is always important to follow proper preventive measures to reduce exposure to biting mosquitoes.

• Maintain screens on doors and windows

• Wear long sleeves and long pants

• Avoid heavily shaded areas

• Use insect repellants containing DEET

• Limit outdoor evening activities

Natural Enemies:

Although mosquitoes have many natural enemies, they are not an effective control measure. Although birds and bats feed on mosquitoes, making nest or roost areas for these predators does not provide adequate mosquito reduction. The mosquito fish, Gambusia, and guppies are also known to eat mosquito larva, and can be purchased for stocking ponds or pools. However, these fish cannot survive in temporary pools or standing water, where the larvae are most likely to breed.

Mechanical Control:

Several types of traps which claim to provide mosquito control are available. However, most of these are not effective in controlling mosquito populations. Ultraviolet lights and bug zappers are widely advertised--however they attract very few mosquitoes and should not be used for mosquito reduction. Other mosquito traps are also becoming available and may reduce mosquito populations if used correctly. However, some of these traps may be very expensive.

Indoor Control:

The use of toxic insecticides indoors is not a safe method of mosquito control. It is best to make sure all screens on windows and doors are maintained to keep mosquitoes from entering.

Repellents:

A great deal of research has gone into finding and developing effective insect repellents. Some compounds that were once recommended have been removed from the market because of possible side effects upon humans. Repellents containing DEET (N-diethyl-meta-toluamide) are the most effective and commonly used repellents. DEET is very effective for most people. Research has shown that products containing DEET in concentrations higher than 30% are unnecessary and increase the possibility of adverse skin reactions. Some people show allergic sensitivity to DEET, particularly in higher concentrations. Before using a repellent, check your personal sensitivity. Be very careful not to use DEET repellents around the eyes, nose or mouth. Repellents containing DEET should not be used on very small children. Repellents containing natural products such as clove oil, citronella, peppermint or combinations of these and other odors are also available, and may provide some temporary repellency. Other products such as citronella candles and mosquito coils may also provide additional protection.

By Kristen Bartlett, 1999