Contributors: C.S. Apperson, Extension Entomology Specialist; J.R. Baker, Extension Entomology Specialist; L. Garcia, Entomologist, Plant Protection Section, NC Department of Agriculture; M.G. Waldvogel, Extension Entomology Specialist.
Order: Diptera
Family: Culicidae
Scientific Name: Aedes sp., Culex sp.,
Anopheles sp., Psorophora sp., Cocquilletidia sp.
Mosquitoes are important pests because their biting activity often interferes with outdoor activities and may transmit disease organisms to people and domestic animals. Most mosquitoes are active during twilight hours and at night. However, around the home, the mosquitoes that breed in discarded containers are active during the day.
Although mosquitoes are primarily annoyances in North Carolina, some species are vectors of disease. Of the human diseases known to be caused by disease organisms transmitted by mosquitoes, malaria, yellow fever, and several kinds of encephalitis have been reported in North Carolina. Small numbers of mosquito-spread encephalitis cases in humans and animals occur sporadically in North Carolina. Malaria and yellow fever have been eliminated. Heartworm disease of dog is also transmitted by mosquitoes. Only seven or eight of the over 50 known species of mosquitoes in North Carolina pose a health hazard.
Description
Adult mosquitoes are long-legged insects with one pair of wings 3 to 4 mm long. The wings legs, back (thorax) and abdomen are variously colored. Mosquitoes can be distinguished from all other two-winged insects by the long beak (proboscis), which is used in feeding, and the scales on their wings. Male mosquitoes have bushy antennae and do not bite.
The small, white, cylindrical eggs taper at one or both ends and darken with age. Eggs of Anopheles and Aedes mosquitoes are laid singly while those of Culex mosquitoes are deposited in raft-like masses. Young larvae are difficult to see because they are light colored or nearly transparent and only about 3 mm long. Mature larvae, on the other hand, are usually greenish brown or brown and up to 10 mm long. The head is distinct and usually dark on all four instars. Upon close inspection, most of these elongate larvae are quite hairy.
Smaller than mature larvae, pupae are comma-shaped, with a slender, curved abdomen. They move through the water in a tumbling motion; hence, they are commonly called 'tumblers".
Biology
All mosquitoes have one common requirement they need water to complete their life cycle. Some mosquitoes, such as Aedes and Psorophora sp., lay individual eggs on the sides of treeholes or discarded containers, or in depressions in the ground that will hold water. The eggs can lay dormant for several years. Some eggs will hatch when they are flooded by rainfall. Several flooding and drying cycles are usually required for all of the eggs laid by one female to hatch.
Other mosquitoes, such as Anopheles and Culex sp., lay eggs directly on the surface of water. These eggs hatch in 24 to 48 hours, releasing larvae that are commonly called "wrigglers" because they wriggle up and down from the surface of the water. Larvae generally feed on microorganisms and organic material in the water, but some mosquitoes prey on the larvae of other mosquito species and are regarded as beneficial. In about 7 to 10 days after hatching, larvae change to the pupal or "tumbler" stage. Several days after emerging from the water, the female mosquito begins to seek an animal for a blood meal before laying eggs. Most female mosquitoes prefer warm-blooded animals, including people, birds, and livestock, although some species prefer to feed on amphibians and reptiles.
Male mosquitoes mate with females one to two days after the females emerge. Males do not bite, but they do feed on plant juices.
Mosquito Species Identification
Since the habitat requirements of mosquito species are known, proper identification of the mosquitoes can be used to obtain information on where to search for and identify likely breeding sites.
Collect some mosquito specimens for identification. Adult mosquitoes attempting to land are easily collected by placing a small jar (such as a baby food jar) over them. If possible, collect several dozen specimens. Place the jar in a freezer overnight. Spread the mosquitoes between sheets of facial or toilet tissue to protect them from damage, then place them back in the jar.
Take the specimens to the county Cooperative Extension Service Center where arrangements can be made to identify the specimens and suggest control strategies.
Mosquito Breeding Sites
Since mosquitoes need water to complete their life cycle, the source of a mosquito problem can be just about anywhere that water can collect. Mosquito populations can be reduced by eliminating breeding sites: remove discarded containers, replace the water in bird baths regularly, and store boats, canoes and other objects so that they do not collect rainwater.
Farm ponds and lakes usually do not breed mosquitoes if they contain fish and are free of weeds, algae or floating debris that serve as harborage for mosquito larvae. Municipal and farm animal waste lagoons may also become breeding sites. Permanent natural bodies of water such as swamps usually contain a large array of predatory insects and fish that keep mosquitoes from reaching nuisance levels.
Road building and maintenance often impedes the drainage of runoff from rainfall, creating mosquito breeding sites. Clogged drainage ditches along roads can become productive mosquito breeding sites. Logging and construction activities often leave tire ruts in the soil. These depressions are ideal breeding sites for "floodwater" mosquito species.
Control
Mosquito control involves monitoring larval and adult populations, public education, source reduction and the use of chemicals. Because some mosquito species can fly far from breeding sites, efforts by individuals to control mosquitos on a single property rarely succeed. In many areas of North Carolina, an informed and participating community can often effectively reduce the number of mosquito breeding sites and virtually eliminate a mosquito problem with little or no chemical usage. However, in many coastal areas, an integrated program utilizing all the principles of control is desirable. Mosquito abatement organizations have been formed to organize community -wide "clean-up" efforts to control pest mosquitoes. County health departments have additional information about area-wide control programs.
Repellents
Some personal protection from mosquitoes can be achieved through the use of insect repellents. Many of these products contain DEET (N,N-diethyl-m-toluamide). Select the desired formulation (e.g., lotion, aerosol spray or cream) containing the highest percent of active ingredient, as stated on the product label, and apply it to exposed skin. Repeated use of repellents over a short period of time is not recommended, especially for pregnant women and children.
Other Control Measures
Installing and maintaining tight fitting window screens and doors will help keep mosquitoes out of structures. Electrocutor traps ("bug zappers") placed out of doors are not effective in reducing or eliminating mosquito populations. Electronic mosquito repellers that emit high frequency sound to "repel" mosquitoes are also not effective.
Claims that certain plants placed around a porch or deck will repel mosquitoes are not supported by scientifically-based test results. Candles containing oil of citronella are often used outdoors to repel mosquitoes from around decks and picnic tables. These products work best when there is relatively little air movement to disperse the chemical.
Bats and birds such as Purple Martins consume mosquitoes as part of the diet. Installing nesting boxes will attract these natural predators to the area. However, the feeding activity of insect-eating bats and birds may not be sufficiently selective to cause noticeable reductions in mosquito populations.
Chemical Control
Chemical control of mosquitoes primarily targets the adult. Outdoor foggers will keep mosquitoes away for several hours, but once the chemical dissipates, the mosquitoes return. Spraying thickets or shrubs along the perimeter of the landscape helps reduce the population of mosquitoes that rest in these areas.
Insecticides are available for controlling larvae, but their application in either large bodies of water or small artificial breeding sites can be difficult and expensive. Control programs targeting mosquito larvae are best left to trained individuals in county or local government agencies. Most of these chemicals are not selective and may even harm beneficial insects. Furthermore, use of these chemicals will provide only temporary reduction in mosquito populations. Modifying or eliminating breeding sites is the only long-term solution to severe mosquito problems.
Small areas, such as bird baths, garden pools, etc, can be treated with a bacterial insecticide that is available at some hardware and garden centers. This product, called Mosquito Dunks, contains a bacterium known as Bacillus thuringiensis var. israelensis (or BTI). This bacterium kills mosquitoes, but will not harm fish, birds or other wildlife. Mosquito Dunks will control mosquito larvae for about 30 days.
The product is most effectively used in small breeding sites ( 100 sq. ft. or less). Simply treating all areas of standing water with Mosquito Dunks without knowing if these areas are actually sources of the problem is a waste of time and money.
Summary
Mosquitoes need water to complete their life cycle. They can breed in almost any source of water. Pesticides are only a short-term solution to nuisance mosquito problems. Solving the problem effectively and safely requires:
Return to Structural and Public Health Pests