Ohio State University Extension Fact Sheet

Ohio State University Extension Fact Sheet

Department

Entomology, 1991 Kenny Road, Columbus, OH 43210-1000


Mosquitoes

HYG-2058-98

William F. Lyon
Richard L. Berry
Michael F. Collart

There are about 60 different species of mosquito in Ohio. Several of them are capable of transmitting serious, possibly even fatal diseases, such as mosquito-borne encephalitis and malaria to humans. Even in the absence of disease transmission, mosquito bites can result in allergic reactions producing significant discomfort and itching. In some cases excessive scratching can lead to bleeding, scabbing, and possibly even secondary infection. Children are very susceptible to this because they find it difficult to stop scratching. Frequently, they are outside playing and do not realize the extent of their exposure until it is too late.

Female mosquitoes can produce a painful bite during feeding, and, in excessive numbers, can inhibit outdoor activities and lower property values. Mosquitoes can be a significant burden on animals, lowering productivity and efficiency of farm animals.

Identification

Adult mosquitoes are small, fragile insects with slender bodies; one pair of narrow wings (tiny scales are attached to wing veins); and three pairs of long, slender legs. They vary in length from 3/16 to 1/2 inch. Mosquitoes have an elongate "beak" or piercing proboscis. Eggs are elongate, usually about 1/40 inch long, and dark brown to black near hatching. Larvae or "wigglers" are filter feeders that move with an S-shaped motion. Larvae undergo four growth stages called instars before they molt into the pupa or "tumbler" stage. Pupae are comma-shaped and nonfeeding and appear to tumble through the water when disturbed.

Life Cycle, Habits and Diseases Carried

Mosquitoes may overwinter as eggs, fertilized adult females or larvae. Eggs, larvae, and pupae must have water to develop. Some female mosquitoes lay their eggs directly on the water surface. Others lay their eggs on substrates above the water line (flood pool mosquitoes); the eggs hatch upon flooding. In some cases, the eggs will remain viable for several years until further flooding occurs. Mosquitoes belonging to the genus Culex lay their eggs in bunches or "rafts." Each raft may contain up to 400 individual eggs. Larvae feed on bits of organic matter dispersed in the water, becoming full grown in about one week. The pupal stage lasts two to three days. Female mosquitoes are ready to bite one to two days after adult emergence. Male mosquitoes do not bite but feed on flower nectar or plant juices. Some mosquitoes have only one generation per year, whereas others may have four or more. Adults may fly 5 to 10 miles, but usually rest in grass, shrubbery or other foliage close to the water breeding area.

Mosquitoes may transmit diseases such as dengue, yellow fever, and malaria to humans. Mosquito-borne encephalitis is a viral inflammation of the brain. Encephalitis can infect humans, horses, and a variety of other mammals and birds. Eastern equine encephalomyelitis (EEE), although very rare is frequently fatal. A small rural outbreak in late 1991 resulted in more than 20 farm animal fatalities, most of which were horses. Transmission of the disease occurs when an infected mosquito takes a blood meal. Birds serve as natural hosts for EEE and St. Louis encephalitis (SLE). St. Louis encephalitis, like EEE is an epidemic disease, meaning that it is usually rare. It can be absent from an area for several years and then reoccur suddenly without warning. LaCrosse encephalitis (LAC) is the third type found in Ohio. It is considered endemic to Ohio and occurs year after year at low levels. Ohio has more recorded cases of this disease than my other state. LaCrosse encephalitis is the least severe of the three types of mosquito-borne encephalitis that are found in Ohio, and occurs most often in children. Small woodland mammals, such as chipmunks and squirrels serve as the natural host for the virus, however LAC virus can also be passed, transovarially, from mother mosquito to her offspring.

Mosquitoes can also transmit filariasis (heartworm) to animals. Dog heartworm is the most significant of these, however in some areas, veterinarians are beginning to see more heartworm in cats.

Common Name Scientific Name Importance
Asian Tiger Mosquito Aedes albopictus LAC, EEE, SLE, Pest
(banded spring mosquito) Aedes canadensis LAC, Pest
Eastern Treehole Mosquito Aedes triseriatus LAC
(flood-water mosquito) Aedes tivittatus Pest
Vexans Mosquito Aedes vexans Pest
Common Malaria Mosquito Anopheles quadrimaculatus Malaria, Pest
Cattail Mosquito Coquillettidia perturbans EEE, Pest
Northern House Mosquito Culex pipiens SLE
Key:
LAC = LaCrosse Encephalitis
EEE = Eastern Equine Encephalomyelitis
SLE = St. Louis Encephalitis

Control Measures

What Doesn't Work

There have been a number of natural and man-made mosquito repellents, attractants, and predators touted as effective against mosquitoes. In truth, they don't do much good and cannot be used to effectively control mosquitoes.

A company has been marketing a "mosquito repellent plant" that produces citronella and consequently repels mosquitoes. Citronella oil is produced by a number of different plants. At relatively high concentration, Citronella oil is repellent to mosquitoes. Thus far, there does not appear to be adequate scientific literature to substantiate the claim that enough Citronella is released by a stationary plant to repel mosquitoes. Most likely the plant would have to be physically damaged in order to release enough citronella to repel mosquitoes and the effect would be very short lived.

Dietary studies indicate that mosquitoes are insignificant in the purple martin diet. Studies of bat stomach contents show beetles as the dominant food. Ultraviolet or black lights and sonic devices indicate ineffective control.

Prevention

Since most of the mosquitoes that transmit encephalitis will not travel very far, the risk of contracting encephalitis can be minimized by controlling the mosquito breeding sites which are in close proximity to your home. Water management, to prevent mosquito breeding, is essential for control. Eggs do not hatch unless they are in water. Remove old tires, buckets, tin cans, glass jars, broken toys and other water-catching devices. Change water in bird baths and wading pools once or twice a week; clean out roof gutters holding stagnant water; and place tight covers over cisterns, cesspools, septic tanks, barrels, and tubs where water is stored. Never over-apply lawn and garden irrigation; fill, drain or treat tree holes; and drain or fill stagnant water pools, puddles, ditches, or swampy areas. Inspect water in plant containers, water-holding stumps, keep grass mowed around bodies of water, stock ponds and reservoirs with fish. Ohio Department of Natural Resources is discouraging the release of fish such as Gambusia since they are not indigenous to Ohio.

Use adequate screens with 16 x 16 or 14 x 18 mesh on windows and doors. Screen doors should open outward and close automatically.

Repellents

Repellents applied to the skin and clothing will prevent mosquito bites for one to five hours depending on the person, type, and number of mosquitoes and the type and percent of active ingredient in the repellent. Repellents are available as aerosol sprays, pump sprays, creamsticks, lotions, or foams.

N, N-Diethyl-m-toluamide (Deet) is very effective and widely used as a repellent but it should not be used indiscriminately as severe allergies can develop. Formulations containing high concentrations of Deet, 50% or more, should not be used on children. Formulations containing 5 to 10% Deet will work just as well as those containing 90% or more, however, they will not last as long.

Avon Skin-So-Soft has been widely used as a mosquito "repellent" for a number of years without being labeled. Avon Products, Inc. has recently obtained EPA approval and is now marketing some of its Skin-So-Soft products for use as a mosquito repellent.

Indoor Control

Space sprays or aerosol "bombs," containing synergized pyrethrins 0.1%, are effective against adult mosquitoes. Frequent treatments may be needed during problem periods.

Outdoor control

Adulticides

Space sprays or aerosol foggers, containing pyrethrins, will give rapid knockdown of adult mosquitoes. However, it is a temporary treatment with little residual effect. Residual sprays applied to tall grasses, weeds, trees, shrubs, and outbuildings, one to two days before use of the area, is effective. Use water solution or emulsions instead of oil-based formulations to prevent plant injury. Some insecticides registered for residual mosquito control include: carbaryl (Sevin), chlorpyrifos (Dursban) and malathion. There are a number of different formulations available. Follow specific label directions when applying.

Note: Malathion and carbaryl (Sevin) are extremely toxic to honey bees. Do not spray plants when in bloom. Mow weedy areas before treatment. Bee losses are minimized by spraying late in the afternoon when bees are gone or when temperatures are below 45 deg F. Malathion and methoxychlor are highly toxic to fish.

Larvicides

Homeowners may apply Mosquito Dunks (made with Bacillus thuringiensis Berliner var. israelensis or B.t.i.) to kill mosquito larvae in the water. This natural ingredient is harmless to other living things and is biodegradable. (Summit Chemical Co. 800-227-8664).

Methoprene (Altosid XR) is another safe material for control of mosquito larvae. It is an insect hormone which retards the development of larvae ( disrupts molting) and prevents mosquitoes from developing into adults (Clarke Mosquito Control Products, Inc. 800-323 -5727).

Altosid XR Briquets can be placed even on ice for season-long control. Treat swamps, ponds, and marsh areas in early spring before thawing. These extended-release briquets will provide up to 150 days of uninterrupted mosquito control once they hit the water. It can be applied by hand and the product is labeled for use in known fish habitats.


NOTE: Disclaimer - This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.


All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-6181



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