KENTUCKY MOSQUITOES AND THEIR CONTROL

By M. F. Potter and F. W. Knapp, Entomologists

University of Kentucky Department of Entomology

Mosquitoes whether they occur in the home, around the yard or at a family outing, can make life miserable. Many recreational and work activities have been ruined by the constant annoyance and irritation caused by the bites of these pests. In addition, some mosquitoes are capable of transmitting serious diseases including malaria and encephalitis to man and heartworm to dogs. This publication will explain how and where mosquitoes breed and what can be done to control them in and around the home.

MOSQUITO BIOLOGY

Successful long term mosquito control requires a knowledge of where and how they develop. All mosquitoes pass through four life stages: egg, larva, pupa and adult. The first three stages must have water for development. The number of days from egg to adult varies. Some mosquitoes can complete their life cycle in less than a week, or development can be extended to several months, depending on species and temperature.

In Kentucky, there are two major groups of mosquitoes, Culex sp. and Aedes sp., which have markedly different egg-laying habits. Mosquitoes of the Culex group lay their eggs on the surface of water in rain barrels, bird baths, tin cans, old tires, car bodies, cisterns, roof gutters and any other container which holds water. Mosquitoes of the Aedes group deposit their eggs at the base of vegetation bordering streams or in low lying areas subject to flooding. Also, this group can deposit their eggs above the water line in artificial containers (such as tin cans, old tires, etc.) or in tree holes that hold water. These eggs will hatch when inundated with rain water.

After the eggs hatch, the larval stage begins. Mosquito larvae are often called "wrigglers". Wrigglers are most commonly seen just below the surface of the water. Many species breathe through a tube (siphon) that extends upward from the end of their bodies toward the water surface. The larvae feed on microorganisms found in the water and grow rapidly, eventually passing through four molts. After the fourth molt has taken place the mature larvae transform into pupae. Mosquito pupae are also quite active and are often called "tumblers" because of their tumbling motion in water when disturbed. After a few days the pupae transform into adults. The adult male mosquito feeds only on nectar and plant juices whereas, the females are blood feeders and generally require a blood meal before they can lay eggs. Several different species of mosquitoes feed on humans. Mosquitoes also feed on most mammals and birds and some feed on reptiles and amphibians.

MOSQUITOES AND DISEASE

The feeding habits of female mosquitoes are not only annoying, but in some cases can result in the transmission of disease. Malaria and yellow fever used to be common mosquito-borne diseases in Kentucky but they have been successfully eliminated through wide-spread public health efforts. Currently, viral encephalitides are the most important diseases transmitted by mosquitoes to man (for example, St. Louis and LaCrosse encephalitis. Birds are important natural hosts for these viruses, which are transmitted to man through the bite of an infected mosquito. Small mammals such as rabbits, squirrels and chipmunks may harbor other forms of viral encephalitides which can also be transmitted to humans. Symptoms of viral encephalitis in humans range from mild to severe and may include high fever, convulsions and delirium. Homeowners can further reduce their chances of infection by eliminating breeding sites for mosquitoes on their own property.

Dog heartworm is a filarial (nematode) disease that can be transmitted by mosquitoes to dogs and cats. Infected pets may develop severe circulatory problems and display symptoms such as coughing, labored breathing and loss of vitality. Preventive drug treatment is available throughout the mosquito breeding season through veterinarians.

MOSQUITO CONTROL

Breeding Site Reduction

The most effective way to control mosquitoes is to find and eliminate their breeding sites. Eliminating large breeding areas such as swamps or sluggishly moving streams or ditches may require community-wide effort. Homeowners, however, can take the following steps to prevent mosquito breeding on their own property:

1. Destroy or dispose of tin cans, old tires, buckets, plastic sheeting or other containers that collect and hold water. Do not allow water to accumulate at the base of flower pots or in pet dishes for more than 2 days.

2. Clean debris from rain gutters and remove any standing water under or around structures, or on flat roofs. Check around faucets and air conditioner units and repair leaks or puddles that remain for several days.

3. Change water in bird baths and wading pools at least once a week and stock ornamental pools with top feeding predacious minnows. Known as mosquito fish, these minnows are about 1 - 1-1/2 inches in length and can be purchased or seined from streams and creeks.

4. Fill or drain puddles, ditches and swampy areas, and either remove, drain or fill tree holes and stumps with mortar.

5. Eliminate seepage from cisterns, cesspools, and septic tanks.

6. Eliminate standing water around animal watering troughs.

7. Irrigate lawns and gardens carefully to prevent water from standing for several days.

ADULT MOSQUITO CONTROL

Adult mosquitoes can fly long distances, therefore, it is often necessary to supplement larval control on your premises with control measures directed against mosquito adults.

Mechanical Barriers

Mosquitoes can be kept out of the home by keeping windows, doors and porches tightly screened (16-18 mesh). Those insects that do get into structures can be eliminated with a fly swatter or an aerosol space spray containing synergized pyrethrin.

Repellents

Persons working or playing in mosquito-infested areas will find repellents very helpful in preventing mosquito bites. Use repellents containing ingredients such as diethyl phthalate, diethyl carbate, diethyl toluamide (DEET), and ethyl hexanediol. Check the label for these active ingredients. The area of skin to be protected should be covered evenly, because mosquitoes will find and bite untreated spots. It is often helpful to use spray repellents on outer clothing as well as the skin. Repellents are formulated and sold as aerosols, creams, solids (sticks) and liquids. You should keep repellents away from eyes, nostrils and lips. Protection generally may be expected up to 6 hours following application.

Vegetation Management

Adult mosquitoes prefer to rest on weeds and other vegetation. Homeowners can reduce the number of areas where adult mosquitoes can find shelter by cutting down weeds adjacent to the foundation and in their yards, and mowing the lawn regularly. To further reduce adult mosquitoes harboring in vegetation, insecticides may be applied to the lower limbs of shade trees, shrubs and other vegetation. Products containing allethrin, malathion, carbaryl or chlorpyrifos have proven effective. Paying particular attention to shaded areas, apply the insecticides as coarse sprays onto vegetation, walls and other potential mosquito resting areas using a compressed air sprayer. Always read and follow label directions before using any pesticide.

Insect Electrocutors

Numerous devices are available for purchase which claim to attract, repel or kill outdoor infestations of mosquitoes. Most of these devices are ineffective and should be thoroughly researched before being purchased. Insect electocutors (bug zappers) utilizing ultraviolet light as an attractant have been shown to be ineffective in reducing outdoor populations of mosquitoes or their biting activity.

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!

Revised: 1/94