Community Mosquito Management

A community can best handle mosquito problems when an organized abatement district (tax-supported) is established. Qualified personnel with adequate funds can then be hired to conduct an effective mosquito-control program. Under Illinois law, the Mosquito Abatement Districts Act (70 ICCS 1005/et. seq.) enables voters, by referendum, to organize tax-supported mosquito abatement districts.

In an area without a mosquito abatement district, local community leaders must direct and implement the program themselves; successful programs must have persons who are qualified to direct effective mosquito-control operations. This fact sheet is intended to assist communities that are not part of an established abatement district. Professional advice can be obtained by contacting:

or your unit office of the University of Illinois Cooperative Extension Service. In addition, the following facts about mosquitoes and suggestions for their control should be helpful.

Mosquito Facts
Mosquitoes are among the most common pests of people. Their biting is an annoyance and an irritation. They can carry numerous diseases that affect humans and their pets or livestock. In Illinois, although disease transmission is extremely rare, there are 3 kinds of encephalitis (St Louis Encephalitis, La Crosse Encephalitis and Western Equine Encephalitis) which mosquitoes can transmit to humans, as well as a nematode affecting dogs (dog heartworm).

Although, disease transmission is the most commonly cited reason for considering mosquitoes to be a public health problem, the presence of large numbers of biting pests will influence the physical and mental well being of most people. Mosquitoes also cause economic loss to livestock as a result of blood loss and irritation. In addition, mosquitoes can reduce recreation activities which will result in a loss of tourist income, and they can depress property values on land adjacent to areas where they are produced.

Immature mosquitoes are worm-like creatures called larvae that need to live in water while they feed on the microbes or decaying organic matter. Depending on the species, the adult female lays her eggs on standing water or in places that later become flooded. Larvae are rarely found in lakes and ponds with deep water and clean margins (without excessive vegetation and stagnant pools) or in flowing water such as streams and rivers. Mosquitoes can be classified by where the larvae are found:

1. floodwater or temporary pool
2. treeholes and artificial containers
3. standing water

Knowing which type of habitat a mosquito species prefers will help in providing effective control.

Generally, the peak biting periods of mosquitoes occur just before and after dark, and again just before dawn. However, each species has its own peak period of biting activity. Male mosquitoes do not bite, but feed on the nectar of flowers and plant juices. At other times, outside the biting periods, adult mosquitoes can be found resting in grass, shrubbery, or other foliage.

A Synopsis of the Mosquitoes of Illinois by H.R. Ross and W. R. Horsfall published in 1965 as "Illinois Natural History Survey Biological Notes No. 52" is still used by many mosquito control districts as an aid to developing their own key. No keys are perfect. In general, it is best to acquire some training in mosquito identification from someone trained in Medical or Veterinary Entomology before attempting to identify mosquitoes. Most trained entomologists develop their own keys and rely on mosquito taxonomists for further help.

Floodwater and temporary pool mosquitoes common to Illinois include the inland floodwater mosquito (Aedes vexans), the saltmarsh mosquito (Aedes sollicitans), and the dark rice-field mosquito (Psorophora columbiae). The eggs of these mosquitoes, which are laid singly on damp soil, require a drying period and may remain dormant for months, hatching within minutes after being covered by shallow water. The inland floodwater mosquito breeds in areas subject to flooding, such as marshy areas, low wetlands, or poorly drained areas, and is the most important pest mosquito in the state. The saltmarsh mosquito is found chiefly in southern Illinois in association with improper handling of sulfuretted wastes from strip mines and salt water from oil-field operations. The dark rice-field mosquito and other closely related species will develop in temporary pools, roadside ditches, shallow depressions, and even wheel and animal tracks that fill up during rains.

Floodwater and temporary-pool mosquitoes will complete their development from egg to adult in 8 to 14 days. There can be several generations a season if there is adequate rainfall to flood or inundate their egg-laying sites. Heavy populations occur in 10 days to two weeks after the egg-laying sites are flooded. The adults are persistent biters and will bite throughout the day if disturbed. Most floodwater mosquito species are strong flyers. Over a period of days, they may migrate several miles from their breeding sites. These factors make the floodwater mosquitoes very serious pests in Illinois.

The tree-hole mosquito, Aedes triseriatus, can be a serious pest near wooded areas, as the females are easily disturbed and will bite throughout the day. Eggs are laid singly just above the water line in tree holes and hollow stumps or artificial containers like old tires. As rainfall fills these cavities and covers the eggs, the larvae hatch and develop. The tree-hole mosquito is a carrier (vector) of LaCrosse Encephalitis.

The Asian tiger mosquito (Aedes albopictus) is another species which can be found associated with artificial containers, especially old tires. In Asian countries this recent immigrant carries encephalitis or other viruses to humans. It is an aggressive species which feeds throughout the day.

Standing-water mosquitoes, such as the northern house mosquito (Culex pipiens) and related species, develop in overgrown ponds, stagnant and shaded pools, poorly managed waste-effluent lagoons, catch basins, puddles in drainage ditches, as well as in artificial containers such as old tires, tin cans, children's toys, bird baths, and roof gutters. These mosquitoes lay their eggs on the surface of the water in groups (rafts). The mosquito larvae become full grown in about 7 to 10 days and feed on bits of organic matter in the water. The pupae transform into adults in 3 to 4 days. The adult female is ready to bite in another day or two, remaining near the larval development site in order to feed. The northern house mosquito is an important vector of St. Louis encephalitis.

The larvae of Anopheles quadrimaculatus, which was the primary vector of malaria in the eastern United States, are primarily found in permanent fresh water pools, ponds, and swamps that contain aquatic vegetation or floating debris. The females lay their eggs singly on the surface of the water. Although malaria no longer is a threat in Illinois, the malaria mosquito can be a serious pest near wetlands.

Suggestions for Controlling Mosquitoes in a Community

1. Determine the Species Present. Monitor mosquito populations during the summer with light traps, biting counts, and other methods. (See "Mosquitoes in Illinois: Recommendations for Prevention and Control" by the Illinois Department of Public Health)
2. Locate Larval Development Sites. Locate and map "mosquito breeding sites" both within and for at least 5 miles (preferably 15 miles) outside the city. Outlying flooded areas must be managed for successful suppression of floodwater (Aedes) mosquitoes. Continue to watch for new sites or sites overlooked in the initial survey.
3. Eliminate Larval Development Sites. Make short-term and long-term plans to eliminate as many of the mapped sites as possible by leveling, filling, and draining. Pay particular attention to drainage ditches, catch basins, grassy depressions and lowland areas. Consideration must be given to the legal aspects of mosquito control in wetlands or wildlife habitats.
4. Clean Water Margins. Remove vegetation and debris along the margins of ponds, lakes, and streams and fill or drain backwater pockets. Do not allow vegetation to overhang the water. Mow the grasses and weeds along the margin frequently. Stock the water with top-feeding minnows. Contact your local State Department of Natural Resources Office (usually located in the county seat) to determine which species of minnows can be released for control of mosquito larvae.
5. Use Insecticides as a Supplement to Cultural Practices. Anyone who conducts mosquito control on property other than their own must have a General Standards (Operators) Exam license and be supervised by a Licensed (Category 8) Applicator. The Illinois Department of Public Health supplies study materials for this test which is administered by the Illinois Department of Agriculture. Training sessions are conducted in the winter by the University of Illinois Cooperative Extension Service. The study text used for the Category 8 examination, "Mosquitoes in Illinois: Recommendations for Prevention and Control", is an excellent source for general insecticide information. It can be obtained from the Illinois Department of Public Health and the University of Illinois Cooperative Extension Service.

In Illinois there are no legislated regulations governing decisions on when to apply insecticides for mosquito control, as long as pesticide label instructions are followed. Some communities have developed thresholds for various species beyond which action is taken. With the appropriate experience, larval population numbers can be used to predict when resulting adult populations will rise beyond the level tolerated in a community. Although this sort of data may take some time to develop, it may be both a time and money saving technique in the long run. Some communities practice tighter larval control inside community environs than in the surrounding regions.

To control mosquito larvae or wigglers. Check for the presence of mosquito larvae with a white dipper. Apply an insecticide treatment according to label directions to stagnant water areas when the determined number of larvae are found. Repeated treatments will be needed during periods of mosquito abundance. A single treatment should stop the emergence of new mosquitoes for 10 to 14 days. Treehole mosquito populations are more difficult to sample, but the best treatment remains the removal or drainage of artificial containers.

To control mosquito adults (for emergency relief when adult mosquitoes are numerous). Apply a fog to grass, weeds, and shrubs; along wooded areas, ditches, roadsides, and parking lots; and in parks and around the perimeter of playgrounds. Fogs kill only those mosquitoes hit by the chemical. Their effect is of short duration, usually a matter of a few hours to a few days. Fogging is best done in the evening just before or just after dark when mosquitoes are most active and when atmospheric conditions are such that the fog will remain near the ground. Do not apply the treatment if the air temperature is below 60° F or as stated on the insecticide label. Fogging at other times of the day has an arguable psychological benefit but does not eliminate as many adult mosquitoes. Repeated treatments will be needed, and their frequency will depend on the effectiveness of the larval-control program and frequency of rainfall. A control program aimed at only the adult mosquitoes is rarely satisfactory because not all the adults are killed and additional ones are produced or rapidly move into the treated areas.

Type of application equipment to use. Thermal fog generators are available for applying fogs. Ultra-low volume (ULV) applicators are available, or existing equipment can sometimes be adapted to apply the undiluted concentrate as a fine aerosol or cold fog. Power sprayers or small hand-operated tank sprayers can be used to apply larvicides, spray catch basins, or apply a residual "barrier treatment" along the margins of a woods. Granular and briquet formulations of mosquito larvicides are also available for treating small larval sites such as ditches or catch basins. All mosquito control personnel must be licensed by the Illinois Department of Agriculture.

Precautions. KEEP THE PUBLIC INFORMED about mosquito control operations. Before any applications of fogs are made, notify the public of the date and time of applications whenever possible. Individuals with severe allergy conditions and persons with asthmatic problems may wish to stay indoors or plan to be away from the community during the treatment hours. Car finishes may be spotted with certain insecticide sprays and owners may wish to house them in the garage during the treatment hours. The understanding and cooperation of the general public are necessary if the program is to be a success.

For individual homeowners. A fact sheet on mosquitoes and their control in and around the home is available as NHE-94 from the your unit office of the University of Illinois Cooperative Extension Service. The efforts of individual homeowners to control mosquitoes on their properties can greatly enhance the success of a community in solving mosquito problems.

For more information on managing mosquitoes and chemical recommendations, see the University of Illinois Urban Pest Management Handbook or contact your unit office of the University of Illinois Cooperative Extension Service.

Prepared by Entomologists at the University of Illinois, Illinois Natural History Survey, and Illinois Department of Public Health. For additional copies, contact your unit office of the University of Illinois Cooperative Extension Service.

Urbana, Illinois 1995. Issued in furtherance of the Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Dennis R. Campion, Interim Director, Cooperative Extension Service, University of Illinois at Urbana-Champaign.

Entomology Fact Sheet, NHE-132, Revised 4/96

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