Mosquito Control

The Madison Health Department oversees a Mosquito Control Program that consists of a number of distinct but complementary components. The Town’s Mosquito Control Program is based on an integrated pest management (IPM) approach. The primary goal of this program is to control the population of mosquitoes in order to reduce the public health threat of mosquito-borne diseases and the nuisance associated with large numbers of biting mosquitoes.

External Resources

Town Mosquito Control

The Town's mosquito control contractor applies a biological insecticide (Bacillus thuringiensis israelensis; Bti) to portions of Town salt-marshes and Town-owned properties in which larvae are present, based on the inspections noted above. This Bti is placed weekly during the warmest part of the summer, and biweekly in the spring and fall. In addition, the contractor places another biological insecticide (Bacillus sphaericus) into catch basins in which there is a likelihood of mosquito breeding. The catch basins are treated several times per year, beginning in mid-June and ending in mid-September. These insecticides attack only mosquito larvae, and do no harm to other aquatic organisms.

Bti is a cousin of other varieties of Bt that are commonly used in gardens to control cabbage loopers and other caterpillar pests. Bacillis sphaericus is targeted to the Culex species of mosquito, which are some of the most competent vectors of West Nile virus, and thrive in dirty waters with high organic contents, such as catch basins.

Pesticide Spraying

Commercial ground-level spraying to control adult mosquitoes is the least effective and the most environmentally controversial form of mosquito management. The Town does not normally conduct such spraying; however, if a significant mosquito-borne threat to public health were detected in town, the Town Health Department and First Selectman, in consultation with the State DEP and Department of Public Health (DPH) could recommend ground-level spraying to control adult mosquito populations in targeted areas. In that case, and after alerting the public, a mild insecticide would be sprayed into the air of the affected area

The insecticide would probably be a pyrethroid, applied by a truck-mounted ultra-low volume mist sprayer. This technique ensures the maximum coverage of the area with minimal insecticide. Pyrethroids are synthetic versions of natural insecticides derived from chrysanthemum flowers and exhibit very low toxicity to mammals. These insecticides break down in sunlight in 4 hours and leave no residue.

Mosquito Control Activities for Residents

The Town’s mosquito control program does not directly address fresh water mosquito populations on private property. That task falls to property owners and the simple act of eliminating standing water can have a substantial effect on mosquito populations. During the warmest months, water that stands for more than 5 days will probably be actively breeding mosquitoes. 

Mosquitoes that have been shown to most commonly carry West Nile virus and eastern equine encephalitis do not normally travel more than few hundred yards in their lifetime, and thus, individual actions on each property are important in controlling the potential spread of these diseases. If mosquito populations aren’t sufficiently controlled in the larval stage, large numbers may develop into adults in just a few days during the warmest weather.

  • Dispense of water-holding containers, such as ceramic pots, used tires, tire swings.
  • Drill holes in the bottom of containers such as those used for recycling.
  • Clean clogged roof gutters.
  • Turn over objects that may trap water when not in use, such as wading pools and wheelbarrows.
  • Change water in bird baths on a weekly basis.
  • Clean and chlorinate swimming pools, and when not in use, cover pools.
  • Use landscaping techniques to eliminate areas where water can collect on your property.


The Town employs a mosquito control contractor to regularly inspect and if necessary, treat known mosquito breeding areas in salt-marshes and near publicly-owned properties throughout town. These inspections consist of collecting samples of standing water and counting the number of mosquito larvae and pupae present.

Logging Complaints
The Madison Health Department logs complaints from residents of the incidence of heavy mosquito activity in areas throughout town and passes this information on to the contractor.

All of these surveillance activities provide a picture of the abundance of mosquito populations and their life stages, as well as the identification of disease-carrying mosquitoes. This surveillance system allows population reduction activities to be targeted for maximum effect.

Personal Protection

  • Minimize time spent outdoors when mosquitoes are most active, especially between dusk and dawn.
  • Be sure door and window screens are tight-fitted and in good repair.
  • Wear shoes, socks, long pants, and a long-sleeved shirt when outdoors for long periods of time, or when mosquitoes are most active. Clothing should be light colored and made of tightly woven materials that keep mosquitoes away from the skin.
  • Use mosquito netting when sleeping outdoors or in an unscreened structure and to protect small babies when outdoors.
  • Consider the use of mosquitoes repellent, according to directions, when it is necessary to be outdoors.
  • Repellents should be applied only to exposed skin and/or clothing (as directed on the product label). Do not use under clothing.
  • Never use repellents over cuts, wounds, or irritated skin.
  • Don't apply to eyes and mouth, and apply sparingly around ears. When using sprays do not spray directly onto face; spray on hands first and then apply to face.
  • Do not allow children to handle the products, and do not apply to children's hands. When using on children, apply to your own hands and then put it on the child.
  • Do not spray in enclosed areas. Avoid breathing a repellent spray, and do not use it near food.
  • Use just enough repellent to cover exposed skin and/or clothing. Heavy application and saturation is unnecessary for effectiveness; if biting insects do not respond to a thin film of repellent, apply a bit more.
  • After returning indoors, wash treated skin with soap and water or bathe. This is particularly important when repellents are used repeatedly in a day or on consecutive days. Also, wash treated clothing before wearing it again.
  • If you suspect that you or your child are reacting to an insect repellent, discontinue use, wash treated skin and then call your local poison control center. If/when you go to a doctor, take the repellent with you.


Bird Testing  

Recently, there has been a great deal of media and public attention given to eastern equine encephalitis (EEE) and West Nile virus (WNV), two important mosquito-borne diseases.

When West Nile virus first appeared in New England, it was noted that crows (and several other bird species) were very susceptible to the virus. For several years, the Connecticut Department of Public Health operated a testing program wherein dead birds located by residents were collected by local health departments and tested for West Nile virus by the State Health Department. The purpose of the program was to determine where the disease was spreading. At this point, West Nile virus has spread throughout the state and so the program has been discontinued.

Mosquito Testing
During the breeding season, the Connecticut Agricultural Experiment Station collects mosquitoes from a trap site in Madison (and from numerous other sites in the state) and analyzes these mosquito pools for the presence of WNV and EEE. The station issues regular press releases with the test results.