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Fact Sheet







Managing Mosquitoes Using Chemical Insecticides

Insecticides used for mosquito management are grouped into two categories. Larvicides are used to control immature (larval) mosquitoes in aquatic habitats. Adulticides are used to control adult mosquitoes. All insecticides used by the MMP are registered with the U.S. Environmental Protection Agency and the DEP's Pesticide Unit. They are safe to the environment and do not pose any adverse threat when used in accordance with the label. 

Larviciding is the most efficient and effective chemical method of managing mosquitoes because the larvae are concentrated in relatively small, well defined, and aquatic habitats. Larvicides are applied to mosquito-breeding habitats when there is an abundance of larvae. If larval control methods are successful, the need for adult mosquito management is greatly reduced or eliminated. The primary breeding habitats in Connecticut include salt marshes, freshwater swamps and marshes, wet woodlands and river floodplains. The MMP currently is charged with treating only state-owned tidal wetlands unless there is a declared public health emergency.

Larvicides are applied in small areas using hand-held equipment. Currently, the primary larvicide used by the MMP is the bacterial compound Bti (Bacillus thuringiensis var. israelensis). Bti must be ingested by the feeding larvae to be effective. Bti targets mosquitoes but can affect other flies such as black flies and some midges. It has a short effective life (two to three days) and must be reapplied to each new generation of mosquitoes. 

Chemical control using adulticides is initiated when the EEE virus is detected in mammal-biting mosquitoes. Adulticiding provides an immediate but short-term reduction in adult mosquito numbers. Truck-mounted equipment is used to create tiny, ultra-low volume (ULV) droplets of insecticide that drift through the swarm of mosquitoes. Truck-mounted applications are used in relatively small-populated areas, such as towns and housing developments. In the event that the DEP Commissioner declares a public health emergency, aircraft can be used to aerially apply adulticides to much larger areas.

The primary adulticide used by the MMP is resmethrin, a synthetic pyrethroid. This product has the same active ingredient as several over-the-counter yard sprays. Resmethrin is short-lived (three to four days) and must be reapplied to each mosquito infestation. It is safe to the environment and human health when applied as directed. Adulticiding is more costly than larviciding since adulticides are usually applied over larger areas. 

The MMP is actively evaluating new mosquito control products as they become available. New products must provide consistent mosquito control, be environmentally safe and nonhazardous to humans and be costeffective. If new products meet these requirements, they are considered for possible use by the MMP.