State of Connecticut Mosquito Trapping and Arbovirus Testing Program

The Connecticut Agricultural Experiment Station (CAES) is part of the state’s Mosquito Management Program. Each year, more than 25 scientists and staff members trap, identify, and test mosquitoes for viruses that can cause disease. They also study different types of mosquitoes and the viruses they may carry.

In 1999, CAES scientists were the first in North America to grow and study West Nile virus from infected mosquitoes. They found which mosquito types spread the virus the most. They also learned that the American robin is a common host for these mosquitoes. This bird plays an important part in spreading the virus. Some mosquitoes that live near salt and freshwater marshes can move West Nile virus from birds to people. These mosquitoes act as a “bridge vector.”

CAES scientists look for other viruses in the state. These include Eastern Equine Encephalitis (EEE), Jamestown Canyon, and La Crosse viruses.

More information about the Connecticut Mosquito Management Plan and mosquito trapping and testing methods can be found at the bottom of this page.

FIGHT the BITE! - Insect Repellent Essentials: A Brief Guide

Mosquito Trapping and Arbovirus Surveillance Program Brochure

MOSQUITO TESTING RESULTS

Cumulative Mosquito Testing Summary:

Statewide mosquito trapping and testing will start on June 1, 2026

Latest Testing Results -

Towns with West Nile Virus (WNV) Infected Mosquitoes:

Counties with West Nile Virus (WNV) Human Cases:

Towns with Eastern Equine Encephalitis (EEE) Infected Mosquitoes:

To reduce the risk of being bitten by mosquitoes, residents should:

• Minimize time spent outdoors between dusk and dawn when mosquitoes are most active.

• When it is necessary to be outdoors, use mosquito repellents containing an EPA-registered active ingredient, including DEET, Picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol (PMD), or 2-undecanone. EPA registration of skin-applied repellent products indicates that they have been evaluated and approved for human safety and effectiveness when applied according to instructions on the label.

• Wear shoes, socks, long pants, and a long-sleeved shirt when outdoors for long periods of time, or when mosquitoes are more active. Clothing should be light-colored and loose-fitting and made of tightly woven materials that keep mosquitoes away from the skin.

• Wear clothing and gear treated with permethrin. Permethrin is an insecticide that kills or repels mosquitoes and ticks.

• Be sure door and window screens are tight-fitting and in good repair.

• When sleeping outdoors, use tents or mosquito netting in an unscreened structure. Treat camping gear with permethrin when possible.

• Cover strollers and baby carriers with mosquito nets when outside.

State of Connecticut Eastern Equine Encephalitis (EEE) Response Plan

State of Connecticut West Nile Virus (WNV) Response Plan

Map of Mosquito Trapping Stations: [2020 to 2026] [2019]

List of Mosquito Trapping Locations: [2020 to 2026] [2019]

Summary of Testing Results 2025
Summary of Testing Results 2024
Summary of Testing Results 2023
Summary of Testing Results 2022
Summary of Testing Results 2021
Summary of Testing Results 2020
Summary of Testing Results 2019

2025 West Nile Virus Activity Map
2025 West Nile Virus Activity Graph
2024 West Nile Virus Activity Map
2024 West Nile Virus Activity Graph
2023 West Nile Virus Activity Map
2023 West Nile Virus Activity Graph
2022 West Nile Virus Activity Map
2022 West Nile Virus Activity Graph
2021 West Nile Virus Activity Map
2021 West Nile Virus Activity Graph
2020 West Nile Virus Activity Map
2020 West Nile Virus Activity Graph
2019 West Nile Virus Activity Map
2019 West Nile Virus Activity Graph

State of Connecticut Mosquito Trapping and Arbovirus Testing Program--Historical Information (1998-2018)

The State of Connecticut Mosquito Management Program
(https://portal.ct.gov/mosquito) (for additional mosquito and virus information)

CAES Center for Vector Biology & Zoonotic Diseases

Identification Guide to the Mosquitoes of Connecticut Theodore G. Andreadis, Michael C. Thomas, and John J. Shepard

Entomology Today Article : Mosquito Populations Linked Across Further Distances Than the Viruses They Carry

Connecticut Mosquito Management Plan

In 1997, Public Act 97-289, "An Act Concerning Mosquito Control and Aerial Application of Pesticides", created the Mosquito Management Program to monitor mosquito breeding populations for the prevalence of infectious agents that can cause disease in humans and to determine when measures to abate any threat are necessary. The original focus of the program was to monitor the threat of Eastern Equine Encephalitis (EEE). The Act authorizes the necessary measures to abate any pest-borne threat, including prevention and remedial measures, and allows for the aerial application of broad spectrum chemical pesticides to address an imminent peril to the public health, safety, or welfare posed by pests, including mosquitoes that carry the EEE virus.

The Mosquito Management Program is coordinated by the Department of Energy and Environmental Protection (DEEP). The DEEP is responsible for the systematic identification and monitoring of mosquito breeding sites, the provision of technical assistance to municipalities and private property owners regarding mosquito control, and the collection and communication of information and data. The Connecticut Agricultural Experiment Station (CAES) is responsible for the trapping, identification, and arbovirus testing of mosquitoes. The Department of Public Health (DPH) is responsible for reviewing all mosquito test data and consulting with the DEEP and the CAES regarding the epidemiologic significance of such results. Based upon its evaluation of the potential human health risks, the DPH advises as to appropriate personal, municipal, and state actions to reduce such risks. An EEE/WNV Working Group, consisting of staff from the DEEP, DPH, CAES, and DAG modifies, as necessary, the State EEE/WNV surveillance and response plans and reports to and advises the Commissioner of the DEP regarding their implementation.

The Mosquito Management Program is a health-based program that focuses on preventive efforts and mosquito monitoring for early detection of EEE and WNV. It is based on an integrated pest management (IPM) approach, which includes a combination of surveillance, education, source reduction, larval and adult mosquito control and personal protection measures.

Public health surveillance is the ongoing and systematic collection, analysis, and interpretation of health data in the process of describing and monitoring a health event. This information is used for planning, implementing, and evaluating public health interventions and programs. Surveillance data are used both to determine the need for public health action and to assess the effectiveness of programs. Surveillance activities are at the core of Connecticut’s Mosquito Management Program and include surveillance for EEE and WNV in mosquitoes, wild birds, domestic animals and poultry, and humans. The objectives of surveillance are to:

Rapidly detect the occurrence of EEE and WNV and the extent of its geographic distribution.
Assess the potential threat to humans and domestic animals or birds.
Guide implementation of control measures and justify the need for additional mosquito trapping locations.
Determine whether transmission is occurring outside of the mosquito-wild bird cycle.
Obtain data to assess the risk of EEE or WNV infection to domestic animals and poultry and assess the need to develop a vaccine for domestic animals.

Mosquito Surveillance

The Connecticut Agricultural Experiment Station is responsible for trapping, identifying and testing mosquitoes for EEE and WNV virus. Mosquito trapping is conducted daily from June through October at 108 permanent locations throughout the state. Trap sites include freshwater swamps (red maple/white cedar), residential vegetated areas along waterways, wetlands, and undeveloped wood lots known or suspected to support mosquito populations that have tested positive for EEE or WNV, are capable of supporting such populations, or are near locations where EEE-related human, horse, pheasant, or emu deaths, or WNV human, horse, or bird deaths have occurred. This program provides information on the:

Composition and relative abundance of mosquito species.
Seasonal and spatial distribution of mosquito species that are potential vectors.
EEE and WNV infection rates in mosquitoes.

Mosquito traps are set and attended by CAES staff every 10 days on a regular rotation. Two trap types are used at all trapping stations : 1) a CO₂-baited CDC Light Trap, designed to trap host-seeking adult female mosquitoes (all species); and 2) a Gravid Mosquito Trap, designed to trap previously blood-fed adult female mosquitoes (principally Culex species). A third trap, the BG Sentinel Trap, is used at select locations to monitor populations of the Asian Tiger Mosquito (Aedes albopictus). In the event that EEE or WNV-infected mosquitoes are detected at a trapping station, the frequency of trapping is increased, to a minimum of once per week, in order to assess potential public health risks

All of the virus isolation work is conducted in certified Bio-safety level 3 laboratories at the CAES. Viruses are isolated in Vero cells and identified using RT-PCR based assays. These include: West Nile, Eastern Equine Encephalomyelitis, Jamestown Canyon, Cache Valley, Highlands J, LaCrosse, Potosi and St. Louis encephalitis viruses. Weekly test results are reported to the DPH, DEEP, and DAG and published on the CAES and CT Mosquito Management website. Complete processing of mosquitoes (from collection to virus isolation and identification) usually requires 6-10 days.

Connecticut State The Connecticut Agricultural Experiment Station

State of Connecticut Mosquito Trapping and Arbovirus Testing Program