State of Connecticut Mosquito Trapping and Arbovirus Testing Program

The Connecticut Agricultural Experiment Station (CAES), a separate state agency, is responsible for trapping, identifying, and testing mosquitoes for encephalitis viruses. More than 25 scientists and support staff conduct the statewide surveillance program annually. Research is also an important component. During 1999, Station scientists were the first to culture and characterize the West Nile encephalitis virus from mosquitoes collected in North America. They also have identified the major mosquito vectors of West Nile virus in Connecticut. In addition, Station scientists found that the American robin is a favorite host for some mosquitoes and is an important carrier of the virus. Other findings revealed that Culex salinarius, a mosquito that breeds in brackish and fresh water, is the probable "bridge vector" moving the virus from birds to mammals. Of the top 100 science stories of 2005, Discover Magazine (January 2006 issue) ranked these recent discoveries at #43. Other results indicating the presence of Potosi and La Crosse viruses in the state represent new records for New England.

Insect Repellent Essentials: A Brief Guide  

MOSQUITO TESTING RESULTS - Updated October 12, 2021

Cumulative Mosquito Testing Summaries:

Week of: [June 14] [June 21] [June 29]

[July 5] [July12] [July 19[July 26]

[August 3] [August 9] [August 16] [August 23] [August 30]

[September 6] [September 13] [September 20] [September 27]

[October 4] [October 12]

Towns with West Nile Virus Activity
Branford, Bridgeport, Canaan, Chester, Cornwall, Darien, Easton, Fairfield, Farmington, Glastonbury, Greenwich, Hamden, Hartford, Litchfield, Lyme,  Manchester, Meriden, Middlefield, Milford, Monroe, New Britain, New Canaan, New Haven, Newington, Newtown, North Branford, North Haven, North Stonington, Norwalk, Orange, Plainfield, Ridgefield, Somers, South Windsor, Southington, Sprague, Stamford, Stratford, Waterford, West Haven, Westport, Wethersfield, Wilton

Towns with West Nile Virus Human Cases
Bridgeport, Hartford, West Haven

2021 West Nile Virus Activity Map

2021 West Nile Virus Activity Graph


Towns with Eastern Equine Encephalitis Activity

2021 Eastern Equine Encephalitis Activity Map


State of Connecticut Eastern Equine Encephalitis (EEE) Response Plan


Map of Mosquito Trapping Stations: [2021] [2020] [2019]

List of Mosquito Trapping Locations: [2021] [2020] [2019]

Summary of Testing Results 2020

Summary of Testing Results 2019 

2020 Eastern Equine Encephalitis Activity Map 

2020 Eastern Equine Encephalitis Activity Graph 

Map of Eastern Equine Encephalitis Virus Activity 2019  

2019 Eastern Equine Encephalitis Virus Activity Graph  

2020 West Nile Virus Activity Map  

2020 West Nile Virus Activity Graph  

Map of West Nile Virus Activity 2019  

2019 West Nile Virus Activity Graph  

Map of Zika virus Activity 2019

No Zika virus Activity Detected in Mosquitoes for 2019

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

Follow this link to the State of Connecticut Mosquito Management Program
( (for additional mosquito and virus information)

CAES Center for Vector Biology & Zoonotic Diseases


State of Connecticut
Zika Virus Surveillance and Response Plan, 2016

Symposium on EEE and Other Mosquito-Borne Diseases in Connecticut (March 9, 2020)

Symposium Agenda 
Reflections on the Ecology and Epidemiology of EEE in the Northeastern US
EEE in Connecticut: Risk Assessment and Response to the 2019 Outbreak
Mosquito Surveillance for EEE Virus and Other Arboviruses in Connecticut
Biology, Ecology, and Feeding Behavior of Mosquitoes in Connecticut
Options for Mosquito Control  

Additional Information

Surveillance for Mosquito-Borne Disease Among Connecticut Residents
Jamestown Canyon Virus Revisited: Are We Neglecting an Under Recognized Mosquito-Born Disease

Symposium on Vector-Borne Diseases in Connecticut (March 6, 2015)

2011 Results-Based Accountability Report to the Connecticut General Assembly

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


West Nile Virus Brochure  


Andreadis, T.G. 2009. Trapping and Testing Program for Mosquito-Borne Viruses to Begin June 1. Connecticut Department of Agriculture, Connecticut Weekly Agricultural Report, Wednesday, June 10, 2009.  

Connecticut Academy of Science and Engineering. 2009. Experiment Station in Forefront of Efforts to Monitor, Test for Mosquito-Borne Viruses. 24(2).

West Nile Virus. Connecticut Epidemiologist. June 2014. R. Nelson, T. Andreadis and P. Armstrong.


Human Case of Eastern Equine Encephalitis - Connecticut 2013. Connecticut Epidemiologist. R. Nelson, T. Ciesielski, T. Andreadis and P. Armstrong.


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 Environmental Protection (DEP). The DEP 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 DEP 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 DEP, 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 91 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 horse or emu deaths, or WNV bird or horse 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). 

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 in an enzyme-linked immunosorbent assay (ELISA) against specific reference antibodies to seven viruses known to occur in North America. These include: West Nile, Eastern Equine Encephalomyelitis, Jamestown Canyon, Cache Valley, Highlands J, LaCrosse, and St. Louis encephalitis viruses. A molecular technique (RT-PCR) is also used to identify WNV. Weekly test results are reported to the DEP and DPH and released through DEP Communications. Complete processing of mosquitoes (from collection to virus isolation and identification) usually requires 8-10 days.