Though prolonged hot, wet weather led to a high number of mosquitoes in Connecticut this year, residents have been spared an outbreak of the deadly Eastern Equine Encephalitis virus — possibly because the virus didn’t reach the state until too late in the season to become widespread in the mosquito population.
“I’ve been getting a lot of complaints from people about how bad the mosquitos have been this year, and that’s not a figment of your imagination. It was a bad year in terms of just the sheer number of mosquitoes,” said Phil Armstrong, director of the Mosquito Monitoring Program with the Connecticut Agricultural Experiment Station.
The station set the same number of traps this year as last year — a total of 108 across the state — and they captured and tested 365,878 mosquitos through Oct. 4. That’s 172,687 more than they tested through November last year, nearly a 90 percent increase.
Mosquitoes have a boom and bust life cycle. This year, with a high rainfall in August and September coupled with unseasonably warm temperatures, the conditions were right for a population boom — plus, the mosquito season has extended longer than normal, he said.
This year’s high mosquito population played a role in the prevalence of West Nile Virus, which has been identified in 207 mosquitos so far this year — 64 more than last year and 125 more than in 2019. And that includes 12 in the last week alone, even as the cooler weather has started to make the mosquitoes less active, Armstrong said.
There have been three human cases of West Nile in Connecticut so far this year, and it could have been much worse given the levels of virus researchers found in the mosquitoes they tested, Armstrong said.
“We’re still detecting the virus,” he said. “It is winding down, and the risk is less than where we were weeks ago, but it’s still there, and they will continue to transmit the virus until we get a killing frost.”
This year, despite high mosquito populations, only two mosquitoes have been found with Eastern Equine Encephalitis, known as EEE. Both were trapped in Voluntown on Sept. 23.
Armstrong said the relative lack of mosquitoes found with EEE this year may have just come down to timing.
“I think we were lucky this season, and it’s largely a function of it being introduced into our state so late in the season that it didn’t have time to become amplified and become a problem,” he said.
If the disease is introduced into the state early enough in the season — as late as early August — and the mosquito population is large enough, the virus can spread quickly. That’s what happened in 2019, when there were 31 cases of EEE in humans across seven states — much higher than the average of 11 cases a year in the U.S.
Last year —when a prolonged drought led to a lower mosquito population —only two mosquitoes were found that carried EEE — one trapped at Stonington High School on Aug. 5, 2020, and another at the Hampton Reservoir a week later.
In 2019 — when the major outbreak of EEE resulted in four people in Connecticut contracting the disease, and three dying from it — the station tested 122 mosquitoes that carried EEE.
The mosquitoes that transmit EEE live in freshwater swamp forests, making them difficult to control with pesticides. That’s why testing is important — if EEE is identified, people can take precautions to keep themselves safe — like limiting the amount of time they’re outside around dusk and dawn, and wearing long sleeves and using insect repellant, Armstrong said.
Like West Nile, EEE is carried to Connecticut and other northeastern states by birds from the south, he said. Infected birds transmit the disease to mosquitoes that bite them, and those mosquitoes in turn transmit the disease to other birds they bite.
Armstrong cautioned there is still a risk, as the station found two mosquitoes carrying the virus just two weeks ago, but Connecticut has not had the conditions this year that would typically lead to an outbreak.
“The mosquitoes become less active when the temperature dips below 50 degrees, but they’ll survive until the first hard frost — a killing frost,” Armstrong said. “If you’re a gardener, it’s the first frost that kills all your tender perennials, that’s what’s needed to really knock the mosquitoes down for the season.”