Why B.C. might see more mosquitoes in the years to come

Climate change could cause B.C. to have even more mosquitoes than it already does, according to experts.

With temperatures already rising from climate change, it could increase “growing degree days,” Stefan Iwasawa, a vector specialist with the BC Centre for Disease Control (BCCDC), told Daily Hive in an interview.

“That’s how many days during the year are hot enough or warm enough for the mosquito life cycle to progress,” he said.

In the winter, when temperatures drop, mosquitoes go dormant. Once warmer temperatures come back, their life cycles continue: larvae will start to hatch and eventually emerge as adults. For example, he said that for a lot of mosquito species, a 25-degree day is optimal.

“If you have more of those days, you’re going to have more of those life cycles being completed,” he said.

While it depends on the mosquito species and where they’re located in B.C., he said it could mean that instead of having one or two generations of mosquitoes a season, it could be 10 to 12.

“You can see that exponential growth,” Iwasawa said.

Not only would these additional mosquitoes be a nuisance, but the concern is that they would increase the chance of being bitten by a mosquito that potentially contains a pathogen.

Further, a warmer climate in B.C. means that there could be an opportunity for various mosquito species to move north into the province.

For example, Iwasawa said that climate change is allowing the habitat in the Lower Mainland and Vancouver Island to support the Asian tiger mosquito, which is known to transmit chikungunya, a virus of human health concern.

He said that the Public Health Agency of Canada has completed modelling, where it found that if climate change goes a certain way (“and the way we’re going currently”), there is a chance that both the mosquito and pathogen could survive.

Need for mosquito surveillance

Last summer, BCCDC conducted a pilot project of mosquito surveillance in the Sea to Sky Corridor in response to three pediatric cases of encephalitis that were reported in the Whistler region in 2024. These cases were the result of infection with California serogroup virus.

“It certainly can occur in B.C., but it’s rare, and it is sporadically distributed across Canada, originating in California, as you may have guessed,” said Smith.

She said that it is important to monitor mosquito-borne viruses to have that baseline data on what mosquitoes and viruses are in a specific region, so that they can see how these evolve over time.