Climate change could double mosquito generations in B.C.

Climate change could dramatically increase mosquito populations across B.C., with potentially serious consequences for disease transmission, according to experts at the BC Centre for Disease Control.

Rising temperatures increase "growing degree days" — the number of days hot enough or warm enough for mosquitoes to complete their life cycle. When temperatures drop in winter, mosquitoes go dormant, but once warmth returns, their life cycles resume: larvae hatch and eventually emerge as adults. For many mosquito species, a 25-degree day is optimal for development.

"If you have more of those days, you're going to have more of those life cycles being completed," said Stefan Iwasawa, a vector specialist with the BCCDC. Instead of one or two generations per season, some species could see 10 to 12, representing exponential growth.

The concern extends beyond nuisance bites. More mosquitoes increase the chance of being bitten by one carrying a pathogen. Warmer climate in B.C. also means habitat on the Lower Mainland and Vancouver Island could support the Asian tiger mosquito, which transmits chikungunya — a virus of human health concern. The Public Health Agency of Canada has completed modelling suggesting both the mosquito and pathogen could survive in B.C. if climate change continues on its current trajectory.

Last summer, the BCCDC conducted a pilot mosquito surveillance project in the Sea to Sky Corridor after three pediatric cases of encephalitis were reported in the Whistler region in 2024, caused by California serogroup virus. Monitoring mosquito-borne viruses helps establish baseline data on what mosquitoes and viruses exist in specific regions, allowing health authorities to track how these evolve over time.

The surveillance work underscores a growing need to understand shifting disease patterns as the climate warms.