Mosquitos are thriving in Quebec thanks to this summer’s heavy rainfall and heat

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If you’ve noticed more mosquitos and wasps than normal at this time of year, experts say it is probably not your imagination.

While the mosquito data for summer 2024 has not yet been analyzed, the record rain and high humidity levels Quebec has had this summer have provided ideal breeding environments for mosquitos, said Étienne Normandin-Leclerc, an entomologist and collections coordinator at the Université de Montréal’s Institut de recherche en biologie végétale.

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“Through general observations, we certainly get the impression there are more mosquitos,” he said, adding the uptick is not at all surprising considering the record rainstorms Quebec has experienced this summer.

On July 10 and 11, the remnants of Hurricane Beryl dropped 100 millimetres of rain on parts of the province, and less than a month later on Aug. 9, tropical storm Debby dumped another 150 to 173 millimetres more.

“When we have big rains like that we will get a lot of stagnant water and puddles in the forests, in the suburbs and in the cities; everywhere. That makes for good mosquito habitat,” he said.

Professor Christopher Buddle, an entomologist and professor in McGill’s Department of Natural Resource Sciences whose research focuses on the biodiversity of insects and spiders, said the rain this summer has been particularly “good” for mosquitos. But it is also true that every year at about this time, people tend to notice an increase in mosquitos and wasps.

So is it just the time of year, or are the numbers really up?

“The answer is a little of both,” Buddle said. “Every year in late summer there are certain species of mosquitos that tend to increase later in the season and it’s also the time when the nests of social wasps, things like yellow jackets etc., are getting larger so there are more of them around too.”

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Mosquito larvae are aquatic, so they need standing water to thrive. Depending on the species, they take days or weeks to mature into adults.

“There do seem to be a lot of mosquitos around in late summer and I would say there are more than average and it’s largely because we’ve had a fairly warm and certainly a very wet summer,” Buddle said.

Is there a way to know for sure? Some government agencies and research institutes do trap and count mosquitos each year to analyze whether populations are changing in certain regions, and to monitor disease transmission. The traps use fans, light, heat, synthetic carbon dioxide, and products that mimic the smell of sweat to attract them and trap them.

Buddle said it is quite difficult to determine whether there are more mosquitos one year over another.

“But certainly anecdotally, what most people agree on is that this is a bad mosquito year. … And until we get a hard frost and killer days, they are going to be around.”

Homeowners are advised to empty any standing water on their property, such as in old tires or flowerpots.

Both researchers acknowledged that some humans tend to attract more mosquitos and get bitten more often than others. This may be due to the smell of a person’s shampoo or perfume, the chemical composition of their sweat, as well as the amount of carbon dioxide they produce. People with larger bodies and those who are exercising tend to produce more CO2, which attracts mosquitos. Body heat and moisture also attract the bugs. Some studies have suggested that mosquitos prefer people with Type O blood over other blood types. Research also suggests mosquitos are attracted to dark coloured clothing, especially black and navy.

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Quebec’s health department warns that mosquitos can transmit dangerous viruses such as West Nile virus, California serogroup viruses (CSV) and Eastern equine encephalitis (EEE) virus.

To be less attractive to mosquitos, Normandin-Leclerc advises using insecticide spray with DEET, wearing pale clothing, and taking a shower before heading into the woods. Applying certain natural essential oils, such as citronella, thyme, lavender oil has also been shown to be effective at reducing the number of mosquitos in one’s vicinity, but only by about 30 per cent, he said.

Both researchers said that wasps are on the increase in the Montreal region, likely due to climate change.

“We didn’t have as many nests a few years ago,” said Normandin-Leclerc. “What explains it? The increase in average summer temperatures. Wasps are influenced by hot weather because their metabolism increases with the temperature … which means the larva will demand more to eat,” and adult wasps will go searching for sugars and protein.

In early summer, the worker wasps are mainly interested in fibre to help build the nests. As summer wears on, and the young demand food, the adult wasps will go looking for picnic foods.

Buddle said though wasp bites hurt, they are usually harmless, unless one is allergic. He advised not to swat at or otherwise anger wasps, especially near their nests.

mlalonde@postmedia.com

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