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Late spring, high water on Fraser River ‘a perfect scenario’ for mosquito breeding

‘We understand the frustration with the current abundance of mosquitoes,’ says contractor
Morrow BioScience technician looks for mosquito larvae to treat in back channels of the Fraser River. (Morrow BioScience)

Fraser River adjacent communities across B.C. are experiencing high levels of mosquito annoyance this year.

It was a very wet spring, combined with sustained near-peak levels on the Fraser, that have produced the “perfect scenario” for floodwater mosquito breeding, according to Morrow BioScience operations manager Shaun Calver.

“We understand the frustration with the current abundance of mosquitoes,” Calver said. “We expect to see localized changes in density as the current mosquito population moves around with wind patterns.”

Staff with Morrow BioScience, the mosquito control contractor, are monitoring sites regularly and responding to input from residents.

Fraser River water levels are slowly going down, but rain in the forecast this weekend may extend the high-water timeline.

“We are out treating all floodwater mosquito habitat within the Fraser Valley and Metro Vancouver by ground and by air,” said Calver.

Adult mosquitoes typically disperse within a week after the peak Fraser levels (July 4) are recorded. Depending on ambient temperatures, mosquitoes are expected to stay at nuisance levels for three weeks following the freshet peak.

If temperatures are higher than average, mosquitoes will disappear more quickly.

They do not conduct spraying or fogging to kill adult mosquitoes but rather treat floodwaters with a larvicide to kill mosquitoes in the larval stage.

In a bad year people will call the FVRD mosquito hot-line to demand they “spray” for adult mosquito eradication. But that toxic method of mosquito control went the way of the dodo decades ago. These days they use a bacterial agent, Bti, to kill mosquito larvae, which is non-toxic to pets, fish and wildlife. It is in granular form ladled by hand, or dropped from a helicopter into the water.

Calver advises residents to help reduce breeding sites around their properties by dumping or refreshing standing water daily. These areas include bird baths, old tires, clogged gutters, animal troughs, and kiddy pools, to name a few.

RELATED: 2021 wasn’t quite as bad for mosquitoes

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Jennifer Feinberg

About the Author: Jennifer Feinberg

I have been a Chilliwack Progress reporter for 20+ years, covering the arts, city hall, as well as Indigenous, and climate change stories.
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