The COVID-19 pandemic may have helped make 2020 an especially bad year for mosquitoes.
Weather and river conditions have been the main drivers of one of the worst mosquito seasons in recent times. Occupancy limits in the helicopters where pesticides are applied to mosquito breeding areas may also have under-treated some of the main blood-sucking pest habitats.
A report to the Fraser Valley Regional District states that the season was fairly normal until June 5, when the river initially peaked. But instead of slowly declining in the summer, river levels fell and then rose again, peaking again on June 30th – above the level of the first peak.
Every year the FVRD commissions a private company to treat larvae in mosquito breeding areas along the river. In 2019, these were packed on June 21. In 2020, the mosquitoes, which were persistently high, hatched until August. The last treatments were applied on August 17th.
RELATED: Mosquito locations are monitored and mapped throughout the Fraser Valley
In total, Morrow BioScience, the company tasked with treating and removing mosquitoes, used just under 20 tons of a pesticide. (The pesticides are not sprayed; rather, a larvicide, which the FVRD says is environmentally friendly, is used in granular or liquid form. The mosquito larvae ingest a poisonous protein that kills them.) Even 2012, another bad mosquito year, was 14,489 kg applied – 30 percent less than this year total.
Each application of the pesticide kills about 90 percent of the larvae. But in 2020 there were just too many mosquitos.
“Because of the extremely high larval frequency in 2020,” the FVRD report said, “the remaining 5 to 15% of surviving larvae hatched in adults were enough to cause unfortunate nuisances in many lowland areas near the Fraser cause flow. “
Last year only four people called a mosquito hotline that can be used to report the pests. This year 130 calls were received. Of these, the vast majority – 99 – came from Chilliwack residents. And most of them came from Fairfield Island, the Chilliwack residential area closest to the Fraser River and surrounded by mud.
The mosquitoes on Fairfield Island could be an indirect consequence of the COVID-19 pandemic.
Helicopter and boat crews were restricted due to COVID-19 security protocols. While the FVRD staff report states, “These limitations are not believed to have materially affected the effectiveness of the treatment.” A separate report by Morrow BioScience suggested possible effects.
“It is possible that web sites were not treated as thoroughly as usual,” said the Morrow BioScience report. “The high number of worrying phone calls related to Fairfield Island [in Chilliwack] indicate the possibility that locations on this island have been overlooked. “
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