

More on mosquito counting

Every spring, the City of Winnipeg’s Insect Control Branch fires up a nuisance-mosquito control program that begins with applying larvicides bodies of standing water, monitoring the development of mosquito larvae and counting the bloodsuckers that show up in city traps.

JEFF DE BOOY / WINNIPEG FREE PRESS ARCHIVES A Winnipeg Insect Control Branch worker counts mosquitoes caught in one of the city's traps.

Nuisance mosquito species are those that are not known to transmit diseases to people. They include Ochlerotatus dorsalis and Ochlerotatus fitchii, which usually mature in the spring, and Aedes vexans, a nasty biter that matures closer to the summer.

The Insect Control Branch monitors 28 traps inside the city and another nine on the fringes of the city. Thanks to a council-approved policy created to prevent politicians from monkeying around with mosquito control, the city can not spray for adult mosquitoes until two conditions are met:

The city-wide average trap count is above 25 for two consecutive days. The nine traps outside city limits don’t factor into this. At the same time, one quadrant of the city has to have an average trap count above 100.

It’s widely accepted mosquito fogging is cosmetic: It only reduces the number of adults on a temporary basis. Preventative measures such as larviciding and eliminating bodies of standing water are considered way more effective. More than anything, precipitation, temperature and soil moisture — basically, the weather — determines whether we wind up with a lot of mosquitoes in any given summer.

Nuisance-mosquito monitoring is entirely separate from a provincial program that monitors the numbers of Culex tarsalis, a species that begins biting people later in the summer and is known to convey West Nile virus to humans. The province — not the city — determines whether the city will fog for West Nile-carrying mosquitoes.