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Blood-feeding Culex tarsalis.
Blood-feeding Culex tarsalis. Used with permission from UC IPM, J.K. Clark, photographer. © Regents of the University of California

Calgary is home to more than 20 of the 44 species of mosquito currently known to occur in Alberta. The majority of species are termed floodwater species, these overwinter in the soil as eggs in areas prone to seasonal flooding and hatch during spring and summer rain events. There are four mosquito larval stages and a pupal stage that are found in the water. When adults emerge, and after mating, the females seek out a blood meal which is used to develop eggs, and this of course is the main cause of their annoyance to us.

A small number of species overwinter as mated female adults and deposit their eggs as rafts on the water surface of semi-permanent pools. Among these species is the primary vector of West Nile virus in Alberta, Culex tarsalis. There are a number of factors that contribute to Culex tarsalis being a competent virus vector and one of these is its readiness to feed on both birds and mammals, potentially picking up the virus from birds and transmitting the virus to a human if it takes another blood meal. The likelihood of contracting the virus and developing severe symptoms is low, but devastating for those susceptible to West Nile virus neurological syndrome.

Mosquito surveillance and control in Calgary

CO2 trap for assessing populations of host-seeking mosquitoes
CO2 trap for assessing populations of host-seeking mosquitoes (blue cylinder is a dry ice flask that releases CO2 to attract mosquitoes, a battery operates a fan that draws mosquitoes into the net)

Populations of Culex tarsalis are monitored using CO2 traps by The City of Calgary Parks Integrated Pest Management (IPM) unit. Numbers of Culex tarsalis in Calgary are generally low through the early part of the season and peak later in the summer, they are set back by control operations and unseasonably cool periods.

Adult and larval mosquito populations of all species are monitored by IPM throughout the season, and the data collected is used to determine the need for mosquito control and the efficacy of treatments conducted. Mosquitoes are controlled by IPM using granular products registered and regulated by the Federal Pest Management Regulatory Agency. These products are applied to standing water that have more than the minimum control threshold of mosquito larvae. Products are applied both from the ground and aerially and are highly specific to mosquito larvae having almost no effect on other organisms or the environment.

Personal protection from mosquitoes

For further information on mosquitoes in Alberta, West Nile virus, and information on personal protection from mosquito bites please visit the Alberta Health website and the Public Health Agency of Canada website.