A lot depends on our weather. For example, following heavy snowfall, Edmonton saw an increased snow melt in the spring of 2011, followed by a significant amount of rain over the summer. This resulted in substantial standing water, which is habitat for mosquitoes to develop. This was in sharp contrast to the previous few years in which we experienced a drought in Edmonton and area, which meant far fewer mosquitoes during those years.

The City of Edmonton has a long-standing mosquito control program. Our approach is:

• To treat standing bodies of water, such as roadside ditches and non-permanent field pools. We target mosquito larvae, the stage before they become adult mosquitoes. Treating larvae is a safe and effective way to control the pests.
• Standing water is treated using helicopters, equipment mounted on vehicles and equipment that pest control crews carry on their backs.
• The City’s mosquito control program starts in the spring when crews target standing water following the snow melt. Throughout the summer, crews will initiate rounds of spraying based on the amount of rainfall and larvae detected in standing water.
• We also treat select areas for adult mosquitoes, given the right conditions. This includes appropriate weather and the presence of perimeter vegetation. These areas are typically around large outdoor festivals or events and have a higher population of adult mosquitoes that warrant additional treatment.

The City uses a number of tools to monitor adult mosquitoes. While these help determine species and can show population trends, they are not a primary factor in determining our control program. Our dip tests for larvae are given more consideration when it comes to determining when to spray. The City monitors mosquitoes using the following traps.

1. New Jersey Light Traps
   • These are our standard light traps, placed in strategic locations around the city and surrounding rural areas. These are used to monitor general population trends and information on mosquito migration.
   • The City monitors for various mosquito species; however, the City uses the light trap data for comparison purposes. This is because the light traps are the long-standing means of capturing adult mosquitoes and provide comparative data that cannot be obtained with the other traps.
2. CDC Traps (Carbon Dioxide Baited Trap)
   • These are battery-powered and use sublimating dry ice as the carbon dioxide source. These traps are usually put up for 24 hours. Because they use dry ice rather than a dim light bulb, these traps collect considerably more mosquitoes and have an added benefit of less bycatch, meaning fewer moths and other night-flying insects. This makes the specimens much cleaner and easier to process.
   • These traps have several disadvantages, which include fairly high failure rates (battery disconnects, hoses coming off, etc.). They are expensive and laborious to operate on a continual basis, and processing the larger samples takes a correspondingly longer time.
   • These traps are useful for monitoring around outdoor events and for targeting specific areas (such as for West Nile virus monitoring), as well as getting relative numbers of species that aren't typically drawn to our light traps (like the daytime biter Ochlerotatus spencerii).
   • Because CDC traps have not been used consistently in the same sites over and over again, we have no comparative data, so they are not useful for general population level monitoring.
3. Mosquito Magnets (Carbon Dioxide Baited Trap)
   • These are commercial products, electrically-powered and use propane as a carbon dioxide source supplemented with an octenol lure. We have had three of these operating since 2011 to improve our ability to track the population of species not typically drawn to our light traps.
   • A few mechanical issues have occurred, but they seem to be functioning reasonably well so far. These traps are considered less reliable and staff continue to evaluate whether they would work long-term. Because this method of trapping is a recent development, little comparative data is available.
4. Oviposition Traps
   • These are organic-rich, water-baited traps. Essentially, these are buckets of smelly water with a battery-powered fan with a catch-bag sitting overtop. They are intended to collect Culex tarsalis females, which come to organically rich water to lay their eggs.
   • These have not been deployed since 2004/05 and, to date, have not attracted Culex tarsalis.
5. Larval Surveys
   • Staff also collect samples while monitoring mosquito larvae and rear them in the lab for identification. This gives us a better indication of species and the rate at which they’re developing, but it is not as helpful in determining populations.

Experience has shown that controlling larvae is more effective because it reduces the number of mosquitoes before they can develop into adults. It is also a more proactive, environmentally-friendly and safer approach than controlling adult mosquitoes.

We consider a number of factors before we implement another round of spraying:

• Weather: If we have experienced significant rainfalls resulting in standing bodies of water, we have more sites for larvae to develop.
• Larvae: We constantly monitor standing water for larvae. If these numbers are high, then we will initiate another round of spraying.
• Adults: We trap mosquitoes in light traps placed in locations around the city. An increasing trend in the number of mosquitoes is another factor we consider.

Typically, spraying is triggered by two inches (50 ml) of accumulated rainfall as measured in City of Edmonton rain gauges, and when monitoring shows a considerable amount of mosquito larvae in temporary standing bodies of water.

The City identifies mosquitoes caught from various trap systems including light traps, CDC traps and Mosquito Magnet traps for any sign of Culex tarsalis. In addition, we track the accumulation of degree days in the region. If conditions warrant and the risk increases, the City steps up its monitoring. This includes putting out more CDC traps in strategic locations, increasing larval surveillance in sites likely to serve as development habitat for Culex tarsalis, and intensifying identification of our mosquito catches to ensure that the disease vector is not present. 

If Culex tarsalis larvae are detected, they will be targeted for larval control.  If adult Culex tarsalis are found during the period when West Nile virus transmission is a danger, then the City will explore coordinating efforts with the Province for increased CDC monitoring and testing adult mosquitoes for presence of the virus.

We feel the safest and most environmentally sound approach is to mainly focus on treating temporary standing water for larvae. In treating larvae, the City avoids harming other beneficial species, such as dragonflies, which consume mosquitoes. While treating mosquitoes at the adult stage immediately kills the pests, new crops of mosquitoes will move in to replace them. Treating larvae kills the pests before they develop.

The City cannot treat running water, as per the product label.

Stormwater ponds, and creeks and rivers, are not prime habitat for mosquito development. So, spraying those bodies of water will have little impact, if any, on the number of mosquitoes.

The products we use to control mosquito larvae are registered by Health Canada's Pest Management Regulatory Agency (PMRA).  Health Canada's decision to register a pesticide is only made if the product does not pose unacceptable risks to people or the environment when used according to label directions.

Treatment of mosquito development sites are only permitted by pesticide applicators who are certified by the Alberta Environment and Sustainable Resource Development (ESRD) ministry and meet stringent standards for the application of mosquito control products according to allowable uses and restrictions defined by Health Canada on the product's label.

We recommend ensuring that you remove all standing water, cover rain barrels, check to ensure your screens don’t have holes, and keep your lawn cut.

Residents are advised to wear repellent, pants and long-sleeved shirts when enjoying the outdoors. Light-coloured, loose-fitting clothing also helps prevent mosquito bites.