Mosquitoes in Your Back Yard

Events of 2002 have shown that not only has West Nile Virus spread into Ontario, but also is rapidly spreading across all of North America. It became apparent that there were many more cases in Ontario than originally reported and at least 16 human deaths.What can you do to help protect yourself and your family? The first thing is to make your own mosquito management plan. Start with an assessment of your property. Look for any possible mosquito breeding sites. Make a list of these or if you have a larger property, mark down sites on a copy of your property survey plan. There are two types of breeding sites to inspect for. The first is water from snowmelt pools in which spring mosquitoes breed and which generally dry up in the summer. The second is permanent standing water or water from summer rains in which summer mosquitoes breed. At this point, it is believed that summer mosquitoes, especially culex pipiens, are the main vectors of West Nile Virus.

Shallow, stagnant, still water provides ideal breeding sites for mosquitoes. They are not able to breed in deep water or swift moving streams and rivers. Summer mosquitoes use a variety of sites including:

  • shallow ponds or ponds with heavy weed growth around the edges
  • wheel ruts or depressions that act as temporary pools
  • ditches in which water lays
  • unused swimming or wadding pools and covers
  • eaves troughs
  • drains, culverts and ditches
  • bird baths, rain barrels and plant trays
  • discarded containers such as old tires, cans, buckets, tarps, toys etc.
  • septic fields and catch basins

Mosquito control should be aimed at the larval stage. Once you have identified potential breeding sources then try to eliminate as many as possible. Fill in wheel ruts and shallow depressions. Clean ditches so that water will flow through them without pooling. Remove vegetation growth from around pond edges, have the edges graded to a steeper angle or have them dug out. Place gravel or sand around pond edges. Add aerators or fountains to ponds to cause water movement. Add mosquito-eating fish to larger ponds.

Chemicals for controlling larvae are called larvicides. These can only be applied to water that does not flow out of your property. Two of these, Vectobac and Aquabac contain a bacterium, B.t.i., which is specific to mosquitoes and is not harmful to people, pets, other organisms or the environment.

Adult mosquitoes avoid being out in the direct sun. Keeping long grass, weeds and brush cut reduces resting sites. Make sure all screens are in good repair and fit tightly. Consider screening in porches or gazebos to create a place where you can sit out in the early morning or at dusk. Use personal protection as your first line of defense. This includes:

  • wearing light coloured, loose fitting, long sleeved shirts and long pants with a bug net type hat
  • avoiding activity outside at dawn and dusk during peak biting season
  • using a biting insect repellent. Products containing DEET are still considered among the most effective.

Chemicals for controlling adult mosquitoes are called adulticides. These can be used in hand held sprayers or foggers. Results from these types of treatments are very temporary and localized. Pyrethrins and malathion are available as adulticides.

There are a variety of devices and gizmos available on the market for controlling mosquitoes. Many of them are not effective. I will discuss some of them in a future article.

This should provide the basis for your mosquito management plan. You can carry out the survey and treatment program yourself or hire a qualified pest control company to do it for you. The important thing is to implement a plan early in the season as it is too late in Aug. or Sept. when WNV reaches its peak.