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West Nile Virus and Mosquito Control. K. Bennett, R.P. Bio. Manager, Environment Services May 2003. Discussion. West Nile Virus Target species of mosquitoes Target mosquito habitat Integrated Pest Management Principles Treatment methods Potential program for 2004. West Nile Virus (WNV).

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West Nile Virus and Mosquito Control

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West Nile Virus and Mosquito Control

K. Bennett, R.P. Bio.

Manager, Environment Services

May 2003


  • West Nile Virus

  • Target species of mosquitoes

  • Target mosquito habitat

  • Integrated Pest Management Principles

  • Treatment methods

  • Potential program for 2004

West Nile Virus (WNV)

  • Discovered in the West Nile region of Uganda 1937; appeared in New York City,1999

  • The BC Health Ministry is expecting West Nile to appear in BC this summer.

  • Crows, Ravens and Jays are the local reservoir for the virus, but many species of birds are infected worldwide.

  • Certain species of mosquitoes become infected by biting an infected bird.

  • West Nile Virus is then spread to humans by the bite of an infected mosquito.


  • The risk of becoming seriously ill as a result of the West Nile Virus is very low and most people who become infected experience no symptoms or have very mild illness.

  • However, in rare situations, it can cause encephalitis (inflammation of the brain).

  • Mammals usually do not pass the virus on and are considered a “dead-end” host

  • The virus is not spread by direct person-to-person contact, or from animal to human

Target Species of Mosquitoes

  • Not all mosquitoes bite people

  • Some mosquitoes prefer birds for the blood meal

  • Some mosquitoes bite both

  • Not all species can transmit WNV

  • The target species, therefore bite both people and birds and are capable of transmitting the disease

Target Species of Mosquitoes

  • There are 5 species in BC capable of transmitting WNV;

  • In the Lower Mainland, the target species are Culex pipiens (the “house mosquito”) and Culex tarsalis.

  • Both bite birds and people, although Cx. pipiens bites mainly birds and occasionally people

  • Cx. Pipiens is more common than Cx. tarsalis

Target Species of Mosquitoes

  • Cx. tarsalis and Cx. pipiens overwinter as mated females

  • Lay eggs on the edges of water after a blood meal in the spring

  • Both have several generations per season

Target Mosquito Habitat

  • Cx. pipiens and Cx. tarsalis prefer stagnant, contained water

  • Cx. pipiens prefers water with high organic content, low oxygen, such as stale bird baths, pool covers, stagnant ditches, polluted ponds, where there are few predators

  • Cx. Pipiens is the most common mosquito in artificial containers

  • Healthy wetlands keep mosquito populations in check

Integrated Pest Management

  • Identify the adult species present

  • Identify the target habitat

  • Map and record the habitat

  • Survey the habitat for the presence of larvae

  • Target the larval stage for treatment

  • Educate the public on personal protection and elimination of stagnant water around the home

Treatment Methods

  • Once habitat is identified and known to produce the target species, then the water can be either drained or treated to kill the larvae.

  • Treatment is with Bacillus Thuringiensis (Bt)

  • Bt targets mosquito larvae specifically with little impact on non-target species.

  • Bt will be available to the public for use on private property

  • Spraying for adult mosquitoes is not desirable and least effective


  • Survey for target mosquito habitat

  • map identified sites to the GIS

  • monitor sites for larvae

  • Treat with Bt as needed

  • Use contractor; or

  • Mosquito control program “in –house”

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