1 West Nile Virus and Mosquito Control K. Bennett, R.P. Bio. Manager, Environment Services May 2003

2 Discussion West Nile Virus Target species of mosquitoes Target mosquito habitat Integrated Pest Management Principles Treatment methods Potential program for 2004

3 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.

4 WNV  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

5 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

6 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

7 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

8 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

9 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

10 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”