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West Nile Virus Battle Begins Near Osoyoos
– Larvicide harmful only to mosquitoes –
(OSOYOOS TIMES — August 9, 2006) –
By Julie TurnerrnOsoyoos Times
In an effort to reduce the numbers of West Nile Virus-carrying mosquitoes within the Regional District of Okanagan Similkameen (RDOS), a mosquito spraying program is now underway in the area.
UBC Biology major Nigel Lindsey, with the environmental services firm D.G. Regan and Associates, has been out in the field throughout the province this summer, and was in Osoyoos last week monitoring catch basins, ditches and ponds throughout the area to determine mosquito populations and to treat the areas with pesticides. On Tuesday morning, he was at the irrigation canal walkway just north of the high school, and at an oxbow at the head of Osoyoos Lake.
Dipping a scoop into the water, Lindsey pulled up several cups and examined them for larvae. The information gathered here will go to the BCCDC (British Columbia Centre for Disease Control), which has been identifying mosquitoes and mapping their sites, Lindsey says. There can be thousands of mosquito larvae in a small cup of water.
Although there have been no reports of West Nile Virus (WNv) in British Columbia, Lindsey says all the conditions in the South Okanagan increase the risk factors for the virus. Those conditions include habitat (plenty of surface water and catch basins), temperatures (warm weather can speed up the mosquito's life cycle) and the fact the two WNv-carrying mosquitoes, Culex tarsalis and Culex pipiens, exist in the area. Experts feel it is only a matter of time before WNv is found to be in B.C. Culex tarsalis larvae, one of the two vectors for WNv, were found in oxbows at the head of Osoyoos Lake. Human transmission of WNv happens when a mosquito bites an infected bird and then in turn bites a human. Birds, especially corvids (crows, ravens, jays, etc.) are most susceptible to the disease.
The Culex tarsalis mosquitoes thrive in areas which have an extended period of warm weather and water high in nutrients. A good example would be ponds in orchards. Storm water catch basins have water all year round, are often warm, and contain nutrients such as grass clippings, which help feed mosquito larvae.
WNv-carrying mosquitoes are out from the second week of July through the end of August. The life cycle of a mosquito, from egg to larva to pupa to adult, can vary depending on the breed and temperature. Only female mosquitoes bite in order to get a blood meal to feed their developing eggs. Once she lays her eggs, the female usually dies. Male mosquitoes feed on pollen.
Two types of larvicide are being used in the area, Vectobac and Vectolex. The Vectolex larvicide is made up of small granules, and when tossed into the water, the larvicide lasts up to six weeks; Vectobac consists of larger chunks, and once spread are effective between two to 10 days.
The material is broadcast throughout the water, about 7.5 kg per hectare, and is ingested by the larvae. Vectolex and Vectobac are harmful only to mosquitoes. The product is actually made of food-grade corn granules, tainted with bacteria, and coated in a food grade wax. Lindsey says sometimes ducks and other birds, accustomed to being fed grain by humans, will move in and eat the grain, so some stealth is required when treating the water. The biodegradable products will not hurt other insects, fish or animals, but they won't do much good if they are scooped up by birds.
Lindsey will continue his work up the Okanagan Valley over the next couple of weeks. We'll do our initial blast this week, and depending on which pesticide we use, will follow-up on all the catch basins with another treatment.
The West Nile Virus Mosquito Vector Control Program is completely funded by the province. This year, the RDOS applied for funding on behalf of Osoyoos, Oliver, Penticton, Summerland and Princeton and received $127,839. Contractors D.G. Regan and Associates are carrying out the program for this year, at a cost of $65,000. The balance of the funding is being directed at mapping of mosquito sites, the creation of an emergency plan to deal with WNv, and advertising and education.
Homeowners can help reduce the mosquito problem by eliminating habitats, which includes draining standing water in flower pots, wheelbarrows, old tires, etc. weekly, and regularly changing water in pet dishes and bird baths. To reduce the risk of being bitten, wear loose, light-coloured clothing, avoid areas where and when mosquitoes are most active and apply insect repellent containing DEET. Serious symptoms of a mosquito bite include: ongoing fever, muscle weakness, stiff neck, confusion, severe headache, sensitivity to light or extreme swelling at the site of the mosquito bite.