The Truth About Mosquitoes And Backyard Ponds...
By Julie Bawden Davis
Ponds usually bring good things to the backyard -- like cool comfort, a beautiful view, and interesting wildlife. One visitor to ponds is not so welcome, though. No one wants mosquitoes around because they're a nuisance, and more importantly, because of the possibility that they may carry the deadly West Nile Virus (WNV).
When Problems Arise
"Because humans aren't hosts of the WNV, even though it's in the environment, it rarely infects them" says Harry Savage, research entomologist with the Centers for Disease Control and Prevention (CDC) in Fort Collins, Colorado. "Problems arise when the amount of virus in the environment gets very high, which happens when there are a lot of mosquitoes present and conditions are good for their reproduction. Then the virus spills over to humans. The key is to reduce the population of mosquitoes which will then interrupt transmission to humans."
No Need to Panic
"The West Nile Virus is an "Old World" virus that has been in existence for ten thousand years," says Harry Savage of the CDC. It can infect birds, horses, mosquitoes, humans, and some other mammals. Although it has been in Africa, Eastern Europe, West Asia and the Middle East for many years, it was not detected in the Western Hemisphere until 1999. It is most closely related genetically to strains found in the Middle East.
According to the CDC, as of December 3, there have been 3,775 laboratory positive human cases and 216 deaths. Despite these numbers, the chance of becoming infected with the virus is low and most people who do contract the virus will not have any type of illness. The CDC estimates that 20% of people who become infected will develop symptoms of West Nile Fever, which include fever, headache, body aches, and swollen lymph glands. The illness usually lasts only a few days and does not appear to cause any long-term health effects.
Complications arise when a person contracts West Nile encephalitis or meningitis, which can cause severe headache, high fever, neck stiffness, disorientation, convulsions, paralysis and coma. The CDC estimates that 1 in 150 infected people will develop a more severe form of the disease.
West Nile Virus can be transmitted when an infected mosquito bites a human and takes in blood. Mosquitoes become infected when they feed on infected birds. If the virus reaches the mosquito's salivary glands, it can then be injected into humans. Not all mosquitoes can be infected by the virus, and some species are more likely to be infected than others," says vector biologist Stephen Higgs.
"Only female mosquitoes feed on blood because they need the blood to produce and lay eggs. Mosquitoes don't actually live in ponds, but lay their eggs in ponds and then go looking for a blood meal," says Thomas W. Scott, professor of entomology and director of the Davis Arbovirus Research Unit at the University of California, Davis.
Responsible Pond Owners
Keep the following mosquito control measure in mind:
Julie Bawden Davis is an Orange, California garden writer whose work appears in a variety of national and regional publications. She is the author of the book Houseplants & Indoor Gardening (Black & Decker Outdoor Home Series, 2002.)
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To develop the look of a natural pond you can:
- Go with the native vegetation that thrives in your area.
- Repeat mass groupings using one or two kinds of plants, especially grasses and reeds.
- Surround your pond with trees and shrubs that naturally occur near water, like alders, river birches, dogwoods and willows.
- Plant vigorous natives in the shallow margins, and make sure the center of the pool is more than eighteen inches deep, so natives won't over run the pond.