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Spraying only one option

The City of Andalusia has been spraying along the roadside daily for adult mosquitoes. This form of pesticide - called "adulticide" is the most common approach taken to mosquito population control.

With the current outbreak of West Nile Virus, other methods are being used by those areas hardest hit. One such

method uses a naturally forming substance as a larvicide, to attack and kill mosquito larvae before they mature to the disease-carrying stage in the life-cycle.

According to the Centers for Disease Control, several of these larvicides pose minimal threat to other life forms. One of the most often used is Bti, an environmentally responsible bio-larvicide derived from a naturally occurring spore- and crystal-forming soil bacterium. Bti affects very few other life forms and works through the larvae's own enzymes. It comes in several forms, including pellets and briquettes, which are scattered in water that hosts the larvae.

Bti has no toxic effects on beneficial and predacious insects such as honeybees, beetles, mayflies, dragonflies, damselflies, and true bugs. Among butterflies and moths, low levels of toxicity were observed only in three species.

No toxicity from Bti was observed in fish, oysters, shrimp, crabs, mollusks, flatworms, and frogs. What is more important, the larvicide has no effect on humans or pets.

Another larvicide is based on the Bacillus Sphaericus bacteria and is especially effective in treating the kind of mosquitoes that breed in highly organic water, such as water treatment facilities, storm sewers, animal waste lagoons, and swamps.

The alternative to larvicides is insecticide sprays to kill adult mosquitoes. Used in many residential areas, some kill both mosquitoes and "good insects" that eat mosquitoes. Another drawback is limited effect.

Large numbers of mosquitoes survive adulticide sprays by flying away or finding shelter in gutter downspouts and eaves, under foliage, and other protected areas.

(EDITOR'S NOTE: The Center for Disease Control contributed to this report.)