Mosquitoes are vectors of human and other animal diseases. For example, Culex pipiens mosquitoes can carry the West Nile virus. Humans and horses are what are called dead-end hosts, meaning the virus doesn’t amplify in them. Birds, especially corvids (crows, blue jays, magpies, etc.) are considered amplifying hosts and the disease is spread by mosquitoes taking blood meals from infected birds, then biting humans. Insecticides are used to reduce the number of mosquitoes in the environment, and thus control transmission of the disease. Larvicides, which are designed to affect the aquatic juvenile stage of the life cycle, are added to areas of standing water. Adulticides are sprayed to kill adults. Adulticides are applied at night, when most beneficial insects are not actively flying, and are often used in doses of as little as an ounce per acre (about the size of a football field). Mosquito control districts vary in how much insecticide application they engage in. Where Linda lives, for example, adulticiding doesn’t take place until there are West Nile virus-positive mosquitoes detected during surveillance (the regular trapping and testing of mosquitoes). Repellants (i.e. “bug spray”) are used to keep mosquitoes from landing on humans and attempting to feed.
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