The mosquito population in parts of Dallas and Denton counties actually increased after last summer’s aerial pesticide spraying. But, the Centers for Disease Control found the number of human cases of the mosquito-borne illness went down.
In the final report from the CDC, investigators say there were “small but statistically significant increases in mosquito abundance” in North Dallas County and Denton County after the aerial spraying. But the number of West Nile infected mosquitoes dropped in Denton County, and disappeared completely in parts of south and east Dallas County. West Nile infected mosquitoes stayed about the same before and after spraying in the North Dallas zone, which was the hardest hit with human cases. But, the report says that could be due to the thunderstorms that interrupted plans for two consecutive nights of spraying – the most efficient application.
The CDC report says the number of the human cases decreased in both treated and untreated areas, but “the relative change was significantly greater in aerial-sprayed areas.”
Investigators make several recommendations: including; more coordinated mosquito surveillance; greater attention to treatment of neglected or abandoned swimming pools; and larval mapping – treating breeding grounds to kill the mosquitoes before they hatch.