Last week, the State Water Resources Control Board lifted new federal requirements that aimed to curb pesticide use on the ground, which California's local mosquito districts said hindered treatment of mosquitoes in the larval stage. According to CDC, killing mosquitoes before they hatch into adults is the safest and most effective way to halt the spread of the West Nile virus. Although the districts conducted aerial sprayings, they warned that airborne strategies would cause the pesticides to drift and could pose a hazard to human health.