Mosquito control officials often apply biological or chemical larvicides, with selective action and moderate residual activity, to the aquatic habitats. To have the maximum impact on the mosquito population, larvicides are applied during those periods when immature stages are concentrated in the breeding sites and before the adult forms emerge and disperse. Some mosquitoes can fly from flood plains, coastal marsh areas, or protected habitats to impact urban residential areas. In these cases, it is often necessary to apply pesticides to kill adult mosquitoes. Surveillance data may prompt insecticide applications when mosquitoes are abundant.
Applications usually coincide with the maximum adult mosquito activity in urban residential areas.
They must also apply these pesticides with carefully calibrated equipment that generates the proper-sized insecticide droplets that will impinge on adult mosquitoes while they are at rest or flying. If the droplets are too large, they will fall to the ground. If they are too small, the prevailing winds will carry them away from the target area. Depending on the situation, mosquito control officials may safely apply these insecticides from spray equipment mounted on trucks, airplanes or helicopters. All insecticides used in the U.S. for public health use have been approved and registered by the EPA following the review of many scientific studies.