Vector Control officials today began using a helicopter to drop larvicide on about 1,000 acres of heavily vegetated areas in the San Diego area to reduce mosquito breeding.

"It is important to eliminate mosquito-breeding sites and control mosquitoes in the larval stage, so they don't turn into biting adults that can transmit diseases such as West Nile virus," said Jack Miller, acting director of the county's Department of Environmental Health.

The larvicide, which is not toxic to humans, wildlife or the environment, contains a naturally occurring bacteria designed to dissolve in water that kills developing mosquito larvae for up to four weeks.

Vector Control officials plan to conduct aerial applications to wetlands in the county every three weeks throughout mosquito season.