County aims to take bite out of mosquito breeding on Thursday

Palo Alto Baylands trails will be closed for several hours on Thursday for aerial treatment of mosquitoes, the Santa Clara County Vector Control District said in a press release issued Tuesday.

A helicopter crew will fly over the Baylands with a spray that targets the winter salt marsh mosquito (Aedes squamiger) with naturally occurring microbes and a mosquito-specific hormone. The treatment has been safely and effectively used by the county annually since 1992, the district said.

The aerial spraying is scheduled to start at 7:30 a.m. and will last a few hours.

“Current conditions create a high probability that a significant number of salt marsh mosquitoes will become adults in a few days if left untreated. This species is known to bite viciously during the day and can fly more than 15 miles from its breeding grounds to feed on humans and other mammals,” the district said.

The crew will cover large areas of the Palo Alto Flood Basin marsh to minimize impact to the marsh habitat. A map of the spray area can be found here and information about mosquito control can be found at SCCvector.org.

The same area was treated Feb. 12 for the winter salt marsh mosquito. It is roughly bordered by Adobe Creek to the north, Adobe Creek Loop Trail to the east, East Bayshore Road to the south and Mayfield Slough to the west.

“Recent rains have provided the ideal environment for mosquito larvae to develop in hard to reach areas of the marsh. These treatments will help reduce adult mosquito populations in the area,” Vector Control District Manager Dr. Nayer Zahiri said.

The area will be treated with a naturally occurring soil bacterium (Bacillus thuringiensis var. israelensis, or Bti), which activates when consumed by mosquito larvae, and a mosquito-specific treatment (methoprene) that prevents them from becoming adults. The ecology-friendly application is short-lived in the environment and is not harmful to birds, fish, other insects, wildlife or humans, the district said. More information about these products is available at the vector control district’s website.

The helicopter crew might make low-altitude passes over trails surrounding the treatment area. The district advises the public to avoid areas where the helicopter is operating. Staff will post signage at locations around the treatment area to alert the public.

The winter salt marsh mosquito lays its eggs in the moist soil in late spring and early summer. The eggs can lay dormant for many years, even after repeated flooding. The district asks the public to report mosquito-breeding sources. People can prevent mosquito breeding by dumping standing water on properties, wearing long-sleeved shirts and long pants and applying repellent when outdoors to prevent mosquitoes from biting.

For free assistance on mosquito control, the public can contact the district office at 408-918-4770, or by filling out a service request online.