Vector Control District to Conduct Aerial Treatment of Bay Marshes to Reduce Population of Nuisance Mosquitoes

SANTA CLARA COUNTY, CALIF. — The County of Santa Clara Vector Control District is scheduled to conduct an aerial mosquito-larva-control treatment on Wednesday, Feb. 14, in the Palo Alto flood basin, a nonresidential area along San Francisco Bay.
 
The treatment will prevent the growth of mosquito larvae currently breeding in the flood basin, specifically, those of the winter salt marsh mosquito (Aedes squamiger). The treatment uses naturally occurring microbes and a mosquito-hormone regulator to reduce the mosquito population.  
 
The district has been closely monitoring the development of mosquito larvae in the flood basin. Winter salt marsh mosquitoes can fly up to 20 miles in search of a blood meal. They are opportunistic feeders and aggressive biters.

A helicopter will be used to apply the pesticides to these difficult-to-reach areas. The district has used this safe and effective application method almost every year since 1992. This method also minimizes the impact on marsh habitat.
 
Depending on weather conditions, the treatment will start at approximately 7:30 a.m. and last a few hours. If the weather does not allow for a successful treatment, the district will post updates to its website and social media platforms.
 
“Our team members check these marshes on a regular basis and have done treatments by hand. However, all the recent rain has created pockets of water that we can’t reach by foot. If we don’t conduct the treatment soon, larvae in the area will soon become biting adults.” said Vector Control District Manager, Dr. Nayer Zahiri. “This treatment will significantly reduce the mosquito population and prevent adult mosquitoes from flying off into neighboring communities.”
 
The area will be treated with a naturally occurring soil bacterium (Bacillus thuringiensis subspecies israelensis) that activates when consumed by mosquito larvae and a mosquito hormone regulator (methoprene) that prevents immature mosquitoes from becoming adults. These pesticides do not last long in the environment and, at the low doses used in the treatment of mosquito larvae, are not harmful to birds, fish, beneficial insects, wildlife or humans. Aerial application is used when mosquito breeding occurs over larger areas, a common practice by vector control districts throughout the Bay Area. For more information on the control materials used for these treatments, please visit the district’s mosquito-larva-control webpage.
 
The helicopter may make low-altitude passes over trails surrounding the treatment area, so the district recommends that members of the public avoid areas where the helicopter is operating. The district will post signs at various locations around the treatment area to notify visitors about the treatment. Marsh trails will be closed to the public during the treatment. There is no risk of exposure to pesticides on open trails during the treatment and the public will be able to access all areas after the treatment is complete.
 
The district encourages the public to report mosquito activity and to take preventive measures such as dumping standing water on their property; wearing long-sleeved shirts and long pants in the morning and evening, when mosquitoes are most active; and applying insect repellent when spending time outdoors. For more information on mosquitoes and mosquito prevention, visit the district’s mosquitoes webpage.
 
For free assistance with mosquito control, residents may contact the district office at (408) 918-4770 between 7:30 a.m. and 3:00 p.m. or submit an online service request.
 
Mosquito Control Treatment
Palo Alto Flood Basin



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