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Helicopter Treatment for Winter Salt Marsh Mosquitoes Scheduled


SANTA CLARA COUNTY, CALIF. – Beginning at approximately 8:00 a.m., Wednesday, February 17, 2010, (weather permitting) the Santa Clara County Vector Control District (VCD) will be applying products by helicopter to reduce the emergence of adult mosquitoes. The areas to be treated are the Alviso Marsh, Smith Yard Marsh, New Chicago Marsh, and Zanker Marsh. Aerial treatment is necessary because the areas are too extensive and difficult to be treated from the ground. No residences or businesses fall within the area to be treated.

Commonly called the “California salt marsh mosquito”, Aedes squamiger lays its eggs in the moist soil in late spring and early summer. These eggs can lay dormant for many years, even after repeated flooding. High tides and seasonal rains, together with the short days and cooler temperatures of winter cause the eggs to hatch when they are submerged under water. Although this species has not yet been identified as a West Nile Virus transmitter, , it is known to be a vicious day biter and can fly over 20 miles from its breeding grounds to feed on humans and other mammals.

VCD has been closely monitoring the development of mosquito larvae in the areas to be treated. Current field conditions and mosquito growth trends indicate a high probability that a significant number of salt marsh mosquitoes will become adults in early to mid- March if left untreated. The mosquito fly-off may affect residents from the north coastal areas of the county to as far south as the southernmost part of the City of San José and east to Milpitas.

Approximately 400 acres will be treated with environmentally safe products: methoprene, an insect growth regulator, and Bacillus thuringiensis var. israelensis (Bti). Bti is a natural bacteria that, when consumed by mosquito larvae, produces an insecticidal protein that kills the larvae. These products are mosquito-specific: they effectively control the immature (aquatic stage) mosquitoes, but are not harmful to birds, fish, other insects, wildlife, or humans. More information about these products is available at

Marsh areas to be treated are based on routine surveillance conducted by the VCD. No residences or businesses fall within the area to be treated. Access to the areas will be restricted during aerial applications, but open to the public immediately afterwards. These measures should minimize the number of mosquitoes and mosquito bites to residents in the surrounding communities.

VCD continues to encourage residents to report mosquito-breeding sources and take preventive measures, such as wearing long-sleeved shirts and long pants, and applying repellent when outdoors where mosquitoes are biting.

For more information about mosquito prevention, go to or call 408.918.4770.

Media Contact: Gwendolyn Mitchell/Lingxia Meng, Office of Public Affairs, (408) 299-5119
Posted: February 16, 2010

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