Killing them softly: Santa Clara County to ensure immature mosquitoes never grow up | News | Palo Alto Online |


Killing them softly: Santa Clara County to ensure immature mosquitoes never grow up

Helicopter crews will disperse bacterium over Bayland; trails will be closed Wednesday morning

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Santa Clara County will unleash an eco-friendly larvicide on mosquitoes in the Palo Alto Baylands on Wednesday.

Part of an annual tradition since 1992, the county's Vector Control District — tasked with monitoring and managing the spread of diseases such as the plague, rabies and other maladies that can come from rodents or insects like mosquitoes — will be covering Palo Alto Baylands trails with a soil bacterium esoterically known as the Bacillus thuringiensis israelensis or Bti.

What's more important to know than the egregiously long and hard-to-pronounce name of the bacteria is that the marsh trails of the Baylands are closed to the public during the treatment, which starts around 7:30 a.m. and is expected to last several hours, according to a county press release.

The public is advised to avoid the targeted areas.

Pesky and "known to bite viciously during the day," the winter salt marsh mosquito thrives in the Baylands and parts of the Zanker wetland in north San Jose, where eggs have already been laid in the moist soil, according to the press release. The eggs can stay dormant for several years. But eventually, they hatch and grow into full-grown adults around mid-February to mid-March, capable of feeding on mammals and humans up to more than 15 miles away from the original breeding grounds.

To stop mosquitoes from maturing, crews from the Vector Control District will use helicopters to efficiently cover a large area in the Palo Alto Flood Basin 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.

Bti is one half of the biorational larvicide that will be used against the mosquito population, along with methoprene, a common insect growth inhibitor. It's a certain species of naturally occurring bacteria that survives in the soil and produces proteins toxic to certain insects like mosquitoes when it's consumed, but harmless to humans, birds, fish and other insects such as honey bees.

"We have had tremendous success with these annual treatments," said Vector Control District Manager Nayer Zahiri. "Without this application, the public would notice a dramatic increase in the number of mosquitoes."

The public is encouraged by the district to report any mosquito-breeding grounds and take preventive measures such as dumping standing water around one's property, applying mosquito repellent and wearing long-sleeved shirts and long pants.

For free mosquito control assistance the public can call the district office at 408-918-4770 or fill out a service request online at


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2 people like this
Posted by Resident
a resident of Another Palo Alto neighborhood
on Feb 11, 2020 at 9:38 am

I hope they do a better job than last year and that they repeat the spraying when necessary. Last summer it was miserable just walking around in the middle of the afternoon and sitting out in the evening was impossible.

1 person likes this
Posted by Anon
a resident of Another Palo Alto neighborhood
on Feb 11, 2020 at 9:44 am

Apologies: I'm a little confused about this:

>> Bti is one half of the biorational larvicide that will be used against the mosquito population, along with methoprene, a common insect growth inhibitor.

In particular, what is the impact on butterflies and moths? I saw so few butterflies and (decorative) moths last year that I could probably count them all on my fingers. And yes, I have what is supposed to be a "friendly" garden. Thank goodness I'm still getting lots of hummingbirds.

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