Efforts Aim to Take Bite Out of Carpinteria Mosquito Outbreak
The primary culprit is the black saltmarsh mosquito, and the focus is on finding and treating breeding sources at the salt marsh.
Biting mosquitoes have been exceptionally prevalent in Carpinteria since about the second week of August, apparently because of warm temperatures and high tides in the Carpinteria Salt Marsh. The Mosquito and Vector Management District of Santa Barbara County has received about 65 calls, e-mails, faxes or office visits about the outbreak since Aug. 12. The staff biologist says this may be the most severe outbreak of mosquitoes in Carpinteria since 1997.
Here, the Mosquito and Vector Management District answers frequently asked questions about the mosquito outbreak.
Based on various reports and direct observation, along with routine trapping of mosquitoes conducted by the district Aug. 11-12, the primary culprit is the black saltmarsh mosquito. It is a common mosquito species found throughout North America. As its name implies, it breeds in saltwater and is dark or black in color. This mosquito can be active all hours of the day and can fly 5 kilometers (three miles) from its breeding sources in standing brackish water.
What is the source of the mosquito?
The district believes that most or all of these mosquitoes are originating from many — potentially hundreds — of highly scattered wet sites throughout the Carpinteria Salt Marsh, although a few hydrologically dysfunctional basins within the marsh are the most likely source of the mosquito breeding.
Considering the flight distance by adult mosquitoes of this species, nearly all of the Carpinteria urban area can be affected within a three-mile radius from the marsh. So far we have received calls from people as far north of Foothill Road.
Why are the mosquitoes so bad now?
No one can know for sure, but the exceptionally high tides (7-plus feet) July 30-31 may have led to persistent standing water in shallow depressions throughout the Carpinteria Salt Marsh. When combined with subsequent warm summer days and nights, these standing, brackish water sources are where this mosquito breeds. Adult black saltmarsh mosquitoes can live for more than three weeks while seeking a blood meal that enables their breeding.
What can people do?
While eliminating or appropriately treating standing water always is a good practice to eliminate mosquitoes at a local residence or property, the black saltmarsh mosquito most likely is originating from sources far more distant than a home in town.
Accordingly, the district will focus its efforts in the near term to treating the mosquito breeding sources at the Carpinteria Salt Marsh instead of responding to isolated service requests scattered throughout Carpinteria and the surrounding area. Of course, we encourage residents to continue communicating with us and reporting any mosquitoes seen or felt.
How can people minimize biting?
As usual, people should use insect repellent, wear long sleeves and pants (especially light colors), and close window and door screens, especially at dawn and dusk. Mosquitoes are attracted to the carbon dioxide from a respiring animal.
What is the status of the West Nile virus?
Fortunately, this mosquito species doesn’t carry malaria and has not been reported to carry the West Nile virus in nearly all of the thousands of mosquito samples analyzed throughout California during the past few years, as reported in Arbovirus Bulletins by the California Department of Public Health.
The West Nile virus can be transmitted by mosquitoes to humans and can be fatal to some humans, but no occurrence of the West Nile virus in humans has been reported in Santa Barbara County since two cases in 2005. One virus-positive dead bird was found in 2007 near Lompoc, and a few others have occurred in the county during previous years.
What is the district doing?
We are modifying our field work priorities this week to dedicate more staff time to finding and treating mosquito breeding sources at the Carpinteria Salt Marsh. Accordingly, vector management services to other areas of the county are being postponed to address the mosquito outbreak in Carpinteria.
Field operations at the Carpinteria Salt Marsh also need to be scheduled for coinciding with the lowest tides possible. Eventually, the district will have to focus on other areas of the county where human disease vectors are present. The district has five field workers plus the general manager.
How are the mosquitoes “treated”?
The primary method the district practices to treat mosquitoes is by killing the larvae that are in standing water, before they hatch out into more adult, flying mosquitoes. We typically use a common bio-control product based on the Bacillus bacterium, commonly called Bti. These inert bacteria produce certain protein molecules that aquatic mosquito larvae ingest, leading to their guts getting ripped up and no maturation into adults.
The Bti is purchased commercially (typically brand VectoBac G) in the form of corncob granules affixed with the Bti active ingredient. District staff disperse this dry bio-control product by manually flicking a pouch with a nozzle aimed at the mosquito larvae-laden water.
Why not just spray some pesticide?
That is possible, but would be drastic. Several very toxic liquid pesticides sprayed from the back of a truck or even an aircraft are an option to kill adult mosquitoes flying around town, but this method is highly expensive and results can be short-lived. Also, nearly every other flying insect and arthropod (invertebrate creature) would get knocked out as well. Human health (and pet) advisories also would be necessary.
Pesticide spraying or fogging is warranted only under extreme mosquito infestations where West Nile Virus or other vector-borne diseases are rampant in an area with an imminent human health hazard. The district strives to be proactive in mosquito treatment so such pesticide spraying is not necessary.
What does all of this cost?
The annual benefit assessment (like a property tax) for residential properties in Carpinteria and surrounding area is less than $9 per parcel. Work by the district is funded mainly by that revenue source, with some additional funds paid to the district under contract with UCSB for mosquito management within Carpinteria Salt Marsh Reserve.
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The Mosquito and Vector Management District of Santa Barbara County is an independent special district form of local government.
» wrote on 08/21/08 @ 12:00 PM
The “7-plus feet” must mean the tide elevation was + 7 feet above sea level,as opposed to a minus tide below sea level.
“7-plus feet” reads like it is more than 7 or possible a negative number.
These mosquitoes certainly seem to be a challenge there in Carp., especially as they have to allow the current generation of flying mosquitoes to die off but not be replaced by new ones because the vector district people are killing off the larvae in the water.
» wrote on 08/21/08 @ 01:57 PM
What a waste of taxpayer money.
» wrote on 08/21/08 @ 04:57 PM
The “government” obviously has never been bitten by these mosquitoes nor been subject to the risk of contracting a potentially fatal disease transmitted via mosquitoes. At least some local agencies are explaining to the public what they are doing and why.