The Swat Squad : County Department Takes Aim at Growing Number of Mosquitoes


The rains that have made farmers and back-yard gardeners happy this spring are also causing mosquitoes to buzz in big numbers, according to health officials.

As a result, Ventura County's swat team--the environmental health department--is launching a war on the little bloodsuckers.

Randy Smith, an environmental health specialist with the county, said the primary concern is the diseases that mosquitoes can transmit.

Although outbreaks of mosquito-borne diseases such as encephalitis and malaria are virtually unknown in Ventura County, Smith said, "The more mosquito sources you have, the more possibility of (diseases) being found."

Both encephalitis and malaria are spread when the mosquito draws blood from an infected person. The infectious mosquito then transmits parasites with its next bite.

Beyond disease, there is the nuisance factor. Mosquitoes are lousy guests at barbecues and ballgames. The environmental health department has received 30 mosquito-related complaints in recent weeks, contrasted with two calls during the same period last year.

The war on the mosquitoes is being taken to street drains, flood control channels, creek and river beds and fields that have become marshes. For a mosquito, all of these wet places are great places to lay eggs.

In this war, the trick is to kill the mosquito larvae before they mature.

On Monday, county technician Phil Nickel of the environmental health department donned boots to inspect a marshy field in Thousand Oaks. He said it is one of the county's largest breeding grounds for mosquitoes.

For the past four years, the grassy field near Wendy Drive just south of the Ventura Freeway had remained bone-dry. But recent rains have transformed the field into a shallow pond measuring about 15 to 20 acres wide and a foot deep in some spots.

"This is the worst I've seen it," Nickel said. "There's literally thousands of mosquitoes breeding there."

Nickel said the mosquitoes prefer the shallow parts of the pond, areas that are easily warmed by the sun during the day.

About a month ago, after discovering that larvae had infested the water, Nickel sprayed it with an oil-based insecticide. Two weeks ago, after finding more larvae, he released about 300 larvae-eating minnows. Workers can also plant lethal bacteria that decimates the adults, he said.

Using a small cup attached to a long pole, Nickel inspected the waters again.

"When I first came out here and dipped, there were 20 to 30 of them in there," he said, peering into the shallow bowl. "I guess we're doing a good job. They're not here now."

The county is concentrating its efforts on Thousand Oaks and Simi Valley, primarily because of their proximity to population centers that have had human cases of mosquito-borne diseases, Smith said. It has also targeted Fillmore because of the presence of agricultural fields where slow-moving water is a problem.

Beginning April 14, the county will launch its annual encephalitis virus surveillance program. Workers will place small flocks of chickens in three test sites around the county to monitor the mosquito problem.

The flocks--at Strathearn Historical Park in Simi Valley, the Hill Canyon sewage plant in Thousand Oaks and a state-owned fish hatchery in Fillmore--will be checked for diseases every other week through October.

So far, Ventura County has been lucky, but "the potential is there. We have the mosquito that can transmit the disease," Smith said. "We're looking to stop it before it gets started."

The county is most concerned about the culex mosquito, a hot-weather breed that is prolific during the summer.

Smith warned that mosquitoes can breed in any container that can hold water, such as fishponds, buckets, barrels and wheelbarrows. The county is preparing to issue warnings this week to homeowners to keep containers and back-yard pools and ponds free of standing water.

The wet weather also encourages the growth of other insects that favor moist, wet conditions, such as midges and crane flies.

"They become nuisances, but we do not control those," Smith said. "Sometimes we get a call about mosquitoes and we find the real culprit is the crane fly or midges."

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