Hunting Mosquitoes in Gilroy

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Mark Marden keeps track of chickens, like canaries in a coal mine, checking for Zika and other diseases

On the front line of Santa Clara County Vector Control District’s fight against mosquitoes is Bob Kaufman. Kaufman, 52, the Vector Control Field Operations Supervisor sets out, armed with a scooper, a long pole with a cup on the end, hunting through stagnant streams, abandoned tires and murky swimming pools. The quarry of his hunt, mosquito larvae and after a few hours on the prowl, he’s found his prey inside an old abandoned truck tire on Santa Teresa Boulevard.
“I want to find larvae,” Kaufman said. “If it exists I want to find it. If it doesn’t exist, I’m happy. It’s rewarding to help people by reducing the risk of people contracting West Nile and by reducing other mosquitoes from spreading diseases like malaria and to help people get rid of rats without busting the bank trying to do it.”
For the Vector Control District, pest control isn’t just a job; it’s a science. In what’s a virtual CSI, they have a variety of ways–conventional and unconventional– to track and halt the spread of mosquito-born diseases such as the West Nile Virus and the Zika Virus. Zika has never been detected in Gilroy and Kaufman aims to keep it that way.
Samples taken by Kaufman from West Little Llagas Creek on Highland Ave and Lions Creek by Christopher High School came up empty. However a mile north on Santa Teresa Boulevard, inside two old discarded truck tires, a few larvae are found.
The larvae, only a few millimeters long, slim, brown and with a head out of science fiction, are extracted and poured into a plastic sample bag along with the dirty water where they were found. As the dirt in the water settles to the bottom of the bag, the larvae squirm and wiggle to the surface as they come up for air.
Kaufman, who lives in Gilroy, went to Gavilan and has been with the county for 32 years, is a martial arts enthusiast (he recently tore an ACL performing a move in judo) and has coached his son’s club soccer team. He had not always planned to work for the county in pest control.
“The boss at the print shop I worked at passed me over for a raise and I was complaining about it,” Kaufman said. A friend at Gavilan told him there were animal control openings. He went for it.
At the conclusion of a long and wet winter, testing is well underway for mosquito-borne diseases. When a dead bird is reported, they are on the scene, armed with a variety of tests and traps aimed to halt diseases before they start. Corvids, such as crows and eagles, are especially susceptible to the West Nile Virus and when one is found dead, it indicates that the bird was infected by a mosquito.
“One year we had over 1,000 dead birds and another year we had about 400,” Kaufman said. “Usually people call and report them or we’ll be driving around and we’ll find them. When we find them, we test them.”
Not all mosquitoes are born alike and different diseases are spread by different mosquitos. Some of the most common types of mosquito in Gilroy are the western tree hole mosquito, which spreads heartworm in dogs, the Northern house and Western encephalitis mosquitoes, which can spread West Nile Virus and the Western malaria mosquito which can spread malaria. For each, the county has a different way of attacking the problem.
“California has 50 different kinds of mosquitos,” Kaufman said. “There are different specifics that different mosquitos like. The Western Treehole mosquito needs tree debris and the Culex Pipiens (Northern house mosquito) and Culex Tarsalis (Western encephalitis mosquito) need standing water to breed in.”
Kaufman sees potential breeding spots for mosquitoes wherever he goes. Aside from old tires, rain gutters, trash cans, upturned canoes, or any other thing that might hold stagnant water, are prime real estate for mosquito larvae. Even while at an Oakland A’s game, he’s on the lookout and lets the stadium operations staff know when he’s found a potential breeding ground.
In a shallow and murky pool outside of the Santa Clara Vector Control Office at 80 Highland Ave. in San Martin, Mark Marden tends to some of the natural forces used to combat disease-carrying mosquitoes, such as mosquito fish, the size of a goldfish but with a huge appetite for mosquito larvae. They are the best weapon to use for a pool or a pond. Only a few are needed to clear a large area.
“It doesn’t take many mosquito fish to get the job done,” Marden said. “All they do all day is eat mosquito larvae. They’re native to Australia so we can’t release them into creeks and other natural bodies of water. Anything that’s not native, we don’t want them in the creeks.”
Also, serving a role akin to a canary in a coal mine, only safer, are the seven sentinel flock chickens in Santa Clara County. Rather than becoming someone’s dinner, the chickens play an important, if unwitting, role in mosquito-born disease prevention.
“The sentinel flock is used to monitor the presence of West Nile Virus,” Marden said. “The chickens can carry the virus but they don’t get sick. We take blood from them every two weeks, send the blood to the lab in Sacramento and they’re tested for any West Nile Virus in the blood. If they come up positive we know that the West Nile Virus is present.”
When an infected mosquito is detected, the county sets out various traps designed to catch the mosquitoes. An EVS trap, a contraption fashioned out of an old paint can, is hung in a tree and filled with dry ice. The dry ice, which emits carbon dioxide which attracts the mosquitoes, lets out the heavier than air gas, which draws the mosquitos into the trap, which draws them in and shoots them into a net with a battery powered fan. When an infected bird is found, the county places 40 EVS traps within a mile radius.
Even when the Vector Control District needs to use pesticides, it tries to minimize the impact on other species. The county typically only uses fogging agents whenever West Nile Virus is found.
“I use BTI (Bacillus thuringiensis israelensis) granules, which are used for mosquito larvae and black fly larvae,” Kaufman said. “When they eat it they die but whenever anything else eats it they’re ok or when an animal drinks from the stream they’re fine. We want to kill the mosquito larvae, not the predator. We want to keep them safe because they help to knock down the mosquito population.”

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