Luz Rodriguez, a staffer at the Sacramento-Yolo Mosquito and Vector Control District, looks at thousands of mosquitofish swimming in a pool at the district's facility in Elk Grove, the biggest breeding ground in the world for the mosquito-loving fish. Sue Cockrell/Enterprise photo

Agriculture + Environment

Mosquitofish form first line of defense against pests

By From page A1 | June 20, 2014

The Sacramento-Yolo Mosquito and Vector Control District wages battle against mosquitoes, defending rural and urban populations from a long list of debilitating diseases. And its No. 1 weapon against the deadliest pest on Earth?


Specifically, Gambusia, silver and pinky-finger-sized, that feast on mosquito larvae and other water-laying insects.

The district’s Elk Grove facility is the biggest breeding ground in the world for mosquitofish, as they have been aptly nicknamed; 2.7 million on average are born, grown and deployed each year. “Planting” the fish means fewer pesticides and less manpower are needed to control mosquito populations.

Every day from April to August, field agents load their pickups with 150-gallon fish tanks and deliver the mosquitofish free to rice paddies, abandoned swimming pools and backyard ponds.

A decade or so ago, they tried to drop Gambusia into flooded rice fields from a crop duster, usually used to spread pesticides or seed. It flew as close to the ground as it could, but at 180 miles per hour.

Seventy percent of the fish died, said Tom Hedley the fisheries supervisor.

So, no more airplanes. Technicians now scoop the fish up out of the tank in a net, kneel down and place them gently in the water.

“We try to traumatize them as little as possible,” Hedley said.

Elk Grove houses the biggest mosquito fishery in the world because of the high concentration of rice growers in the Sacramento Valley. The dual-county district was formed when scientists realized that many of the mosquitoes plaguing urban Sacramento were buzzing over from Yolo County.

Then, people were concerned about culix mosquitoes, said Robert Washino, a mosquito expert, professor emeritus at UC Davis and retired 38-year-old trustee of the vector control district. In 1952, the Central Valley suffered an encephalitis outbreak that killed 50 people. Now, folks worry about West Nile virus: So far this season, Yolo County has counted one infected mosquito and four infected birds — three of which were found in Davis.

“And in the last 10 years, we’ve seen the introduction of the aedes mosquitoes, much more urban mosquitoes,” Washino said.

Recently found in the Bay Area and Los Angeles, aedes aegypti mosquito worries public health officials because it can spread dengue and chikungunya viruses. Fish aren’t as effective in cities and neighborhoods, so vector control officers rely more heavily on traps set around the two counties.

Mosquitoes caught in the trap are taken back to the lab in Elk Grove, where they are examined and tallied on a colorful analog machine that resembles a two-tiered children’s xylophone. If the mosquito is a species known to carry West Nile, lab techs grind it into a paste and test for pathogens. Chemicals are deployed only when viruses are found.

Down the hall from the lab, the district raises mosquitoes in addition to fish. The insectary is a stifling, moist room, like summer in Georgia, with white rusting trays full of warm water and, terrifyingly, thousands of mosquito larvae. They look like little sticks, like little dandelion seeds wiggling around in the water, searching for bits to eat so they can grow big, pupate and suck your blood (or that of birds or horses or other animals). Researchers will use them to test pesticide resistance or as learning instruments in classrooms.

But with schools on break, the vector control technicians are in the field full time, delivering hungry fish to still water to gulp down mosquito larvae and keep disease at bay.

— Reach Elizabeth Case at [email protected] or 530-747-8052. Follow her on Twitter at @elizabeth_case

Elizabeth Case

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