Fighting Zika virus in a Silver Lake backyard: The hunt for the ‘cockroach of mosquitoes’

Vector control specialists Yessenia Avilez, left, and Randy Garcia in a backyard in Silver Lake
Vector control specialists Yessenia Avilez, left, and Randy Garcia clear out the debris from a tub of water in a Silver Lake yard as they hunt for mosquitoes that can carry the Zika virus.
(Marcus Yam / Los Angeles Times)

Randy Garcia points a flashlight into a bush and shakes the leaves. Martin Serrano climbs a ladder to peer into rain gutters. Yessenia Avilez ducks under stairs and flips over a plastic tarp collecting water.

In a Silver Lake backyard resembling a small jungle, the team — dressed in khaki shirts tucked into blue slacks — searches for its target.

Serrano and Garcia spot a tub filled with rainwater, leaves floating on the top. There’s movement just below the surface: hundreds of swimming creatures, like tiny tadpoles.

Then something flies out of the water, inches from their faces.


It’s an Aedes mosquito, the villain in the Zika virus epidemic that has broken out in dozens of countries this year. Nationwide, mosquito control workers like these ones are waging a war against the insects, but it will be a difficult one to win.

Aedes mosquitoes, which aren’t native to the Americas, are hardier than mosquitoes we’re familiar with here and local officials have struggled to curb their spread. With the threat of Zika virus looming and summer approaching, that bug problem has turned into a pressing public health concern.

“This is very, very, very serious,” said Edward McCabe, chief medical officer for the March of Dimes and an emeritus professor of pediatrics at UCLA. “We wouldn’t want L.A. to turn out to be ground zero for endemic Zika in the U.S.”

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Though parts of Texas and Florida are at highest risk for Zika, health officials warn that outbreaks could be expected this summer across the U.S., including in Southern California. Experts say limiting mosquito populations is the first line of defense against Zika, but worry insect control agencies aren’t prepared.

We’ve seen them in Doritos wrappers.
Martin Serrano, an L.A. vector control specialist, on the Aedes mosquitoes’ need for little water in which to breed.

An adult Aedes albopictus, also known as the Asian tiger mosquito, is caught for a test sample from a residential backyard during a house call in Silver Lake.
An adult Aedes albopictus, also known as the Asian tiger mosquito, is caught for a test sample from a residential backyard during a house call in Silver Lake.
(Marcus Yam )

Zika spreads when Aedes aegypti, the yellow fever mosquito, bites an infected person and then bites another. Unlike most types of mosquitoes that prefer the blood of animals, Aedes like to bite humans.

With other kinds of mosquitoes, one worker in a truck could spray a quarter of a small city with pesticide in one night and eliminate most of the bugs, said Michael Doyle, head of vector control for the Florida Keys. 

Vector control specialists Yessenia Avilez, bottom, and Randy Garcia spot an adult Aedes albopictus mosquito, also known as the Asian tiger mosquito, in a residential backyard in Silver Lake.
Vector control specialists Yessenia Avilez, bottom, and Randy Garcia spot an adult Aedes albopictus mosquito, also known as the Asian tiger mosquito, in a residential backyard in Silver Lake.
(Marcus Yam )

But spraying doesn’t work well against Aedes mosquitoes and their eggs usually need to be destroyed by hand. So “to cover that same area you need 10 people working for a week,” going door-to-door, he said. 

When Aedes mosquitoes began transmitting dengue, another viral disease, in 2009 in Key West, the agency had to bring in 30 inspectors to work 10 hours a day, six days a week to scour every yard in the city for mosquitoes, Doyle said.


After more than 90 cases of dengue were confirmed in the outbreak, the district added $1 million to its budget for 10 inspectors to continue the check-ups. But that’s not a solution for agencies across the country, he said.

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“We just can’t afford to double our staffs in most of those places,” he said.

On that chilly spring morning in Silver Lake, Serrano and Garcia, vector control specialists with the Greater Los Angeles Vector Control District, dumped out the water and larvae in the tub. Garcia drilled holes in its bottom, as well as in other buckets in the yard.

They’re diligent about eliminating places where water can collect because the mosquitoes can breed using as little as a teaspoon of water. “We’ve seen them in Doritos wrappers,” Serrano said.

In the L.A. region, Aedes mosquitoes are believed to have arrived several years ago in shipments of bamboo plants coming from China to El Monte. They’re now found in at least 12 counties in California, according to the state health department.

Avilez picked up a watering can and aligned one eye with its narrow spout.

The mosquitoes tend to lay their eggs — so small they’re nearly invisible to the human eye — at the waterline of buckets and containers. The eggs can survive several months of drought, waiting to hatch when they come in contact with water.


When the Sahara dried up and became a desert thousands of years ago, Aedes aegypti evolved to survive without a natural source of water, breeding using the water in pots outside people’s homes, said Marten Edwards, a professor at Muhlenberg College in Pennsylvania who studies the species.

They’re so hard to eradicate because they’re essentially domesticated, he said. Unlike the more common Culex mosquito that comes out only at dawn and dusk, Aedes bite during the day when people are active. Often considered the “cockroach of mosquitoes," they can even survive inside people’s homes, he said. 

These aggressive, invasive mosquitoes have become a burden for insect control agencies in California.

In September, when Aedes numbers peaked in Southern California, service requests for Aedes made up 90% of all requests to the L.A. district, said Kelly Middleton, the district’s director of community affairs.

When Serrano would pull up in his truck to inspect a home, neighbors would flock toward him, asking him to also inspect their backyards. “We couldn’t leave a street,” he said.

That was before the Zika virus arrived.

An obscure disease once believed to have only mild symptoms, Zika was declared an international public health emergency this year after an outbreak in Brazil coincided with a spike in babies born with microcephaly. Scientists have since confirmed that the illness, now spreading in more than 30 countries in the Americas, causes many other birth defects as well. 

No one in the U.S. has yet been infected by a mosquito here, though approximately 500 Americans who traveled to countries with outbreaks have returned infected with the virus, according to the U.S. Centers of Disease Control and Prevention.

Health officials say that widespread transmission in the U.S. is unlikely because most homes have air conditioning and screens on windows that keep out mosquitoes. 

Still, federal health officials recently estimated that 30 states have climates that could sustain Aedes mosquitoes, and held a summit last month on improving mosquito control in a time of Zika.

“Everything we look at with this virus seems to be a bit scarier than we initially thought,” said Dr. Anne Schuchat, the CDC’s principal deputy director at a recent news briefing. “So while we absolutely hope we don’t see widespread local transmission in the continental U.S., we need the states to be ready for that.”

In the Central Valley, mosquito workers were baffled when Aedes first showed up in their region in 2013, said Steve Mulligan, head of vector control for a district encompassing parts of Fresno and Kings counties

They were even more surprised when they weren’t able to stop their spread, Mulligan said, adding, “It really does not lend itself to control with conventional or traditional methods.”

The agency is trying a new tactic this summer. As part of a trial with the University of Kentucky, they plan to release male Aedes aegypti that are infected with a bacteria that prevents their eggs from hatching.

A similar pilot project in El Monte last year significantly reduced the female mosquito population, said Susanne Kluh, scientific technical director for the greater L.A. district. 

But such new control methods require federal approval and will likely take several months before widespread use is possible. For now, mosquito control agencies are watching to see what summer brings. 

Last year, the Aedes population in San Diego County grew because of the unusually warm weather, said Chris Conlan, supervising vector ecologist for the county. He said they’re now tracking the mosquitoes, thought to have come from Mexico in 2014.

“But the bottom line is we’re going to have to wait and see what mother nature throws at us,” he said. "Because if we get rain again this year, it’s probably going to become impossible for us to get these things under control.”


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