To Kill Mosquitoes That Spread Zika, Strike Before They Fly

May 26, 2016
Originally published on May 26, 2016 6:59 pm

In the marshy woods of Secaucus, N.J., a mosquito can make a happy home.

With water and shade under a canopy of maple trees, you could barely ask for more to start your own bloodsucking family.

For Gary Cardini, though, this is a battleground.

"You want to get them in the water before they're flying," explains Cardini, who supervises the field team for Hudson County Mosquito Control. "In the water, they're captive. You know where they are."

Every spring, his team of inspectors checks for mosquito larvae in pools of water and then spreads larvicide that kills the larvae after they eat it.

"You need a very small amount to effect a very large decimation of the population," says one of Cardini's inspectors, Maureen LoCascio.

Killing bloodsuckers is also a priority across the Hudson River in New York City, as the health department there prepares for the possible spread of the Zika virus during mosquito season.

States like New York and New Jersey have used pesticides for years to deal with the West Nile virus. But now they're facing Zika — a virus carried by a different kind of mosquito. That's forcing public health officials to rethink how to reduce mosquito populations.

"One of the most important strategies is to never fall behind when trying to control the Aedes mosquitoes," says Jay Varma, New York City's deputy commissioner for disease control.

He cautions that the chances of the Aedes mosquitoes spreading Zika around New York are low. Still, the health department is doubling the number of pesticide treatments for larvae in wetlands this year from three to six times.

But it may not do much to prevent Zika.

Aedes mosquitoes are more likely to grow in "pet food dishes, children's toys, tarps in people's backyards, clogged gutters, boats, rain buckets," according to Greg Williams, superintendent of mosquito control for Hudson County, N.J., where the Aedes mosquito has not been a main target until this year.

"Luckily, it doesn't fly very far," Williams says. "If you and your neighbors can keep your yards free of standing water, then you probably wouldn't need any pesticides to get rid of that mosquito."

That's why he's advising people to "dump and drain" through a public education campaign — while keeping pesticides as an option.

"Sometimes the mosquitoes are still just there for one reason or another, so the spraying is just a little extra added insurance," he says.

But Laura Harrington, an entomologist at Cornell University who specializes in Aedes mosquitoes, says that may be a waste of money and time. She gets frustrated whenever she hears about aerial spraying of pesticides over wetlands or large bodies of water to try to stop Zika.

"We know a lot about the biology of these mosquitoes, and we know that they do not breed in those types of habitats," she says.

All the Aedes mosquitoes need is a container of water that can be as small as a bottle cap, which makes it difficult for mosquito control teams to find and treat their breeding sites.

While there's a relatively low risk of Zika spreading in the U.S., Harrington says she does support using pesticides in infected areas if there is an outbreak.

Studies have shown that pesticides can lower the number of mosquitoes that can spread the West Nile virus. A study published in 2008 found that in Sacramento, Calif., pesticides reduced the mosquito population by as much as 75 percent, thus lowering the risk of human infection.

William Reisen, who co-authored the study, also warns that there's a critical difference between the mosquitoes carrying West Nile and the ones that can carry Zika.

"The problem with the Aedes mosquitoes is that these are mostly day-active mosquitoes," says Reisen, a retired entomologist from the University of California, Davis. These mosquitoes aren't necessarily flying around when the insecticide is sprayed, usually at dusk or nighttime.

It's another complication as cities watch out for Zika and adjust their mosquito strategies.

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KELLY MCEVERS, HOST:

Some parts of the U.S. are trying to prevent the spread of Zika by using pesticides. States like New York and New Jersey have used that method for years to deal with the West Nile virus. But Zika is carried by a different kind of mosquito. NPR's Hansi Lo Wang reports some in public health are rethinking mosquito control.

HANSI LO WANG, BYLINE: Here in the marshy woods of Secaucus, N.J., under a canopy of maple trees, a mosquito can make a happy home.

This is kind of mosquito paradise?

GARY CARDINI: Yeah, yeah, sure, 'cause it's shady. It's relatively cool, so this is a good place for them to breed.

WANG: For Gary Cardini, though, this is a problem. He supervises a field team for Hudson County Mosquito Control.

CARDINI: You want to get them in the water before they're flying. In the water, they're captive. You know where they are. They're a lot easier to treat in the water than it is if they're in the air.

WANG: And that treatment sounds like this.

(SOUNDBITE OF INSECTICIDE SPRAYER)

WANG: One of Cardini's team members, Maureen LoCascio, starts the engine. She straps on a sprayer to her back and trudges through the marsh, gripping a hose that spits out insecticide. It'll kill the larvae swimming in the water after they eat it.

MAUREEN LOCASCIO: And what works so very well about it is that you need a very small amount to affect a very large, you know, decimation of the population.

WANG: Killing bloodsuckers this summer is also a priority across the Hudson River, in New York City.

JAY VARMA: One of the most important strategies is to never fall behind when trying to control the Aedes mosquitoes.

WANG: Jay Varma is the deputy commissioner for disease control in New York. He says the chances of the Aedes mosquitoes spreading Zika around here are low. Still, the city's health department is doubling the number of pesticide treatments for larvae in wetlands this year. But it may not do much to prevent Zika. That's because the Aedes mosquitoes are more likely to grow in...

GREG WILLIAMS: Pet food dishes, children's toys, tarps in people's backyards, clogged gutters, boats, rain buckets.

WANG: Greg Williams heads mosquito control for New Jersey's Hudson County, where the Aedes mosquito has not been a main target until this year.

WILLIAMS: Luckily, it doesn't fly very far. And so if you and your neighbors can keep your yards free of standing water, then you probably wouldn't need any pesticides to get rid of that mosquito.

WANG: That's why he's advising people to dump and drain. And he is keeping pesticides as an option.

WILLIAMS: Sometimes the mosquitoes are still just there for one reason or another. So the spraying is just a little extra added insurance.

WANG: But Laura Harrington, an entomologist at Cornell University, says that may be a waste of money and time. When she sees aerial spraying of pesticides over wetlands or large bodies of water to try to stop Zika...

LAURA HARRINGTON: I think it's crazy. It's frustrating. We know a lot about the biology of these mosquitoes. And we know that they do not breed in those types of habitats.

WANG: Itty-bitty breeding space is all they need, containers of water as small as a bottle cap. So they're not easy to track down. Harrington says it's good to be vigilant by putting on insect repellent, wearing long sleeves and pants and keeping your ward tidy and to treat the relatively low risk of Zika in the U.S. rationally.

HARRINGTON: We're flooded with pictures of babies with small heads. There's a lot of hysteria. And I really think that everyone just needs to calm down, to relax.

WANG: Harrington adds she does support using pesticides if there is an outbreak of Zika in the U.S. And she says it should be targeted to infected areas. William Reisen is a retired entomologist from the University of California, Davis. He says, pesticides have lowered the number of mosquitoes that can spread the West Nile virus. And he adds, there's a big difference between the West Nile carrying mosquitoes and the Zika ones.

WILLIAM REISEN: The problem with the Aedes mosquitoes is that these are mostly day-active mosquitoes. So they're not necessarily flying around when the insecticide may be applied.

WANG: Which is usually at dusk or night time. It's another complication as cities watch out for Zika. Hansi Lo Wang, NPR News. Transcript provided by NPR, Copyright NPR.