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To Kill Mosquitoes That Spread Zika, Strike Before They Fly

Maureen LoCascio, with the mosquito control team in Hudson County, N.J., uses a backpack sprayer to spread insecticide against mosquito larvae.
The Florida Channel
Leon County Judge John Cooper on June 30, 2022, in a screen grab from The Florida Channel.

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."

Mike Iverson, an inspector for Hudson County Mosquito Control, looks for mosquito larvae in a water sample from a marsh in Secaucus, N.J.
/ Hansi Lo Wang/NPR
The Florida Channel
Mike Iverson, an inspector for Hudson County Mosquito Control, looks for mosquito larvae in a water sample from a marsh in Secaucus, N.J.

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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Hansi Lo Wang (he/him) is a national correspondent for NPR reporting on the people, power and money behind the U.S. census.