Fighting A Zika Monster: Why The Aedes Aegypti Mosquito Is So Hard To Control
As little kids, a lot of us lay awake imagining terrifying monsters that were coming for us. Monsters in our closets who'd spring out and get us if the night light wasn't plugged in. Monsters under our beds that would slither up and eat us if our moms left the room before we fell asleep. Monsters that knew our habits, our vulnerabilities.
The Aedes aegypti mosquito is kind of like those monsters. It knows human vulnerabilities and preys on them. But unlike our childhood monsters, the Aedes aegypti mosquito is also a real threat. The species can infect humans with Zika and a host of other viruses: chikungunya, dengue, yellow fever.
That's why Miami-Dade County is spending as much as $100,000 per day on mosquito control efforts, and why lawmakers throughout Florida are pushing for Congress to reconvene and pass a multi-billion-dollar anti-Zika funding package.
But even with billions of mosquito abatement dollars in play, the Aedes aegypti mosquito can be extremely difficult to control, according to mosquito researchers and mosquito control experts.
Matthew DeGennaro studies mosquitoes at Florida International University. He says the mosquito's talent for finding humans lies in its sense of smell.
"At a distance, a mosquito senses the carbon dioxide from you," DeGennaro said. "They fly closer to you, then they start smelling your body odor. And then, as they get a little closer to you, they sense the heat that's coming off your body. Then they land on you."
Only female mosquitoes bite, although they may poke around for a bit first, feeling for a nice, juicy capillary. Then they'll settle in for a blood meal, which can take anywhere from 10 seconds to a few minutes, depending on how hungry the mosquito is.
But Aedes aegypti's talent for finding human blood comes from more than its sense of smell. The mosquitoes have adapted to our habits. Mario Perez, another FIU researcher, says Aedes aegypti targets humans' ankles because we're less likely to notice them and swat them there. And even if we do take a swat at them interrupting that blood meal, they often come back.
"This is a mosquito that's evolved to live in and around us, close to us," Perez says.
And Perez says Aedes aegypti mosquitoes are still evolving. Specifically, they can develop resistance to the pesticides we spray aerially.
"You're going to have a small part of that population that survives the spraying for a variety of genetic and physiological reasons," Perez says. "Those handful that survive, they're the ones that go on to reproduce."
"Eventually, over several generations, you keep spraying them and it doesn't do anything."
Mosquito control officials try to prevent pesticides resistance by changing up the kinds of pesticides they spray. Sometimes, they use a pesticide that targets adult mosquitoes -- like Naled, the chemical that's been sprayed several times over the Wynwood area and parts of downtown Miami. Other times, they'll use a larvicide, which targets mosquito larvae, the immature mosquitoes. And there are multiple types of adulticides and larvicides available, with different chemical formulas that target mosquitoes in different ways.
"It's highly unlikely you'll get a population of mosquitoes resistant to all four, five, six insecticides that they're using," Perez says.
But, he adds, officials "cannot control all the mosquitoes."
One reason is that it's difficult to target Aedes aegypti mosquitoes using aerial spraying. The species is known for lurking in foliage, which deflects droplets of pesticide. Also, the weather in South Florida is very, very mosquito-friendly, making it easy for the mosquitoes to breed.
"The optimum temperature for mosquitoes is 79 degrees," says Allan Cespedes, a manager for Orkin Pest Control in Miami. "That's what we are year-round, pretty much."
The area's mosquito population is also supported by South Florida's rainy season. Female Aedes aegypti mosquitoes lay their eggs in water, so water from heavy rains helps the mosquitoes thrive.
"If you see water collecting in garbage bins, recycle bins, bottles, old tarp, toys, wood, lawn furniture, bird baths -- that kind of stuff -- they will easily be able to start a breeding zone in your yard," Cespedes says.
That's another evolutionary strength of the Aedes aegypti mosquito: It can thrive in urban environments. Even a bottle cap full of water is enough for the mosquitoes to breed. So Cespedes and state and local leaders are encouraging Florida residents to not only wear bug repellent, but also to get rid of standing water. Turn over trash cans. Dry off tarps. Look around air conditioners for a drip. Use a broom to sweep standing water from puddles, or a shop-vac to suck that water up.
"The mosquito can transfer disease, but there are things we can do at home to protect ourselves and our family," Cespedes says. ""Get rid of the standing water. That's the biggest thing."