In light of the zika virus' invasion of a neighborhood north of downtown Miami, here is a story from September 14, 2013, on how mosquitoes are fought in Sarasota County.
Fighting mosquitoes is not rocket science, but more like small-plane science. And year after year, the campaign against mosquitoes is waged from June to November by people like pilot Jason Alred.
Mosquitoes, carriers of disease and aggravation, are adept and elusive fliers, but they are no match for Alred’s 1984 Piper Aztec, a twin-engine plane from which the passenger seats have been removed.
Replacing the seats is a rectangular plastic tank filled with 60 gallons of mosquito pesticide costing $10,000.
Spraying 12,800 acres from an altitude of 300 feet, Alred and loader/observer Tracey Starr release the poison mist through two atomizers, one on each wing.
Alred flies for Vector Disease Control International, under contract to Sarasota County, out of Sarasota-Bradenton International Airport.
VDCI also sprays for a half-dozen Florida counties, Alred said, including Osceola and Seminole.
Taking off at 8 on flight nights, he will cover 300 miles in two hours while targeting sectors of the county identified by Sarasota County Mosquito Control’s monitoring program.
A computer monitors weather equipment on the wing and keeps him on course, or changes the course should the wind shift. He has to fly upwind so the pesticide hits the target.
Spraying and fogging have been the time-tested method for decades. Mosquito-control districts are constantly refining their methods to avoid killing beneficial insects.
It’s called integrated pest management, of which poison is just one weapon in a “precision targeting” strategy. Developers are taught how to prevent mosquito breeding through proper water management. County mosquito technicians eliminate mosquito habitat by controlling water lettuce and hyacinth plants that foster larvae. They spray larvae from the air when they are found.
Monitoring populations is key, says Matthew Smith, Sarasota County’s mosquito-control director. “We have to know the species, understand their biology and spray accordingly. Spray is expensive, and so is flight time.”
Smith’s team sets traps to monitor the male mosquito population. When it peaks, they know the female count will peak a couple of days later. “That’s when we fly the plane,” he said, “to break the cycle.”
When things get bad, they spray mosquito “adulticides” in the air.
“Right now, the numbers are below average,” even though the summer’s rainfall has been above average, said Smith.
“We are doing really well, and haven’t had to spray too much. We saw a spike in June and early July, and we did a lot of larvaeciding and spraying, so we haven’t seen a population rebound,” Smith said.
Dr. Walter Tabachnick, director of the University of Florida’s Medical Entomology Laboratory in Vero Beach, said part of the science of mosquito control is controlling the “environmental impacts on nontargets.”
“Many mosquito-control professionals are strident environmentalists who are looking at every way possible not to impact the environment, and they want to know if there is any claim that they have done so. They go to great lengths to investigate and mitigate to make sure it was due to their actions and that it doesn’t happen again.”
A century ago, the big anti-mosquito breakthroughs were draining landscapes, installing screens and nets, and treating malaria with quinine and other medicines.
Then came DDT, a chemical that was outlawed in the 1970s after mosquitoes developed a resistance to it. Rachel Carson’s landmark 1962 book “Silent Spring” documented its harm to wildlife and humans, helping give birth to the environmental movement.
A big concern when spraying from aircraft and fogging from trucks is the risk of killing honeybees and other beneficial insects, said Tabachnick.
“The improvement in the technology is in the delivery of these pesticides,” he said. “Sprays are adulticides; they are only effective on insects flying through the cloud. Insects that are sheltered are not going to be impacted by that kind of spray.
“The name of the game is to keep the spray in the air as long as possible. Make each droplet of spray like a little balloon.”
As opposed to the clouds of white fog that trucks emitted 50 years ago, mosquito-control districts now use “ultra- low-volume” sprays.
“The ULV droplets are so small that they hang in the air a little longer,” said Tabachnick. “And they are more cost-effective. With those sprays you saw from the truck (in the 1960s), a mosquito flies through the cloud and hits a droplet that contains 500 times the amount of insecticide needed to kill it. That is a waste of product.
“So you now have a drop that contains almost exactly the dose needed to kill, and you have more of those drops. You are going to kill a lot more mosquitoes more effectively. That is part of the science.
“Not only that, but they are much more precise in the delivery of the product to the target area. Planes have GPS and wind-direction gauges. They may spray over you to target an area 2 miles away, allowing for wind direction and speed.”
Control districts also stock ponds and other waterways with minnows that eat mosquito larvae. They must eat well.
DEATH FROM ABOVE
VDCI has five Aztecs for killing adult mosquitoes in the evening and four crop dusters for daytime missions to kill larvae in flooded fields. It also operates trucks that spray pesticide, Alred said.
The onboard tank has a 75-gallon capacity, but regulations limit the load to 60 gallons — 1,000 pounds.
Alred, in a white hazmat suit that is waterproof and “horribly hot,” and Starr load the tank before each flight.
“The pesticide goes directly from the drum to the onboard tank,” he said, but he wears a respirator, face shield and gloves “just for safety.”
The tank has an emergency port for dumping pesticide in the event of a flight emergency.
“I hope I never have to do that,” Alred said. “It would be an environmental nightmare. That is why we fly a twin. If we lose an engine, we can make it to an airport.”
The Miconair AU-4000 Rotary Atomizer is the weapon for aerial spraying. Droplets of mosquito “adulticide” cannot be too large or too small. Alred said 26 microns is the ideal diameter. The droplet size is adjusted by varying the speed of the red rotors.
“We have it cranked all the way up, as fast as you can spin it. The droplet is optimized for killing — too small and it doesn’t kill. Too large and it bounces off,” Alred said. “A grasshopper or butterfly generally won’t die if you subject it to our treatment.”
Neither will a human. “You would have to drink a shot glass of that stuff to kill you,” he said.
Around the home, less-toxic controls are recommended.
“Drain and cover,” says Dr. Carina Blackmore, Florida’s public health veterinarian. “Drain standing water and cover your skin.”
Other methods include using repellant that contains DEET (some people say Avon’s Skin So Soft is effective, but others say its effect only lasts for a few minutes), wearing long sleeves, and staying indoors at dawn and dusk.
Keep the lawn mowed, the bushes trimmed and the weeds pulled — these are mosquito habitats during the cooler months, when most species are dormant.
As their leaves hold rainwater, bromeliads pose a special hazard that is often overlooked.
Sarasota County Mosquito Control advises, “Once a month, spray a light mist of a flying insect spray labeled for adult mosquitoes over bromeliads, and allow it to settle. This keeps away egg-laying adult mosquitoes.”
Even a cup of water can breed a problematic mosquito outbreak on your property. Low spots in your yard should be filled to promote good drainage.
Other mosquito breeding pools, according to University of Florida entomologist Jorge Rey, include potted plants, drainage ditches, plugged roof gutters, pet dishes, old tires, buckets, poorly maintained swimming pools, tree holes, roof debris, ponds, boats and bird baths.
In fact, drainage has been the best mosquito-control method for more than a century. But it may not be the best thing for the environment, as standing water recharges groundwater supplies and promotes a healthy ecosystem.
Just not for people.
The fields of east Sarasota County are a maternity ward for floodwater mosquito larvae, says Sarasota County mosquito-control director Matthew Smith. Females lay eggs in fields where the floodwater has partially evaporated, banking eggs by the billions, and they hatch with the next rain event.
The county sprays larvae from the ground. It is considering hiring a helicopter company to spray larvae in rural fields next year, Smith said.
Sarasota County Mosquito Control spends 64 cents per acre to spray adult mosquitoes from the air.
Mosquitoes can fly 20 miles from where they hatch, or just a couple of hundred yards.
The biggest mosquito in Florida is the gallinipper. It is not very common. But it can penetrate two layers of clothing.
Slap or flick a biting mosquito? Answer: Flick. Slapping them once they are biting can push more toxin into the skin and make the swelling worse. Scratching the itch does not help.
Mosquitoes like to stay close to ground, and come out at night for stealth.
Wear loose-fitting, light clothing, and mosquitoes will be easier to detect.
Female mosquitoes can live up to about 100 days and can lay four or five batches of eggs. Male mosquitoes live only about three weeks. Male mosquitoes do not bite.
Sources: Matthew Smith, Sarasota County Mosquito Control; Walter Tabachnick, Ph.D., director of the Florida Medical Entomology Laboratory in Vero Beach.