Dallas launches air war against West Nile mosquitoes. Is it safe?

Dallas has begun aerial spraying to control mosquitoes carrying the West Nile virus. Officials say the substance is safe, and the EPA has approved its use. But not everyone is convinced.

Mona Reeder/The Dallas Morning News/AP
Jenny Wegley wades into waist-deep water to guide protective tarps over koi ponds at the Dallas Arboretum. The tarps are to protect the aquatic ecosystems from insecticide sprayed over the city from airplanes to reduce mosquitoes carrying the West Nile virus.

Dallas is now engaged in an air war against West Nile disease-bearing mosquitoes.

Beginning Thursday night, aircraft are flying at low level (300 feet), spraying a mosquito-control product called “Duet.” Officials say the substance – which has been approved for both ground and aerial application by the EPA – is safe, spread in low volume (less than one ounce per acre).

But there is some pushback to aerial spraying, which critics say is not wholly effective (it kills adult mosquitoes but not larva) while also killing beneficial insects, including honeybees, ladybugs, and dragonflies, as well as fish, bats, birds, and geckos that prey on mosquitoes.

The social action organization Change.org has begun a petition to stop the spraying.

Duet’s two main ingredients are formulated to mimic the natural substances in chrysanthemums.

“This has been used very, very carefully in many parts of the country,” says William Schaffner, who chairs the Department of Preventive Medicine at the Vanderbilt University Medical Center in Nashville, Tenn.

“Kiddies, babies, old folks, vegetables, cats and dogs – we’re all safe,” Dr. Schaffner told NPR.

David Lakey, Texas Department of State Health Services commissioner, says aerial spraying is “a safe and very effective tool” to control mosquitoes.

But he cautions that “it doesn’t take the place of the basic precautions,” including the use of insect repellent. People in the area also are being urged to drain standing water where mosquitoes can breed and proliferate.

Still, health officials in Dallas recommend that children and pets remain indoors until the spray has dried. That goes for some people with respiratory problems, as well.

"I tell [patients], if they can and they're really sensitive, to leave town," Dallas physician Alfred Johnson told ABC News.

Over the years, spraying to kill insects has been a common though sometimes controversial practice.

Into the mid-20th century, DDT was used extensively until publication of Rachel Carson’s “Silent Spring” in 1962 raised questions about the environmental impact – including its carcinogenic effects on humans and its weakening effect on egg shells. The banning of DDT in the US in 1972 was a major factor in recovery of the endangered bald eagle.

In 1981, California Gov. Jerry Brown faced the difficult decision to use malathion spray to control an infestation of the medfly decimating the state’s fruit crops. After some delay in moving from ground to aerial spraying, the infestation was finally halted. But at least one study since then has connected the chemical to instances of ADHD (attention deficit hyperactivity disorder) in children.

Texas officials say the best defense against mosquitoes and the disease they transmit is to practice the “four Ds”:

  • Use insect repellent containing DEET, picaridin, or oil of lemon eucalyptus.
  • Dress in long sleeves and long pants when outside.
  • Stay indoors at dusk and dawn, when mosquitoes are most active.
  • Drain standing water where mosquitoes breed. Common breeding sites include old tires, flowerpots, and clogged rain gutters.

Drought can increase the risk of mosquito-borne diseases, experts say. Both infected birds and the insects that bite them (then humans) are drawn to the same pools of stagnant water caused by drought.

Thursday night’s spraying was cut short by rain. Four aircraft are expected to resume spraying Friday night. Experts say spraying at night reduces the risk to beneficial insects, including honeybees.

The federal Centers for Disease Control and Prevention reports that as of Tuesday, there had been 693 cases of West Nile virus human infections in the United States (336 of them in Texas) and 26 deaths (14 in Texas). Louisiana is the second most effected state.

Dallas Mayor Mike Rawlings and Dallas County Judge Clay Jenkins both have declared a state of emergency, which led to the decision to spray there for the first time in 45 years.

"I cannot have any more deaths on my conscience because we did not take action," Mayor Rawlings told the AP.

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