Planes began spraying the powerful insecticide naled near Miami Beach on Friday, part of the city's effort to fight the spread of the mosquito-borne Zika virus, which has infected 56 people in Florida so far.

The aerial campaign began at 5am off the Miami Beach coastline to allow winds to carry it across the city. A week of protests over concerns for public safety preceded the spraying, with protesters marching outside city hall and circulating an online petition that gained thousands of signatures. The protests succeeded in delaying the flights, but for only a day.

Experts both inside and outside the government say concerns over naled are overblown, especially since it's one of the few options left to prevent the spread of Zika. There is no evidence that the chemical, used since the 1950s to control mosquitoes, poses any risks to humans.

"We have this long history of using it in the southern US and it hasn't caused [anywhere] near the problems people are claiming," said Dr. Grayson Brown, a public health entymology expert at the University of Kentucky. "[It's] never caused a problem. The objection to it is entirely based on conjecture."

Naled is commonly used across the US, particularly after mosquito-breeding disasters like hurricanes or floods, and the chemical is approved by the Environmental Protection Agency for use in insecticide. Elsewhere around the globe, however, its use for mosquito control is controversial. The World Health Organization has never evaluated naled for that purpose, and the EU banned the chemical in 2012, determining it was dangerous for aquatic life and humans, specifically when inhaled or after coming in direct contact with skin.

'The more caution the better, but there's no reason to be afraid of this stuff.'

But forgoing naled may also carry risks. In July, Puerto Rico ignored pressure from the Centers for Disease Control and sided with public concerns about naled's safety when it decided against using the insecticide. Officials opted to instead use Bti, a ground spray also being used by Miami and Miami Beach. There is no word yet on whether Bti has been effective, but Puerto Rico was put under a state of emergency in August with the number of Zika cases on the island now at more than 15,000.

Concerns about naled were raised last week after reports from South Carolina revealed that the chemical killed off the hives at a commercial honey bee farm. The massacre was blamed on human error; the government did not warn local beekeepers about plans to spray so they could temporarily cover the hives.

Honey bee death rates went up in places where higher levels of naled were recorded near hives, according to a National Center for Biotechnology Information study. During a naled campaign in Puerto Rico in the 1980s, farmers complained the chemical was hurting their bee population, according to emerging infectious disease expert Duane Gubler, who oversaw the program.

"The good thing is that it's not toxic to humans and has been shown to not have any adverse effects on human health," said Gubler, a professor emeritus at Duke University and a former head of the CDC's dengue program.

And yet in the six decades naled has been used as an insecticide to protect crops and kill off mosquitoes, there is no record of it causing health problems in humans.

High doses of naled itself are toxic if direct exposure to skin or lungs occurs, but experts say the concentration used in the insecticide is too low to have that effect.

American Mosquito Control Association technical advisor Joe Conlon recommended precautions like staying indoors, washing produce growing outside, and wiping down outdoor toys during spraying. "The more caution the better, but there's no reason to be afraid of this stuff," he said.

It's unlikely naled will be all it takes to get rid of the aedes egypti mosquito that carries Zika. Experts say the US needs more control options, from new insecticides to innovative tools like genetically modified mosquitoes. Prevention methods like proper sanitation are also essential.

"When these outbreaks happen you always wish you had done more," said Dr. Desiree LaBeaud, a pediatric infectious disease professor at Stanford University. "It takes everyone feeling like they need to do their part to decrease mosquito breeding."