Roughly a third of the world's food crops require help with pollination, but more than 40 percent of the species that perform this vital service are under threat.

Researchers across disciplines have been searching for solutions. Some focus on ways to protect the bees and other crucial pollinators. But others are looking outside of the natural world for ways to protect crops like fruits, vegetables, nuts, berries, and even chocolate and coffee.

Perhaps an army of robotic pollinators could keep humans well-supplied in these foods, some engineers have thought. And that's just the line of thinking that led a team of researchers in Japan to design a small drone capable of pollinating flowers.

After studying honeybees, Eijiro Miyako, a senior researcher at the Nanomaterials Research Institute in Japan, and colleagues realized they could use an ionic liquid gel to pick up the pollen from one flower and deposit it on another. But they couldn't paint the gel directly onto the slippery plastic of the little flying robot they were using. Instead, they needed something like the brush-like hairs that pick up pollen on bees. They tried affixed horsehairs to the drone and then added the ionic gel.

The researchers tested their device on the large, pink flowers of Japanese lilies. And it worked.

"When I could confirm the growing of pollen tubes under fluorescent microscopy," Dr. Miyako writes in an email to The Christian Science Monitor, "I thought that it was just mistakes. But it was true... I was really surprised. And I felt happiness that I'm a scientist."

The researchers describe their success in a paper published Thursday in the journal Chem.

As exciting as this success was for Miyako and the other researchers, it is only a first step. Scientists can build something capable of pollinating plants, but the team has yet to figure out how to apply the concept on the massive scale necessary to make it useful for farmers.

So, could a fleet of robo-pollinators replace, or at least supplement, the bees?

Although the answer isn't a straightforward no, it would be a challenging leap to go from this one little drone pollinating one large flower to an army of drones spreading across fields of crops, says Scott Swinton, an agricultural and environmental economist at Michigan State University who was not involved in the research.

In North America, farmers largely rely on white boxes full of European honeybees, Apis mellifera. These domestic bees live in dense populations with perhaps tens of thousands of worker bees in each hive. That is an enormous amount of pollination power, Dr. Swinton explains.

A fleet of drones to match that "would just be a very formidable cost," he says in a phone interview with the Monitor.

Here's how he breaks it down: "If an almond grower pays rent of $150/hive for 30,000 worker bees, that’s ½ cent per bee. If the bees work for 2 weeks in that grove, it’s 0.035 cents/day … Drone pollinators will have to slide pretty far down the cost curve to compete at that rate," he writes in a follow-up email to the Monitor.

"European honeybees continue to be by far the low-cost providers of this service," Swinton says. "And beating that mark is no easy job."

Taylor Ricketts, director of the Gund Institute for Ecological Economics at the University of Vermont who also wasn't involved in the research, agrees that drones would be a pricey option. "I'm not sure that's going to be cheap enough to not make blueberries hundreds of dollars a pint," he tells the Monitor.

And Dr. Ricketts has concerns about how drones might navigate a plants' biology.

Although it was "clever to align these hairs and coat them with this material," and the successful pollination was intriguing, he says, the device itself might damage the flowers.

"A machine bumping into a flower can actually bruise or bend or break the stigma, that's the female part that actually receives the pollen, and we have to be careful when we're doing that with a paintbrush," Ricketts says. "So I wonder how you make sure you're not doing more harm than good when you have a drone."

Furthermore, he points out, a lily is a particularly easy flower for a drone to pollinate because of the shape of the flower and the easy access to its pollen. To make this more broadly applicable for smaller and more complex flower structures, the drones would need to be particularly agile.

A team of researchers at Harvard University Microbotics Lab have already made a "RoboBee," a tiny drone inspired by bees. So perhaps it is possible to build better drones.

Still, Joshua Campbell, an entomologist at the University of Florida who was not involved in the research, says "pollination systems are extremely complex and will always require insects. There is no substitute for ... bees."

This is because pollination systems, and the insects that use them, have evolved together for thousands or millions of years. "They're so intricate, it's not something that we can piece together in a lab and come up with substitutes," he says in a phone interview with the Monitor.

"I think you can attempt to mimic them, and I'm not saying that you wouldn't have any success getting a plant pollinated," Dr. Campbell says. But the issue comes back to scale. "It's a big difference between pollinating one plant in the lab versus a hundred-acre field of watermelon or blueberries."

As for the technology itself, "It is a promising combination of a new development in particle adhesion coupled to existing drone technology," says Carson Meredith, a chemical engineer at the Georgia Institute of Technology who was not involved in the project.

Unlike the other scientists, Dr. Meredith believes the tiny pollinator-bot could successfully be scaled up, he writes in an email to the Monitor.

But he still sees some hurdles: the scientists still need to figure out how to mass produce their drones, and "how to reload fresh pollen on the drones once they have dropped their payload; can the gel be used over and over again?"

These drones join other proposed technological solutions for pollinating plants, Ricketts says.

In addition to simple hand pollination, he explains, some people have tried blowing pollen onto plants using large-scale devices like leaf-blowers. "They just kind of blow pollen all over the place and hope some lands on the right flower," he describes.

But Ricketts, Campbell, and Swinton say the best solution may already exist – native bees.

"We have these thousands of native bees," Ricketts says. "Many of them we know to be good pollinators."

These wild bees live more solitary lives than their domestic counterparts, building smaller nests in holes in the ground or old trees. But "there are some really cool efforts that are being done to domesticate native bees," Ricketts says. So perhaps one day they will be the new inhabitants of those iconic white boxes, or another sort of controlled hive.

But even without domesticating bumblebees or other native bees, farmers still might be able to take advantage of their pollinating power. All they have to do is make sure to set aside enough land conducive to the bees' habitat.

"To me, the exciting part of this whole idea and solution is that it's not a mystery what these bees need. It's really straightforward," Ricketts says. The bees just need three things: pollen and nectar to sustain them, crevices or holes to build a nest, and protection from pesticides.

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Although it's unclear if native bees could shoulder the burden if all honeybees were to disappear, Ricketts says, "I don't think we've given native bees a shot to prove how well it can be done."

[Editor's note: The original version of this story overstated the percentage of global food crops that rely on animal pollinators. It is around 30-35 percent.]