(CNN)If you want to keep enjoying apples, melons and blueberries, bees need to be healthy and cared for.
Many plants rely almost entirely on bees as natural pollinators to produce some of nature's most nutritious foods, but bee species have been significantly declining in recent decades.
That could be due to pesticides, parasites, competition with other insect species, climate change, plant loss and a mismatch between the plants available and those that bee species enjoy.
In a world without any or enough bees, it may be possible to pollinate fruit-bearing plants using soap bubbles, according to a study published Wednesday in the journal iScience.
The loss of bees is a "worldwide crisis," said study coauthor Eijiro Miyako, an associate professor in the School of Materials Science at the Japan Advanced Institute of Science and Technology.
"Besides, conventional pollinations like hand pollination are very tough work and annoying for farmers," Miyako said. "They really want a convenient automatic pollination method. They are [the] main reasons why we need to make new artificial pollination."
Machine sprayers reduce human labor and reliance on insects, but have been more expensive and wasteful of pollen grains when they miss the flowers, the study said.
Robotic pollination has become more attractive to researchers since robotic pollinators can detect individual flowers, operate autonomously and be programmed, the study said.
In 2017, Miyako and his colleagues published a study in which they used a tiny drone to pollinate blossoming flowers. Although the drone was only two centimeters in diameter, it destroyed the flowers as it bumped into them because it lacked an autonomous controlling system, Miyako said.
So began the search for another method. While blowing bubbles with his son at a park, Miyako had an epiphany: If the soap bubbles didn't do any damage when they hit his son's face, maybe the bubbles would be soft, light and flexible enough to pollinate flowers without harming them. He confirmed that suspicion with an optical microscopy at his lab.
"It sounds somewhat fantasy, but the soap bubble is effective for pollination," Miyako said.
The researchers tested five different commercial surfactants — substances that reduce the surface tension of a liquid, thus increasing the liquid's spreading and wetting properties.
Lauramidopropyl betaine, a surfactant that behaves like soap, was the best option. Its foaming ability produced many stable soap bubbles when researchers triggered the bubble gun once. It also facilitated better pollen germination and growth of the tube that develops from each pollen grain after it's deposited on a flower.
The researchers found that a soap bubble solution with an optimized pH, calcium, other minerals and chemicals was the most effective concentration for germination and for retaining pollen grains on the thin film of the bubbles and transporting them to the targeted flowers.
After three hours of pollination, the pollen activity through the bubbles was higher than that of other methods such as powder pollination or solution pollination (through which powder of pollen grains was applied to the flowers, or a solution of pollen, sugar and agar was sprayed, respectively).
In an orchard, the researchers shot up to 50 pollen-loaded bubbles onto natural pear flowers. Through fluorescence microscopy, they found that the pollen grains landed on the flower pistils and grew pollen tubes. The number of pollen grains on each pistil increased as the soap bubbles grew larger, but the grains decreased and the tubes shortened when more than 10 bubbles were shot, potentially because of toxic accumulation.
After shooting two to 10 bubbles onto the pear flowers, fruits grew after 16 days — at a volume almost the same as that of conventional methods, the study said.
While the fruit-bearing rate of the control group (which didn't undergo pollination) was about 58%, bubble and hand pollination both achieved a rate of around 95%. Soap pollination also called for much fewer pollen grains than other methods did.
"No significant differences were observed between them," Miyako said. "In fact, the shape and size of young pear fruits after soap bubble pollination look the same as hand pollination. But ... our method has more potential advantages in terms of future automation and reduction of pollen grains."
The drone experiment
To create a robotic pollinator, researchers combined an automatic bubble maker that produced about 5,000 bubbles per minute with an autonomous, GPS-controlled drone.
Bubbles were shot