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Soap Bubble Pollination

August 10, 2020

In the distant past of my childhood, conversations about sexual intimacy were rare, and reproduction was described by a euphemistic analogy to "the birds and the bees." Today, middle school grandchildren know more about sex than their grandparents did on their wedding night, either through classroom instruction or by the Internet, the later often giving too much information.

The "birds and bees" analogy combines the essential parts of sexual reproduction, birds' eggs and the bee's deposit of fertilizing pollen. The milieu of my high school years is captured in the 1964 Jewel Akens song, The Birds and the Bees.[1] This short (2:08) record reached the number three position on the Billboard Hot 100 chart.

Jewel Akens (screenshot from a YouTube video)

Jewel Akens, singing The Birds and the Bees on Shindig!.

1960s television was replete with popular music shows like Shindig!, Hullabaloo, Hootenanny, and the venerable American Bandstand.

(Screenshot from a YouTube video.)

Short records had an advantage in the era of Top 40 radio, since disk jockeys needed to fill their time carefully to accommodate scheduled news on the hour or half-hour. That's one reason why the 1967 "The Letter" by the Box Tops had so much airplay at 1:58, peaking at number on on Billboard.[2] This record reached number one on the Billboard Hot 100. Compare this with the 1968 "MacArthur Park" by Richard Harris at 7:21, but still reaching number two on Billboard. Little known fact - Your scientist author was a Top 40 DJ in the 1960s.

Bees, of course, are associated with honey. Beekeeping is a big business, with an estimated two and a half million beehives producing about 70 metric tons of honey in the United States annually. However, the most important function of bees is as pollinators. The list of crop plants pollinated by bees is huge, but they're most important in the pollination of the crops listed in the following table.

Plant Plant Plant
Kiwifruit Brazil Nut Watermelon
Cantaloupe Squash, pumpkin, zucchini Macadamia
Passion Fruit Rowanberry Cashew
Starfruit Turnip, Canola Coriander
Cucumber Cardamom Loquat
Buckwheat Feijoa Fennel
Apple Mango Avocado
Allspice Apricot Sweet Cherry
Sour Cherry Plum Almond
Peach, Nectarine Pear Rose Hips
Raspberry Blackberry Blueberry

Honey bees maintained by commercial beekeepers in the US pollinate food crops worth about $15 billion annually, and about a third of our food is a consequence of pollination that's mostly done by bees.[3] Pollinator were celebrated this year during Pollinator Week, June 22-28, 2020. Pollinator Week was established by a US Senate resolution in 2006, the same year that beekeepers noticed a marked escalation in what's called colony collapse disorder (CCD) when nearly all the worker bees in a honey bee colony disappear. There are many possible causes for CCD, including pesticides, pathogens, and effects from global warming, but no clear consensus.

Western honey bee (Apis Mellifer)

Western honey bee (Apis Mellifer).

Few people today have heard the idiomatic expression, "It's the bees knees," which was one of numerous animal-related expressions, such as "the cat's meow," popular in the 1920s. It means "something that's exceedingly wonderful."

The first and only time I heard the "bee's knees" expression was in conversation with the wife of a Manhattan Project scientist. She also liked the expression, "It's all sixes and sevens," meaning "a muddled mess."

(Portion of a Wikimedia Commons image by Ivar Leidus.)

In a one-year span, from April 2019 - April 2020, U.S. beekeepers lost 43.7% of their honey bees.[3] While bee population declines in the winter, the decline seen in the past winter was actually lower than usual.[3] The big losses happened in summer, 2019, when beekeepers lost 32% of their bees, a decline that's is 10.4% higher than average.[3] Beekeepers attribute this decline to parasitic mites, increased heat, and possibly, pesticides.[3]

While an army of solar-powered microscale robotic drones might replace the pollination provided by honey bee drones, that's not an economical alternative. The traditional method for pollination in the absence of bees, done since antiquity, is to use a cotton swab, or a small brush, to apply pollen grains to flowers.[4-5] An alternative to such time consuming manual labor is machine pollination using blowers, dusters, or sprayers, all of which waste pollen grains by inefficient targeting.[4] An artificial pollinator developed in 2017 acted as a bee would by capturing pollen from some flowers with a drone and a sticky ionic liquid gel for transport to other flowers, but this method caused too much damage to the plants.[4-5]

Researchers from the Japan Advanced Institute of Science and Technology (JAIST) have developed a pollination method in which pollen grains are incorporated into chemically functionalized soap bubbles delivered by an autonomous robotic drone.[4-9] The idea for this method of pollination came to the senior author of the study, Eijiro Miyako, an associate professor in the School of Materials Science at JAIST, while his son was blowing soap bubbles in a park.[6-8] He noticed the bubbles' gently impacting his son's face from a toy bubble blower. As he told BBC News,
"I was playing soap bubbles with my son at a park close to my home, when a soap bubble accidentally hit my son's face... There was no damage because soap bubbles are soft, light, and flexible... But I got an inspiration because I thought the bubbles won't damage the flowers and would be an ideal material for pollination."[8]

A chemically functionalized soap bubble pollinating a campanula flower (Campanula persicifolia).

A chemically functionalized soap bubble pollinating a campanula flower (Campanula persicifolia).

(Portion of a photo by Eijiro Miyako.)

laboratory testing showed that soap bubbles could carry pollen; however, most soaps are too toxic for flowers, so a special soap bubbles mix was developed.[6,8] The selected soap bubble formulation of a 0.4% lauramidopropyl betaine had an optimized pH and added calcium and germination supporting chemicals.[6,9] The soap bubbles held up to 2,000 pollen grains each.[6,9] Pollen activity was observed to be steady three hours after pollination, with the pollen grains growing into pollen tubes on the female reproductive part of the flower, the pistil.[6,7] If a flower was impacted by more than 10 bubbles, the tubes were shorter than normal, perhaps because of an adverse effect of the bubble solution.[7]

Moving from the laboratory to the field, the research team was able to pollinate a variety of the pear tree (Pyrus pyrifolia) on three trees in an orchard, and these trees consequently formed pear fruits sixteen days later at a quantity comparable to hand pollination.[4,7-8] Moving a technology step further, they used an autonomous, GPS-controlled drone to direct soap bubbles at fake lilies, and these bubbles hit their target with 90% success when the drone was moving at two meters per second.[6,8] Miyako, as quoted by BBC News, said, "In fact, the shape and size of young pear fruits after soap bubble pollination look the same as hand pollination. However our method has more potential advantages in terms of future automation and reduction of pollen grains."[8]

Image of a robotic pollinator consisting of a UAV and a bubble maker.

Image of a robotic pollinator consisting of an unmanned aerial vehicle and a soap bubble maker. (Figure 3d of Reference 4, released under a Creative Commons License.)

Bubbles need much less pollen for pollination than hand pollination with a brush, just 0.06 milligrams per flower compared with 1800 milligrams, so farmers would need to gather far less pollen.[7] There are a few problems with the soap bubble method, aside from the chemical effect seen when too many bubbles strike a flower. Raindrops can wash away the pollen-bearing bubbles, and strong winds, even the air flow from the drone propellers, will blow them away.[6-7,9]

While the soap bubble chemicals used in this study were biocompatible, they might still build-up in the environment over time.[4] While bees both collect and deliver pollen, the soap bubbles need a pollen source.[9] Also, some worry that such research might distract from the important task of bee conservation.[7] This work was primarily supported by the Japan Society for the Promotion of Science.[6]


  1. Jewel Akens, "The Birds And The Bees (1965, Remastered)," YouTube video by Memory Lane, May 8, 2019. Alas, only 3,307 views when accessed. The Box Tops, "The Letter," YouTube video by Smurfstools Oldies Music Time Machine, Aug 2, 2018. This video had 138,214 views when accessed.
  2. Richard Harris, "MacArthur Park," YouTube video by gb, August 4, 2013. 3,375,552 views when accessed.
  3. Dharna Noor, "A Record Number of Bees Died Last Summer," Gizmodo, June 22, 2020.
  4. Xi Yang and Eijiro Miyako, "Soap Bubble Pollination," Cell, vol. 23, no. 6 (June 26, 2020), Article no. 101188, DOI:https://doi.org/10.1016/j.isci.2020.101188. This is an open access article with a PDF file here.
  5. Soap bubble pollination is now live!, Japan Advanced Institute of Science and Technology Press Release, June 18, 2020.
  6. Soap bubbles pollinated a pear orchard without damaging delicate flowers, Cell Press Press Release, June 17, 2020.
  7. Erik Stokstad, "Drone-delivered soap bubbles could help pollinate flowers," Science, Jun. 17, 2020 doi:10.1126/science.abd3878.
  8. Blowing bubbles: Soapy spheres pop pollen on fruit trees, BBC News, June 17, 2020.
  9. Theresa Machemer, "Soap Bubbles Can Pollinate Flowers, but Can They Replace Bees?," Smithsonian Magazine, June 22, 2020.

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