The Asian honey bee uses sophisticated ‘stop signals’ to warn others of imminent danger.

By Lola Gayle, Editor-at-large

Honey bees are famous for their figure-eight “waggle dance,” which they use to share information with other bees about where to find food, water sources, and potential new nesting sites. But there’s another sort of sophisticated signal used by bees — in this case to warn nestmates about predators.

During a study in 2016, biologists from UC San Diego and the Chinese Academy of Science found that an Asian species of honey bee uses vibrational “stop signals” when attacked by giant Asian hornets, usually in the form of head-butts that vary depending upon the type of danger and the context.

“Surprisingly, this signal encodes the level of danger in its vibrational frequency, its pitch, and the danger context through the duration of each pulse,” said James Nieh, a professor of biology at UC San Diego who headed the research team. Co-leader of the study was Ken Tan, a professor at Xishuangbanna Tropical Botanical Garden, Chinese Academy of Science.

Six years ago, Nieh discovered that foragers of the European honey Apis mellifera, when attacked at a food source, will return to the nest and deliver stop signals to nestmates recruiting for the dangerous food source, reports Kim McDonald for UC San Diego. These signals were known to inhibit recruitment, but researchers did not know what triggered stop signals.

“Stop signals are usually delivered by a sender butting her head into a recipient. Understanding that these signals can be triggered by danger and reduce recruitment for dangerous food therefore made sense,” explained Nieh.

After his initial discovery, Nieh next wanted to find out if other honey bee species also used stop signals. He and his collaborators at the Chinese Academy of Science and Eastern Bee Research Institute in Yunnan Province conducted their research using the Asian honey bee, Apis cerana, which can be found throughout southern and eastern Asia, from India to China and Japan.

There are two villains to this story: the world’s largest hornet, the “yak-killer” Vespa mandarinia and a smaller, but still formidable hornet, Vespa velutina. Both hornet species are natural enemies of A. cerana.

These hornets attack foraging bees and their nests, so the scientists set up their experiments to see if bees would produce stop signals in both situations, McDonald reports.

“We hypothesized that bigger predators would pose a bigger threat and would change stop signaling, perhaps by producing more signals when attacked by a large predator,” Nieh said. “However, we were very surprised to find that these Asian bees not only produced more stop signals, they also produced different kinds of stop signals.”

Foragers that were attacked reduced their waggle dancing and began producing stop signals that increased in pitch according to predator size. The larger the predator, the higher the pitch. In addition, guard bees and returning foragers attacked at the nest entrance produced longer duration stop signals to warn nestmates about the imminent danger outside.

“Our experiments showed that these different types of stop signals elicited different and appropriate responses. Bees attacked at food sources by bigger hornets produced a kind of stop signal that more effectively inhibited recruitment,” said Nieh. “Bees attacked at the nest entrance produced another kind of stop signal that inhibited foragers from exiting the nest and being exposed to the danger outside.”

According to Nieh, “this is the first demonstration of such sophisticated inhibitory signaling or alarm signaling in an insect.” Previously, such referential alarm signals had only been reported in vertebrates like birds and primates.

Other authors of the study were Shihao Dong, Xinyu Li and Chao Wang of Yunnan Agricultural University and Jianjun Li of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Science.

Findings are published in the open-access journal PLOS Biology.

Top Image: A giant Asian hornet attacks an Asian honey bee forager in China. Photo by James Nieh/UC San Diego

Further Reading

  • How honey bees stay clean while pollinating plants — Georgia Tech
  • Object Recognition in Flight: How Do Bees Distinguish between 3D Shapes? — PLOS ONE, Feb. 2016

Did you know?

When attacked by hornets, Apis cerana japonica will create a living, breathing ball around their attackers. This defensive ball engulfs the predators, incapacitating them until they become overheated and eventually die.

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Image Credit: Takahashi/Wikimedia Commons (CC BY-SA 2.1 JP)

DISCLAIMER: This is a repost of a previous article I wrote during my time trying to get a friend’s site off the ground. After two years and virtually no headway or money — and no promise of how long the site will remain online — I am forced to take back ownership of my content. Portions of the content have been updated.