Honey bees use sophisticated signals to warn peers of danger

A honey bee species found in parts of India, China and Japan, use sophisticated signals to warn their nestmates about the level of danger from predators attacking foragers or the nest, a new study has found.

The scientists said it is the most sophisticated form of alarm signalling found in a social insect.
They found that these bees can produce different types of vibrational "stop signals" when attacked by hornets.

These signals have different effects depending upon type of danger and the context. A bee delivers a stop signal by giving another bee a brief, vibrational pulse, usually through a head-butt.

"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, from University of California, San Diego who led the research team along with Ken Tan, a professor at Chinese Academy of Science.

Earlier, researchers had discovered that foragers of the European honey bee, 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.

These signals were known to inhibit recruitment, the famous waggle dance of the honey bee, but researchers did not know what triggered stop signals.

Researchers conducted their experiments using the Asian honey bee, Apis cerana, which occurs throughout southern and eastern Asia, from India to China and Japan.

"We hypothesised that bigger predators would pose a bigger threat and would change stop signalling, 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," he said.

Attacked foragers reduced their waggle dancing and produced stop signals that increased in pitch according to predator size.

The larger and more dangerous predator triggered higher pitched stop signals that were more effective at stopping waggle dancing than the lower pitched stop signals triggered by the smaller and less dangerous predator.

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.

The study was published in the journal PLOS Biology.