An international team of researchers has documented the unique vibroacoustic signals the eastern honeybees (Apis cerana) use to alert members of their hive when dangerous predators — such as Vespa soror, a giant hornet species that can decimate honeybee colonies through group predation — attack.
Vespa soror hornets attack a hive of eastern honeybees (Apis cerana) in Vietnam. Image credit: Heather Mattila / Wellesley College.
“Asian honeybees use an impressive array of strategies to protect nests from hornet attacks, although little is understood about how antipredator signals coordinate defences,” said Wellesley College’s Dr. Heather Mattila and colleagues.
The scientists studied interactions between Apis cerana honeybees and two species of giant hornets — group-hunting Vespa soror and smaller, solitary-hunting Vespa velutina — in Vietnam.
They collected audio and video recordings of hornet attacks in apiaries of local beekeepers.
Microphones in hives captured almost 30,000 signals made by bees over 1,300 minutes of monitoring.
The authors observed that Apis cerana sound the alarm to their fellow bees to defend themselves against attacks of Vespa soror.
“The process itself was pretty arduous at times,” said Hannah Kernen, also from Wellesley College.
“For each recording, we had to mark out individual signals by hand, and we revisited recordings multiple times to double-check them.”
“These signals are striking and have acoustic properties that are designed to get the attention of colony members, just like the sounds that are shared among alarmed groups of mammals and birds,” Dr. Mattila added.
“For human observers eavesdropping on the bees, their sounds convey a sense of urgency that feels somewhat universal.”
Bees make sounds, and antipredator pipes in particular, at a frenetic pace when giant hornets are directly outside their hive.
“The pipes share traits in common with a lot of mammalian alarm signals, so as a mammal hearing them, there’s something that is instantly recognizable as communicating danger. It feels like a universal experience,” Dr. Mattila said.
Antipredator pipes are different from the sounds that have previously been observed in colonies, including hisses and stop signals.
These newly-discovered signals are harsh and irregular, and their frequencies shift abruptly, similar to the attention-grabbing alarm shrieks, fear screams, and panic calls primates, birds, and meerkats make in response to predators.
In addition to warning the hive about the arrival of giant hornets, the signals result in an increase in bees at their hive’s entrance and the start of their defense actions, which include spreading animal dung around colony entrances to repel giant hornets and forming bee balls to kill attacking hornets collectively.
“Bees are constantly communicating with each other, in both good times and in bad, but antipredator signal exchange is particularly important during dire moments when rallying workers for colony defense is imperative,” the researchers said.
“This research shows how amazingly complex signals produced by Asian hive bees can be,” said Professor Gard Otis, a researcher at the University of Guelph.
“We feel like we have only grazed the surface of understanding their communication. There’s a lot more to be learned.”
The team also noticed that when bees make antipredator pipes, they raise their abdomens, buzz their wings, and run frantically, all while revealing their pheromone-producing Nasonov gland.
The bees’ behavior suggests that they produce multiple types of information to get their nestmates’ attention.
“Apis cerana colonies are a fascinating example of a eusocial insect whose rich use of alarm signals mirrors the features of sophisticated antipredator systems of socially complex vertebrates,” the scientists said.
Their work appears in the journal Royal Society Open Science.
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Heather R. Mattila et al. 2021. Giant hornet (Vespa soror) attacks trigger frenetic antipredator signalling in honeybee (Apis cerana) colonies. R. Soc. open sci 8 (11): 211215; doi: 10.1098/rsos.211215
Source link: https://www.sci.news/biology/apis-cerana-vibroacoustic-signals-10257.html
