Cyprian honeybees kill invading hornets by smothering them

Washington, Sept 18: Cyprian honeybees kill their archenemy, the Oriental hornet by smothering them, a new study by entomologists in the recent issue of Current Biology, has revealed.

“Here, for the first time we detail an amazing defence strategy, namely asphyxia-balling, by which Cyprian honeybees mob the hornet and smother it to death. The domestic bee has never ceased surprising us,” said Gérard Arnold of CNRS in Gif-sur-Yvette, France.

Previous studies had shown that the Asian honeybees similarly attacked hornets, leading the predatory insects to die from the heat inside the ball of bees.
That same murderous “thermo-balling” strategy is used against invaders, mainly hornets, who are armoured with a hard cuticle that is impenetrable to the bees’ most familiar weapon: their stingers.

Scientists knew from earlier studies that various subspecies of the domestic honeybee (Apis mellifera), which form comparable balls around hornets, couldn’t raise the temperature high enough to finish off the heat-tolerant hornets.

Mobbing bees generally went for the gut, targeting the hornets’ abdomen, which is critical for the insects’ ability to breathe. By pumping their abdominal muscles, the hornets bring in air through small openings called spiracles, which are covered by structures known as tergites when air is released.

To find out whether the bees could be blocking the hornets’ breathing, the researchers monitored their respiration under normal conditions and those designed to mimic the balling behaviour, in which they covered either two or four of the insects’ tergites.

The scientists found that the hornets’ respiration declined by about 33 and 87 percent, respectively, in these experiments.

Next, they tested whether the bees could kill hornets whose tergites were held open with tiny plastic blocks. They found that the bees took twice as long to kill such manipulated hornets.

“To kill the high-temperature-tolerant hornet, Cyprian honeybees have developed an alternate strategy to thermo-balling and stinging. They appear to have identified the hornets’ ‘Achilles heel’ by asphyxiating the predator. This ability indicates that under extreme conditions, honeybees can present a high level of adaptation in order to survive,” said Arnold. (With Inputs from ANI)