Cyprian honeybees kill their enemy by smothering them
For the first time, researchers have discovered that when Cyprian honeybees mob and kill their arch enemy, the Oriental hornet, the cause of death is asphyxiation. They reported their findings in the September 18, 2007, issue of Current Biology.
鈥淗ere, for the first time we detail an amazing defense strategy, namely asphyxia-balling, by which Cyprian honeybees mob the hornet and smother it to death,鈥� said G茅rard Arnold of CNRS in Gif-sur-Yvette, France. 鈥淭he domestic bee has never ceased surprising us.鈥�
Previous studies showed that Asian honeybees similarly attack hornets, leading the predatory insects to die from the heat inside the ball of bees. That murderous 鈥渢hermo-balling鈥� strategy is used against invaders, mainly hornets, armored with a hard cuticle that is impenetrable to the bees鈥� most familiar weapon: their stingers.
However, scientists knew from earlier studies that various subspecies of the domestic honeybee (Apis mellifera), which form comparable balls around hornets, couldn鈥檛 raise the temperature high enough to finish off the heat-tolerant hornets, explained the study鈥檚 first author, Alexandros Papachristoforou of Aristotle University of Thessaloniki, Greece. It had been shown that the mobbing bees go for the gut, targeting the hornets鈥� abdomen, which is critical for the insects鈥� 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鈥� breathing, the researchers monitored their respiration under normal conditions and those designed to mimic the balling behavior, in which they covered either two or four of the insects鈥� tergites. The hornets鈥� 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.
鈥淭o kill the high-temperature-tolerant hornet, Cyprian honeybees have developed an alternate strategy to thermo-balling and stinging,鈥� Arnold said. 鈥淭hey appear to have identified the hornets鈥� 鈥楢chilles heel鈥� by asphyxiating the predator. This ability indicates that under extreme conditions, honeybees can present a high level of adaptation in order to survive.鈥�
Source: Cell Press
