AsianScientist (Mar. 21, 2012) – Japanese honeybees (Apis cerana japonica) face a formidable foe in the Asian giant hornet (Vespa mandarinia japonica), a fierce predator that can reach 40 millimeters long or larger.
But the bees have developed a novel defense mechanism: they create a “hot defensive bee ball,” swarming around the hornet and literally cooking it alive.
In the ball formation, a group of more than 500 honeybees vibrate their flight muscles to produce heat. The temperature in the ball quickly rises to almost 47°C, and the hornet is killed by the heat produced after 30-60 minutes.
A new study published recently in the journal PLoS ONE uncovers some of the neural activity that underlies this unusual behavior, which is not practiced by the Japanese honeybee’s European relative.
“The defensive bee ball formation is considered to result from Japanese honeybee-specific selective pressure to avoid predation by the giant hornets that inhabit East Asia, including Japan,” the authors write.
To investigate the brain function behind this unique adaptive behavior, the researchers sampled honeybees as they were engaged in a hot defensive bee ball, plucking them off one-by-one from the ball at different time points.
Using a novel marker gene called Acks to detect the neural activity evoked in the brains of the honeybees that form the bee ball, they found that neurons that make up the higher brain center are active while the bees are part of the hot ball.
The honeybee’s neural responses were found to be thermally-activated. Worker bees artifically exposed to 46°C heat exhibited Acks expression patterns, similar to when they were involved in the formation of a hot defensive bee ball.
Source: PLoS ONE.
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