In the 1950s, hybrid ‘Africanised’ bees were introduced to Brazil to try and boost honey production – but they were much more aggressive than European bees.
In 1957, swarms of the bees were accidentally released – and the so-called ‘killer bees’ spread across South America.
Since then, they have killed more than 1,000 people, and even killed horses.
Scientists have now discovered what makes them tick – and showed they could turn gentle bees into angry ones by an injection.
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The difference is down to chemicals in the insects brains, the researchers say.
Mario Sergio Palma and his colleagues wanted to examine neuropeptide differences between the brains of bees displaying aggressive and non-aggressive behavior.
The researchers stimulated Africanized honeybees to attack by hanging spherical, black leather targets in front of their colonies.
Angry guard bees quickly attacked the targets, becoming embedded in the leather by their stingers. Meanwhile, gentler bees kept their distance.
The researchers collected both groups of bees and analyzed their brains by mass spectral imaging.
In the brains of aggressive bees, two longer neuropeptides were cleaved into shorter ones, but this did not happen in the gentler bees.
The researchers then injected the shorter peptides into anesthetized, non-aggressive bees, and they became aggressive when they woke up.