Brain protein fragments spur honey bees to be more aggressive.

Solvin Zankl/Minden Pictures

What turns bees into killer bees?

Biochemists have tracked down the brain chemicals that make so-called killer bees such ferocious fighters. The compounds, which seem to be present in higher levels in the much-feared Africanized honey bee, can make less aggressive bees turn fierce, according to a new study. The compounds may also play a role in aggression in other animals—indeed, they’ve already been shown to do so in fruit flies and mice.

“This is another example of how behavior evolves in different species by using common molecular mechanisms,” says Gene Robinson, an entomologist and director of the University of Illinois’s Carl R. Woese Institute for Genomic Biology in Urbana, who was not involved in the work.

Honey bees are incredibly territorial, fighting to the death to defend their hive with painful stings. But killer bees—hybrids of the relatively docile European strain of honey bee and a more aggressive African relative—are particularly fierce. The hybrids emerged after African bees were imported to Brazil in the 1950s. By the 1980s, they had spread north to the United States, outgunning resident honey bees along the way. Their massive attacks have killed more than 1000 people.

Mario Palma, a biochemist at São Paulo State University in Rio Claro, Brazil, who studies social behavior in bees, wanted to understand the basis of this aggression. So he and his colleagues swung a black leather ball in front of an Africanized bee hive and collected the bees whose stingers got stuck in the ball during the attack. They also collected bees that remained in the hive. They froze both sets, sliced up their brains, and analyzed the slices with a sophisticated technique that identifies proteins and keeps track of where they are in each slice. The analysis revealed that bee brains have two proteins that—in the aggressive bees—quickly broke into pieces to form a so-called “neuropeptide,” they report this week in the Journal of Proteome Research.

Palma and his colleagues already knew that bee brains had these two proteins, allatostatin and tachykinin. “The surprise came out when we identified some very simple neuropeptides, which were produced in a few seconds” after his team swung the ball and triggered the attack, Palma says. The bees that remained in the hive did not make these neuropeptides, he reports. And when his team injected these molecules into young, less aggressive bees, they “became aggressive like older individuals.”

Researchers have found these molecules in other insects, where they seem to regulate feeding and digestion. But few had associated them with “fight” behavior, says Palma, who adds that they also increase the production of energy and alarm chemicals. They could also stimulate the nerve cells in bees needed to coordinate the stinging attack. “There is a fine biochemical regulation in the honey bee brain,” he says.

Palma’s preliminary studies indicate that Africanized honey bees produce more of these neuropeptides than other honey bees do. His team hopes to eventually use these insights to develop a way to protect people from these killer bees, perhaps through a spray or chemical plug that can be applied to a hive.

The studies may also further the understanding of how the production of how various neuropeptides regulate behavior not just in insects, but also in people, Palma suggests. “In neuroscience, there is still a big gap between understanding how molecular pathways and neural circuits work together to regulate behavior,” Robinson says. This work presents “a great way to bridge this gap.”