Scientists in the US have figured out how to make normal bees act like their ‘killer’ Africanised cousins. Africanised honeybees were developed in the 1950s when Brazilian researchers crossbred European and African bees in an effort to make a breed that produced more honey.

A swarm escaped captivity in 1957, and since then have been linked to deaths of as many as 1000 people, most of them in South America, but there have been reported deaths in the US in recent years.

While smaller and less venomous than normal bees, they attack anyone and anything that gets even close to a nest in massive swarms.

“In a hive of ordinary European bees, about 10 percent will attack if the hive is threatened, but with African bees, all of them attack you,” bee hive owner Allen Miller told the Waco Tribune in 2013, after a farmer was stung to death by a swarm 40,000-strong.

Until now, it’s been unclear why the bees are so angry and aggressive. The latest research, conducted by the American Chemical Society and the University of Sao Paulo State, suggests it’s all in the bees’ brains.

They looked at the difference between killer bees and normal bees’ brains, eventually focusing in on small proteins called neuropeptides, which act as transmitters. The killer bees had short peptides than the normal bees.

When researchers injected the shorter peptides into the brains of normal bees, they “became combative” – effectively creating killer bees. There is a point to this experimentation – they hope that by figuring out why Africanised bees are so violent and aggressive, they’ll be able to stop the spread of the vicious species.

Last year an Arizona beekeeper claimed to have eradicated killer bees from his hives by removing the queens, replacing them with non-Africanised queens, whose offspring are docile. New Zealand remains free of Africanised bees.

Killer bees have something of a reputation, which – to be fair – isn’t entirely undeserved. Their venom isn’t deadlier than your average honey bees, and they’re actually a little smaller than their cousins. But they are aggressive, and it doesn’t take much provocation to incite a swarm of them to turn into a raging, stabbing machine of pain.

Given bees are far more likely to kill you than pretty much any predatory carnivore, the more hostile variety is an animal we should really treat with caution. These tiny striped curmudgeons appeared in the late 1950s, after Brazilian apiarists imported an African variety of Apis mellifera scutellata honey bee with a view to increase honey production.

Of course the bees didn’t quite understand the fine print on their working visas, and were soon off breeding with the plain old Apis mellifera locals, creating the ‘bee-grade’ horror story that is legend to this day.

These aggressive hybrids have since spread as far as northern California, and remain a legitimate threat. More than a few hundred people have lost their lives to their relentless stinging.

But for all we know about their history, remarkably little is understood about what’s going on in their tiny bee brains. To get to the bottom of the mystery, the researchers in this latest study had to collect themselves a sample of killer bees – without getting murdered. They used a pretty clever trick for this.

Balls made out of thick leather were dangled near suspect bee hives, prompting large numbers to decide war was the only answer to these invading spheres of doom, and ram their stingers into the leather. All the researchers needed to do was pluck out the angry bees and pop them into liquid nitrogen.

Bees that calmly kept a distance were also collected, frozen, and placed into a second category. Comparing the full range of brain proteins in both categories of bee using mass spectral imaging revealed a clear, but simple difference.

One of the suspect proteins was called Apis mellifera Allatostatins A, a neuroprotein already understood to play a key role in bee learning and memory, as well as their general development.

The other group of proteins, described as tachykinin-related peptides, aren’t clearly understood, but seem to influence sensory processing. In the aggressive hybrids, these two groups of neuropeptides had been cut into shorter proteins, and were found in different clusters of brain tissue called neuropils.

To verify these proteins were significant in the bee’s behavioural transformation, the researchers put a selection of non-aggressive bees to sleep and injected their brains with truncated forms of the neuropeptides. As expected, the bees weren’t exactly happy when they woke up, with the different brain chemistry thought largely to blame.

Exactly how the size and distribution of these neuropeptides leads to more aggressive behaviour is still a question to be answered, though. Learning more about the cascade of effects these proteins have on a bee’s nervous system could tell us more about the development of bee nervous systems, as well as those of insects in general.

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