European ancestry plays role in 'killer' honey bees' aggressiveness

What causes African hybrid honey bees (AHB), also known as killer bees, to be highly defensive and aggressive? York University researchers have found it was the mixing of African and European genetics that led to hyper-aggression in this invasive strain of honey bees. The findings were detailed in a paper published in the journal Genome Biology and Evolution.

In what has been described as a genetics experiment gone wrong, researchers in Brazil imported a honey bee subspecies from South African and bred them with European-derived honey bees in the 1950s. The idea was to develop a better subtropical honey bee, but bees escaped and mated with the local bees.

“The resulting bees were highly invasive and aggressive, much more than the European honey bees used by North and South American beekeepers at the time,” said Amro Zayed, an associate professor in York University's Faculty of Science, who co-authored the paper led by previous York PhD student Brock Harpur, now an assistant professor at Purdue University.

According to Zayed, the genetics causing this hyper defensiveness were not well known at that time, but the prevailing wisdom was that killer bees are aggressive because South African bees are aggressive.

Amro Zayed

Amro Zayed

The new AHB colonies rapidly reproduced and spread across Brazil and eventually to South America, Central America and, by 1990, the southern United States. Today they have completely replaced the European-derived honey bee in Brazil and are the most common honey bee from Northern Argentina to the southern United States.

The York research team measured the defence response of 116 Brazilian AHB colonies using the Suede Ball test. As demonstrated in a video made by one of the researchers, Samir Kadri, a former York visiting PhD student from Brazil, a suede ball is gently swung for one minute in front of a colony entrance, stimulating a defence response in the bees and encouraging bees to sting the ball.

“We sequenced the genomes of the most aggressive colonies, which would sting the ball 90 times or more per minute, and the least aggressive colonies,” Harpur said. “We then compared the genomes of the most and least aggressive colonies to identify mutations that associate with these differences in behaviour.”

“The most defensive colonies in our study were more related to South African honey bees," Zayed explained, "except at several regions of their genome that influence aggression. Here, they were more related to honey bees from Western Europe. It was the mixing of these two honey bee subspecies that led to hyper aggression.”

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