Faced with a potential threat to the hive, some honeybees take on the suicidal mission of attacking the intruder. These guard bees aren't just angry, they may be insane: Scientists have proposed that their brains are infected with a virus that causes their deranged behavior.
In the brains of honeybees, organs known as mushroom bodies are enlarged relative to most other insects. These cerebellum-like structures play a role in a multitude of tasks related to memory and learning, and changes in gene activity in the mushroom bodies have been linked to behavioral changes (Science, 26 April 2002, p. 741).
While combing the mushroom bodies for evidence of aggression genes, a team of researchers at the University of Tokyo and Tamagawa University in Japan found a weird chunk of RNA that wasn't encoded by the honeybee genome. The RNA was present only in the brains of the bees that went into attack mode when a hornet was dangled in front of the hive, not in the brains of the hive's nurses or foragers.
The RNA appears to belong to a class of viruses known to infect honeybees. The sequence is unique enough that the team thinks it's a previously unknown virus, now dubbed "Kakugo" for "ready to attack" in Japanese. It seems to be infectious, as well. When the researchers ground up the brains of attacker bees and injected the gunk into the heads of nonaggressive bees, there was a marked increase in viral RNA in their brains after 3 days, the researchers report in the February issue of the Journal of Virology.
The team hypothesizes that the virus infects a subset of the hive, turning them into fierce defenders. Previous work has shown that pathogens can alter bee behavior, but confirming that the new virus causes aggression has been tough, says team member Takeo Kubo. Bees injected with infected brain mush were kicked out of the hive, making it impossible for the researchers to establish whether their behavior had changed. Now the team is trying to infect bees with a honey-virus ambrosia in hopes that these bees will be better tolerated by their hive-mates.
That a virus puts the buzz in the bee's bonnet is “an enticing hypothesis,” says Jay Evans, a research scientist at the U.S. Department of Agriculture's Bee Research Laboratory in Beltsville, Maryland. “But it is very speculative,” he says. To convince him, the Japanese team will have to show that the viral infection really does make honeybees stinging mad.