Novel Virus May Contribute to Aggressive Behaviors of Bees
Worker bees of the genus Apis mellifera change with age from attentive nurse to aggressive guard to persistent forager. In a quest to identify genes associated with aggressive behavior in such bees, faculty member Takeo Kubo of the University of Tokyo, Bunkyo-ku, Tokyo, Japan, his graduate student Tomoko Fujiyuki, and their collaborators extracted a novel picorna-like virus from the brains of worker bees. The researchers now believe that the virus could be responsible for aggressive behaviors among such bees during the guard phase of their life cycle (J. Virol. 78:1093-1100, 2004).
“This is the first suggestion that viral infection can affect intrinsic aggressive behaviors,” says Kubo. He and his colleagues named the virus Kakugo, meaning “ready to attack,” and determined that it is closely related to two other honeybee-infecting viruses, the sacbrood virus plus another virus, whose genome sequence is known but is being further characterized.
“It will be important to survey honeybee colonies more broadly to see how robust this association is, so that other explanations can be ruled out,” says Gene E. Robinson, who is professor of entomology and director of the neuroscience program at the University of Illinois at Urbana-Champaign. However, the possibility that infectious pathogens affect social behavior is intriguing, he says, adding, “The authors were careful to point out the work doesn't directly address this.” He also notes another example of infections affecting other types of behavior among bees. Specifically, when infected with the protozoan Nosema apis, bees begin foraging when younger than do uninfected bees.
Another basic unknown is whether the virus shortens the lifespan of bees that it infects. If so, their aggressive behavior might help not only to protect the hive against intruders but also to remove the pathogen from the colony by more quickly ending the lives of those insects that are infected, the Japanese investigators note, pointing out that bees typically die during the aggressive act of stinging.
To distinguish aggressive worker bees from nonaggressive “escapers,” Fujiyuki and Kubo dangled a live hornet, Vespa mandarinia japonica, in front of a beehive. The aggressive workers, which “scrambled and grappled with the hornet were collected with tweezers and immediately anesthetized on ice.” Escapers, those that fled the scene, were also collected. Only attackers carried the virus, and only in their brains, not elsewhere in their bodies.
To test whether the virus was infectious, the researchers pureed guard bee brains and injected some of that material into the brains of noninfected foragers. Meanwhile, they also ground up brains from uninfected forager bees or used buffered solutions to inject still other forager bees. The bees inoculated with guard-bee brain lysate showed increasing levels of virus over three days, whereas the other bees did not.
“Our research could be an important clue towards understanding the regulation of aggressive behavior,” Kubo and Fujiyuki say. The work may also be medically significant, Kubo adds, citing an example from human medicine. “Some researchers find a weak correlation between viral infection in the human brain with behavioral and mental disorders, like the infection of borna disease virus. The molecular and neurological basis of this phenomenon is totally unknown, and it is quite difficult to analyze mechanisms of how viruses could affect human behaviors.” On a mundane but potentially practical level, understanding and perhaps learning to control aggressive behavior among bees could prove helpful to apiary workers, he suggests.
David Holzman writes from Lexington, Mass.