CHAMPAIGN, Ill. -- It's a dirty job and only about 1 percent do it at any one time. But middle-aged honey bees that serve as undertakers -- removing dead bees from the hive -- appear to be a distinct cadre of workers that are developmentally ahead of their peers.
In this social world known for its division of labor, there also were unexpected discoveries by researchers: Undertakers don't get better with experience, and they don't do well working together.
The findings are detailed in papers by Gene E. Robinson, a University of Illinois entomologist, and his former postdoctoral researcher Stephen T. Trumbo, now a professor at the University of Connecticut in Waterbury, Conn. The study on development, also written by U. of I. entomologist Zhi-Yong Huang, appears in the September issue of Behavioral Ecology and Sociobiology. The research on the undertakers' learning, or lack thereof, will be published in the fall in the journal Ethology.
The work -- which involved identifying the undertakers, marking them with tiny, colored and numbered plastic tags, and following them closely through middle age -- provides the first close look at undertakers. Since bees' nests are built in cavities, such a specialty is important for keeping the nests clean.
"Undertakers had very similar activity levels as other bees," Trumbo said. "They just do a little bit less of the other middle-aged tasks, like building the comb and storing food brought in by older foragers. They also remove debris, which fits in nicely with undertaking."
Undertakers also develop slightly faster than other midde-aged bees, moving on to foraging before food storers and hive builders. Middle age lasts about 10 days. Undertakers usually removed dead bees for a day or two, but "one extraordinary bee remained at the task for 13 days," Trumbo said.
Undertakers respond to the odor of the dead, locating the bodies and carrying them out of the hive for 50 to 100 meters before dropping them. The researchers also monitored how swiftly undertakers worked.
"We didn't find any evidence for learning for this particular task," Trumbo said. "This rules out one of the major hypotheses that has been put forward for middle-aged specialization: That social insects will get better and better at what they do."
Previous research had shown that learning is important for the older foragers, who get more efficient as they learn what flowers are producing nectar at what time. Not only did undertakers not improve in efficiency, Trumbo said, they also got in each other's way and slowed their efficiency.
Robinson had shown previously that some bees are genetically inclined to be undertakers. "We're beginning to get a clearer picture of the behavioral profiles of interesting types of specialist bees, such as undertakers," Robinson said. "Understanding the career choices of bees is a useful model for understanding behavior in general. This new information should enable us to develop new hypotheses about how neurons and genes in the brain function to produce the marvelously complex behavior seen in honey bee society."
Journal
Behavioral Ecology and Sociobiology