Just as travelers figure out which restaurant is good bythe numbers of cars in the parking lot, bumblebees decide which flowersto visit by seeing which ones already have bee visitors.
Bumblebeesthat watched other bees forage on green artificial flowers were twiceas likely to choose the green flowers over orange flowers when it wastheir turn to forage, according to new research.
The finding is the first demonstration that insects can learn by just watching the behavior of other insects.
"Studyinga variety of different animals -- everything from chimpanzees to bees-- that show some kind of social learning, will give us a betterunderstanding of how social learning occurs," said behavioral ecologistBradley D. Worden of The University of Arizona in Tucson. "One of thecool things we're finding out from bees is that complex behavior andadvanced forms of learning can come from small brains."
Worden, apostdoctoral research associate in UA's department of ecology andevolutionary biology, conducted his work on the brainy bees with DanielR. Papaj, a UA professor of ecology and evolutionary biology. Theteam's report has been released online and will be published in anupcoming issue of Biology Letters of the Royal Society. The NationalScience Foundation funded the research.
Charles Darwin was oneinspiration for the study because he wrote about the possibility thathoneybees were watching and learning from bumblebees, Worden said.
While observing bumblebees in the field, Worden, too, got the impression that bees were copying the behavior of other bees.
"Honeybeesand bumblebees are social creatures -- they live in these colonies,"Worden said. "We know that they communicate with one another, at leastin the nest, but nobody had really studied whether outside the nestthey're paying attention to what other individuals are doing." SoWorden and Papaj designed experiments to test whether Darwin's musingsmight be true.
They trained Bombus impatiens bumblebees to visita particular color for food by using artificial flowers -- green ororange paper circles that were 7 cm (about three inches) in diameter.At some of the "flowers" the bees could feed at cotton wicks soaked insugar water. Without training, bumblebees tended to prefer orange overgreen. The bees, who can easily see the difference between the twocolors, learned to prefer the color that had the sugar water.
Thetrained bumblebees visited a feeding arena that had three green andthree orange circles. A small plexiglass tube with an observation portwas positioned 25 cm (about 10 inches) away. Other bumblebees, one at atime, were allowed to press their faces against the port and watch fromthree to 12 trained bees feed for 10 minutes. At that distance, anobserver bee could tell that there were bees on the flowers, butprobably couldn't tell exactly what the bees were doing.
A separate set of observer bees served as controls: they got to watch the feeding arena for 10 minutes with no bees in it.
Thenthe lights were turned off and, behind the scenes, the feeding bees andtheir flowers were removed. A new set of three green and three orangeartificial flowers was set up in the feeding arena, but the flowers hadno food and the location of the particular colors was different fromwhat the bumblebee had observed.
The observer bees were thenallowed, one at a time, to visit the artificial flowers. Observers thathad watched bumblebees feed on green were twice as likely to visit thegreen circles. To make sure that odor cues were not somehow influencingthe observer bees, Worden made model bumblebees using life-size resinmodels of bumblebees painted in bee colors and with real bumblebeewings glued on. He then repeated the experiments with a new set ofobserver bumblebees watching the "behavior" of the models.
When it was their turn to forage, the watchers preferred the color that the model bees were "visiting."
Whilehoneybees do a dance to communicate to hive mates the location of goodflowers, bumblebees do not. Worden speculates that watching other beesin the field may be particularly important for bumblebees because theycannot find out from their hive mates exactly where the good flowersare located.
Papaj noted that Darwin's original proposition, thatone species of bee may watch and learn from other species of bees,remains to be tested. He added that such "eavesdropping" would greatlyexpand a colony's sources of information about rewarding flowers.
Worden and Papaj plan to conduct more research to determine when bees copy others and when they learn on their own.
Related Web sites:
UA Dept. of Ecology and Evolutionary Biology
UA Center for Insect Science
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