By Susan Milius, Science News
Note to plotters of world domination: Don’t get discouraged about your weaker brains.
So-called killer bees have readily displaced the long-established European honeybees throughout Central America and the southern United States. Yet the invaders don’t perform as well as invadees in lab tests of learning and memory, says behavioral ecologist Margaret Couvillon of the University of Sussex in Brighton, England.
In lab tests, fewer of the invasive bees learned to associate a puff of jasmine odor with an upcoming reward of sugar water, Couvillon and her colleagues found. Also, fewer of the invaders that did learn remembered their lesson the next day. The researchers report the findings online November 11 in Naturwissenschaften.
“Perhaps learning has a cost,” Couvillon says. “If it were cost-free, wouldn’t we all be getting smarter?” She cites research on fruit flies that suggests investing in superior learning saps resources from other competitive abilities.
“We still know very little about how learning performance is actually adapted to real ecological conditions,” comments Nigel Raine of Royal Holloway, University of London in Egham, England, who has studied learning in bumblebees.
Killer bees can certainly take over territory. The strain grew out of a breeding program that introduced an African honeybee subspecies to Brazil in 1956 for crossing with the European subspecies that was a beekeeper standard. The hybrids, called Africanized bees, escaped and spread in what Couvillon calls “a spectacular biological invasion.”
To see whether superior cognitive powers contribute to the killer bees’ success, Couvillon, then at the University of Arizona, and her colleagues examined killer bees as well as unhybridized European honeybee colonies at the U.S. Department of Agriculture’s Carl Hayden Bee Research Center in Tucson.
Couvillon tested bee learning using a long-standing protocol: puffing odors at bees before touching sugar water to their antennae. When researchers gave bees a second whiff, about half of European honeybees stuck out their tonguelike proboscises as soon as the odor wafted by again, anticipating another drop of sugar water. The bees acted like Pavlov’s dogs, drooling at the sound of a bell they associate with food, Couvillon says.
Only about half as many killer bees picked up the association after a single trial, the researchers found. Even after three trials, about three quarters of the European honeybees were drooling at the odor but only half of the killer bees were.
Raine says that now he'd like to know the real-world consequences of learning differences. In bumblebees he and his colleagues tested, colonies of the slowest learners collected 40 percent less nectar than the fastest learners did.
Maybe the learning disparity in hybrids reflects the different origins of the European and African subspecies, says Thomas Rinderer of the USDA, ARS Honey Bee Breeding Genetics and Physiology Research Laboratory in Baton Rouge, Louisiana. African bees come from a landscape where the rainy season triggers widespread flowering. "Site and odor memory are less important," he speculates.
Bee lineages long selected and propagated by people may learn differently than do free-roaming hybrids, suggests comparative psychologist Charles Abramson of Oklahoma State University in Stillwater. In learning experiments, lab rats typically outperform wild-collected relatives, he says.
Superior odor learning may not look promising as an explanation for the triumph of killer bees, but faster rates of growth and reproduction might, Couvillon says.