idway through a honeybee's fleeting, bittersweet, and, yes, busy little life, a momentous transformation occurs: the 2-week-old worker must abandon her cloistered career as a hive-keeping nurse, and venture out into the world to forage.

She must learn to navigate over great distances at 12 miles per hour, select the finest flowers, assemble bits of pollen and droplets of nectar into a load nearly as heavy as she is, and then find her way back home. Once there, she must convey the coordinates of her discovery to her sisters in the classic cartographic waggle, the bee dance.

And all this behavioral complexity is packaged in a brain no bigger than the loop of a letter b printed on this page.

Now researchers have identified a crucial genetic component of the great bee leap from homer to roamer. They have discovered that just before the transition, the activity of a gene aptly named the foraging gene increases sharply in the parts of the bee brain that absorb and interpret visual and spatial information.

That molecular surge is clearly the key to the vocational switch. When the scientists fed young bees sugar water laced with a drug that stimulated the foraging gene prematurely, the bees assumed their hunting post far ahead of schedule.

The new research builds upon previous work in fruit flies, and demonstrates that, at least among insects, relatively tiny shifts in gene activity can have striking effects on behavior. The work also suggests that one way to explore the combustible field of behavioral genetics is by looking at creatures that possess an impressive array of skills, as bees do, yet that are sufficiently far from human beings to discourage anybody from glibly misapplying the results.

Dr. Gene E. Robinson of the University of Illinois at Urbana-Champaign and his colleagues reported their findings in the April 26 issue of the journal Science.

"There are very few examples of complex behaviors being tied to a single gene," said Dr. Thomas Insel, director of the Center for Behavioral Neuroscience at Emory University in Atlanta. "This happens to be one of the coolest."
Dr. Fred Gould, a professor of entomology at North Carolina State University in Raleigh, said: "When you're looking at physiology, it can be pretty obvious if a genetic change affects renal function, or causes blindness. But behavior has seemed more amorphous." The new work, he said, "gives me a lot of hope that we'll be able to make progress in understanding the genomics of behavior."

How far that progress will extend remains to be seen, of course. Dr. Robinson said that while there was an equivalent of the foraging sequence in the DNA of humans and other mammals, "one thing we are not talking about here is the shopping gene."

Dr. Robinson and his colleagues were inspired to examine the foraging gene in bees by recent results from the laboratory of Dr. Marla B. Sokolowski at the University of Toronto. The Canadian team discovered that there were two alleles, or variants, of the foraging gene in fruit flies, one more active than the other. Flies inheriting the active form developed into so-called rovers, flitting about widely in search of food, while those bestowed with the less vigorous forage allele matured into sitters, content to lounge around and eat whatever fruit was in the immediately vicinity.

Bees and flies are separated evolutionarily by 300 million years, yet Dr. Robinson saw the two fly styles as rough analogies for the two stages of being a bee. As nurses responsible for cleaning up the hive and brood care, bees were like sitter flies; when the bees turned to foraging, they became like rover flies.

Isolating the bee version of the foraging gene (and finding only a single variant of it), the Robinson group determined that the gene affects bee behavior, not from the start, as it does with flies, but in stepwise fashion.

For the first two weeks of bee life, the gene is relatively silent. For the second two weeks of its life, the gene is busy indeed, activated with particular vigor in the optic lobes and the so-called mushroom bodies of the bee brain. The mushroom bodies, named for their resemblance to the fungus, are the main centers for processing a multitude of sensory signals, including those involved in sight, balance and orientation — exactly the facilities that a bee must call on in her new responsibilities as breadwinner.

To demonstrate that the upswing in foraging gene activity was not simply a result of the bee's growing older, but instead was linked to the new behavioral demands, the researchers manipulated hive population dynamics. They removed the foragers, leaving only nurses behind. With no bees bringing home the essential ingredients for honey, some of the nurses turned to foraging precociously. And though they were only days old, rather than weeks, their foraging gene had snapped to life.

Similarly, the researchers were able to recruit nurses to the foraging trade early by feeding them a compound that stimulated the foraging gene.

The researchers have a basic idea of how the foraging gene operates. Using its instructions, a cell generates a protein called a protein kinase, which plunks little molecular bundles onto other proteins in the cell, altering their shape and thus their function. Hence, the real question about the foraging gene is, what proteins does its specified protein interact with? And how does all that molecular commotion end up putting the buzz in a bee's bonnet?

One way to begin sorting out the many genetic players in a bee brain, as well as a bee body, Dr. Robinson said, is through a bee genome project, deciphering all the subunits of bee DNA as has been done, more or less, with the human genome.

The National Institutes of Health is now deciding which genomes of which species are worth decoding in their entirety. Among the candidates are chickens, dogs, sea urchins, cows, freshwater turtles and an assortment of nonhuman primates.

Dr. Robinson believes in his bees. "With a honeybee, you get a lot of bang for your buck," he said. "It has a modest-sized genome, yet it has sophisticated behavior, it learns, it's highly social and because it's an insect, there's a possibility we can understand it in great depth."