Bees log flight distances, train with maps

After decades of work, two teams of scientists have cracked some long-standing puzzles regarding how honeybees buzz around without getting lost.

Ideas about honeybee odometers proposed by the great bee researcher and Nobel laureate Karl von Frisch turn out to be dead wrong, say Mandyan V. Srinivasan of the Australian National University in Canberra, a Canberra colleague, and coauthors at the University of Würzburg in Germany. In the Feb. 4 Science, they report their own simple key to reading honeybee odometer distances.

Von Frisch discovered that a honeybee finding food buzzes back to the hive and dances out the direction and distance for its sisters. He argued that it measures distance by the pressure in its stomach, indicating how much food it had burned. However, Harald A. Esch of the University of Notre Dame in Indiana found evidence against this idea in the 1990s.

Srinivasan set up what he calls “probably the ultimate test” pitting the energy-use theory against the idea that bees monitor distance by the flow of visual images. He trained bees to fly into a narrow, 6-meter-long tunnel with food near the far end and monitored their dances when they returned.

He covered the inside of the tunnel with a random pattern resembling a demented checkerboard. The visually textured pattern created the illusion of a lot of territory speeding past. It fooled the bees into exaggerating the length traveled by a factor of 31. Using the dimensions of the tunnel, Srinivasan and his colleagues calculated that an image moving about 18 degrees across the bee’s eye triggers 1 millisecond of dancing. “We can calibrate the odometer,” he says gleefully.  Esch calls the odometer-calibration experiment “just genius.” As a student, he had worked with the late von Frisch and adds, “I think he would be convinced.”

Another team of bee watchers used specialized radar to make the first maps of bee training flights. Without at least one orientation flight before it begins to forage, a displaced bee can’t find its way home, explains Elizabeth A. Capaldi of the University of Illinois at Urbana-Champaign.

These training flights have teased researchers for decades, she explains. The bee begins with characteristic hovering in front of the hive—very easy to study. Then, the bee zooms out of sight.

To keep up, Capaldi tracked bees by attaching wires that reflect radar signals in a distinctive way. Coauthor Joseph R. Riley of the University of Greenwich in Malvern, England, pioneered the technique, called harmonic radar.

By watching hives 12 hours a day, the team observed signs of progressive learning. In later flights, a bee spends about the same time training but flies faster and covers more ground. Each flight typically sticks to a narrow corridor, the researchers report in the Feb. 3 Nature.

“It seems a sensible strategy, though I don’t know if I’d have predicted it,” comments insect-orientation specialist Thomas Collett at the University of Sussex in Brighton, England. He welcomes the radar paper as “more than a first step” at studying how foragers learn.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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