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Planet Earth

Tree-Sucking Clock-Watchers

By Josie GlausiuszNovember 1, 2000 6:00 AM


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The ancient Chinese considered cicadas symbols of rebirth because of their unique life cycle: Living quietly underground for years on end, they rise en masse to mate, lay eggs, and die. Modern suburbanites, like their Chinese predecessors, still marvel at the insects' inexplicable ability to emerge at exactly the right moment. Now Richard Karban, an ecologist at the University of California at Davis, has cracked the cicadas' well-kept timekeeping secret.

In an effort to outwit the root-sucking insects, Karban unearthed 15-year-old cicada nymphs of the Magicicada species, which normally wriggle out into the sun every 17 years, and shipped them to a climate-controlled room in Davis. There he attached them to the roots of peach trees that had been manipulated to blossom twice every year. The cicadas emerged a year early, fooled by the double-blooming trees. Karban concludes that cicadas count the passage of time by monitoring physiological signals from trees. Each spring, as trees prepare to flower, a burst of sugars and proteins flows through the roots. Cicadas tap into the roots for food and, it seems, to clock the seasons as well. It was a satisfying conclusion to Karban's rather idiosyncratic obsession. "I've dreamed about tricking cicadas into emerging early for most of my adult life," he says.

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