Bees enjoy nectar's caffeine shot

That spurs them to return to the same type of plant, boosting its prospects for pollination and the future of the plant species.

Maybe it shouldn't be a surprise that one of the flowers is the coffee plant. Its nectar offers about as much caffeine concentration as a cup of instant coffee, according to researchers.

But some citrus plants serve caffeine too, albeit in lower concentrations. It's found in the nectar of orange and grapefruit blossoms.

The caffeine helps a bee remember that the flower's scent promises a tasty payoff, the researchers said. So the bee will seek out those flowers, transferring their pollen.

How could researchers tell the caffeine boosts a bee's memory? In an experiment that used lab tools instead of flowers, they trained individual bees to expect a sugary drink when they smelled a certain floral scent. Some bees got nectar-like concentrations of caffeine in their drink; others didn't.

Then after a day or more, they exposed the insects to the same scent and watched to see if they extended their feeding tubes in response, a sign they were ready to sip. After 24 hours, the bees that had gotten caffeine were three times as likely to remember as bees that hadn't. After 72 hours, they were twice as likely.

Bees can't taste caffeine at levels found in nectar, but the researchers found it affects certain brain cells involved in memory.

The work, by Geraldine Wright of Newcastle University in England and co-authors, was reported Thursday by the journal Science.

Gene Robinson, a bee biologist at the University of Illinois who didn't participate in the study, said it provides strong evidence that coffee and citrus plants use the caffeine strategy. Now the question is how many plants might use this trick, he said in an email. After all, bees pollinate thousands of species.

Wright said in an email that other plants are now under study, but that only about 100 species can make caffeine.

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