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Patrick Guilfoile: Plants benefit from giving bees their cup of morning Joe

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Certain plants, including coffee and citrus plants, produce high levels of caffeine.

It costs the plant a good deal of energy to make these compounds, and consequently, there must be some strong pressure on the plant to make caffeine. In most cases, the reason appears to be toxicity- at high levels, caffeine is toxic, and therefore, plants that produce this bitter substance are able to ward off herbivores.

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Recently, though, scientists from the United Kingdom and the U.S. detected caffeine in the nectar of coffee and citrus flowers.

In some ways, this was a surprising observation, as bees are sensitive to the bitter taste of caffeine, and these plants produce more fruit when bees pollinate their flowers. Consequently, it seemed that the plants could be dissuading their pollinators. Careful measurements, though, indicated that the level of caffeine was low enough (no more than the concentration in a cup of coffee) that bees couldn’t detect a bitter taste.

This led to the question of why there would be any caffeine in the nectar at all. These scientists knew that caffeine has been associated with improved memory in humans, and wondered whether the same might be true in bees. Working in the laboratory, researchers conditioned bees to associate a scent from flowers with a sugar solution. In some cases, bees were fed a sugar solution that contained caffeine, and in other cases, the bees drank caffeine-free sugar water. Based on these experiments, the researchers found that bees fed a sugar solution with caffeine had a much better memory. About three times more bees could remember the scent associated with the sugar water the next day if it contained caffeine, and twice as many bees still retained the caffeine-promoted memory 3 days later.

The scientists next tried to get to the nitty-gritty of how caffeine enhanced the bees’ memories.

They knew which region of the bee brain was involved in memory formation.

Using sensitive measurements of electrical activity in bees’ brains, they found that caffeine increased the activity of nerve cells required to establish memory in bees. Consequently, it appears that caffeine increases the likelihood that bees would retain a memory of a particular floral scent by activating a particular set of nerves required for memory formation.

From the plant’s perspective, this could be a very good thing.

Bees that remember the scent are likely to come back again and pollinate more flowers, allowing the plant to produce more fruit and seeds, and increasing the likelihood the plant will produce more offspring.

Many plants produce chemicals that act on the nervous system of animals.

Based on this discovery, it will be interesting to learn if other plants use drugs to trick bees into preferentially favoring their flowers.

More information is available in: “Caffeine in floral nectar enhances a pollinator’s memory of reward.” Science 339:1202-1204, March 8, 2013. G. Wright and others and “Caffeine boosts bees’ memories” in the same issue of Science, p 1157-1159 by Lars Chittka and Fei Peng.

— Patrick Guilfoile has a doctorate in bacteriology and is the associate vice president for academic affairs at Bemidji State University.

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