Plants lace their nectar with drugs to make bees return

Plants may be spiking their nectar with addictive drugs to lure insects into spreading their pollen.

Geraldine Wright at Newcastle University, UK, and colleagues trained bees to associate a scent with a sugary reward. Bees given sugar water laced with caffeine were twice as likely to remember the scent ? and stick their tongues out in anticipation ? three days later, than bees fed on sugar alone.

To see how the caffeine was affecting the bees' memories, the team looked at what happened in their brains when they were injected with the stimulant. Sure enough, the caffeine triggered changes in the neurons' ability to pass messages vital for olfactory learning and memory.

Small amounts of caffeine and other chemicals such as nicotine are present in the nectar of more than 100 plant species. Plants use these often nasty-tasting chemicals to deter predators, but Wright's work suggests that they also use them to keep pollinators loyal to their flowers. It's a matter of getting the dose right; leak just the right amount into their nectar to lure in the bees, but not too much so that the bitter taste puts them off.

Looking at how far bees will go to get their caffeine hit ? and whether they willingly put themselves in danger ? could answer a fascinating question, says Wright: "Can an insect become addicted to a drug?"

More work on bees could also shed light on how coffee affects us. The evidence for caffeine's memory-enhancing capacity in humans is inconclusive, says Wright. Bees share many of our cerebral molecular building blocks, in particular the receptors for the neurotransmitter adenosine, which caffeine binds to. "We are confident that this is a common property across the animal kingdom," says Wright.

Journal reference: Science, doi.org/kqq.

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