Plants trick honeybees with caffeine
Plants lace their nectar with caffeine to encourage bees to keep returning and pollinate them in the process.
Caffeine is abundant in plants, mostly in the leaves, seeds and stems. It is very bitter, which helps to deter most animals from snacking on the plants.
But the chemical has also been found in low concentrations in plant nectar, where the effects are quite the opposite. Researchers at the University of Sussex have shown that honeybees find this substance irresistible and will encourage other bees from their colony to forage repeatedly from caffeine-laced flowers too.
Lead author Margaret Couvillon explains that this trickery benefits the plant, rather than the insect.
"The presence of caffeine in the nectar can cause the honeybees to behave as if the nectar is of much better quality than it really is."
The researchers trained honeybees to collect from one of two feeders. Both contained equally sweet, nectar-like solutions, but only one of them contained caffeine. Their behaviour was then observed, including foraging and recruitment of other bees and how they acted when the substances were taken away.
The caffeinated substance caused the bees to increase their foraging and those honeybees performed many more waggle dances, which tell their nest mates that there is something good in the landscape they need to exploit.
The bees that had foraged on the caffeine substance persistently came back to check the empty feeder much more than the other bees and were far less likely to explore the area nearby for other sources of nectar.
The findings, published in Current Biology, show that caffeine is causing the honeybees to overestimate the quality of the nectar produced by plants. This could suggest that the whole colony of bees may not be utilising the nearby resources equally.
Couvillon explains that caffeine changes the partnership between the honeybees and the plant.
"The relationship between the pollinator and the plant is less of a cooperative relationship and more of an exploitation."