4 Apr 2016

How Bees Become Addicted To Caffeine

from Albany Daily Star
Researchers in United Kingdom have found that certain plants actually produce caffeine to attract bees and help in pollination.
Scientists at the University of Sussex said they thought the plants produce the caffeine in their nectar to fool bees into thinking it contains more sugar than it actually does. The insects will repeatedly visit those flowers, helping the plants maximize pollination.
Francis Ratnieks, a professor of apiculture at the university, said bees communicate by moving their abdomens a certain way — or, as he calls it, “dancing.” He said the caffeine increases that dancing.
In their experiments, Ratnieks and his colleagues used two artificial flowers that contained sucrose and water, and one contained caffeine as well. “The one with caffeine attracted more bees,” he said, and “the bees who were foraging made more dances — about four times as many dances.”
Identification numbers were glued to those bees exposed to caffeine, and the bees were then sent back to the hive. Those bees’ dances then influenced the behavior of others in the hive, and many bees were directed to revisit sites where caffeinated nectar had been found, even after the feeder ran dry.

The scientists theorized that plants use caffeine to manipulate bees in a way that is good for the plant, but not so good for the bees. The caffeine, they said, tricks bees into thinking that the nectar is of a higher quality and has more sugar than it really does.

According to scientists studying the phenomenon, plants produce caffeine within their nectar in order to fool bees into thinking there is more sugar in it than it actually has and attract them more. The trick makes bees return to the same plant over and over again and help that particular plant more in the process of pollination.
Francis Ratnieks, a professor of apiculture at the University of Sussex, has explained that bees use a series of specific movement patterns in order to communicate with one another. This dance-like pattern is created by the bee through specific movements of its abdomen and it seems that caffeine enhances it.

In order to observe and study how the added caffeine affected the bees, researchers performed an experiment using two artificial flowers. One contained only sucrose and water, the other one contained caffeine as well. More bees were attracted to the flower that also contained caffeine. It was also established that bees which collected nectar from the artificial flower that contained caffeine performed up to four times more dances than the bees which did not.

The researchers glued tags with identification numbers to the bees who had been exposed to caffeine and monitored them afterwards, when they were sent back to their hive. The dances that these tagged bees performed affected the activity of the other bees in the hive, as many other bees were directed to revisit the plants that produced caffeinated nectar. They continued to revisit the same plants where the caffeine had been found even after the feeders had run dry and there was no more nectar.

This caused scientists to conclude that the plants which secrete caffeine are using it to manipulate bees into coming back to them and helping them maximize their pollination. And while the plant is obviously benefitting from the return of the bees, the caffeine addiction might not be so great for the bees themselves. The nectar tricks the bees into thinking that the nectar they are collecting contains more sugar than it actually does.

And while earlier research has shown that caffeine helps boost bees’ memories and helps them remember the location of the flower they visited, the fact that they return to a plant with a lower quality nectar and keep collecting what they think is superior nectar is certainly not beneficial for the insects themselves.

Bees exposed to caffeinated nectar did indeed forage more often. But while they checked their caffeinated flowers almost obsessively — and did four times the usual number of dances to alert the rest of the colony to the flower’s presence — they ignored equally nutritious, decaf flowers.

“One thing that really surprised me was how long the effect lasted,” Couvillon said. “We saw that if they just had one, three-hour exposure to the caffeinated nectar on the first day, they would come back [to the empty feeder] for many more days, and more often within each day.”

The control bees — the ones who hadn’t had caffeine — would check the flower they’d fed at previously, but would quickly move on to forage for food elsewhere.

“If they’ve had caffeine, they’re less likely to check the surrounding area,” Couvillon said. “They’re really hooked on that location.”

Caffeine can be found in the nectar of coffee and citrus plants, among others. This drugging effect helps explain why caffeine — which plants put in their roots and leaves to turn off herbivores with the bitter taste — also shows up in nectar, which is meant to be sweet and appetizing. Researchers had previously investigated nicotine in nectar for the same reason, but found that these plants actually used nectar bitterness to their advantage: Bees, repulsed by the bitter taste of the nicotine, would move more quickly from flower to flower.

“That’s a behavioral effect that’s similar to its primary purpose in the stem and leaves,” Couvillon said. “But the caffeine seems to be drugging the bees.”

The caffeine addiction isn’t exactly harmful, at least as far as Couvillon and her colleagues can tell. But it throws off the efficiency of the colony. By ignoring identical plants that lack caffeine, they’re foraging sub-optimally. They’re not taking full advantage of their potential food sources.

“I think when people think about pollination, they think of the collaborative nature of it, the nice, sweet partnership of it,” Couvillon said. “But as with many partnerships, there’s potential for conflict. One side will always want to cheat the other if they could get away with it.”

No comments: