If you need your morning coffee to perform well at work, you have something important in common with bumble bees.
Researchers led by Sarah Arnold, a senior lecturer of insect behavior and ecology at the University of Greenwich, have provided the first evidence that caffeinated bees are better equipped to find target crops, regardless of whether those targets contain caffeine. In other words, a little caffeine buzz helped the bees do their everyday jobs more efficiently.
Scientists have already shown that these bees will preferentially return to flowers that contain caffeinated nectar, which can improve their memories and boost their efficiency as foragers and pollinators.
But Arnold and her colleagues have now “disentangled the effects of caffeine improving memory” from the bees’ perception of “caffeine as a reward,” according to a study published on Wednesday in Current Biology. The results suggest that caffeine-primed bees really do have better memories, an insight that could be used to enhance the efficiency of commercial bees in pollinating specific crops.
“Previous work by other teams has shown that honeybees (which have many similarities in their brains to bumblebees) fed caffeine retain memories of odors for longer,” said Arnold in an email. “Other studies have found that bees make more visits to caffeinated food sources, but it can be hard to work out whether that’s because the caffeine itself acts as a reward, or because it helps them remember that the particular characteristics of that location/flower indicate a good food source.”
To decouple the rewarding effects of caffeine from the stimulant’s actual effect on bee memory, Arnold and her colleagues devised an experiment that provided doses of caffeine only at the nest.
Before the bees left the nest to forage, some were also trained to associate an artificial odor reminiscent of strawberry flowers with a sweet sugary reward. The study involved 86 bees divided into three groups: the first was given a caffeinated version of the sugary reward, the second was given the sugary reward with no caffeine, and the third received the sugar solution but did not learn to associate it with the strawberry scent.
The bees were then released into a flight arena that contained artificial flowers with the strawberry scent, along with “distractor” flowers with another fragrance. Both types of flowers provided a sugar reward, but neither type contained caffeine.
Seventy percent of the caffeinated bees visited the strawberry-scented flowers first, compared with 60 percent of the second group of bees that linked the strawberry odor to the non-caffeinated sugar reward. Only 44.8 percent of the bees that were given the sugar reward, without the association to the strawberry smell, visited the strawberry-scented flowers first.
“We anticipated that caffeine should help focus the bees on the crop,” Arnold said. “We thought it was likely that bumblebees that had previously consumed caffeine and sugar in association with a synthetic flower odor inside the nest would seek that smell out more when outside the nest…and indeed they did.”
The study suggests that the caffeinated bees had stronger memories of the link between the strawberry odor and its sugar reward, relative to the bees who had not received caffeine. Interestingly, this effect was short-lived, meaning that the caffeine-primed bees eventually stopped expressing a bias toward the strawberry-scented flowers. This may be because the caffeinated group figured out that they were getting the same rewards from both flowers.
“What we think is most likely is that the two sorts of robotic flowers in the arena (with the synthetic strawberry flower odor, and the distractor odor) both offered an equal food reward, were easy to find, in a small and simplified environment,” Arnold explained. “So rapidly the bees realized that whether they sought out the ‘primed’ odor or not, they received a good energetic reward of sugar solution and could visit either type of flower.”
The study offers a new perspective on the brains of bees that may ultimately improve the efficiency of commercial pollinators. If agricultural bees were caffeinated in their nests, and trained to pollinate target crops, they could boost farm production while also reducing competition with their wild bee counterparts over flowers.
There’s “so much more to do!” Arnold said. The new study “opens up questions about what aspects of bee behaviour caffeine (which occurs naturally in some plants’ nectar) and other nectar natural products might influence, and under what circumstances, and how this might be applied more widely in crop pollination.”