Caffeine Buzz Boosts Bees’ Ability To Find Specific Blooms

Researchers have demonstrated that by supplying bees with caffeine it is possible to boost their ability to remember the smell of a specific flower. The team’s findings were published in Current Biology, July 28, 2021.

In the study, inexperienced Bombus terrestris – buff-tailed bumblebees – were provided with either:

• a pure sugar solution, which acted as a control group
• a sugar solution and a “target odor”, which was a synthetic replica of the odor of strawberry flowers
• a “caffeine-laced” sugar solution and the target odor mentioned above

 In total, the team looked at 86 bees across the three different scenarios above, from multiple different colonies.

“We used boxes of commercial bumblebees, much as a grower would use to pollinate strawberry crops. These boxes all contained a nest (a queen bumblebee and workers) and we assigned each box to one of three groups,” says the paper’s first author, Dr. Sarah Arnold, from the Natural Resources Institute, University of Greenwich.

The study was designed to investigate caffeine-mediated memory in free-flying bees when target flowers were not baited with caffeine. The bees in this study were supplied with each of the three solutions at the nest, nowhere near the flowers, whereas previous studies exploring caffeine-related behavior have used baited flowers containing caffeine as part of the reward.

Stop and smell the roses… robotic flowers

Arnold notes that the robotic flowers used in the study were the invention of a Finnish team a few years back, their work was published in Ecology and Evolution. “Jan[-Hendrik Dudenhöffer], the postdoc on our project, being really great at coming up with creative solutions, adapted their designs so the system could be controlled from a laptop PC,” adds Arnold. Dudenhöffer adapted the basic design of the original flowers and programmed unique algorithms for the study.

The researchers allowed the bumblebees to feed for a day, the bees from each colony were then individually released into the “flight area” – a large, boxed area – containing the robotic flowers. Half of the robotic flowers were laced with the synthetic strawberry target odor, while the other half contained a distractor scent.

Arnold explains why they chose to use artificial flowers as opposed to real flowers: “There are a few really handy advantages of robotic flowers – they refill automatically, with a controlled amount of sugar each time. If you used real flowers, a bee can sometimes drain all the flowers of nectar in a short period of time and then lose motivation to forage; they could potentially start chewing the flowers trying to extract more nectar and this can affect the results of the experiment.”

She continues, “With the robotic flowers they can keep on making choices. Robotic flowers are easier to clean, so we can control the conditions better, and unlike real flowers, don’t wilt over time.”

Arnold notes that one of the most exciting elements related to the experiment’s design, was the use of a small infrared beam, which served to detect when a bee visited the flower automatically: “This means that the visits were recorded by a computer, not a human experimenter, meaning it’s more objective and exact timings of all the visits can be measured.”

“Bee” free

Once loose in the flight arena, the bees had to decide which of the two types of robotic flowers to visit – either the flowers with the strawberry odor they had previously been exposed to at the nest, or the distractor flowers.

If the bees had failed to grasp the positive association between the target odor of the strawberry flowers and the sugar reward, then you would assume that they would visit the two types of flowers equally.

“We predicted that the bees receiving caffeine would have learned that the strawberry flower odor signifies a good food reward, and that the caffeine would make that memory stronger, so when they flew in the arena, they’d make more visits to target flowers with that odor. And sure enough, that is what we observed,” says Arnold. Seventy percent of the bees in the caffeine-laced group visited the strawberry flowers first.

“The bees with caffeine visited the target flowers more often during their early foraging trips compared to either of the other groups of bees,” adds Arnold.

Real-world applications

The team’s findings could have valuable real-world applications, for example, they could be useful to growers of pollinator-dependent fruit crops. “Growers use commercial colonies of bees to pollinate their crops, especially early in the year when there are few wild bees around, but sometimes the commercial bees don’t all forage well, and sometimes the bees leave the crop and visit other plants,” notes Arnold.

It could be possible to “prime” commercial bumblebees so that they are trained to pay particular interest to the crop flowers, resulting in improved pollination. Arnold highlights the benefits, “This could benefit the grower, the consumer and even wild bees as they won’t have to compete with commercial bees that are visiting wildflowers and hedgerows!”

“The project overall also included field trials looking at caffeinated bees on real crops, but the results are not published yet! We’d love to continue this work in the future – so much still to do, understanding how caffeine and related alkaloids can influence other aspects of bee behavior, seeing how this can benefit other crops, and so on!” concludes Arnold.

Reference: Arnold SEJ, Dudenhöffer J-H, Fountain MT, et al. Bumble bees show an induced preference for flowers when primed with caffeinated nectar and a target floral odour. Current Biology. 2021;31:1-5. doi: 10.1016/j.cub.2021.06.068

Sarah Arnold was speaking with Laura Elizabeth Lansdowne, Managing Editor for Technology Networks.