In the experiment, bees were presented with a scent just before feeding on a sugar solution laced with different doses of caffeine.
That caffeine provided an edge, boosting the bees’ long-term memory, the researchers discovered. Compared with bees trained on sugar water alone, bees trained on sugar water doped with caffeine were three times as likely to remember 24 hours later that the floral scent came with a reward. After 72 hours, the caffeine-trained bees were twice as likely to remember the scent-reward connection.
Interesting the bees would be able to recall the specific flower, especially if they had visited a kazillion flowers. Another summary:
Pollination systems are biological markets, where flower visitors choose between flower species on the basis of their quality, such as the sweetness and amount of nectar per flower. Plants in turn compete for pollinators and advertise their product through colorful visual displays and scents. A key challenge in floral advertising is that signals must be not only attractive but also memorable (1): The more distinct a flower signal, the more likely a pollinator is to remember it, increasing the probability that pollinators will visit more flowers of this species while ignoring competing flower species. On page 1202 of this issue, Wright et al. (2) report that some plant species appear to gain an unfair advantage in this competitive market by manipulating the memory of bees with psychoactive drugs.
I'm not sure if 'unfair advantage' is the best possible wording, as it is all's fair in love and way and all that. But this is a fascinating glimpse of the world of pollination.
A bit more pedantic description, straight from the abstract:
Plant defense compounds occur in floral nectar, but their ecological role is not well understood. We provide evidence that plant compounds pharmacologically alter pollinator behavior by enhancing their memory of reward. Honeybees rewarded with caffeine, which occurs naturally in nectar of Coffea and Citrus species, were three times as likely to remember a learned floral scent as were honeybees rewarded with sucrose alone. Caffeine potentiated responses of mushroom body neurons involved in olfactory learning and memory by acting as an adenosine receptor antagonist. Caffeine concentrations in nectar did not exceed the bees' bitter taste threshold, implying that pollinators impose selection for nectar that is pharmacologically active but not repellent. By using a drug to enhance memories of reward, plants secure pollinator fidelity and improve reproductive success.
Interesting stuff and not surprising, actually.