The sight of a pollen-laden bumblebee buzzing from flower to flower is a pleasant sight during the summer months, as these fuzzy friends are important for pollination. A new study in Current Biology on the buff-tailed bumblebee (Bombus terrestris) suggests that when it comes to learning the location of flowers, size does indeed matter for these insects.
"It might not be widely known that pollinating insects learn and develop individual flower preferences, but in fact bumblebees are selective," said first author of the study Natalie Hempel de Ibarra, associate professor of neuroethology at the University of Exeter, in a statement.
When departing from a newly-found flower, bees perform a “learning flight” where the bee turns around to face the flower. This allows it to take in the appearance of the flower and its surroundings. This means that "On leaving a flower, they can actively decide how much effort to put into remembering its location,” said Professor Hempel de Ibarra, "The surprising finding of our study is that a bee's size determines this decision making and the learning behavior."
In a greenhouse, the researchers set up artificial flowers that contained 10, 20, 30, or 50 percent sucrose. A camera captured the bees’ learning flights and found that their duration and amount of time facing the “flowers” increased the more sucrose they contained.
The researchers then focused on the significance of bee size, as measured by the width of the thorax, the midsection where the wings are attached. In this set of experiments, responses to 20 and 50 percent sucrose solutions were examined. It was found that the responses of large bees differed from those of small bees. For smaller bees, there was no difference in learning flights between the higher and lower sucrose percentages. Large bees, however, spent more facing the “flower” and had longer learning flights when it contained 50 percent sucrose and spent less time when it contained 20 percent. They also studied the drinking volume of the bees. Large bees drank more when the sucrose concentration was 50 percent and less when it was 20 percent. Small bees didn’t show as much of a preference.
These results indicate that larger bees learn little about less rewarding flowers and focus on highly rewarding ones, whereas smaller bees are less picky. This could be down to bees of different sizes having different roles in the colony. Professor Hempel de Ibarra explains, “Large bumblebees can carry larger loads and explore further from the nest than smaller ones. Small ones with a smaller flight range and carrying capacity cannot afford to be as selective, so they accept a wider range of flowers. These small bees tend to be involved more with tasks inside the nest – only going out to forage if food supplies in the colony are running low."