Assessing the limits of delay of gratification in bumble bees

The ability to resist immediate temptation for a better, delayed outcome is thought to underpin advanced cognition. Traditionally, this ability has been studied in large-brained animals. However, to understand its evolutionary origins, it is necessary to expand the study to species with different life histories and ecological pressures, such as insects. Here, we investigated the ability to endure delayed gratification in the bumble bee Bombus terrestris using a delay maintenance task that assessed the capacity to sustain a delay for a large reward. Bees were first individually trained in a foraging arena to associate two differently coloured flowers either with an immediately accessible small reward (a 5 µl drop of 30% sucrose) or a delayed large reward (four 5 µl drops with a 15-s delay). Bumble bees were then tested over 10 delay choices between the two flowers/rewards. Finally, bees were tested in a delay maintenance test in which the 15-s delay was extended indefinitely. Overall, our findings suggest that bumble bees did not consistently choose the delayed reward over the immediate one across the ten trials, and their ability to sustain delay was highly variable across individuals. Although a small subset of bees (n = 5) exhibited prolonged waiting times comparable to those observed in mammals, birds, and fish (with one individual resisting for up to 364-s), the overall lack of consistency suggests that self-control in bumble bees may be limited and related to either ecological constraints or their foraging strategy. These results provide new insights into the evolutionary origins and drivers of self-control.