Learning in two contexts: the effects of interference and body size in bumblebees

We examined the effect of learning a new task on the performance of a previously learned task with the same set of visual cues in bumblebees, Bombus impatiens. Previous studies have shown that given a binary choice at each task, bumblebees do not show retroactive interference, or mistakes in the first task, if the two tasks are in different contexts, feeding and nest location. Here we tested whether adding a third, unrewarded choice to each task affects the performance of bees learning in two contexts. In addition, we examined whether workers differ in their expression of interference and learning ability based on size. Performance of workers at a feeder task was degraded by the introduction of training to a second task at the nest entrance. Mistakes at the feeder were biased toward the color cue that was not rewarding in both tasks; suggesting that irrelevant or background stimuli are more prone to decay or forgetting during interference. With respect to interference, we did not find an effect of body size on the amount of interference; however, size was related to how quickly interference occurred. Among individuals showing retroactive interference, larger bees showed interference earlier in phase 2 than did smaller bees. Overall, larger workers learned each task more rapidly than smaller workers. We conclude that the timing of interference is a tradeoff between acquisition of the new task and performance at a previously learned task. Given that foragers in nature tend to be larger than nest workers, we suggest that size-related learning differences be considered as a factor in division of labor between large and small bumblebees.