Conditional discrimination and response chains by worker bumblebees (Bombus impatiens Cresson, Hymenoptera: Apidae).

We trained worker bumblebees to discriminate arrays of artificial nectaries (one, two, and three microcentrifuge tubes inserted into artificial flowers) from which they could forage in association with their location in a three-compartmental maze. Additionally, we challenged bees to learn to accomplish three different tasks in a fixed sequence during foraging. To enter the main three-compartmented foraging arena, they had first to slide open doors in an entry box to be able to proceed to an artificial flower patch in the main arena where they had to lift covers to the artificial nectaries from which they then fed. Then, the bees had to return to the entrance way to their hive, but to actually enter, were challenged to rotate a vertically oriented disc to expose the entry hole. The bees were adept at associating the array of nectaries with their position in the compartmental maze (one nectary in compartment one, two in two, and three in three), taking about six trials to arrive at almost error-free foraging. Over all it took the bees three days of shaping to become more or less error free at the multi-step suite of sequential task performances. Thus, they had learned where they were in the chain sequence, which array and in which compartment was rewarding, how to get to the rewarding array in the appropriate compartment, and finally how to return as directly as possible to their hive entrance, open the entrance, and re-enter the hive. Our experiments were not designed to determine the specific nature of the cues the bees used, but our results strongly suggest that the tested bees developed a sense of subgoals that needed to be achieved by recognizing the array of elements in a pattern and possibly chain learning in order to achieve the ultimate goal of successfully foraging and returning to their colony. Our results also indicate that the bees had organized their learning by a hierarchy as evidenced by their proceeding to completion of the ultimate goal without reversing their foraging paths so as to return to the colony without food.