Learning, memory retention and the division of labor in the bumblebee Bombus occidentalis (Hymenoptera: Apidae)

ABSTRACT Age-dependent division of labor is a common feature of eusocial bees. For example, in Apis mellifera the young individuals work inside the nest, whereas their older sisters labor outside. These transitions between tasks rely on cognitive abilities (e.g. foragers learn faster than nurses). Unlike honeybees, bumblebee workers exhibit a wide variation in body size. Large individuals usually forage whereas small bees serve as nurses. We tested whether learning and memory retention correlate with division of labor in Bombus occidentalis. We trained workers of different size, age and experience to associate an odor and a reward in the proboscis extension reflex paradigm. Once established, memory retention was tested after two and five hours. We did not find any significant effect of age or experience. However, we found a significant correlation of body size with memory retention (p< 0.03) and a weak effect on learning ability. In contrast to honeybees, young workers of Bombus are mature enough to forage. Furthermore, larger workers have a longer memory span than small ones, which is an advantage during foraging. In both species learning and memory abilities support their respective systems of division of labor and might enable particular workers to perform specific cognitively challenging tasks.