Elemental and non-elemental olfactory learning using PER conditioning in the bumblebee, Bombus terrestris

Learning olfactory stimuli and their implications is essential in bumblebees for orientation and recognition of nest sites and food sources. To evaluate associative learning abilities in bees under controlled environmental conditions, the proboscis extension response (PER) assay is a well-established method used in honeybees and has recently been successfully adapted to bumblebees. In this study, we examined the cognitive abilities of workers of the eusocial bumblebee, Bombus terrestris, by training individuals in different olfactory learning tasks using classical PER conditioning. We compared learning performance for four different floral odors. Individuals were able to solve absolute (A+) and differential (A+ vs. B-) conditioning tasks, and no differences were found between single odors and odor combinations, respectively. Furthermore, bumblebees performed well on a positive pattern discrimination task (A-, B- vs. AB+), but failed to solve the negative pattern discrimination (A+, B+ vs. AB-). Our results indicate that workers of B. terrestris possess elemental olfactory learning abilities, but, in contrast to previous findings in honeybees, fail in more complex tasks, such as negative pattern discrimination. We discuss possible ultimate causes that have led to the difference in learning capabilities between bumblebees and honeybees.