Octopamine affects gustatory responsiveness and associative learning performance in bumble bees

Octopamine has broad roles within invertebrate nervous systems as a neurohormone, neurotransmitter and neuromodulator. It orchestrates foraging behavior in many insect taxa via effects on feeding, gustatory responsiveness and appetitive learning. Knowledge of how this biogenic amine regulates bee physiology and behavior is based largely on study of a single species, the honey bee, Apis mellifera. Until recently, its role in the foraging ecology and social organization of diverse bee taxa had been unexplored. Bumble bees (Bombus spp.) are a model for the study of foraging and learning, and its neural basis, but whether octopamine similarly affects sensory and cognitive performance in this genus is not known. To address this gap, we explored the effects of octopamine on sucrose response thresholds and associative learning in Bombus impatiens via conditioning of the Proboscis Extension Reflex (PER) using a visual (color) cue. We found that octopamine had similar effects on bumble bee behavior as honey bees, however, higher doses were required to induce these effects. At this higher dose, octopamine lowered bees sucrose response thresholds and appeared to enhance associative learning performance. Adding to recent studies on stingless bees (Meliponini), these findings support the idea that octopamines role in reward processing and learning is broadly conserved across Apidae, while pointing towards some differences across systems worth exploring further.