The effects of acute stress on learning and memory in bumblebees

Abstract

Stress has complex effects on learning and memory, depending on both the type of stress and when the animal experiences it. Honeybees and bumblebees are agriculturally important pollinators for whom the effects of stress are extremely relevant. These pollinators are often transported long distances during which colonies experience severe physical disturbance, causing stress to individuals prior to their release for pollination. Under natural foraging conditions, bees are excellent at learning about the flowers they forage from, including associations between floral stimuli and rewards. However, it is not clear how stress might affect bees’ abilities to learn and remember floral features. Here we address the effects of acute stress on learning and memory in the bumble bee, Bombus impatiens. Using the Proboscis Extension Response (PER) protocol, we look at stress effects on learning and memory in three experiments. After being trained to a conditioned stimulus, we addressed: (1) the effect of 24h and (2) 30min of stress on the recall of this learned association and (3) the effect of stress on subsequently learning an association. We found that 24h of stress after learning appeared to improve memory recall, and there was a trend in the same direction for 30min of stress. However, bees that were stressed prior to learning an association did not differ from unstressed bees in their ability to learn or remember an association. Our finding that stress has effects on memory in the bumblebee could have implications for their use in behavioral experiments and for promoting the success of both managed and wild populations.