Honeypot visitation enables scent learning and heightens forager response in bumblebees (Bombus impatiens)

Bumblebees integrate cues associated with food that they experience within their nest. Both experienced and naïve workers rely on odours in the nectar collected by foragers and stored in honeypots to gain information about currently available food sources. The ability of workers to retain memories of these odours and to orient towards them when they leave the nest affects both foraging efficiency and food yield for the colony. In this study, we added sugar solution containing a floral scent (i.e. training scent) directly to empty honeypots within nests of Bombus impatiens in the absence of all other stimuli normally associated with successful foragers. To assess bee learning and memory, we quantified the effects of (a) the number of exposures to the training scent during conditioning, (b) the number of days elapsed post-conditioning (3 days vs. 6 days) and (c) bee age, on appetitive choice of the training scent relative to an unfamiliar scent. A high proportion of the bees of all ages (i.e. 74–80%) contacted the scented syrup we supplied briefly to colonies, with most contacting it once but some as many as 14 times. Most of the bees that may have experienced the training scent in the hive atmosphere but failed to contact a honeypot containing the scented sucrose solution (i.e. bees for which the training scent was familiar but unrewarded) exhibited no response to either the familiar or unfamiliar scent; the few that responded had no preference for either scent. More frequent contact with the scented sucrose increased the likelihood a bee would respond to the scent subsequently. Bees that contacted the scented nectar 1–4 times during conditioning preferred the rewarded odour when tested 3 days later, but after 6 days their scent choice was random, suggesting they retained no memory of it. In contrast, bees that contacted the scented nectar 5–14 times chose the rewarded odour over an unrewarded odour 23 of 24 times when tested 6 days after exposure. This is the first confirmation of social learning in B. impatiens. Our results highlight the importance of direct contact with scented nectar in honeypots and the strong long-term memory of a rewarded scent acquired through relatively brief but repeated exposure to it.