Motivational modulation of flight speed in foraging bumblebees

The set of cognitive mechanisms employed by foraging bees is the subject of intense research due to the importance of pollination as an ecological process and as a study system in comparative psychology. Yet, our understanding of how reward valuation influences flight behaviour, and, more generally, the motivational control of behavioural vigour, remains limited. Here, the flight behaviour of individual bumblebees Bombus impatiens was recorded during a series of foraging trials in which the reward intrinsic value and predictability was manipulated. The bees could access a feeder whose sugar concentration varied from trial to trial following an increase, constant peak, and decrease pattern. Neither the feeder itself nor its position changed during the experiment. Hence, potential differences between trials could be interpreted in the context of decision-making and behavioural vigour, rather than search behaviour. The average flight speed towards the feeder increased when the sugar concentration was both high and constant, and returned to baseline as it became lower. This suggests that, as in other species including humans, the behavioural vigour of foraging bees towards a potential reward reflects its expected value. This motivational modulation of flight speed offer new ways of interpreting and studying decision-making in foraging bees.