Movement patterns of honeybee foragers: Motivation and decision rules dependent on the rate of reward

The movement pattern of honeybees Apis mellifera working on a patch of artificial flowers and its dependence on food-source profitability were analysed by varying the flow rate of sucrose solution provided by a set of artificial flowers. Three sucrose Bow rates were used (0.085, 0.17 and 0.34 mu l/min per flower) and twenty bees per flow rate were measured over one entire visit to the patch. It is shown that 1) bees had the same landing rate at the lower and the intermediate flow rates but foraged significantly faster at the higher flow rate. 2) For the three flow rates tested, the landing rate remained constant throughout the entire foraging visit, thus being unaffected by the progressive increase in the weight transported in the crop. 3) Only the probability of an immediate return to a previously visited flower significantly increased with the flow rate. Such immediate returns occurred whenever the reward experienced at a flower greatly surpassed the mean reward expectation per flower. 4) However, bees returning immediately to the last visited flower did not find reward in it. It is suggested that bees go faster when the offer becomes better as a result of an increase in the foraging motivation that would lead to an incitement of foraging movements and that the progressive increase in the weight transported does not change the motivational levels.