Risk-sensitive foraging: choice behaviour of honeybees in response to variability in volume of reward

We tested risk sensitivity towards variability in volume of reward with har nessed honeybees, Apis mellifera, in a proboscis-extension conditioning par adigm. We conditioned each subject to turn its head and extend its probosci s towards one of two presented odours; one odour was associated with a cons tant reward volume and the other with a variable reward volume that was eit her low or high, with probabilities P=0.75 and (1-P)=0.25, respectively. Th e volumes of rewards were varied among three experimental conditions. In co nditions I and II, the variable reward option included a low reward of zero (i.e. reinforcement was withheld in the low reward value); in condition I, the mean of the variable and of the constant reward options were the same, and in condition II, the variable reward option had a higher mean reward t han the constant reward option. The behaviour of subjects did not differ be tween treatments and the majority of individuals were risk averse. In condi tion III, the variable reward option did not include a zero reward and the mean reward did not differ between options. Very few of the individuals ass igned to condition III developed a preference for either reward option. Thu s, honeybees are risk sensitive to variability in volume of reward in some conditions and the degree of risk sensitivity depends on characteristics of the reward distributions. The most salient characteristic may be a relativ e measure of variability, such as the value of the coefficient of variation of reward. The experimental paradigm that we developed is a powerful tool for studying the mechanism of risk sensitivity in bees,as well as other asp ects of learning, decision making, perception and memory. (C) 1999 The Asso ciation for the Study of Animal Behaviour.