RESUMEN
Amino acids are common constituents of floral nectars and can be critical components in the diets of insect pollinators. Yet the means through which insects detect amino acids can be complex and arise from pre- and post-ingestive mechanisms. Furthermore, the response to an amino acid can change depending on an insect's nutritional status. Here we use a sensitive feeding assay and Proboscis Extension Response (PER) conditioning in the honey bee to assay the effect of glycine, which is a common constituent of nectars and pollens. Subjects preferred to feed on a sucrose stimulus that contained glycine, and the highest relative preference was recorded for the highest concentration of glycine. However, the highest response rate occurred at lower than maximal concentrations and differed depending on the physiological status of the subjects. These results are consistent with a model in which subjects attempt to maintain a physiological target amount of glycine/amino acid relative to other nutrients. All concentrations of glycine enhanced the rate and magnitude of a conditioned response to an odor in the PER assay, which demonstrates that animals can learn to modify their responses to an odor conditioned stimulus based on the presence of amino acid. This capability would enhance a honey bee's ability to evaluate the quality of floral nectars, which are associated with, among other things, odor cues given off by flowers. In future studies these techniques will allow us to evaluate the physiological roles that amino acids play in honey bee diet and choice behavior.
RESUMEN
We tested risk sensitivity towards variability in volume of reward with harnessed honeybees, Apis mellifera, in a proboscis-extension conditioning paradigm. We conditioned each subject to turn its head and extend its proboscis towards one of two presented odours; one odour was associated with a constant reward volume and the other with a variable reward volume that was either low or high, with probabilities P=0.75 and (1-P)=0.25, respectively. The volumes of rewards were varied among three experimental conditions. In conditions 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 than the constant reward option. The behaviour of subjects did not differ between treatments and the majority of individuals were risk averse. In condition 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 assigned to condition III developed a preference for either reward option. Thus, 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 relative 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 aspects of learning, decision making, perception and memory. Copyright 1999 The Association for the Study of Animal Behaviour.