Effect of an amino acid on feeding preferences and learning behavior in the honey bee, Apis mellifera.
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.