Olfactory discrimination ability and odor structure-activity relationshipsin honeybees

Using the training procedure introduced by von Frisch in 1919, we tested th e ability of free-flying honeybees to discriminate a conditioning odor from an array of 44 simultaneously presented substances. The stimuli included h omologous series of aliphatic alcohols, aldehydes and ketones, isomeric for ms of some of these substances, as well as several terpenes and odor mixtur es, and thus com prised stimuli of varying degrees of structural similarity to any conditioning odor. We found (i) that the honeybees significantly di stinguished between 97.0% of the 1848 odor pairs tested, thus showing an ex cellent discrimination performance when tested in a free-flying situation w ith an array of structurally related substances; (ii) a significant negativ e correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length with all aliphat ic substance classes tested; (iii) that both the position and type of a fun ctional group also affected discriminability of odorants in a substance cla ss-specific manner; and (iv) striking similarities in odor structure-activi ty relationships between honeybees and human a nd nonhuman primates tested previously on a subset of substances employed here. Our findings demonstrat e that the similiarities found in the structural organization of the olfact ory systems of insects and vertebrates are paralleled by striking similarit ies in relative discrimination abilities. This strongly suggests that simil ar mechanisms of odor coding and discrimination may underlie olfaction in v ertebrates and insects.