Olfactory Detectability of L-Amino Acids in the European Honeybee (Apis mellifera)

• The honeybee is one of several insect model systems for the study of olfaction, yet our knowledge regarding the spectrum ofodorants detectable by Apis mellifera is limited. One class of odorants that has never been tested so far are the amino acids,which are important constituents of floral nectar. Using the proboscis extension response paradigm, we assessed whether theodor of amino acids is detectable for honeybees and determined olfactory detection thresholds for those amino acids that weredetectable. We found that honeybees are able to detect the odor of 5 of the 20 proteinogenic amino acids when presented ata concentration of 50 or 100 mM. Median olfactory detection thresholds for these 5 amino acids were 12.5 mM with L-tyrosineand L-cysteine, 50 mM with L-tryptophan and L-asparagine, and 100 mM with L-proline. All detection thresholds were muchhigher than reported concentrations of amino acids in floral nectars. We conclude that in the foraging and feeding context,honeybees are likely to detect amino acids through taste rather than olfaction. Across-species comparisons of the detectabilityof and sensitivity to amino acids suggest that the number of functional genes coding for olfactory receptors may affect botha species’ sensitivity for odorants and the breadth of its spectrum of detectable odorants.

Nyckelord

amino acids

Apis mellifera

detection

honeybee

olfaction

sensitivity

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