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Olfactory detection of amino acids

Detectable amino acids

Five out of the 20 amino acids tested turned out to be detectable to the honeybees when presented at a concentration of 100 mM. These five are L-tyrosine, L-proline, L-cysteine, L-tryptophan and L-asparagine. 

Acquisition curves for detectable amino acids. The graph shows the percentage of bees that associated the odor of the amino acids with a reward. Individual curves represent the percentage of proboscis extension reflexes (PER) to a given amino acid odor (CS), and each data point represents a mean value across animals.

Non-detectable amino acids

Honeybees did not detect the odors of L-alanine, L-arginine, L-aspartic acid, L-glutamic acid, L-glutamine, glycine, L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-serine, L-threonine, L-valine. There was no significant difference between the percentage of AA-bees responding towards the odor of the amino acids and the percentage of control-bees responding towards the background stimulus alone.

For some of these amino acids (L-aspartic acid, L-methionine, L-histidine, L-leucine, glycine and L-serine) the responses towards the amino acid odor was even lower than the responses towards the background stimulus alone. 

Detectability of amino acids. R = Responses (number of proboscis extension reflexes in the last unrewarded trial). N = Sample size (number of possible proboscis extension reflexes in the last unrewarded trial). AA = amino acid group. Con. = control group. Significant values set as p < 0.05, calculated with the use of Fisher’s exact tests.

Olfactory detection thresholds

Distribution of olfactory detection thresholds for L-tyrosine, L-proline, L-cysteine, L-asparagine and L-tryptophan. Given is the number of honeybees that reached their detection threshold at a given concentration per odorant. L-tyrosine (N=9), L-proline (N=10), L-cysteine (N=10), L-asparagine (N=10), L-tryptophan (N=8).

The honeybees’ median olfactory detection thresholds for these five amino acids are 12 mM for L-tyrosine and L-cysteine, 50 mM for L-asparagine and L-tryptophan, and 100 mM for L-proline.

Comparison to vertebrate species

The present results indicate that the honeybees’ olfactory detection thresholds for amino acids are generally higher than those found for vertebrate species.

Olfactory detection thresholds for L-proline, L-cysteine, L-methionine and L-tyrosine. Each data point represents the lowest concentration that mice, spider monkeys and humans have been reported to detect, and the lowest concentration that the honeybees in the present study were able to detect (Mice: Wallén 2010; Spider monkeys: Engström 2010; Humans: Laska 2010, Dietz and Traud 1978 (cited by Laska 2010)).


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Last updated: 05/18/11