The role of nectar aminoacidic composition in pollinator preference

Amino acids are the main nectar components after sugars. In addition to protein amino acids (among which Proline is the main one) non-protein amino acids (eg GABA, β-alanine) are also present and sometimes very abundant, but their contribution to floral attraction to pollinators is not completely clear. Gentiana lutea subsp. Symphyandra is a perennial and generalist plant; in the studied area, bumble bees are the more important and efficient pollinators. Previous analysis have revealed high concentration β- alanine in G. lutea nectar, and field observations indicated an anomalous behaviour in Bombus individuals that collect nectar from this plant, but not in those collecting pollen (Rossi et al., 2014). To investigate the role of nectar amino acids in plant-pollinator relationship, we analyzed nectar preference under laboratory conditions, using experimental micro colonies of B. terrestris fed with artificially produced nectars. Each trial consisted in the preference analysis (by consumption) of 4 different solutions simulating G. lutea nectar, 3 of them enriched with β-alanine or proline or both amino acids. Nectars were paired in the 6 possible comparisons (dual choice feeding test). Solutions were administered by syringes and consumption was checked at regular intervals (24, 48, 72, and 96 hours). Five trial were performed on B. terrestris workers and two on males. The same tests were carried out with honeybee foragers (Apis mellifera L.) for comparison, since previous studies (Bertazzini et al., 2010) showed a preference for nectars added with Proline in honey bee workers. The results of the single paired comparisons, analysed by t test, indicate a preference of B. terrestris workers for nectars enriched with β-alanine. Nevertheless, ANOVA test on average individual consumption gave inconsistent results among the 5 different trials, although nectars enriched with β-alanine and with both amino acids are the most consumed. MANOVA analysis shows that the preference is influenced not only by the presence of amino acids, but also by the colony of origin and the kind of paired choice. On the contrary, in the two tests performed on B. terrestris males a clear preference for the control solution is observed. Among the enriched solutions, however, also males prefer β-alanine. The results of honey bees tests are under processing.