Pollen amino acids and flower specialisation in solitary bees

Pollen nutrient composition could be important in host-plant selection of oligolectic bees. In this study, pollen samples from 142 plant species were analysed separately for water-soluble and protein-bound amino acids. The composition of amino acids varied strongly among plant species, but taxonomically related species had similar compositions. All plant species contained the entire set of essential amino acids, although some in small quantities. Total concentration of free-and protein-bound amino acids was significantly lower in pollen sources used by oligoleges than in other pollen sources. Pollen sources of oligoleges showed a lower concentration of essential amino acids and deviated more strongly from the ideal composition of essential amino acids as determined for honey bees than plants not hosting oligoleges. However, this trend was not confirmed on a cruder phylogenetic plant family level, where pollen chosen by oligolectic bees was similar to other pollen.