Amino acids (AA) compared between plants hosting oligolectic bees vs. plants not known to host oligoleges. Box whisker plots showing median, quartiles and range. Plants hosting oligoleges showed a significantly lower pollen quality in terms of total amino acid concentration (Mann-Whitney U-test; Z = − 2.69, P = 0.0072) and total essential amino acids (Z = − 2.64, P = 0.0082), whereas the fractions of free and free essential amino acids did not show significant differences (all Z ≤ 0.92, all ) (N_oligolectic = 91, N_generalised = 51).