Pollen Protein Content and Developmental Success of the Solitary Bee Osmia bicornis: Amino Acid Thresholds for Larval Pollen Resources?

Performance of Osmia bicornis larvae fed on six diets with different pollen species composition (one wild collected by foraging adults), each with known levels of nine essential amino acids (EAA; leucine, lysine, valine, arginine, isoleucine, phenylalanine, threonine, histidine, methionine), was investigated. Four of the pollen diets consisted of individual pollen species and two were mixtures of either four or five species (including one naturally foraged by adult O. bicornis). The diets fell into four statistically distinct groups with different EAA contents (ranked from Group I (highest EAA) to Group IV (lowest EAA; pine pollen). The highest larval survival rate was recorded with the wild-foraged diet (Group III) with no survival in Group IV. Similar survival occurred for all other diets. Where larvae survived (Group I–III), there was no effect of diet on the time to commencement of larval stages, cocoon completion or larval development time (egg hatch to pupation), or on pupal weight. The findings provide corroborative evidence of the existence of amino acid thresholds for larval success, but the need for further work is discussed in relation to their multidimensional nutritional requirements and variation of the nutritional content of pollen.