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

## TL;DR

This study explores how the amino acid content in pollen affects the survival and development of Osmia bicornis larvae, finding that wild-foraged diets yield the best results.

## Contribution

The study identifies amino acid thresholds for larval success in Osmia bicornis and evaluates the effectiveness of wild-foraged versus artificial pollen diets.

## Key findings

- Wild-foraged pollen diets (Group III) showed the highest larval survival rates, while pine pollen diets (Group IV) had no survival.
- Larval survival was not affected by diet composition within Groups I–III, nor was development time or pupal weight.
- The findings support the existence of amino acid thresholds for larval success in Osmia bicornis.

## Abstract

Bees provide a key ecosystem service as pollen vectors, and many flowering plants produce nutritionally rich pollen/nectar that offer a wide range of bee-essential nutritional components. The nutritional profile of pollen from different plant species varies, and selection by foraging adults is important when balancing the nutritional content of pollen fed to larvae. Improved understanding of their nutritional requirements is therefore important when selecting plant species for conservation habitats. Protein is an important component of bee diets and earlier work has linked amino acid levels in larval pollen diets with bee colony/population success. A threshold level has been proposed below which bumblebee colony development is poor, with significant improvement when exceeded, but little further advantage being gained by further increases thereafter. Dietary requirements differ between bee species/taxonomic groups, and this explorative study investigates the rationale behind dietary effects on solitary bees, focusing on the impact of the amino acid content of larval diets on the developmental success/survival of Osmia bicornis, the relevance of putative amino acid thresholds to the species, and whether larval pollen provisions selected/collected by foraging adults result in higher survival rates than artificial constructs. The findings are discussed in conjunction with other nutritional factors.

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.