Trees for bees: could woody plant pollen be used as a consistent resource in bee-focused agri-environment schemes?

Bee populations have declined in many parts of the world, raising concerns over their conservation and the pollination services they provide. As a result of declines in agricultural areas, agri-environment schemes have been designed and implemented in order to reverse these trends. Until now, these schemes have largely focused on providing an abundance of herbaceous flowering plants which predominantly provide pollen and nectar during the summer, but flowering trees and shrubs may have been overlooked as a source of earlier-flowering resources. Using Bombus terrestris (L.) micro-colonies, we investigated differences in pollen quality from eight woody and six herbaceous plant species using composi-tional analyses and efficacy assays. Pollen from herbaceous plants had a higher average crude protein and lipid content, but there were no differences in the protein:lipid ratio when compared to woody plants. However, when measuring amino acids directly, woody plants had a slightly higher total and essential amino acid content. Despite these minor differences, micro-colonies fed on woody plant pollen produced a greater mass of larval offspring and had a lower rate of larval ejection. There was substantial variation between individual studied plant species, and whilst no individual woody plant pollen outper-formed the best herbaceous pollen, they all exceeded the performance of the worst herbaceous pollen. This consistent performance suggests that woody plants may be good candidates for inclusion in bee-focused agri-environment schemes in order to provide suitable pollen resources in the early part of the season.