The importance of nutrition for bumblebees and solitary bees; implications for pesticides and stewardship

Critical to supporting populations of wild and managed species in agricultural systems arean improved understanding of mechanisms by which bees enhance crop quality and yield; the factors influencing pollen selection by foraging bees (including pollen diversity and amino acid concentrations); the influence of pollen profiles in determining individual and colony performance; and the response of individuals toinsecticidesin nectar. Laboratory and field studies addressed these questions using Osmia bicornisandBombus terrestris audax.In a mixed lowland farm system, O. bicornisreproductionand plant utilisationwas investigatedin florally-enriched vegetation. A high selectivity for pollen was observed and in the laboratory larval survival was related to the pollen profile of the diet. The role ofpollen diversity andamino acid concentrations wereinvestigated in both foraging behaviour and survival, but requires clarification, although poor survival in the laboratory was associated withlow amino acid concentrationsin a single-species diet of Pinuspollen. In B. terrestris audax, laboratory colony performance was greatest in pollen diets with high concentrations of essential amino acids, but again no consistent relationship with the diversity of pollen species was detected. Results suggest that composition of off-crop vegetation, including those offered in agri-environment schemes, could be modified to better support wild and managed bee populations. Managed O. bicornis, in a cherry orchard experiment, were shown to improve fruit quality, demonstrating a potential commercial application of improved understandingof pollinator biology. Management interventions in farm systems, however, need to consider the potential impacts of insecticides. In laboratory experiments, foraging B. terrestrisused colour cues when selecting flowers, but chemical cues to detect nectar spiked with neonicotinoids. Observed sub-lethal toxicity was reversible when clean nectar was offered but further work is required to confirm the mechanism (behavioural or physiological) leading to these findings