Foraging preferences of bumble bee castes

By McHugh et al.

Field margin from the experiment

Arable field margins are important areas on agricultural land where insect pollinators can find floral resources. Both cultivated margins and floristically enhanced margins are English agri-environment scheme options that can provide these much-needed floral resources. Floristically enhanced margins are most commonly sown with a wildflower seed mix, whilst cultivated margins have typically been ploughed or harrowed between 5-15 cm in depth and left to naturally regenerate with species from the seed bank. Cultivated margins are often a less popular option due to their messy appearance and the risk of arable weeds moving into the adjacent crop.

In this study we examined plant foraging preferences of different bumble bee species to caste level (female workers, male drones, and queens) in both cultivated and floristically enhanced margins. We also conducted detailed botanical surveys of the margins, recording all vascular plants and their percentage of cover. Overall, our results emphasised the importance of plant species within the daisy family that were emerging from the seed bank, as they provided floral resources foraged upon by all bumble bee species and castes. We also found that bumble bee foraging preferences were more likely driven by high nectar sugar content of certain flower species, rather than being attracted to flower species that were growing in particularly high densities.

Bumble bee queens weren’t recorded regularly, suggesting that these margins aren’t providing the preferred floral resources of many bumble bee queens. However, when queens were recorded, they were found to favour earlier-flowering species and species with longer corollas, showing that their requirements need to be met with specific floral traits. Female worker bumble bees across all species showed high levels of overlap in the flower species that they visited. However, this was not the same across all castes, for example, only the buff-tail males were found to forage on beaked hawk's-beard in cultivated margins. This shows the importance of providing a high diversity of floral resources in order to support all species and castes that make up bumble bee populations.

Overall, our findings highlight the importance of continuing to establish multiple AES habitat types in order to fully support bumble bees and other pollinating insect populations on farmland.

Read the scientific publication in JPE.