Investigating the ecology of the Great Yellow Bumblebee (Bombus distinguendus) within the wider bumblebee community in North-West Ireland

Abstract

Bumblebees are a key pollinator group globally which have declined over time. However, while some species remain common others are rare and have declined at a sharper rate. The Great Yellow Bumblebee (Bombus distinguendus Morawitz) is classified as ‘Endangered’ on the Irish Red List, and ‘Vulnerable’ at European level. We aimed to investigate the ecology of B. distinguendus within the wider bumblebee community in its only remaining Irish population to inform conservation management. Eight true bumblebee species were recorded in total in four habitat types surveyed, with highest species richness in species-rich grassland and highest abundance in urban habitats. Highest numbers of B. distinguendus were found in two designated nature reserves. However, outside these reserves the species was only found in three of twelve sites surveyed in both species-rich and coastal grassland habitats. B. distinguendus is a late emerging species in this region with a foraging preference for Common Knapweed (Centaurea nigra). Availability of key forage species was lowest when numbers of B. distinguendus were highest, potentially limiting survival of this species. Some smaller suitable habitats in urban areas and roadside verges were not used by the species, which suggests potential issues with habitat connectivity, patch size and/or availability of nesting and hibernation sites. Based on our findings, we suggest that existing species-rich and coastal grassland sites should be conserved, and other areas restored, for B. distinguendus in Ireland. Conservation management should focus on delaying cutting grasslands until late September, winter grazing of stock and reducing pesticides and fertilisers with the aim of increasing forage availability in late season, and ensuring that suitable habitats are connected in the landscape to allow adequate habitat area as well as movement and dispersal of the species to new areas.