Quantitative evidence for foraging preferences of shrill carder bumble bee (Bombus sylvarum) queens

Abstract

Introduction Bumblebees are facing declines globally due to agricultural intensification and climate change. In the UK, the shrill-carder bumble bee, Bombus sylvarum, has dramatically declined and is now restricted to five isolated populations across England and Wales. A key life-cycle stage for bumblebees is the spring queen, who is responsible for colony establishment, but we lack quantitative data to inform conservation practice for this life stage. Aim/methods To quantify foraging preferences and floral resource dependency of spring queens in B. sylvarum. We determined the floral resources preferred by B. sylvarum queens across their activity period, along with the potential for inter-specific resource competition. Results At the start of the season, B. sylvarum queens foraged solely on Lamium album and Trifolium repens. Later they increased their foraging breadth but predominantly foraged on Vicia villosa and Rhinanthus minor. Plant-pollinator networks indicate the potential for competition with more common bumble bee species, with B. sylvarum queens exhibiting a broader foraging range than these potential competitors. Discussion As the season progresses, the foraging diversity of B. sylvarum queens increases. Later in the season, the lower species specificity index for B. sylvarum queens suggests that these queens are less specialised than their congeneric competitors. Implications for insect conservation: Our results show that early in the season B. sylvarum queens rely on two floral species. Managing sites to maintain and increase strong populations of these plant species will likely enhance queen success, which is crucial to enable colony establishment and population growth.