Flowers for health: the importance of flower diversity and composition for maintaining the health and disease resistance of bumblebee pollinators

Bumblebees are important pollinating insects for many crops and wild flowering plants. Due to multiple factors that include agricultural intensification, many populations have experienced severe declines and several species are now listed in the UK Biodiversity Action Plan. Bumblebees rely exclusively on nutrients derived from pollen and nectar, and nutrition is crucial for the development and activation of the immune system. Four microbial pathogens are known to infect bumblebees, and previous work has shown a variety of interactive effects between host nutritional status and pathogen epidemiology. Of the studies that investigated nutritional immunology in bumblebees, almost all have been carried on a limited range of common species because others, notably long-tonged species, have been difficult to rear in captivity. As a result, we lack knowledge of the nutritional needs of many declining species. Here, I test methods for rearing two long-tongued species in captivity and investigate the effect of diet on incipient colony development. A new technique to encourage oviposition and brood care was trialled successfully, and I observed interspecific differences between bumblebee queens on each diet. I also find evidence to support the idea that the nutritional content of pollen, not only plant species diversity, determines bumblebee health. In the wild, floral resources play an important role in regulating bumblebee populations and that of their pathogens. The abundance, diversity and composition of floral resources vary dramatically across the landscape, but studies investigating the effects of floristic composition on host-pathogen dynamics in bumblebees remain scarce. I compare floral resource availability, bee health and pathogen prevalence across three important UK habitats: farmland, gardens and nature reserves. I found that gardens contained the greatest species richness of flowers and had the largest, healthiest bees, despite increased parasitism. Farmland consistently provided the least floral resources, but habitats were complementary to each other in resource provision. I observed interspecific differences in bee health across habitats and report on the prevalence of bumblebee pathogens C. bombi, N. bombi and N. ceranae. Floral resources have a substantial effect on bumblebee health and pathogen dynamics, but these effects appear to vary between species. To support taxonomically diverse bumblebee communities, it is essential that the nutritional needs of a wider range of bumblebee species are considered.