Pollinator protection: the role of nutrition on individual and colony-level bumblebee health and immunity, and pathogen susceptibility

Bumblebees are ecologically and economically important pollinators, and as a result are commercially-produced to provide pollination services to agriculture. Managed bumblebees have been implicated in the spread of parasites, which may reduce their effectiveness for crop pollination and pose a spillover risk to wild pollinators. It is thought that by improving the health of commercially-reared bumblebees through diet enhancement, or the reduction of environmental stress through shipping, it may be possible to mitigate this risk. This thesis investigated the effect of diet quality and environmental stress during shipping on individual and colony-level bumblebee health, immunity and tolerance to three common pathogens of bumblebees, C. bombi, N. bombi and N. ceranae. An effect of diet enhancement was found across multiple scales, individual and colony, across colony life stages, and general measures of health and specific immune function. At the individual-level, nutritionally enhanced diets (with an elevated protein content compared to standard diets) were shown to support the growth of bigger bees, which in turn was found to be a good indicator of individual health and immunity, as well as supporting larval survival during pathogen challenge. At the colonylevel diet was shown to support colony development, with diet enhancement supporting colonies with more individuals across all life stages but most noticeably in the number of new reproductives. Better quality diets were shown to offer significant protection against the negative effects of shipping stress, with shipped colonies experiencing a significant reduction in numbers of larvae, new males and queens. In addition, the results showed that improved health directly affects individual larval survival and therefore the colony’s capacity to withstand pathogen stress. These results demonstrate diet quality can have important direct and indirect effects on the health and immunity of commercially reared bumblebees. In addition, an improved diet may have the potential to mitigate the significant and long-lasting effects of shipping-stress on colony development, as well providing a protective effect against pathogen stress. These results clearly have significant implications for commercial production but also provide further evidence as to the importance of diet quality throughout the colony cycle and the long-lasting impact of environmental stress on colony development which are also important considerations in planning floral resources for wild bee conservation.