The value of pollination services to the world economy has been estimated at $200 billion, and there is mounting concern that declines in pollinator numbers will have considerable economic costs. Bumblebees are important pollinators of a range of plant and crop species in North America. There is evidence that certain species are in decline, but it is not clear what factors are driving these changes. Bumblebees are attacked by a range of parasites, all of which can have impacts on colony fitness, and despite their potential of to be important factors affecting bumblebee populations, only a few studies have begun to document their abundance in North America. Furthermore, we are only beginning to understand what factors affect a bee’s likelihood of parasite attack or infection. This research asks: (1) How common are the internal parasites Crithidia bombi, and Nosema bombi and parasitoid conopid flies in bumble bees of Massachusetts; and (2) What factors are correlated with parasitism for an individual bee? I present results from a multi-site survey of bumble bee parasitism that documented the abundance of these three parasites, and tested whether species, sex, date of collection, bee body size, and location were correlated with the probability of parasitism.
Results/Conclusions
Conopid flies, Crithidia bombi, and Nosema bombi were all sufficiently abundant to potentially impact bumblebee populations, and parasite abundance in Western Massachusetts is in general higher than has been documented in wild bees elsewhere in North America. Conopids infected 22% of all bees, Crithidia infected approximately 51% of bees and Nosema infected 11% of bees captured. Furthermore, the risk of parasitism varied in a systematic way for individual bees, and different factors appeared to be important for each type of parasite. Conopid flies attacked female bees more than males and were found more frequently in intermediate sized bees. Crithidia parasitism was significantly related to bee species, collection date and site. Certain species and sites had higher infection rates of Crithidia, and infection exhibited a unimodal pattern of prevalence over the season. Nosema parasitism was significantly higher in males as well as some host species, and infection generally declined over the season. This study highlights patterns of parasitism in New England bumblebees, which are considerably higher than those found elsewhere. Future work could address some of the potential causes behind these patterns, including differences in land management, or spill-over of pathogens from managed bumble bees.
