Does size matter? Pollen foraging behavior of native bumble bee colonies in the presence of a mass flowering resource

The European honey bee, Apis mellifera , provides pollination services for diverse crops, but parasites and diseases have reduced their availability and increased the cost of hive rentals. Thus, there is increased interest in evaluating the efficacy of wild bees, particularly bumble bees, as alternative pollinators. The objective of this study was to determine the effects of colony size on the pollen foraging behavior of the native bumble bee, Bombus vosnesenskii, in the presence of mass flowering resources. Lab-reared colonies, initiated by collection of wild queens, were partitioned into two size classes based on their larva to worker ratio, and placed adjacent to a flowering red clover field in western Oregon. To determine impacts of colony size on foraging behavior, individual bumble bee workers from large and small colonies were marked and observed during peak foraging periods. Data analyses suggest the duration of pollen foraging trips is greater in small colonies, when compared to large colonies. To examine resource utilization, pollen pot samples were extracted from colonies weekly, weighed, and analyzed for floral composition. A two-sample t-test indicated a significant difference in weights across size classes, during the final week of the study as large colonies had the greatest amount of stored pollen compared to small colonies (P=0.026). This data, along with data pertaining to floral composition will be presented. Relationships of colony size with the presence of an abundance of flowering resources, and implications for sustainability of pollination services in cropping systems and wild habitats will be discussed.