New York Natural Heritage Program
American Bumble Bee
Bombus (Thoracobombus) pensylvanicus (De Geer, 1773)
Insects

Threats [-]
The primary threat to species in the subgenus Thracobombus leading to their rapid, recent decline has been attributed to exotic pathogens. Cameron et al. (2011) showed a higher proportion of B. pensylvanicus individuals infected by the pathogen Nosema bombi than other bumble bees with stable global populations. In addition, habitat loss, insecticides, and urbanization are known long-term threats for many bumble bees (Schweitzer et al. 2012).

Conservation Strategies and Management Practices [-]
Any efforts to protect wild bumble bee populations from pathogen exposure would benefit American bumble bees. Suggested actions would include using mesh to prevent escape of bees from commercial breeding greenhouses, proper disposal of commercial bees, sanitation in greenhouses, and development of molecular screening. Tight restrictions on importing bumble bees and elimination of parasites from commercial populations has been suggested as ideal (Meeus et al. 2011, Schweitzer et al. 2012).

Limiting exposure of American bumble bee to insecticides would also benefit them. Suggested actions include avoidance of application to flowers that bumble bees are attracted to and application of solutions or soluble powders (rather than dusts or wettable powders) to the ground in calm wind and warmer tempertures during periods of dewless nights to minimize the impact to resident bumble bee populations (Schweitzer et al. 2012). Organic farming has also been suggested to benefit bumble bees. 

Ensuring habitat resources for foraging, nesting, and overwintering will also benefit B. pensylvanicus. Habitats for these needs should be within close proximity to each other and without road or railroads between them, which may be barriers to dispersal. Suggested actions for habitat managment should include ensuring nectar availability throughout the spring and summer by improving flower abundance and species richness and species with overlapping blooms. Select food plants for B. pensylvanicus include vetches, clovers, goldenrods, Hypericum, and Eupatorium (Colla et al. 2011). If mowing of fields occurs, summer is the best time and mower blades should be raised to avoid ground nests. Staggering cutting times in different field areas will ensure nectaring sources are always available. Increasing available nesting habitat may be accomplished by reducing tillage in fields, leaving unplowed strips vegetated, or even providing artificial nesting boxes. Managing for rodents and ground-nesting birds should also benefit bumble bees (Schweitzer et al. 2012).

Research Needs [-]
Further research is needed to determine more information on habitat requirements, threats, climate change effects, and insecticide effects for American bumble bee.