The rusty patched bumble bee (Bombus affinis) is named after the small rust-colored patch visible on worker bees' abdomens. This bee was historically found throughout the eastern and upper midwestern United States. However, surveys between 2003 and the present have found only a small number of this species in Illinois and Wisconsin. The rapid decline is believed to be caused by an introduced pathogen, possibly Nosema bombi, which was likely picked up by queen bees sent to European rearing facilities and then sent back to the United States in the early 1990's. It is hypothesized that after the return of these newly infected bees, the disease then spread to wild populations of rusty patched bumble bees, Franklin's bumble bees (B. franklini), western bumble bees (B. occidentalis), and yellowbanded bumble bees (B. terricola). A decline in each of these species was noticed in the late 1990's. Additional threats to bumble bees include other pests and diseases, habitat destruction, pesticides, invasive species, natural pests or predators, and climate change. Rusty patched bumble bees are known pollinators of wildflowers, cranberry, plum, apple, alfalfa, and onion seed.

References: Bumble bees: rusty-patched bumble bee (Bombus affinis), Xerces Society; Decline of bumble bees (Bombus) in the North American Midwest, J. C. Grixti, L. T. Wong, S. A. Cameron, and C. Favret, Biological Conservation, 2009, vol. 142, pp. 75-84; Evidence for decline in eastern North American bumblebees (Hymenoptera: Apidae), with special focus on Bombus affinis Cresson, S. R. Colla and L. Packer, Biodiversity and Conservation, vol. 17, no. 6, June, 2008, pp. 1379-1391