The exact cause of the decline is unknown, but evidence suggests a synergistic interaction between an introduced pathogen and exposure to pesticides, specifically insecticides and fungicides, which was also noted in the species assessment. Prior to its listing as endangered in 2017, the species experienced a widespread and steep decline.
This historical range continued south to the northeast corner of Georgia and reached west to the eastern edges of North and South Dakota, as noted in the species status assessment in 2016. Historically, the rusty patched bumble bee was broadly distributed across the eastern United States and upper midwest, as well as in southern Quebec and Ontario, in Canada.
The rusty patched bumble bee is one of about 21 species of bumble bees in eastern United States, and was listed as federally endangered in 2017.
