During the last few years, the bumblebee Bombus ternarius Say has markedly decreased in numbers in Vilas County in northern Wisconsin while Bombus terricola Kirby has increased. The great ecological similarity of these species suggests that interspecific competition may cause or facilitate this replacement.
Thomson, James D.
"A Local Replacement of Bombus Ternarius by Bombus Terricola in Northern Wisconsin (Hymenoptera: Apidae),"
The Great Lakes Entomologist: Vol. 11
, Article 5.
Available at: http://scholar.valpo.edu/tgle/vol11/iss2/5