Key to Alpinobombus species for females

1 Cheek <1.25× longer (oculo-malar distance) than broad (breadth of the mandible at its base between and including condyles) (Fig. 140)........................................................................................... 2

- Cheek> 1.25× longer than broad (Fig. 141)................................................................ 5

2 (1) Hind tibia outer (corbicular) surface coarsely rough and matte with the microsculpture (surface texture) interrupting the reflective highlights (Fig. 142); if the hair of T2 is extensively orange then there are often broad patches of black hairs in the anterior lateral corners, the orange often appearing faded (Figs. 2, 25‒31)............................................... 3

- Hind tibia outer surface smooth and shining with the microsculpture scarcely or not interrupting the reflective highlights (Fig. 143); if the hair of T2 is extensively orange then the orange hairs extend into the anterior lateral corners with almost no black hairs, the orange often bright (Figs. 1, 16‒17)............................................................... 4

3 (2) Europe or Russia, hair of T3 either orange or black or both, rarely with yellow or grey hairs (Figs. 2, 23‒31) B. pyrrhopygus

- North America or Greenland, hair of T3 black but often with many yellow or grey hairs either scattered in the middle third or in a posterior fringe or both (Figs. 3, 40‒51)......................................................... B. polaris

4 (2) Europe, hair of T2‒3 predominantly orange with no yellow (Figs. 1, 16‒17)................................ B. alpinus

- North America, hair of T2‒3 yellow or black with no orange (Figs. 90‒100)............................. B. neoboreus

5 (1) North America, hair of T3 usually predominantly yellow for its entire breadth, sometimes with black hairs extensively inter- mixed, T4 either entirely black or at most with a few yellow hairs laterally (Figs. 105‒111)................ B. kluanensis - North America or Europe or Russia, hair of T3 predominantly black, sometimes with a dense yellow posterior and/or lateral fringe, T4 either black or with patches of either orange or yellow or white (Figs. 60‒70, 78‒84, 117‒118, 125‒126)....... 6

6 (5) Hair of T3‒6 either with some orange or white, or if completely black then either the side of the thorax (mesepisternum) is usually completely yellow or the thorax is entirely black (the worker caste is common) (Figs. 60‒70, 78‒84)............. 7

- Hair of T3‒6 completely black and the side of the thorax is extensively black (the worker caste is extremely rare) (Figs. 117‒118, 125‒126).................................................................................... 8

7 (6) Europe or Russia, hair of the face (base of the antenna) black, the side of the thorax (mesepisternum) usually predominantly black, T3 usually completely black (Figs. 4, 60‒70)................................................. B. balteatus

- North America, hair of the face usually with some yellow, the side of the thorax usually predominantly yellow, T3 extensively black but usually with a broad posterior and lateral fringe of either yellow or orange (individuals from Ellesmere Island are darker like B. balteatus) (Figs. 5, 78‒84).......................................................... B. kirbiellus

8 (6) Europe or Russia, hair of the pale bands usually dark chestnut brown (or pale yellow from Wrangel Island) (Figs. 6, 125‒ 126)..................................................................................... B. hyperboreus

- North America or Greenland, hair of the pale bands usually pale straw yellow (Figs. 1 17‒118)................. B. natvigi