ECOLOGY OF SPECIES OF BOMBUS (HYMENOPTERA: APIDAE) IN SOUTHERN ALBERTA: VII. SUBGENUS BOMBUS

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Abstract
Two of the five Nearctic species of the subgenus Bombus Latr. occur in southern Alberta. Both are bush-inhabiting species. One, B. occidentalis Greene, is confined to the treed areas of southern Alberta whereas the other, B. terricola Kby., although found throughout the treed areas of the province, is much more prevalent in the central and northern regions. Both species emerge and establish nests early, and nest almost exclusively in hives reached by means of downward-sloping tunnels. Many queens of B. occidentalis camouflage or restrict tunnel entrances by dragging grass in and around them. B. occidentalis produced 8.6±0.5 eggs in the first broods, 4.2±1.1 eggs per cell in the second and third broods, and 6.6±0.9 eggs per cell in the fourth brood. This species is intermediate in rank among southern Alberta species of Bombus Latr. in its ability to produce wax. As are other early emerging species, it is heavily depredated by Psithyrus spp.