Ecology of Species ofBombusLatr. (Hymenoptera: Apidae) in Southern Alberta. V. SubgenusSubterraneobombusVogt

Both Nearctic species ofSubterraneobombusoccur in southern Alberta, butBombus(Subterraneobombus)appositusCress. is confined to the wooded areas whereasB. (S.)borealisKby. is confined to the prairie. Both are adaptable in their nest-selecting habits and are among the latest species ofBombusto emerge and establish nests in their respective habitats. Both species made large first broods;B.appositusaveraged 13 ± 3 cocoons in 119 first broods.B.appositusnever had more than two broods of workers, andB.borealishad only one. Both constructed pollen pockets beside and beneath the young larvae of the second and succeeding broods. Queens ofB.appositusrequired about 23 days to rear the first workers. The largest workers of both species were considerably smaller than average-sized queens. Colonies of both species were relatively small; those ofB.appositusaveraged less than 100 individuals, the largest being 246. Both species were apparently sparse producers of wax. Queens of both species apparently mated with males in the nest or immediately upon leaving the nest. New queens ofB.appositusdug about one inch into the ground to hibernate. Females of the cuckoo bee,Psithyrus insularis(Sm.), succeeded in having their young reared to maturity in nests ofB.appositus.