Ecology of Species of Bombus Latr. (Hymenoptera: Apidae) in Southern Alberta. II. Subgenus Bombias Robt.

Abstract

In southern Alberta, the distribution of Bombus (Bombias) auricomis is confined to wooded areas whereas that of B. (Bombias) nevadensis encompasses prairie and wooded areas. Perhaps B. nevadensis survives on the prairie because it hibernates well below the surface of the soil.When given equal opportunity to nest in surface or underground hives, B. nevadensis nested in three surface and 18 underground hives. Both species began to establish nests between mid-May and mid-June.Both species laid one egg per cell in all broods, vertically in the first brood and horizontally in later broods. Larvae were fed individually in all instars of all broods, except perhaps during early instars of the first brood when pollen was packed beneath them through pockets made at both ends of the brood mass.The eggs in the first brood layer were usually laid within 4 days. The cells beneath the shallow incubation groove were usually the first made and the ones from which adults first emerged. Queens of B. nevadensis required about a month to rear sufficient workers to take care of the foraging duties of the new colonies. Egg cells of succeeding broods were built side by side in groups or lines on cocoons of previous broods and were not primed with pollen.Both species were prolific producers of wax. More pots for the storage of honey and pollen were added as colonies increased in size.Colonies of both species were usually small, apparently because the queens usually found time to rear only one brood of workers and perhaps because only one egg was laid in each cell. The largest colony, of B. nevadensis, produced 139 individuals. The workers of a brood sometimes varied greatly in size. The workers of succeeding broods were progressively larger, the last ones produced being almost as large as queens. Males of B. nevadensis mated by grasping the queens when they were flying, then copulating on the ground. After mating, queens hibernated at a depth of about 3 inches in the soil.Males and females of Psithyrus insularis were reared in nests of B. nevadensis. P. suckleyi also established in a nest of this species. The big-headed fly, Physocephala texana, was a destroyer of B. nevadensis. Ants pillaged first broods not protected with an insecticide.