|scientific name Bombus nevadensis |
Distributed in prairie and woodland habitats, nests primarily underground (Hobbs 1965).
Queens found flying from early April to late September, males from early July to late August, and workers from late May to late September (Thorp et al. 1983).
Bombus nevadensis belongs to the subgenus Bombias in which females have large ocelli well below the supraorbital line and malar space longer than wide; males have protuberant compound eyes, convergent above, with straight penis valves (Thorp et al. 1983). Both sexes of Bombias are further distinguished by hind tibia with a fringe of very short hairs (Williams 2008). Bombus nevadensis females have head and pleura covered with black pile, while the face and pleura of males have yellow pile. The dorsal side of the first three abdominal segments is covered with yellow pile, while the rest are covered with black pile in both sexes (Franklin 1912). The only close ally in the western hemisphere, Bombus auricomus, can be distinguished by a broad black interalar band on females and by apical abdominal segments with black pile on males.
Bombus nevadensis are large bumble bees with queens varying in length from 18 mm to 22 mm; in wing spread from 42 mm to 48 mm; and in width of second abdominal segment from 9.5 mm. Workers range in length from 15 mm to 18 mm; in wing spread from 38 mm to 42 mm; and width of second abdominal segment from 9 mm to 9.5 mm. The length of males varies from 13 mm to 17 mm; wing spread from 32 mm to 37 mm and the width of the second abdominal segment from 7 mm to 8.5 mm.
Alford (1975) outlines the life history of Bombus nevadensis. Newly mated B. nevadensis queens overwinter beneath the soil litter and emerge from their hibernacula in late spring. Queens are transitory for a time, growing in size while collecting pollen and looking for a suitable nest. Once a suitable nest has been found, the queen constructs an apple sized hollow structure within it. The queen deposits her eggs in parallel rows within a mound of pollen on the floor of the structure; she also constructs a honeypot for storing nectar. Newly hatched larvae begin consuming the pollen mound, requiring the queen to continue provisioning it. The queen periodically incubates her brood by sitting upon it and respiring to generate body heat. The larvae spin cocoons in the final instars, as do the pupa; the cocoons may be re-used later for storage of pollen or nectar. Upon pupation, the emerged adults take nectar from the honey pot. Once the nest consists of the new young workers and the queen it can be considered a social unit and is referred to as a colony. Species of the subgenus Bombias are unique as the eggs for subsequent generations are laid singly (rather than in clumps) in cells atop the pupating first generation of workers. The new generation of workers are now responsible for provisioning of the growing larva and the honey pot. The caste differentiation of each generation varies throughout the year, with the first generations containing all workers, followed by a worker/male split, followed by mostly males, followed by a male/queen split, followed by mostly queens. The factor initiating queen production has not been established but it appears the colony must reach a size capable of maintaining nest temperatures and food stores before queens are produced. Young queens remain in the colony and will mate during their first week. Males leave the hive and do not return; they establish a methodical flight path and mate with encountered queens. Only the newly mated queens will overwinter in hibernacula; males, founder queens, and all workers perish.
Bombus nevadensis queens required an average 30.5 days to produce the first brood which had an average 12.4 larvae (Hobbs 1965).
Bombus nevadensis was reported in California foraging on 7 plant families with 15 genera; most of the diet was from the families Leguminosae, Compositae, Saxifragaceae and Labiatae (Thorp et al. 1983).
Western nearctic region, eastern neartic border (Williams 1998)
Hobbs (1965) reported parasitism of colonies by Bombus insularis and conopid flies.
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