Overview

Comprehensive Description

General Description

Bombus melanopygus belongs to the diverse subgenus Pyrobombus Dalla Torre which is characterized by a malar space of medium length but longer than its apical width and antennal flagellum 2.5 to 3x the length of the scape. The penis valves of the males are usually hook shaped (Thorp et al., 1983).  Bombus melanopygus has a large body densely covered in long, fine pile (Franklin 1912). Abdominal segment 1 is yellow, segments 2 and 3 are red or orange, and the remaining segments (4-6) are black. The anterior scutum and the vertex of head and face are covered in a mixture of black and yellow pile and appear clouded (Thorp et al. 1983; Curry 1984). Males tend to have less black pile on the face and the third antennal segment is shorter than the fifth but longer than the fourth (Franklin 1912). Body size and wingspan varies between castes: queens are 15 to 18 mm with wingspans of 29 to 36 mm, workers range between 11 to 15 mm with wingspans of 25 to 29 mm, and males are 9 to 13 mm with wingspans of 21 to 26 mm. Wings are darkly stained brown (Franklin 1912). The penis valve is rounded at the apex with a sharp angle at middle of apical curvature. The gonostylus is short and sternite 8 is uniformly thick (Thorp et al. 1983).
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Distribution

Western Nearctic region (Williams 1996).
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occurs (regularly, as a native taxon) in multiple nations

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National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)) This is a bumblebee found mainly in North America west of the Rocky Mountains. Various sources disagree substantially about the actual distribution, but most include Washington (e.g. Seattle area), and all include Oregon and coastal California. Kearns and Thomson (2001) add Douglas and Washoe Counties in northwestern Nevada. Others give a much larger range. Some of this discrepancy reflects differences in taxonomy, e.g., the Bumblebee.org website lists Oregon, California, and Nevada for Bombus edwardsii (now usually considered conspecific), and Alaska to Idaho and Colorado for B. melanopygus. A Xerces Society identification guide (Evans, 2009). illustrates both forms or taxa and indicates the typical morph is northern and montane while the "edwardsii" coloration occurs mostly along coast, but that form also occurs inland in southern parts of the range. The Discover Life range map (as of May 2010) cannot be fit to the taxonomy used here. It is clearly a composite including some more widespread taxon that goes east across Canada--no attempt was made to resolve the details. The composite range for both forms or subspecies appears to include northern and coastal California, most of Oregon and Washington and east into northwestern Nevada and Idaho, British Columbia, and apparently into Alaska.

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Physical Description

Type Information

Lectotype for Bombus edwardsii Cresson, 1878
Catalog Number: USNM
Collection: Smithsonian Institution, National Museum of Natural History, Department of Entomology
Sex/Stage: Female;
Preparation: Pinned
Collector(s): Lorquin
Locality: Col.. Date:Not recorded, California, United States
  • Lectotype: 1878. Proceedings of the Academy of Natural Sciences of Philadelphia. 184.
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Ecology

Habitat

Underground nests in Cordilleran forest and Boreal-Cordilleran transition zones and common on alsike clover Trifolium hybridum L. (Hobbs 1967). There are some reports of surface nesting (Thorp et al. 1983).
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Trophic Strategy

Polylectic, adults consume nectar and pollen from a variety of 61 plant families, primarily Salicaceae, Violaceae, Compositae, and Leguminosae in California (Thorp et al., 1983).
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Associations

Flowering Plants Visited by Bombus edwardsii in Illinois

Bombus edwardsii Cresson: Apidae (Bombini), Hymenoptera
(observations are from Graenicher)

Asteraceae: Cirsium arvense sn cp (Gr); Caprifoliaceae: Lonicera oblongifolia sn (Gr), Lonicera reticulata sn fq (Gr); Salicaceae: Salix discolor [unsp sn] (Gr)

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

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Life History and Behavior

Cyclicity

Flight period of queens ranges early February to late October; workers: early April to early September; males: early May to early September (Thorp et al, 1983).
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Life Cycle

Bombus melanopygus has an annual colony cycle. Queens emerge in early February from shallow hibernacula dug into the soil to forage and find suitable nest sites, often in abandoned mouse nests. Pollen is collected and manipulated by the founding queen into a ball. Eggs are laid in vertical rows on the top of the ball and covered over with pollen and wax. A nectar pot previously constructed allows the queen to feed while incubating the brood clump at 30-32° C. Larvae hatch after 4-5 days and begin to feed on the pollen mass. The queen continues foraging and regurgitates nectar to the larvae through openings on the top of the brood cells. After 4 molts, larvae spin loose silk cocoons and pupate. The queen now lays a second and third batch of eggs on top of the pupal cocoons using the pollen and wax from the first batch. Female workers emerge 4-5 weeks after the first eggs are laid and take over foraging and nest construction activities. The queen now exclusively constructs egg cells and lays eggs. As the colony expands upwards and outwards and workers increase in number, fertilized eggs become young queens and males emerge from unfertilized eggs. Caste differences are physiological and large numbers of workers are able to provide the food necessary to rear queens. Males are often produced before the new queens and will leave the colony almost immediately after emergence. Young queens may perform both nest and foraging duties prior to mating. Both sexes mate multiple times. Males will mount the queens in the air and continue coitus for several minutes on a nearby surface until kicked off by the female. Once mated, queens prepare for hibernation by eating and increasing vital fat body reserves. The colony declines in late October; workers, males, and the original queen die. The newly mated queens overwinter in small cells in the soil in preparation for spring. (Adapted from Alford 1975 and Thorp et al., 1983).
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Bombus melanopygus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 39
Species With Barcodes: 1
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Conservation

Conservation Status

Unknown (Cane and Tepedino 2001).
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National NatureServe Conservation Status

Canada

Rounded National Status Rank: NU - Unrankable

United States

Rounded National Status Rank: N4 - Apparently Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Ranking is confounded by widely disparate ranges given in recent references and limited information found for the northern parts of the range or from relatively natural habitats. Apparently though this bumblebee, as defined here, is fairly common from at least British Columbia well into California. It can persist well in urban parks and farmland. It possibly is somewhat of a local floral specialist near San Francisco, but unlike some bumblebees, the abundance of B. melanopygus is apparently not negatively correlated with that of B. vosnesenskii there. It is not certain how widely either of these observations from McFrederick and LeBuhn (2005) apply away from San Francisco. While more information would likely resolve the rank to G5, for now the species is ranked G4G5, apparently to demonstrably secure. If recognized as a subspecies, B. melanopygus edwardsii from much of the US range would probably rank T4, perhaps T5.

Environmental Specificity: Unknown

Comments: A generalist for nesting sites, but may be more specialized than usual in terms of floral visitation. McFrederick and LeBuhn (2005), in the San Francisco area, found this species only in study sites with Ceanothus thrysiflorus which these bees commonly visited.

Other Considerations: McFrederick and LeBuhn (2005) found abundance of B. melanopygus to be unaffected by that of the superabundant B. vosnesenskii. They suggest this could be because B. melanopygus can nest either below ground (often old rodent nests) or above ground, e.g. in old bird nests and so is less affected by competition from that species than are species that nest only below ground. However, in the San Francisco area they found this species only in study sites with Ceanothus thrysiflorus.

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Global Short Term Trend: Relatively stable (=10% change)

Comments: This is one of the few bumblebees still found regularly in San Francisco and is rather common in the Willamette Valley in Oregon, so it is apparently tolerant of urban and agricultural environments. Little information was found regarding more northern parts of the range but this species is not listed as in general decline by Xerces Society or others and is regarded as common in British Columbia.

Global Long Term Trend: Unknown

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Threats

Degree of Threat: Unknown

Comments: Apparently does rather well in some agricultural areas and can survive in cities to some extent. This subgenus is not suspected to be impacted by exotic diseases or parasites.

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Wikipedia

Bombus melanopygus

Bombus melanopygus, the black-tailed bumblebee,[1] is a species of bumblebee native to western North America from British Columbia to California, and as far east as Idaho.[2]

In the southern part of its range, the third and fourth segments of the abdomen are black instead of the red color seen in the northern populations, and this black color form was formerly known by the name Bombus edwardsii.[3]

References

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Names and Taxonomy

Taxonomy

Comments: Subgenus: Pyrobombus

Currently Bombus "edwardsii" is included in this species and it has been treated as a subspecies or a mere color form which would have no taxonomic standing. The analyses by Owen et al. (2010) support conspecificity.

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