Bombus


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  Bombias annotated checklist
Bombias
Back to tree Number of species in equal-area (611,000 kmĀ²) grid cells with an equal-interval blue scale.
3 species

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B. auricomus
B. auricomus worker visiting Trifolium.

Bombias
ecology and behaviour

 

HABITAT: Open grasslands and mountain meadows.

 

FOOD-PLANTS: Medium to long tongue-length bumblebees visiting medium to deep flowers.

 

NESTING BEHAVIOUR: Nests underground or on the surface. Larvae are reared in separate wax cells throughout their development, non-pocket makers except for the early broods.

 

MATE-SEARCHING BEHAVIOUR: Males have enlarged compound eyes relative to the females. They perch and race after potential mates (e.g. Hobbs, 1965; Schremmer, 1972).

 

Subgenus BOMBIAS Robertson
Bombias Robertson, 1903:176, type-species Bombias auricomus Robertson by original designation
Bombus (Bombias) Franklin, 1913:138
Bombus (Confusibombus) Ball, 1914:78, type-species Bombus confusus Schenck by monotypy
Bombus (Sulcobombus) Krüger, 1917:65, type-species Bombus confusus Schenck by subsequent designation of Sandhouse, 1943:602
Nevadensibombus Skorikov, [1923]:149, type-species Bombus nevadensis Cresson by subsequent designation of Frison, 1927:64
Confusobombus Skorikov, [1923]:156, type-species Bombus confusus Schenck by subsequent designation of Richards, 1968:214
Bremus (Boopobombus) Frison, 1927:59,62 (proposed as a section name but stated by Frison to include those forms considered by Franklin, 1913, to belong to the subgenus Bombias Robertson), type-species Bombias auricomus Robertson (= Bombus auricomus (Robertson)) by subsequent designation of Williams, 1995:339.

 

TAXONOMIC STATUS: For a discussion of why several former subgenera have been synonymised within this subgenus see Williams et al. (2008 [pdf]) .

 

Part of the bumblebee phylogenetic tree including all Bombias species from an analysis of DNA sequence data for five genes (Cameron et al. 2007 [pdf]). Values above branches are Bayesian posterior probabilities, values below branches are parsimony bootstrap values.

 

auricomus

confusus
nevadensis

 

Bombus (Bi.) confusus Schencksubgeneric listall names
confusus Schenck, 1859:135
paradoxus Dalla Torre, 1882:18
festivus Hoffer, 1882:80, not of Smith, 1861:152 (= B. festivus Smith)
16 names

TAXONOMIC STATUS: B. confusus and B. paradoxus differ in the colour pattern of the pubescence (e.g. Reinig, 1939: fig. 19). Rasmont (1988) reports that in north western Europe, the yellow-banded and white-tailed B. paradoxus occurs only as rare individuals within the population of predominantly unbanded and red-tailed B. confusus. In contrast, all of the individuals that I have seen from the disjunct population in Central Asia have the yellow-banded and white-tailed B. paradoxus colour pattern.

MORPHOLOGY: photos of male genitalia.

DISTRIBUTION: Palaearctic Region.

IUCN CONSERVATION STATUS: Preliminary assessment as VULNERABLE (Williams & Osborne, 2009) by criterion A2 (IUCN, 2001, 2008) that it has undergone a a substantial decline in area of occurrence and numbers of records in >50% of the range since 1950.

 

Bombus (Bi.) nevadensis Cressonsubgeneric listall names
nevadensis Cresson, 1874:102
5 names

TAXONOMIC STATUS: See comments on B. auricomus.

MORPHOLOGY: photos of male genitalia.

DISTRIBUTION: W Nearctic Region, E Nearctic border. A single queen of B. nevadensis has been reported from Hidalgo, Mexico, by Milliron (1971) and Hurd (1979), although the species is not included for Mexico by Labougle (1990).

 

Bombus (Bi.) auricomus (Robertson)subgeneric listall names
auricomus (Robertson, 1903:176 [Bombias]) examined
2 names

TAXONOMIC STATUS: B. nevadensis and B. auricomus have been regarded both as conspecific (e.g. LaBerge & Webb, 1962; Milliron, 1971; Thorp et al., 1983; Laverty & Harder, 1988) and as separate species (e.g. Franklin, 1913; Rasmont, 1988; Scholl, Thorp, Owen & Obrecht, 1992; Poole, 1996).

B. nevadensis from western North America was not mentioned in the original description of B. auricomus from Illinois (lectotype worker by designation of Milliron, 1971:78), although the latter was described using characters of morphology and of colour pattern. The two taxa have generally been distinguished on the basis of the extent of the black pubescence on the dorsum of the female thorax and laterally on the male gastral terga (e.g. Franklin, 1913).

The only study to investigate variation in characters used to distinguish the two taxa at a fine spatial scale in their area of overlap was by LaBerge & Webb (1962). They reported (p. 26) that 'Throughout the broad middle half of Nebraska nevadensis seems to be rather rare and most specimens, although referable to subspecies auricomus show some indication of intergrading with the typical subspecies [nevadensis] in the west. ... Many specimens from Nebraska in the range of the typical subspecies [nevadensis] show some tendency toward the darker coloration of subspecies auricomus.' They concluded that these variable bees are all parts of the same species.

Recently, Scholl et al. (1992) distinguished two groups of individuals on the basis of differing mobility morphs of five enzymes. The individuals in one enzyme group were all extensively dark-banded, and Scholl et al. associated these with the name B. auricomus. However, individuals in the other enzyme group, which Scholl et al. associated with the name B. nevadensis, apparently included not only the contrasting, extensively pale individuals (B. nevadensis), but also a few of the extensively dark-banded individuals (B. auricomus) similar to those in the first group (8/49 individuals had gastral tergum I almost completely black; 3/49 individuals had the scutellum predominantly black). Thus the enzyme evidence does identify two groups of individuals, but (1) these do not appear to correspond precisely to the two traditional colour groups; (2) some of the key areas likely to support intermediate or recombinant individuals still need to be sampled for enzyme variation (e.g. in the Dakotas, L. Day in litt.); and (3) inheritance of enzyme and colour states needs to be better understood, including the unusual enzyme morphs of the heterozygous bees (detected in 20/141 queens). They concluded that these bees represent two species.

A. Scholl (in litt.) reports a further intriguing morphometric study. A random subsample of 20 queens from the enzyme study was scored for 15 characters and analysed by linear discriminant analysis. This method seeks a combination of characters that best discriminates any two a priori sets, which in this case were three measurements of parts of the radial cell, eye and antenna. However, although this approach may be useful for discriminating previously recognised taxa, it does not necessarily provide evidence that they are separate species (it could also be used to discriminate morphological subsets within a single, variable population, e.g. among domestic dogs).

From an examination of 41 females, so far I have found only one subtle morphological character to distinguish eastern, banded bees (B. auricomus), on the one hand, from western unbanded (B. nevadensis) and banded (e.g. Vancouver Island) bees, on the other. This concerns the anterior part of a band of large punctures along the inner eye margin, dorsally opposite the ocelli, just before these punctures meet a more anterior, very dense patch of small punctures. The western bees have areas between the large punctures conspicuously shining, with few fine punctures and lacking microsculpture. In contrast, the eastern bees have these areas appearing rather dull, often with more of the fine punctures, and more particularly with a very fine, wrinkled or reticulate microsculpture. A similar difference may be present in the males, posterio-laterally to the ocelli, though the sample sizes available to me are too small to allow much confidence.

I regard these bees as two separate species. Evidence from comparisons of DNA sequences from the 16S gene is consistent with the two taxa being separate species (Cameron et al., 2007 [pdf]).

MORPHOLOGY: photos of male genitalia.

DISTRIBUTION: E Nearctic Region, W Nearctic border.

 

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