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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).
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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.
Bombus
(Bi.) confusus Schenck
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 Cresson
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)
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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