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Extracted from: Milliron H.E., (1973). A Monograph of the Western Hemisphere Bumblebees (Hymenoptera: Apidae; Bombinae). The Entomological Society of Canada, No. 89.
Description. Queen. Length, 18.5 mm; width at wing bases, 9.0 mm; abdomen, 9.5 mm, width across T2, 9.5 mm; front wing length, 14.5 mm, width, 5.0 mm. Head: Frontal outline (excluding mouthparts) rather narrowly trapezoidal, above weakly arcuate, the temples evenly rounded, medially about as high as widest dimension; vertical region weakly concave, moderately sloped toward occiput and for the most part rather densely covered with small and medium punctures; ocelli situated in a weak arc just below the supraorbital line, about equal in size and separated from one another by distinctly less than their diameters; compound eyes notice ably more broadly rounded below than above, their inner margins nearly parallel except becom ing convergent above; malar space nearly l i times longer than distance between (and including) mandibular articulations, irregularly weakly convex, with sparse irregular small somewhat oval punctures; labrum about 2i times wider than median thickness, the ventral margin nearly straight except rounded at lateral corners, the weakly arcuate shelf moderately sharp, close to ventral margin and transversely extended beyond middle of transversely rather arcuate tubercles which are well but not sharply separated, mostly medium punctate and have somewhat conical and slightly elevated mesal summits; flagellum nearly twice as long as scape, FI little more than li times longer than rectangular F2, slightly longer than F3 and about 2/3 the combined lengths of F2 and F3; clypeus rather strongly and evenly convex, the approximate upper half noticeably more densely covered with both medium and small punctures than lower half especially medially below, at broadest part near base about l i times wider than median height. Legs: Mesobasitarsite rectangular except at very base and distal end, the outer surface nearly flat, little more than 3 times longer than widest part which is about equal to longest hairs of posterior fringe, the sharply acute distoposterior angle extended noticeably beyond the blunter distoanterior one with a moderately deep emargination between; widest part of hind tibia about equal to length of longest hairs of posterior fringe, the outer surface (corbicula) for the mostpart rather strongly and evenly convex longitudinally and microscopically alutaceous (or granulose); metabasitarsite with outer surface broadly and shallowly concave, the widest part nearly twice as broad as the length of the longest hairs in the posterior fringe, the posterior margin weakly arcuate near base, straight beyond, the acute distoposterior angle extended noticeably beyond the blunt (near right angled) distoanterior one with very shallow gradual emargination between. Pubescence: Fine, of medium length and density, somewhat longer on vertex, much of the scutellum and on abdominal T4-5, the distal margins of most abdominal sterna with longer pile than elsewhere on sterna; mesobasitarsal posterior fringe longest near base, gradually becoming short distally; most hairs of corbicular fringe rather long, the fringe not dense, the hairs straight or nearly so except for a few arched distal ones; metabasitarsal posterior fringe of medium length near base becoming very short distally, not dense, most hairs slightly curved. Color: Black, except thoracic pleura, a trace on the pronotal lobes and along posterior margin of the pronotum, a trace along extreme anterior margin of scutum (cf. under Comments), along posterior margin of the scutellum, and on abdominal Tl-2 and most of T3 yellow, most of the abdominal yellow of a slightly deeper shade, and posterior margin of the fifth abdominal segment fringed with burnt sienna which covers all of segment six. Wings uni
formally moderately infumated with brownish black.
Worker. Length, 12.5 mm; width at wing bases, 6.5 mm; abdomen, 6.0 mm, width across
T2, 6.5 mm; front wing length, 10.0 mm, width, 3.5 mm. Aside from differences in size, essentially like the queen except the following principal points are notable: Head has a less punctate clypeus, the malar space appears very slightly longer in relation to the distance between (and including) mandibular articulations, the lateral ocelli touch the supraorbital line and FI is comparatively slightly longer. Color pattern is the same as that of the queen except that traces of yellow on the pronotum and anterior margin of the scutum are (usually) variable from faint to being entirely absent as is the yellow along the posterior margin of the scutellum; sometimes there is a noticeable admixture of black hairs beneath the wing bases and on the metapleura; the yellow on the thoracic pleura and abdominal Tl-3 is as pale as that on the thoracic pleura of the queen or even more so, and sometimes the burnt sienna on the distal margin of abdominal T5 is replaced by black at least laterally (cf. under Comments). Wings are somewhat paler than those of the queen.
Male. Length, 12.5 mm; width at wing bases, 6.0 mm; abdomen, 6.0 mm, width across T2, 6.0 mm; front wing length, 11.0 mm, width, 3.7 mm. Head: Frontal outline (excluding mouthparts) trapezoidal, its widest part about equal to the median height, nearly straight across the vertex, the temples somewhat abruptly rounded; vertical region nearly flat, not strongly inclined toward occiput, moderately well covered with small punctures; ocellar half of ocello- cular area mostly smooth, the ocular half with some small punctures; ocelli positioned in a weak arc, removed from one another by about their diameters, the lateral ones at least touching the supraorbital line; compound eyes more broadly and evenly rounded below than above, slightly bulging, their inner margins mostly parallel except converging above; malar space un evenly convex with some small punctures especially over lower half, little longer (if any) than distance between (and including) mandibular articulations; labrum little more than twice as wide as median thickness, its ventral margin for the most part weakly arcuate, the weak callosi ties flattened, with few punctures, not sharply divided by a strong depression; clypeus with median height nearly equal to widest part near base, moderately and rather evenly convex, wellcovered with small and medium punctures which are sparser medially on the lower half; flagellum between 5 and 6 times longer than scape, with most segments slightly crenulate, FI little longer than quadrate F2 and at most only slightly more than i of F3, FI and F2 combined little (if any) longer than F3. Legs: Mesobasitarsite narrow, subrectangular, about 31 times longer than broadest part which is as wide as the longest hairs of the posterior fringe, the outer surface shallowly concave longitudinally, the subacute distoposterior angle extended consider ably beyond the more or less rounded distoanterior one, with a weak emargination between; outer surface of hind tibia rather evenly convex longitudinally, shining and somewhat sparsely pubescent, the widest part not quite equal to length of longest hairs of posterior fringe; metabasi- tarsite nearly rectangular, with rather strong (posterior) angle at the base, for the most part'at least about H times wider than most of the longer hairs of the posterior fringe, the outer sur face broadly and shallowly concave longitudinally, shining, covered with fine recumbent pubescence, the distal end subtruncate {i.e., with a shallow emargination between the two equally extended, more or less rounded distal angles). Pubescence: Fine and rather even like that of the female but somewhat looser and not as dense, especially on the abdomen. Genitalia, seventh and eighth abdominal sterna (PI. XV) are representative of this taxon (cf. under Comments). Color: Head black except a noticeable amount of light yellow on lower portion of gena (cheek) and fine intermixed paler hairs on the face; pattern on thorax like that of the worker, the dorsum almost totally black, there being only a faint trace of yellow on the pronotum, the extreme anterior margin of the scutum and along the posterior margin of the scutellum, the thoracic pleura almost completely light yellow with only very few black hairs beneath tegulae; abdominal Tl-2 and most of T3 (which has few black hairs at the sides) deeper yellow than that on thoracic pleura, T4 black, T5 black except its distal burnt sienna fringe (also the corresponding sternum distally) which is also the color on T6 and all of seg ment 7, the abdominal sterna 2-5 with black or blackish pile and longer more pallid distal fringes. Wings less deeply infumated than those of the queen but similar in color to those of the worker.
Bombus nigrodorsalis montezumae subspecies of Bombus weisi
Description. Queen, Worker. Size and structure like those of the corresponding females of the nominate subspecies except the queen of this subspecies (usually) is more extensively and coarsely punctate on the clypeus, and the outer surface of the hind tibia is often more noticeably alutaceous or granulose; the same differences might frequently also apply to the worker. Color: Pattern as in the nominate subspecies except that the yellow on the pronotum is reduced to a mere trace along the posterior margin and sometimes a very few yellow hairs at the anterolateral corners of the scutum; the yellow along the posterior margin of the scutellum is often more reduced than that in the nominate subspecies and at most only a very few black hairs occur just below the tegulae (or wing bases) and on the metapleura; the yellow of the abdominal pattern most often is concolorous with that on the thoracic pleura; while abdominal T1 is entirely yellow, T2 sometimes has a noticeable admixture of black hairs toward the sides, T3 has at least the approximate lateral fourth entirely black (the median yellow part on this tergum typically is broader basally and narrowly rounded distally, cf. under Comments), T5 like 4 is entirely black, a noticeable amount of black occurs on the ultimate abdominal segment especially basally, and the abdominal venter is black except for the last sternum (hypopygium) which is (like the epipygium) at least predominantly covered with burnt sienna pubescence. Wings sometimes slightly lighter than those of the nominate subspecies especially in the queen.
Male. Structurally (including size) like the corresponding sex of the nominate subspecies. Genitalia, seventh and eighth abdominal sterna similar to those representing the nominate sub species (PI. XV) (cf. under Comments). Color: Pattern (including color) like that of the nominate subspecies except that there is no trace of yellow on the extreme median anterior margin of the scutum and yellow on the scutellar posterior margin is either reduced or absent; the yellow on the abdominal terga (1-3) is usually paler than that of the nominate subspecies, is much reduced on T3, and T4 is black as is T5 entirely, T6 and at least much of T7; abdominal venter black. Wings slightly paler than those of the nominate subspecies.
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