|
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, 24.0 mm; width at wing bases, 11.0 mm; abdomen, 12.0 mm, width across T2, 12.0 mm; front wing length, 19.5 mm, width, 7.5 mm. Head: Frontal outline (excluding mouthparts) trapezoidal, a little higher medially than widest dimension, the upper angles at temple broadly rounded, between them the occiput nearly straight; vertical region for the most part nearly flat and inclined toward occiput, mostly covered with medium punc tures; compound eyes noticeably more broadly rounded below than above, their inner margins subparallel to weakly convergent above; ocelli somewhat closer together than their diameters, located in a weak arc just below the supraorbital line; little less than ocellar half of ocellocular area smooth, remainder of this area covered with small punctures to vague microscopic puncta- tion; malar space about as long as distance between (and including) mandibular articulations, rather evenly convex and smooth except for few minute punctures; labrum nearly twice as wide as thick, with its ventral margin and prominent shelf rather evenly arcuate, extending to about the middle of tubercles which are flattened ventrally, mesially moderately conical, irregularly
punctate and well separated by a rather deep intertubercular depression; flagellum about If times longer than scape, FI nearly If times as long as subquadrate F2 and distinctly longer than F3, being about 2/3 as long as F2 and F3 combined; clypeus rather evenly and strongly convex, approximately 1/3 wider near base than median height, covered for the most part with small and medium punctures which are sparser medially below. Legs: Mesobasitarsite subrectangular, nearly 4 times longer than widest part, its outer surface rather shallowly concave longitudinally, the spinate distoposterior angle considerably extended beyond the blunt distoanterior angle, only a shallow emargination between; outer surface of hind tibia (corbicula) alutaceous and not smooth and especially polished, for the most pare broadly and weakly convex longitudinally, widest part considerably broader than length of longer hairs comprising the posterior fringe; metabasitarsite with its outer surface rather deeply and broadly concave longitudinally, the posterior margin of segment arcuate only near base, virtually straight beyond to distal end, the distal angles similar to those of the mesobasitarsite but the emargination between is wider and deeper. Pubescence: That on head and abdomen looser and somewhat longer than the rather short, even, fine, and very dense thoracic pile especially on dorsum; basal half of mesobasitarsal posterior fringe of medium length (longest hairs scarcely as long as widest part of the segment) diminishing in length to becoming very short at distal end; metabasitarsal posterior fringe with only a few longer hairs (longest not more than £ as long as widest part of segment) near base, beyond becoming short to very short at the distal end. Color: Head, thoracic pleura below line from bases of hind wings forward, legs, abdominal Tl, T2 (except trace of yellow mid-basally), T4-6 and entire venter black; entire thoracic dorsum, few hairs mid-basally on abdominal T2 and all on T3 a rich golden yellow (sometimes more pallid to nearly lemon yellow, cf. under Comments). Wings rather uniformly infumated with brownish black, with a somewhat violaceous luster under certain lights.
Worker. Length, 15.0 mm; width at wing bases, 8.0 mm; abdomen, 8.0 mm, width across T2, 9.0 mm; front wing length, 16.5 mm, width, 6.0 mm. Except for its smaller size, much like the queen; often the corbiculae are more shiny. Generally, the yellow pattern is more pallid and might even approach a straw or canary yellow (cf. under Comments).
Male. Length, 17.5 mm; width at wing bases, 8.5 mm; abdomen, 9.0 mm, width across T2, 8.0 mm; front wing length, 17.0 mm, width, 5.5 mm. Head: Frontal outline (excluding mouth- parts) rather narrowly trapezoidal, little higher medially than its widest part, the upper angles rather evenly rounded, the occiput only weakly arcuate; vertical region nearly flat, not strongly sloped and for the most part covered with medium punctures; ocelli positioned in nearly a straight line just below the supraorbital line, removed from one another about as far as their diameters; ocellocular area mostly smooth with only small or obscure punctures in the ocular half; com pound eyes only little more broadly rounded below than above, their inner margins almost parallel; malar space about as long as distance between (and including) mandibular articulations, evenly convex and for the most part covered with minute punctures; labrum irregularly flattened, its ventral margin nearly straight, little more than twice as wide as its median thickness, the callosities much reduced and inconspicuous; flagellum at least 4i times longer than scape, most of its segments distinctly crenulate, FI about 2/3 as long as rectangular F2, the combined lengths of these segments only a little more than that of F3. Legs: Mesobasitarsite narrowly subrec tangular, its outer surface longitudinally concave, the distal end virtually truncate; metabasitarsite subrectangular, the posterior margin weakly arcuate near base and beyond nearly straight, its outer surface for the most part rather deeply concave longitudinally, the distal end subtruncate (with only a shallow emargination between the distal angles). Pubescence: Relatively short, dense, and rather even throughout except somewhat longer and looser on most of the scutellum; mesobasitarsal posterior fringe of medium almost even length throughout; posterior fringe on hind tibia medium in length, dense and even; metabasitarsal posterior fringe sparse, short, and of rather even length throughout. Genitalia (not figured) similar to that of M. (M.) brasiliensis (Lep.) (PL XIV) but differ from that by possessing several distinctive features principal among which are the following: The distal end of the squama is sharply truncate; the end of the mesal process of the squama is more or less curved upwardly; the distal end of the volsella projects much farther beyond the squama and its mesal process is much more prominent; the ectal margin of the sagitta is more sharply angulate medially and the sagittal head is longer. Some of the features above (e.g., those pertaining to the mesal process of the squama, the volsella, and the sagittal head) are similar to the condition found in the genitalia of M. (M.) opifex (Sm.) (cf. that species, also on PI. XIV). The shape of the seventh abdominal sternum resembles that of brasiliensis but is distally evenly rounded and this sternum bears more prominent hairs; the shape of the eighth abdominal sternum also resembles that of brasiliensis but the more heavily sclero- tized arms from the base converge medially and terminate with the formation of two separate, less sclerotized small elongate oval spots (similar to the condition found in M. (M.) morio (Swed.), also on PL XIV, but larger). Color: Face predominantly pale yellow intermixed with some black hairs, remainder of head largely golden-yellow except for a few intermixed black hairs on the vertical region; thoracic dorsum, as well as thoracic pleura anterior to hind wing bases, trace mid-basally on abdominal T2 and all of T3-4 golden-yellow; remainder of thorax, legs, and remainder of abdomen (except usually some dull pallid hairs along distal margins of the abdominal sterna) black. Wings infumated as deeply as in the other castes, at most only slightly less so.
Comments. Except for size differences, especially in the worker caste where the smallest specimens might not be much more than one-half the given length, few minor morphological inconsistencies have been noted; likewise, the color pattern is very stable except that on some few queens (and possibly true of some workers as well) I have detected a small trace of yellow distolaterally on abdominal T l, and on the same specimens the narrow patch of yellow extends across most of the very base of T2. This species is one of the easiest to identify.
|
