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Extracted by H. E Milliron. A Monograph of the Western Hemisphere Bumblebees (Hymenoptera: Apidae; Bombinae) II. The Genus Megabombus Subgenus Megabombus. The Entomological Society of Canada, Ottawa 1970. pp. 239-330.
Description. Queen. Length, 22.0 mm; width at wing bases, 10.5 mm; abdomen, 11.0 mm, width across T2, 12.0 mm; front wing length, 20.0 mm, width, 7.5 mm. Head: Frontal outline (excluding mouthparts) roundly trapezoidal, its widest dimension about equal to the median height, the temples evenly rounded, the vertex transversely weakly arcuate; vertical region unevenly flattened to weakly convex medially, for the most part covered with small (follicular) punctures, only moderately sloped toward occiput; ocellocular area with some microscopic to medium punctures, the ocellar half mostly smooth; compound eyes somewhat more broadly and evenly rounded below than above, their inner margins subparallel except evenly convergent above; ocelli rather small, placed closer together than the diameter of median ocellus in a weak arc well below the supraorbital line; ocellocular line about f the interocellar line; malar space shorter than distance between (and including) mandibular articulations, very weakly convex (irregularly so) and with only some microscopic punctures; labrum about twice as wide as its median thickness, its ventral margin mostly irregularly arcuate, the shelf rather sharp, prominent and arcuate, the tubercles subconical, flattened below and coarsely sculptured above, their sharp mesal summits well separated by a moderately deep intertubercular depression; flagellum about If times longer than scape, FI nearly equal to the combined lengths of F2 and F3, the latter noticeably longer than short rectangular F2; clypeus irregularly weakly convex being nearly flat medially below the middle and medially weakly convex above the middle, well covered with small and medium punctures. Legs: Mesobasitarsite subrectangular, little more than 3f times longer than widest part which is about equal to the length of longest hairs of the posterior fringe, the outer surface shallowly concave longitudinally, neither distal angles sharp the posterior one extended slightly beyond the anterior one, without any emargination between; outer surface of hind tibia with its distal half microscopically granulose, the proximal half less granulose and longitudinally rather sharply convex, the widest part of segment greater than length of longest corbicular hairs; metabasitarsite subrectangular, its outer surface broadly concave, the widest part more than twice that of the length of longest hairs of the posterior fringe, the posterior margin rather evenly but not strongly arcuate from base to distal end, the distal angles similar to those of mesobasitarsite. Pubescence: That on head and most of thorax fine, dense, short, and rather even except somewhat longer and looser posteriorly on the scutellum; that on most of the abdominal dorsum moderately short, dense, a little coarser, on most of T3-5 somewhat longer and looser; mesobasitarsal posterior fringe only moderately dense, composed of straight
(or nearly so) short hairs to those of medium length the latter confined to the proximal half of the posterior margin; hind tibial posterior fringe rather dense, short at proximal end of margin becoming rather long beyond then shorter distally, composed of weakly arcuate hairs except those distally are strongly arcuate; metabasitarsal posterior fringe not dense, composed of short straight stout hairs to those that are finer and of medium length, the latter along about the proximal half of margin. Color: Head black; thoracic dorsum golden-yellow except for a broad interalar black band, remainder of thorax black; legs black; abdominal Tl-2 golden-yellow, remaining terga rufescent (sometimes with a yellowish tinge), abdominal SI-2 black, the remaining sterna pale rufescent. Wings deeply and uniformly stained with brownish black with a slight violaceous reflection under certain lights.
Worker, Length, 14.5 mm; width at wing bases, 7.0 mm; abdomen, 6.5 mm, width across T2, 7.0 mm; front wing length, 13.0 mm, width, 5.0 mm. Except for size and a few minor differences (such as the clypeus tending to be more evenly convex) this caste is structurally and chromatically very similar to the queen; the wings are considerably less deeply stained.
Male, Length, 18.0 mm; width at wing bases, 8.0 mm; abdomen, 9.0 mm, width across T2, 8.0 mm; front wing length, 13.0 mm, width, 4.5 mm. Head: Frontal outline (excluding mouthparts) roundly trapezoidal, the widest dimension equal to median height, the narrow temples arcuately rounded, the vertex transversely nearly straight; vertical region nearly flat, only slightly inclined toward the occiput and well covered with small (follicular) punctures; ocelli medium in size, situated much closer together than their diameters in a weak arc that is well below the supraorbital line; ocellocular area narrow (not as wide as the diameter of a lateral ocellus), practically smooth; interocellar line nearly twice as great as the ocel locular line; compound eyes somewhat bulging, noticeably more widely and evenly rounded above than below, their inner margins straight and a little closer together above than below; malar space short, little more (if any) than half as long as the distance between (and including) mandibular articulations, smooth with a narrow transverse convexity ventrally; labrum little more than twice as wide as its median thickness, the ventral margin arcuate, the callosities weak and not well defined; flagellum about 2i times longer than scape, FI nearly f as long as the combined lengths of rectangular F2 and F3 the latter nearly H times longer than F2. Legs: Mesobasitarsite subrectangular, little more than 4 times longer than widest part which is about twice as wide as the length of longest hairs of the posterior fringe, the outer surface nearly flat, the distal angles both more or less rounded, the distoanterior one somewhat extended beyond the distoposterior one with a very shallow emargination between; outer surface of hind tibia only weakly convex, microscopically granulose to nearly smooth, the widest part of segment nearly equal to the length of longest hairs of the posterior fringe; metabasitarsite nearly rectangular, the outer surface weakly concave longitudinally, the distal end subtruncate, the widest part about I the length of longest hairs of the posterior fringe. Pubescence: Short, dense, fine, and even except somewhat longer distally on abdomen; mesobasitarsal posterior fringe short, moderately dense and even, consisting of mostly straight hairs; hind tibial posterior fringe moderately dense, for the most part long, composed largely of weakly arcuate hairs; metabasitarsal posterior fringe moderately dense, consisting of long straight to weakly arcuate hairs, those at the very base of margin and distally shorter and straighter. Genitalia and seventh and eighth abdominal sterna (PI. X V III). Color: Head black except face largely covered with fine yellowish intermixed with stronger black hairs, a few yellowish hairs intermixed on the vertex; thoracic dorsum tawny or pale brownish yellow except for a rather indefinite (black and yellowish mixed) interalar band of medium width, the thoracic pleura largely tawny yellow except for some black beneath wing bases and on the metapleuron, the thoracic venter black; legs black; abdominal Tl-4 tawny yellow with a faint rufescent tinge, T5-7 pale rufescent yellow, abdominal sterna 1-2 mostly dark (blackish) the remaining sterna pale rufescent yellow. Wings evenly stained with light brown, much paler than those of the queen or even those of the worker.
Comments. No significant morphological variability was detected among the females. I have seen only a single male of this species. A few remarks should be made concerning the coloration and pattern of females; the yellow is some times considerably brighter and the rufescent pile is sometimes very vivid and sometimes dull or even faded; the width and sharpness of the interalar black band varies to some extent especially in the worker caste. It is probable that the male is somewhat faded or it is a senile specimen and that normally individuals of this sex should appear at least somewhat brighter.
Franklin (1913: 143) stated “This species apparently has its closest ally in crotchiF. However, I am of the opinion that its closest relative is dentatus Handl. occurring in Southeast Asia; there are additional taxa in Central and South America that show similar affinities with other species of the Oriental Region.
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