Reprinted with permission from the University of Nebraska State Museum from:
Ribble, D. W. 1968. Revisions of two subgenera of Andrena, Micrandrena Ashmead and Derandrena new subgenus (Hymenoptera: Apoidea). Bulletin of the University of Nebraska State Museum 8: 1-124.
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Ashmead (1899) described Micrandrena in a key to genera, and listed pacifica as the type and only included Species. His description of Micrandrena constitutes the description of pacifica. Later Cockerell (1909) described pacifica in a conventional manner. In 1932 Cockerell recognized pacifica as a synonym of melanochroa, and Linsley (1951) on the authority of Timberlake placed vagans in synonymy. Andrena fragariana (from Wisconsin) now also is considered a synonym of melanochroa (from Washington). I have been unable to separate the eastern and western specimens of this species. Two or three east-west trends exist (see Variation).
Andrena melanochroa is one of the most easily recognized Micrandrena as determined specimens indicate. Only occasionally do specimens bear names other than melanochroa or one of its synonyms. Andrena melanochroa is a small, entirely dark species with a distinctly punctate clypeus. The enclosure of the propodeum is entirely covered with distinct and relatively coarse rugulae. The female has a rather narrow hind tibia for Micrandrena with long scopal hairs. The male can be distinguished by the dark clypeus, short, dull antennae, and the large, distinctive genital capsule (figs. 54-56).
The descriptions below are based mainly on a female (May 21, 1922, Elsie M. Foster) and a male (May 25, 1933, H. B. James) from Boulder, Colorado. A total of 231 specimens of melanochroa were examined during this study. No series contain more than a few specimens. However, Knerer and Atwood (1964) state this species can be, at least locally, very much more abundant than pinned specimens indicate.
FEMALE. MEASUREMENTS AND RATIOS. — Length, 6.0 mm; width of mesothorax, 1.9 mm; wing length from tegula, 5.0 mm; facial length/width, 1.1; foveal length/width, 3.20.
INTEGUMENTAL COLOR. — Black to dark brown (without reflections of other colors) except: veins and pterostigma amber; tegula amber; terga with wide amber apices; sterna with narrower amber apices; color otherwise as in piperi.
STRUCTURE. — Sculpturing in general finer over entire body than in piperi. Head otherwise as in piperi except: scape reaching to one ocellar distance from middle ocellus, nearly as long as flagellar segments 1-5; flagellar segment 1 slightly shorter than 2 and 3 combined; eye about four times as long as broad in anterior view; galea relatively slender; maxillary palpus with segments in ratio of about 1.5:1.7:1.5:1.3:1.0:1.3, apical half of segment 5 and segment 6 extending beyond galea; labial palpus with segments in ratio of about 2.0:1.2:1.0:1.2; labrum about four times as wide as long; labral process slightly more than half as wide and two-thirds as long as entire labrum, evenly rounded from side to side; clypeus about one and one-half times as wide as long, protruding beyond lower margin of eye by about width of eye in lateral view, apically punctures more distinct, apically surface very shiny and shagreening very weak; surface between ocelli about as shiny and rough as surface above fovea; facial fovea reaching upper eye margin.
Mesosoma as in piperi except: metanotal surface rougher than mesoscutal; enclosure of propodeum with surface covered with small irregular rugae; posterior and lateral surface of propodeum not separated by carinae, posterior and dorsolateral areas not raised above enclosure, shagreening rough like metanotal surface; corbicular surface with few indistinct punctures, shagreening less granular, more even and further apart than on dorsolateral area; hind tibia slightly broadened; pterostigma moderately large; first transverse cubital vein ending about three vein widths from pterostigma.
Metasoma as in piperi except pygidial plate raised in center, edges not turned upward.
VESTITURE. — Hairs as in piperi except: tarsal hairs all white; hairs on dorsum of thorax long, not moss-like; terga 1-4 hairs (except for apical fasciae) longer, mostly simple, abdomen not having a dusty appearance; apical fasciae absent on tergum 1, weak, broadly interrupted medially on terga 2-4.
MALE. MEASUREMENTS AND RATIOS. — Length, 6.0 mm; width of mesothorax, 1.5 mm; wing length from tegula, 4.5 mm; facial length/width, 1.1; flagellar segment 1/segment 2, 2.41.
INTEGUMENTAL COLOR. — Black to dark brown (without reflections of other colors) except: clypeus entirely dark; color otherwise as in piperi.
STRUCTURE. — Sculpturing in general finer over entire body than in piperi. Head otherwise as in piperi except: scape nearly as long as flagellar segments 1-4; segment 1 slightly more than twice as long as 2, half again as long as 3; segment 2 tapered slightly toward base; ultimate segment slightly more than one and one-half times as long as wide; eye four times as long as broad in anterior view; maxillary palpus with segments in ratio of about 1.2:1.3:1.3:1.2:1.0:1.8; labial palpus with segments in ratio of about 2.2:1.5:1.0:1.7; labrum nearly three times as wide as long; labral process expanded towards base, apex truncated; clypeus half again as broad as long, apically punc¬tures more distinct, apically surface very shiny and shagreening absent.
Mesosoma as in melanochroa female except: propodeum with lateral surface sculptured about like dorsolateral surface, shagreen¬ing coarser and more irregular than on metepisternum; hind tibia unmodified.
Exposed metasoma as in piperi.
Sternum 7 distinctly emarginate at apex, producing two large rounded lobes, each bearing numerous long, branched setae (fig. 57). Sternum 8 (fig. 58) much like piperi except basal plate slightly different in outline. Genital capsule very large for size of bee. Gonocoxite bent downward; apex expanded in lateral view, elongate, dorsolateral part with many, mostly branched setae, ventral part with few minute, simple setae; dorsal lobes reduced in size. Penis valve bent downward, apex narrowly rounded in lateral view, medially greatly expanded (figs. 54-56).
VESTITURE. — Hairs as in piperi except apical abdominal fasciae absent on tergum 1.
VARIATION. — Cockerell (1932) in separating vagans from fragariana and melanochroa (now all three names are considered synonyms) indicates some of the variation found in this species. He uses several color characters: antennal, to veal hairs, stigma, tegula and hind tarsal hairs. Pinned specimens fade from black to reddish in time; the color variations described by Cockerell are due mostly to aging and is unreliable in separating populations. The variation in foveal width and in the lower ends of the foveae that Cockerell describes does not seem to exist. A third group of characters that Cockerell uses are considered mostly individual variation. The lower part of the clypeus may be smooth or have very fine reticular shagreening between the punctures. There is a little variation in the size and configuration of the rugulae on the enclosure of the propodeum (as there is all species in the piperi group). Head width and total length both indicate overall size. Within any population there is a little variation in size, and there is an overall tendency for material from the western part of the range to be larger in size. In summary some material from Boulder (type locality for vagans) could be placed in what Cockerell considered fragariana or melanochroa on the basis of the characters he used in separating the three.
Boulder specimens appear to have a more slender galea than specimens from other parts of the range; those from the western part of the range appear to have the widest galea. The rolling of the galea makes this character hard to quantify. The labral process varies a lot in size in the female, and considerable variation is found in the same population. In general specimens from Boulder (including the female described above) tend to have the smallest processes while specimens from the western part of the range tend to have the largest processes.
Reprinted with permission from: Mitchell, T.B. 1960. Bees of the Eastern United States. North Carolina Agricultural Experiment Station Technical Bulletin No. 141.
Andrena (Micrandrena) melanochroa fragariana Graenicher
FEMALE — Length 6 mm.; face slightly longer than broad; clypeus broadly convex, projecting about one-third below suborbital line, smooth, somewhat shining, punctures very minute and obscure, well separated where clearly visible; facial foveae narrow, occupying about half of space between eyes and ocelli, covered with yellowish-white tomentum; space between margin of vertex and lateral ocelli no more than half their diameter; cheeks slightly narrower than eyes, rounded posteriorly, surface obscured by short and rather dense pubescence; malar space lacking; basal segment of flagellum subequal to 2nd and 3rd combined; process of labrum very short, broadly semicircular, breadth three or four times its length; pubescence of head, thorax and legs short, rather dense, greyish; thoracic integument dull, rather densely tessellate, punctures of dorsum of thorax exceedingly minute and obscure, barely visible; pleura without visible punctures; dorsal area of propodeum nearly horizontal, broad, extensive, triangle quite densely granular; propodeal corbicula short and poorly developed, without an anterior fringe, greyish-white; trochanteral floccus rather short, whitish; hind tibiae broadened apically, width at apex about twice that of the basitarsi, scopa rather dense, composed of rather short, simple, whitish hairs; front and mid basitarsi slightly narrower than their respective tibiae; 2nd submarginal cell slightly shorter than 3rd, receiving 1st recurrent slightly basad of middle; abdominal terga dull, densely tessellate, practically impunctate, obscurely greenish, the apical impressed area rather narrow and shallow, becoming narrowly yellowish-hyaline along rims, discal pubescence extremely short, suberect, whitish, forming very narrow and thin, whitish, apical fasciae on terga 2-4, this rather widely interrupted on tergum 2, tergum 5 with a brownish, apical fimbria.
MALE — Length 5 mm.; clypeus broadly convex, projecting nearly one-half below suborbital line, smooth and somewhat shining; punctures rather deep, distinct and close beneath rather thin, whitish pubescence; space between margin of vertex and lateral ocelli no more than half their diameter; cheeks slightly narrower than eyes, rounded posteriorly, surface obscured by rather dense, whitish pubescence; malar space lacking; basal segment of flagellum slightly longer than 2nd segment, slightly shorter than 2nd and 3rd combined; process of labrum rather short and broad, apex rather broadly truncate; mandibles short, with a small but distinct, inner, subapical tooth, overlapping but very slightly; pubescence of head, thorax and legs entirely whitish; thoracic integument dull, quite densely tessellate, punctures of dorsum of thorax very minute and obscure, barely visible; pleura without visible punctures; dorsal area of propodeum quite extensive, nearly horizontal, triangle finely subrugose or granular; all basitarsi slender and elongate, considerably narrower than their respective tibiae; 2nd submarginal cell slightly shorter than 3rd, receiving 1st recurrent slightly basad of middle; abdominal terga smooth, but rather dull, microscopically tessellate, obscurely greenish, without visible punctures, apical depressed area occupying about one-third median length of discs, entirely black to the rims, discal pubescence very short, suberect and whitish, fasciae very poorly developed; apical portion of sternum 8 slender and elongate, sides nearly parallel, apex rather narrowly rounded; tip of penis valves extremely slender, base more bulbous but not excavated, gonocoxites rather slender, only slightly dilated apically, gonocoxal lobes very slightly produced, broadly rounded.
DISTRIBUTION — Minnesota to Nova Scotia, south to North Carolina and Georgia; March to July.
FLOWER RECORDS — Fragaria, Potentilla and Rubus.
Andrena (Micrandrena) melanochroa melanochroa Cockerell
This subspecies is recorded as A. vagans from Nova Scotia, visiting Fragaria, by Brittain and Newton (1934). There are no other eastern records of the typical form, however, and it is suspected that this is the subspecies fragariana.