Reprinted with permission of the American Entomological Society from:
LaBerge, W. E. 1971b. A revision of the bees of the genus Andrena of the Western Hemisphere. Part IV. Scrapteropsis, Xiphandrena, and Rhaphandrena. Transactions of the American Entomological Society 97: 441-520.
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Andrena nigra is a relatively primitive member of the Scrapteropsis and is related to the imitatrix-morrisonella group of species from which it can be distinguished in both sexes by its dark vestiture and by the densely punctate scutellum and mesoscutum. Among the other species of Scrapteropsis only Andrena phenax Cockerell has entirely dark vestiture, and it is known only in the female sex. The female of nigra can be readily separated from that of phenax by the densely punctate mesoscutum. The male of nigra has pale dorsal thoracic hairs, but is separable from the group to which phenax belongs (the stipator group) by the densely punctate mesoscutum and relatively densely punctate terga. Both sexes of nigra are distinctive in the narrow, pointed, spear-shaped galeae.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 11-14 mm; width, 3.0-4.5 mm; wing length, M = 3.93 ± 0.157 mm; FL/FW, M = 1.00 ± 0.004; FOVL/FOVW, M = 2.83 ± 0.030.
INTEGUMENTAL COLOR. — Black except as follows: mandible with apical half dark rufescent; flagellar segments dark brown to dark reddish-brown below; wing membranes moderately infumate, brownish, veins dark brown to black; pronotum often rufescent; terga often rufescent basally; sterna rufescent basally; distitarsi dark rufescent, femora usually dark rufescent.
STRUCTURE. — Antennal scape length equals first four flagellar segments; flagellar segment 1 as long as segments 2 plus 3; segment 2 slightly longer than 3 and equal to 4; segments 2-4 each broader than long, segments 5-9 quadrate. Eyes each about one and three-fourths as long as broad, inner margins parallel. Mandible bidentate, short. Galea narrow, acutely pointed, spear-shaped; surface dulled by fine reticular shagreening. Maxillary palpus surpasses galea by last two segments or more, segmental ratio about as 0.8:1.0:0.9:0.9:0.8:0.8. Labial palpus with first segment much flattened, slightly curved; segmental ratio about as 1.0:0.8:0.6:0.6. Labral process trapezoidal, narrowed and thickened in apical half, emarginate apically, basal half concave with fine transverse striations; labrum below process convex, with elongate punctures and several short, indistinct cristae. clypeus with deep round punctures separated mostly by half a puncture width, median impunctate line absent or extremely narrow, surface shiny. Supraclypeal area dulled by minute crowded punctures. Face above antennal fossae with coarse longitudinal rugae and coarse interrugal punctures. Facial fovea broad, shallow, narrowed below but not abruptly, above separated from lateral ocellus by less than half an ocellar diameter. Vertex above lateral ocellus equals about one ocellar diameter, dulled by abundant round punctures and fine tessellation. Genal area in profile slightly broader thane ye (about as 6:5); surface with abundant round punctures separated by half to one puncture width, shiny, weakly shagreened posteriorly.
Pronotum without dorsoventral ridge or humeral angle, with small punctures and fine reticular shagreening; moderately shiny dorsally. Mesoscutum with crowded small punctures separated by half a puncture width or less and fine reticular shagreening dulling surface. Scutellum and metanotum similar to mesoscutum. Propodeum with dorsal enclosure with irregular rugae forming irregularly shaped areola, without transverse ruga posteriorly; dorsolateral and posterior surfaces with small crowded punctures and fine tessellation; lateral surface with abundant punctures separated by one or more puncture widths and coarse tessellation. Mesepisternum with distinct round punctures separated by half to one puncture width and fine tessellation. Pterostigma about as broad as from inner margin prestigma to wing margin; second submarginal cell receives vein first m-cu in outer half to third; vannal lobe hind wing broad, long. Tibial spurs normal; hind femur without ridge on posterior surface.
Metasomal tergum 1 with deep round punctures separated mostly by one to one-half puncture widths except in narrow apical impunctate rim, surface shiny, unshagreened but often with sparse weak longitudinal striae. Terga 2-4 similar but punctures more crowded. Pygidial plate broad, with broadly rounded apex, internal raised triangular area weak to absent. Sterna 2-5 with narrow apical areas impunctate, basal areas with small punctures separated by half to one puncture width, surfaces shiny, shagreening weak or absent.
VESTITURE. — Entirely black to dark brown. Thoracic dorsum with hairs irregular in length but mostly short; terga without apical fasciae. Pollen-collecting hairs typical for subgenus, internal corbicular hairs simple.
MALE. . MEASUREMENTS AND RATIOS. — N = 12; length, 10-12 mm; width, 2.5-3.0 mm; wing length, M = 3.73 ± 0.112 mm; FL/FW, M = 1.05 ± 0.008; FS1/FS2, M = 1.13 ± 0.033.
INTEGUMENTAL COLOR. — Black with same exceptions as female but tergal apical areas usually slightly translucent.
STRUCTURE. — Antenna short, not surpassing midscutellum; scape length equals first two and one-half flagellar segments; flagellar segment 1 usually slightly longer than segment 2; segment 2 slightly shorter than 3, quadrate to slightly longer than broad; segments 3-11 longer than broad. Eyes each about two and one-half times as long as broad, inner margins converging slightly toward mandibles. Mandible and galea as in female. Maxillary palpus as in female but segmental ratio about as 0.7:1.0:0.8:0.8:0.7:0.8. Labial palpus as in female but ratio about as 1.0:0.7:0.6:0.7. Labral process as in female but broader and more deeply emarginate apically; labrum below process convex, shiny. Clypeus as in female but without trace of median impunctate line. Supraclypeal area, face above antennal fossae and vertex as in female. Genal area in female but with longitudinal striations posteriorly.
Thoracic form and sculpturing as in female except as follows: propodeum with lateral surface duller with more crowded punctures. Wing venation, tibial spurs and hind femora as in female.
Metasomal terga 1-5 sculptured as in female terga 1-4 but punctures separated largely by two or more puncture widths; tergum 2 with punctures separated by one to one and one-half puncture widths or slightly more. Tergum 7 with extremely narrow, pointed pygidial area. Stern 2-5 with apical areas impunctate; basal areas with punctures separated by one to two or more puncture widths; surfaces shiny, shagreening weak to absent. Sternum 6 flat, with deep apical emargination.
Terminalia (Figs. 11-15) similar to those of imitatrix but note the following: sternum 6 with apical bidentate area narrower; sternum 8 with more rounded apex and longer hair; gonocoxite with dorsal lobes straight, not curving outward.
VESTITURE. — Black to dark brown except thoracic dorsum with long white or cinereous hairs but often with some brown hairs posteromedially on mesoscutum and medially on scutellum. Terga without apical fasciae; sterna 2-5 with subapical fimbriae of short plumose dark brown hairs.
TYPE MATERIAL. — The holotype female of nigra was collected at Los Angeles, California, by Coquillett, and is in the collection ofhte Provincial Museum, Quebec, Canada. The holotype male (PHT) of griseonigra was collected in Los Angeles, California, by Davidson. The holotype female (PHT) of subtristis was taken in Los Angeles, California, by Davidson.
DISTRIBUTION. — This species ranges from Baja California north to central California. One female from "Catalina Mts." in Arizona, collected on June 26, 1917 by Oslar, may be mislabeled (see Thorp, 1970). In addition to the types listed above, 75 females and 11 males have been examined from localities listed below (including type localities).
MEXICO. — BAJA CALIFORNIA DEL NORTE: La Zapopita (4 mi SW in Valle de Trinidad). UNITED STATES. — ARIZONA: Catalina Mts. CALIFORNIA: Antioch; Beaumont; Carpenteria; Claremont; Indian Wells Canyon, Kern Co.; Kramer Hills, San Bernardino Co.; Jacolitas Canyon, Fresno Co.; Llano (and 5 mi SE); Lone Pine; Los Angeles; Panoche Canyon (25 mi SW of Mendota); Panoche Hills, Merced Co.; Sage (5 mi S); San Diego; San Francisco; Temecula (9 mi E).
FLORAL RECORDS. — Andrena nigra has been collected most frequently from flwoers of Phacelia sp., but too few records are available to state flower preferences more precisely. It has been collected from flowers of Layia platyglossa, Malacothrix sp., Phacelia sp., P. distans.