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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This unusual bee from Texas and Oklahoma is closely related to A. atlantica. The female of unicostata differs from that of atlantica by having only one complete ventral ridge on the hind femur. by the more coarsely punctate terga and the less coarsely sculptured propodeum. The male of unicostata differs from that of atlantica by the longer first flagellar segment in relation to the second segment, the more finely sculptured propodeum (outside of the dorsal enclosure), and the more densely punctate terga. The males are also remarkable in that they exhibit a tendency towards having only two submarginal cells, a rare condition in the Scrapteropsis-Biareolina group of species.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 9-11 mm; width. 3.0-3.5 mm; wing length, M = 3.75 ± 0.106 mm; FL/FW, M = 1.06 ± 0.012; FOVL/FOVW, M = 4.38 ± 0.104.
INTEGUMENTAL COLOR. — Generally as in alleghaniensis but the hind tibial spurs testaceous to rufescent.
STRUCTURE. — Antennae with scape distinctly shorter than first four flagellar segments, otherwise as in imitatrix. Structure and sculpturing of head otherwise as in alleghaniensis except as follows: maxillary palpal segments in ratio of about 0.9: 1.0: 0.8: 0.8: 0.5: 0.5; labial palpal ratio about 1.0: 0.8: 0.5: 0.4: facial fovea narrow as in atlantica, separated from lateral ocellus by more than one ocellar diameter.
Structure and sculpturing of thorax as in alleghaniensis except as follows: scutellum more sparsely punctate (as in atlantica); propodeum with dorsolateral and posterior surfaces finely punctatorugose. Wing venation and tegula as in alleghaniensis except hind femur with only one complete ridge along ventral surface, a short portion of a second ridge sometimes present basally (not in holotype).
Terga sculptured as in alleghaniensis but punctures much denser, on tergum 2 basal area punctures separated mostly by half a puncture width and apical area with punctures smaller and sparser at least near basal area; terga 3 and 4 with progressively sparser punctures. Pygidial plate and sterna as in alleghaniensis.
VESTITURE. — Generally as in atlantica but mesoscutal hairs often somewhat shorter, although erect, almost scale-like, and terga 5 and 6 with brown or reddish-brown hairs.
MALE. MEASUREMENTS AND RATIOS. — N = 20; length. 7-10 mm; width. 2.0-2.5 mm; wing length, M = 3.34 ± 0.201 mm; FL/FW, M = 1.10 ± 0.007; FS1/FS2, M = 1.11 ± 0.012.
INTEGUMENTAL COLOR. — Generally as described for alleghaniensis but wing veins usually reddish-brown including pterostigma and hind tibial spurs red (allotype) to testaceous.
STRUCTURE. — Head with structure and sculpturing of alleghaniensis except first flagellar segment slightly longer than second and second distinctly shorter than third segment. Thorax with structure and sculpturing as in alleghaniensis except propodeum with dorsolateral and posterior surfaces finely or moderately punctatorugose, never coarsely so. Wing venation as in alleghaniensis except a tendency towards one submarginal cell being absent (not allotype) in one or both wings (five out of thirteen males lack one cell in one or both wings). Legs as in alleghaniensis. Terga with sculpturing as in alleghaniensis but punctures more crowded, tergum 2 with basal area punctures separated mostly by one to two puncture widths and often less. Sterna as in alleghaniensis.
Terminalia as in figures 32-36; note the following: sternum 7 truncate apically with minute median emargination; sternum 8 much as in alleghaniensis; genital capsule much as in alleghaniensis but penis valve slightly less expanded basally.
VESTITURE. — Generally white to cinereous: form and distribution of hair as in alleghaniensis and atlantica.
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