Reprinted with permission of the American Entomological Society from:
LaBerge, W. E. 1977. A revision of the bees of the genus Andrena of the Western Hemisphere. Part VIII. Subgenera Thysandrena, Dasyandrena, Psammandrena, Rhacandrena, Euandrena, Oxyandrena. Transactions of the American Entomological Society 103: 1-144.
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This small species from the mountains of the west coast states is closely related to A. segregans. Both sexes of ribblei can be distinguished from those of segregans by the integument being more consistently metallic, the wing membranes being moderately infumate and the metasomal tergal fasciae being thinner, frequently interrupted medially and usually completely absent on the first tergum. The species is named in honor of Dr. D. W. Ribble who first recognized it as being new to science and who has contributed considerably to our knowledge of the North American Andrena.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 7-9 mm; width, 2-3 mm; wing length, M = 3.04 ± 0.134 mm; FL/FW, M = 1.05 ± 0.006 FOVL/FOVW, M = 3.58 ± 0.062.
INTEGUMENTAL COLOR. — Black with faint but distinct metallic blue or blue-green reflections especially on face, thoracic dorsum and tergal discs, except as follows: mandible with apical half (holotype) or less rufescent; flagellum below dark brown (holotype) to reddish-brown; metasomal terga 1-5 with apical areas translucent, rufescent; sterna 2-5 narrowly hyaline apically; wing membranes moderately to lightly infumate, brown, veins dark brown (holotype) to reddish-brown; tegula piceous (holotype) to rufescent; tibial spurs testaceous.
STRUCTURE. — Antennal scape length equals about first three and three-fourths flagellar segments or longer; flagellar segments as in segregans. Eyes, mandible, malar space and galea as in segregans. Maxillary palpus as in segregans but segmental ratio about as 1.0:0.9:0.9:0.7:0.7:0.7. Labial palpus as in segregans but ratio about as 1.0:0.5:0.5:0.6. Labral process and labrum as in segregans but process tends to be slightly narrower near apex. Clypeus as in segregans but often entirely shagreened (holotype) but not obscuring punctures and apicomedial half at least moderately shiny. Supraclypeal area, genal area, vertex and facial fovea as in segregans. Face above antennal fossae as in segregans but rugulae longitudinal and slightly coarser.
Thoracic form and sculpturing as in segregans. Wing venation as in segregans but vein 1st m-cu meets second submarginal cell at middle of cell to slightly beyond middle (holotype) of cell.
Metasomal terga sculptured as in segregans but discal punctures often obscured by more dense reticular shagreening (holotype). Pygidial plate as in segregans but apex more acute. Sternal sculpturing as in segregans.
VESTITURE. — As in segregans except as follows: tergum 1 without apical fascia or fascia represented by a few long hairs on either side (holotype). Terga 2-4 with apical pale fasciae weak, thin, interrupted.
MALE. MEASUREMENTS AND RATIOS. — N = 15; length, 7-8 mm; width, 1.5-2.0 mm; wing length, M = 2.64 ± 0.068 mm; FL/FW, M = 1.09 ± 0.010; FS1/FS2, M = 1.44 ± 0.039.
INTEGUMENTAL COLOR. — As in female but mandible usually with apical third rufescent.
STRUCTURE. — Antenna and eyes as in segregans. Mandible, malar space and galea as in female. Maxillary palpus as in female but segmental ratio about as 1.0:1.0:0.8:0.8:0.7:0.8. Labial palpus as in female but ratio about as 1.0:0.5:0.5:0.5. Labral process and labrum as in segregans. Clypeus as in female but more often shiny in apical half (lightly shagreened in allotype). Supraclypeal area, genal area, vertex and face as in female.
Thoracic form and sculpturing as in female. Wing venation as in female but vein 1st m-cu meets second submarginal cell from just before middle (allotype) to beyond middle of cell.
Metasomal terga and sterna sculptured as in segregans but often terga with discs with punctures obscured by dense reticular shagreening (allotype). Sterna 6 as in segregans. Terminalia as in figures 115-118.
VESTITURE. — As in segregans but terga 1-5 with apical fasciae weak, thin, usually absent on tergum 1 and interrupted medially on terga 2 and 3 and often 4.