Reprinted with permission of the American Entomological Society from:
LaBerge, W. E., Bouseman, J. K. 1970. A revision of the bees of the genus Andrena of the Western Hemisphere. Part III. Tylandrena. Transactions of the American Entomological Society 96: 543-605.
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This large western bee is related to perplexa but is readily distinguished from that species in both sexes by the form of the pronotal humeral angles, as described below, the opaque thoracic dorsum dulled by coarse tessellation and the shorter vertex. The female of subtilis is further distinctive in the metallic reflections on the dulled terga, the narrow pygidial plate, the often rather pointed labral process and the broad face and facial foveae. The male of subtilis is distinctive in the pointed basitibial plates and the extremely broad genal area which is somewhat angulate behind.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 11-15 mm; width, 3.0-4.5 mm; wing length, M = 5.39 ± 0.179 mm; FL/FW, M = 0.91 ± 0.004; FOVL/FOVW, M = 3.31 ± 0.039.
INTEGUMENTAL COLOR. — Black except as follows: mandible with apical third rufescent; flagellar segments 2-10 dark brown below; wing veins and pterostigma deep blackish-brown to reddish-brown, membranes moderately infumate, brown; distitarsi and often basitarsi moderately rufescent; terga (especially terga 2-4) usually with faint metallic reflections.
STRUCTURE. — Antennal scape length equals first four flagellar segments or almost; flagellar segment 1 equal in length to segments 2 plus 3, 2 shorter than 3 and 3 shorter than 4, segments 2 and 3 quadrate or shorter than broad, segments 4-10 longer than broad. Eyes each four times as long as broad, inner margins parallel. Malar space, mandible and galea as in perplexa. Maxillary palpus as in perplexa but segmental ratio about 0.8:1.0:0.9:0.8:0.7:0.6. Labial palpus as in perplexa but ratio about 1.0:0.8:0.8:0.5. Labral process about twice as wide at base as long or slightly wider, simple, broadly V-shaped to rounded apically, slightly thickened at apex; labrum below process without a conspicuous transverse sulcus, usually with a single median crista and several weak rugulae laterally, or with several weak longitudinal rugulae. Clypeus as in perplexa but impunctate midline often complete to posterior margin. Supraclypeal area and genal area as in perplexa. Vertex above lateral ocellus equal to only slightly more than one ocellar diameter (about as 9:11 or 12), opaque, dulled by dense coarse tessellation and small punctures (crowded especially above ocelli). Face above antennae as in perplexa. Facial fovea separated from lateral ocellus by one ocellar diameter or slightly more, about as broad near lower end as near upper end.
Pronotum with humeral angle poorly developed, forming a rounded lip distinctly but narrowly separated from mesoscutum, posterior margin between humeral angles straight, oblique lateral carina shallow, with gradually sloping sides; surface dulled by fine dense tessellation and minute punctures. Mesoscutum and scutellum with obscure, extremely shallow punctures separated by half or more puncture widths, surfaces opaque, dulled by dense, coarse, regular tessellation (scutellum occasionally slightly shinier). Metanotum and propodeum as in perplexa. Mesepisternum with extremely shallow punctures separated by one-half to two puncture widths, surface dulled by regular tessellation. Wing venation as in perplexa. Tergum 1 with extremely minute punctures separated mostly by two to four puncture widths (scarcely larger than tessellations), surface dulled by fine, dense, regular tessellation but apical area shinier than basal area. Terga 2-3 with minute punctures slightly larger than on tergum 1; apical area punctures in basal half to two-thirds of area and separated by two to four puncture widths; basal area punctures separated mostly by one to two puncture widths; surfaces dulled by fine reticular shagreening. Tergum 4 similar but punctures much sparser. Pygidial plate narrow, V-shaped, rather sharply pointed unless worn, without raised internal triangle. Sterna 2-5 as in perplexa but punctures more crowded.
VESTITURE. — Essentially as in perplexa in paler specimens. Dark specimens as follows: vertex with dark reddish-brown hairs; outer surfaces tibiae and tarsi dark brown; inner surfaces hind tibiae dark brown; hind femora pale brown; apical 3 or 4 terga and sterna with brown to black hairs. MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 9-14 mm; width, 2.0-3.5 mm; wing length, M = 4.34 ± 0.271 mm; FL/FW, M = 0.86 ± 0.006; FS1/FS2, M = 1.13 ± 0.017.
STRUCTURE. — Antennae moderately long, in repose reaching back to middle of scutellum; scape length equal to first two and one-third flagellar segments or less; flagellar segment 2 slightly shorter than segment 3, segments 1-11 longer than broad. Eyes each three and one-half to three and three-fourths times as long as broad, inner margins parallel. Malar space, mandible and galea as in perplexa. Maxillary palpus as in perplexa but segmental ratio about 0.9:1.0:0.8:0.7:0.7:0.6. Labial palpus as in perplexa but ratio about 1.0:0.6:0.5:0.6. Labral process as in perplexa. Clypeus rounded, punctures small, round, crowded except in median, elongate, shiny, impunctate area, surface shagreened only posteriorly. Supraclypeal area dulled by minute punctures and coarse tessellation. Face above antennae with strong longitudinal rugae becoming irregular near midline, with abundant interrugal punctures. Vertex and genal area as in female but genal area broader and moderately angulate behind.
Pronotum with well-formed triangular humeral angle; oblique suture shallow, with sloping sides; surface dulled by minute punctures and fine tessellation. Thorax sculptured as in female with the following differences: scutellum and mesoscutum often slightly shinier; lateral surfaces propodeum duller, with more abundant punctures. Wing venation as in female. Terga sculptured as in female except as follows: tergum 2 with basal area punctures separated mostly by two puncture widths or more, punctures minute, obscure; tergum 4 similar to 3, each with basal area punctures as in female terga 2 and 3 but smaller and obscure; tergum 5 like female tergum 4; terga 2-5 dulled by fine reticular shagreening. Sterna as in erythrogaster but sternum 6 without longitudinal median sulcus and with apical margin moderately reflexed.
Terminalia as figured (Figs. 36-40); note the following: gonocoxite with median dorsal lobe short, but slightly longer than in erythrogaster, apical process with hairs moderately abundant; sternum 7 with deep V-shaped emargination; sternum 8 as in perplexa but apical part much shorter and neck region broader.
VESTITURE. — Generally ochraceous or pale ochraceous; clypeus with dense long beard; terga 2-5 with apical areas with extremely weak, lateral fasciae (unless worn); sterna 2-5 with weak subapical fimbriae of extremely long hairs but interrupted medially; sternum 6 without well-formed subapical fimbria; inner surfaces hind basitarsi yellow.
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