Reprinted by permission of the Regents of the University of California from:
Donovan, B. J. 1977. A revision of North American bees of the subgenus Cnemidandrena (Hymenoptera: Andrenidae). University of California Publications in Entomology: 1-107.
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The three species in the Costillensis group, A. costillensis, A. columbiana, and A. pachucensis are quite similar in structure and vestiture. However, A. costillensis females are readily distinguished from A. columbiana by the light yellow-white vestiture throughout, and from A. pachucensis by the dull, somewhat shiny scutum. There are also slight differences in the clypeus and labral process among the three species. Males of A. costillensis and A. columbiana are very difficult to separate, and it is possible that many of the males placed in A. columbiana are really males of A. costillensis.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 7.3-9.5 mm; width, 2.4-2.9 mm; wing length, M = 2.57 ± 0.127 mm; FL/FW, M = 1.04 ± 0.110; FOVL/FOVW, M = 3.19 ± 0.190.
INTEGUMENTAL COLOR. — Black except as follows: antenna reddish-brown ventrally beyond second flagellar segment; mandible with apical half red; tibial spurs white lightly tinged with yellow; mediotarsi, distitarsi yellow-brown; basal half of tarsal claws yellow, apical half red; tegula, wing veins brown, pterostigma light yellow, wing membrane with broad, apical area lightly to moderately darkened, lightly darkened along veins in remainder.
Metasomal terga and sterna moderately to widely hyaline apically; pygidial plate dark red-brown.
STRUCTURE. — Scape longer than flagellar segments 1 to 3; flagellar segment 1 equal to flagellar segments 2 plus 3; flagellar segment 2 a little shorter than flagellar segment 3. Eye a little less than 4 times longer than wide, with inner margin moderately diverging above except for upper end incurved. Malar space 9 times wider than long. Mandible in repose extending for a little more than one-fourth its length beyond middle of labrum, with notch of mandible tooth equidistant between middle of labrum and mandible apex. Galea moderately tessellate, dorsal surface nearly 1.5 times wider than lateral surface. Maxillary palpus reaching to apex of galea, segmental ratio 0.7:0.9:0.8:0.8:0.6:0.6. Labial palpus laterally compressed, hardly curved, apical segment attached subapically, segmental ratio 1.3:0.6:0.5:0.6. Labral process weakly recurved apically, twice as wide as long; depth of apical emargination one-sixth length of labral process. Clypeus moderately protuberant, extending below eyes for less than half its length, with large punctures separated medially by 1 diameter or slightly less; punctures smaller, closer dorsally and laterally, upper third with moderate to heavy shagreening, very narrow apical margin lightly shagreened. Supraclypeal area with medium-sized punctures obscured by moderate shagreening. Genal area less than twice as wide as eye, with small punctures separated by 3 diameters, with moderate shagreening except for very narrow, shiny area near eye. Vertex above lateral ocellus equal to 1 ocellar diameter, with medium-sized punctures separated by 1 diameter or less, with moderate tessellation. Supra-antennal area with longitudinal rugulae and indistinct interrugal punctures. Facial fovea 3 times longer than wide, widest and rounded above, narrower, more pointed below, reaching above to a line above median ocellus, reaching below to a line a little less than equidistant between antennal fossa and clypeus.
Pronotum with humeral angle and ridge well developed; humeral ridge scarcely depressed where crossed by pronotal suture, with small to medium-sized punctures separated by 1 diameter, whole pronotum moderately shagreened. Scutum with medium-sized punctures nearly obscured by moderate tessellation. Scutellum with nearly large punctures separated by 1 or more diameters, with moderate tessellation on posterior half; anterior half with tessellation almost absent, nearly shiny. Metanotum with rough, moderate tessellation obscuring medium-sized punctures. Propodeal enclosure with anterior fringe of indistinct rugulae, posterior half with broad, shallow, median, longitudinal depression, whole area moderately tessellate; dorsoposterior surface as for metanotum; lateral corbicular surface with medium-sized, widely irregularly spaced punctures in anterior third, with light tessellation. Mesepisternum with nearly large punctures separated by 1 diameter, with moderate tessellation tending to obscure punctures. Metepisternum with very small punctures on upper half, with reticular shagreening. Mesobasitarsus widest medially, 2.6 times longer than wide, equal in width to metabasitarsus. Metabasitarsus widest medially in basal third, more than 3 times longer than wide, two-thirds width of metatibia. Metatibia widest apically, curved ventrally, length less than 3 times width. Wing with pterostigma 4 times longer than wide, vein 1st m-cu meets second submarginal cell less than one-third distance from end of cell.
Metasomal terga 1 to 4 with small discal punctures separated by 2 to 3 diameters but closer on apical margins of discs; tergum 5 with large, irregularly spaced, discal punctures. Pygidial plate narrowly rounded apically, sides and middle nearly flat; anterior half with small, close punctures, posterior half smooth. Sternum 1 with small, median, apical, V-shaped emargination, with medium-sized punctures separated by 2 diameters; sterna 2 to 6 with slightly smaller punctures similarly distributed.
VESTITURE. — Yellow-white throughout. Clypeus with vestiture thinner medially. Scutum and scutellum with hairs throughout, but hairs short dorsomedially on scutum. Propodeal corbicula with long, plumose hairs in anterior third. Trochanteral floccus imperfect.
Metasomal terga 1 to 4 with apical fasciae of recumbent hairs, fasciae obscuring half of terga, except fascia of tergum 1 with most hairs erect, not obscuring surface; remainder of discs of terga 1 to 4 with sparse, erect hairs, longest on tergum 1, shorter on tergum 2, shortest on terga 3 and 4. Tergum 5 with hairs not obscuring surface in anterior half. Sternum 1 with long, erect hairs; sterna 1 to 5 with apical fringes of short, widely and nearly evenly spaced plumose hairs; sterna 2 to 5 with subapical fimbriae well developed in lateral thirds, poorly developed in median thirds; remainder of sterna with sparse, erect hairs, shortest anteriorly.
MALE. MEASUREMENTS AND RATIOS. — N = 4; length, 6.2-6.8 mm; width, 1.9 mm; wing length, M = 2.15 ± 0.065 mm; FL/FW, M = 1.01 ± 0.076; FS1/FS2, M = 1.26 ± 0.128.
INTEGUMENTAL COLOR. — Antenna red-brown ventrally beyond first segment; mandible with apical third red; tegula hyaline shining dark brown; wing veins dark brown; pterostigma yellow; wing membrane lightly darkened apically. Tibial spurs white with Very light tinge of yellow. Mediotarsi, distitarsi, basal half of tarsal claws yellow; apical half of tarsal claws red.
Metasomal terga with depressed apical area hyaline. Sterna widely hyaline apically.
STRUCTURE. — Scape equal to flagellar segments 1 plus 2 plus more than half of flagellar segment 3; flagellar segment 1 longer than flagellar segment 2; flagellar segment 2 very slightly shorter than flagellar segment 3. Eye a little more than 3 times longer than wide, with inner margin moderately diverging above except for somewhat incurved upper end. Malar space, mandible and galea as in female except mandible without ventrobasal lamella. Maxillary palpus with most of apical segment projecting beyond apex of galea, segmental ratio 0.6:0.7:0.6:0.7:0.7:0.6. Labial palpus with basal segment laterally compressed, curved, apical segment attached subapically, segmental ratio 1.3:0.6:0.5:0.7. Labral process strongly reflexed, twice as wide as long, depth of apical emargination half length of reflexed area. Clypeus weakly protuberant, extending below eyes for less than half its length, with large punctures; punctures as much as 2 diameters apart in lower median area, crowded in upper and lateral areas, shiny. Supraclypeal area with crowded, medium-sized punctures and light shagreening. Genal area less than twice as wide as eye, produced to a weakly developed, blunt projection opposite about midpoint of eye, with medium-sized punctures separated by 1 to 2 diameters; small posterior area shagreened, remainder shiny. Vertex as in female. Supra-antennal area with longitudinal rugulae with large, closely spaced, interrugal punctures. Parocular areas with large, closely spaced punctures.
Pronotum with humeral angle and ridge well developed except humeral ridge broadly depressed where crossed by pronotal suture, area above pronotal suture with strong, dorsoventral rugulae, pronotum dorsally with obscure, medium-sized punctures, area above humeral ridge strongly shagreened, area below humeral ridge shiny or nearly so. Remainder of mesosoma as in female except as follows: propodeal enclosure with rugulae in anterior half more strongly developed than in female; lateral areas of propodeum with medium-sized, widely spaced punctures and dense, reticular shagreening.
Metasomal terga 1 to 5 as for female terga 1 to 4 except punctures less distinct, tessellation very light, surfaces nearly shiny on terga 3 to 5. Sternum 1 with median, apical, V-shaped emargination, larger than in female, sterna 1 to 6 with small to medium-sized punctures separated by 3 diameters; sternum 1 shiny, sterna 2 to 6 lightly shagreened, nearly shiny. Sternum 7 (fig. 28) with basal apodemes weakly angled on outer posterior margin; apex of sternum truncate with long hairs laterally, inner apical margin excavated. Sternum 8 (fig. 29) with neck region widening strongly in basal half, apex not expanded; neck region with abundant, long hairs, basal region pointed basally. Gonoforceps (figs. 25 to 27) in dorsal view with oblique ridge reaching outer edge. Penis valves moderately expanded medially, narrowing to lobe-like apex; in lateral view projecting well below gonoforceps.
VESTITURE. — White tinged lightly with yellow. Clypeus with long, abundant hairs obscuring surface. Scutum with long, erect hairs throughout. Scutellum with long, erect hairs except on nearly shiny areas.
Metasomal terga 1 to 5 with apical fasciae obscuring a little more than one-half terga; fascia on tergum 1 with hairs more erect, less dense; terga 2 to 5 with fascial hairs recumbent; remaining discal areas of terga 1 to 5 with erect, sparse hairs, longest on tergum 1, shorter on tergum 2, shortest on terga 3 to 5. Sternum 1 with sparse, long, erect hairs; sterna 1 to 5 with moderately developed, apical fringes; sterna 2 to 6 with long hairs laterally, shorter hairs medially.
VARIATION. — In females the width above the facial fovea varies slightly.