Reprinted with permission of the American Entomological Society from:
LaBerge, W. E. 1973. A revision of the bees of the genus Andrena of the Western Hemisphere. Part VI. Subgenus Trachandrena. Transactions of the American Entomological Society 99: 235-371.
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The females of Andrena nuda are readily recognized by the almost bare mesoscutum. The few peripheral hairs on the mesoscutum are short, densely branched and pale in color. The form of the terga, propodeum and facial foveae of the female is similar to that of A. rugosa to which nuda is closely related. The male of nuda is less easily recognized. The terga of the male have long apical areas (on tergum 2 half as long as tergum or slightly more) which are weakly punctate when compared to the basal area of the same tergum. The mesoscutum is relatively weakly punctate and not depressed along the midline as in rugosa. The last exposed sternum is emarginate as in forbesii, not entire as in rugosa and sigmundi.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 8-10 mm; width, 2.5-3.0 mm; wing length, M = 3.74 ± 0.126 mm; FL/FW, M = 1.03 ± 0.006; FOVL/FOVW, M = 3.99 ± 0.066.
INTEGUMENTAL COLOR. — Black except as follows: mandible with apical half or more rufescent; antennae dark brown; tegulae brown; wing membranes clear, slightly yellowed, veins reddish-brown to red; distitarsi often rufescent.
STRUCTURE. — Antenna as in rugosa but scape slightly longer than first four flagellar segments together. Eyes each about three and one-half times as long as broad, inner margins parallel. Malar space, mandible and galea as in sigmundi. Maxillary palpus as in sigmundi but ratio about as 1.0:1.0:0.8:0.8:0.8:0.6. Labial palpus as in sigmundi but ratio about as 1.0:0.7:0.6:0.6. Labrum as in sigmundi. Clypeus with deep round punctures separated mostly by half a puncture width or more, without median impunctate line but usually with small, subapical, shiny, raised area which may be slightly elongated along midline posteriorly; surface shiny. Supraclypeal area as in rugosa. Genal area with extremely sparse, minute punctures; surface shiny, unshagreened. Vertex and face above antennal fossae as in rugosa. Facial fovea as in rugosa.
Pronotum as in sigmundi but small punctures distinct and round and surface moderately shiny at least dorsally. Mesoscutum throughout with sparse round punctures separated irregularly by one to six puncture widths or more; parapsidal lines short; surface dulled by regular coarse tessellation. Scutellum flat with large, coarse, round punctures separated by half a puncture width or slightly more; surface tessellate, dull. Metascutum similar to scutellum but punctures slightly smaller and more crowded. Propodeum as in sigmundi but area outside of enclosure coarsely reticulorugose. Mesepisternum coarsely rugatulopunctate anteriorly (with bottoms of large punctures shiny to moderately shiny), becoming discretely punctate posteriorly with interpunctural surface tessellate. Posterior hind tibial spur normal. Anterior femur with basal angle rounded (not as in quintiliformis). Wing venation as in sigmundi but second submarginal cell short, usually no longer than one-fourth of first cell along posterior margin.
Metasomal tergum 1 as in rugosa but basal area punctures sparser, separated irregularly by one to five or six puncture widths and apical area punctures minute, separated mostly by two or three puncture widths (with broad impunctate apical margin); surface shiny (slightly shagreened in basal area). Terga 2-4 as in rugosa but punctures sparser (as in tergum 1) and apical areas shiny, slightly shagreened if at all. Pygidial plate and sterna as in sigmundi.
VESTITURE. — White to pale ochraceous. Mesoscutum bare except narrow lateral fringes. Mesoscutal fringes, posterior pronotal lobes, scutellum and metascutum with short, densely plumose, erect hairs (some longer, less densely plumose hairs present on scutellum). Terga with pale apical fasciae absent or extremely weak, otherwise as in sigmundi. Pollen-collecting hairs as in sigmundi but inner surfaces hind tarsi and tibiae with golden-yellow hairs.
MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 7-9 mm; width, 1.5-2.0 mm; wing length, M = 3.19 ± 0.155 mm; FL/FW, M = 1.18 ± 0.007; FS1/FS2, M = 0.71 ± 0.011.
INTEGUMENTAL COLOR. — Black with same exceptions as female but antennae dark brownish-black below and terga usually with narrow translucent rims (often slightly smoky basad).
STRUCTURE. — Antenna as in sigmundi but flagellar segment 1 distinctly shorter than segment 2 and about as broad as long, segment 2 about equal in length to segment 3 and about one and one-third times as long as broad. Eyes as in rugosa. Malar space, mandible and galea as in female (see sigmundi). Maxillary palpus as in sigmundi but segmental ratio about as 1.0:0.9:0.8:0.6:0.6:0.6. Labial palpus as in sigmundi but ratio about as 1.0:0.6:0.6:0.6. Labrum as in sigmundi. Clypeus as in female but punctures slightly smaller, crowded, without subapical shiny boss or this small. Supraclypeal area and vertex as in female but vertex "with more punctures. Face above antennal fossae as in female but rugae finer and punctures more abundant. Genal areas as in sigmundi but punctures slightly sparser.
Pronotum as in female. Mesoscutum as in sigmundi but anteriorly punctures slightly sparser, discrete; parapsidal lines short. Scutellum, metascutum and mesepisternum as in sigmundi. Propodeum as in sigmundi but area outside of enclosure coarsely reticulorugose. Posterior hind tibial spur and wing venation as in female.
Metasomal tergum 1 as in rugosa but punctures of basal area and basal half of apical area round, distinct, separated by one-half to one puncture width, apical area impunctate in apical third or more; surfaces shiny, unshagreened except occasionally basal area slightly so. Terga 2-5 with apical areas medially as long as basal areas or longer; basal areas with distinct round punctures separated by one-half to one puncture width and moderately dulled by reticulotransverse shagreening; apical areas broadly impunctate apically, with small sparse punctures in basal two-thirds, punctures separated mostly by two puncture widths, surfaces shiny. Sterna 2-5 sparsely punctate, reticularly shagreened. Sternum 6 emarginate apically. Terminalia as in sigmundi; see figures 52-53.
VESTITURE. — Generally white to pale ochraceous; terga 2-5 with apical pale fasciae weak or absent (occasionally denser at extreme sides), otherwise vestiture as in sigmundi.
Reprinted with permission from: Mitchell, T.B. 1960. Bees of the Eastern United States. North Carolina Agricultural Experiment Station Technical Bulletin No. 141.
FEMALE. — Length 10 mm.; face very slightly longer than broad; clypeus slightly convex, projecting slightly more than one-third below suborbital line, coarsely and deeply punctate, punctures close except near middle apically; facial foveae rather broad above, occupying about two-thirds of space between eyes and ocelli, covered with pale ochraceous tomentum, abruptly and very strongly constricted below, this part not much more than one-third width of upper part, and widely removed from margin of eye; space between margin of vertex and lateral ocelli subequal to their diameter; cheeks very slightly broader than eyes, rounded posteriorly, smooth and shining, rather distinctly but finely punctate below where the punctures are well separated, becoming very sparse, minute and obscure above and on lateral portions of vertex; malar space very short; basal segment of flagellum slightly shorter than 2nd and 3rd combined; process of labrum rather short and broad, rather narrowly truncate apically; pubescence of head short, entirely whitish, faintly tinged with yellowish, but very sparse above; whitish on thorax laterally, becoming very short and scale-like, subappressed and pale ochraceous around wing bases and on scutellum; pubescence of legs pale ochraceous; scutum largely bare and shining, with rather deep and distinct, moderately coarse punctures, these widely separated and very sparse over entire disc, those on scutellum deep, coarse and uniformly close, somewhat obscured by the pubescence; pleura coarsely rugose anteriorly, becoming smoother and more obscurely punctate posteriorly; dorsal area of propodeum oblique, triangle obscurely delimited from adjacent areas, coarsely striate; propodeal corbicula short, poorly developed, pale ochraceous, with a distinct anterior fringe; trochanteral floccus rather thin and poorly developed, hairs moderately elongate; hind tibiae slightly dilated apically, apex not quite twice width of basitarsi, scopa quite dense, hairs simple, rather short, entirely whitish-ochraceous; fore and mid basitarsi slightly narrower than their respective tibiae, 2nd submarginal cell much shorter than 3rd, receiving 1st recurrent about one-third from apex; abdominal terga somewhat shining between fine, well separated punctures, but these not sparse, apical impressed areas extremely broad, occupying medially almost entire length of disc, becoming faintly reddened along rims, discal pubescence largely absent, sparsely represented at extreme sides of basal portions, entirely pale, fasciae not developed, tergum 5 with a golden-brown, apical fimbria.
DISTRIBUTION. — Colorado to New York, south to Georgia; March to June.
FLOWER RECORDS. — Acer, Crataegus, Ilex, Prunus, Pyracantha, Pyrus, Rubus and Salix. Also recorded by Robertson (1929) on Aruncus, Erigenia, Heracleum, Pastinaca, Ptelea, Rhus, Staphylea, Taenidia, Viburnum and Zizia.
Described using the synonymous name: Andrena pseudobscura Mitchell
MALE. — Length 8 mm.; clypeus rather strongly convex, projecting about one-third below suborbital line, smooth and shining between deep, close and quite coarse punctures; space between margin of vertex and lateral ocelli slightly shorter than distance between them; cheeks subequal to eyes in width, rounded posteriorly, deeply, closely and rather finely punctate, punctures somewhat more coarse but still quite close above and on vertex laterally; malar space very short; basal segment of flagellum short, hardly longer than width at apex, slightly shorter than 2nd segment; process of labrum short and rather broad, subtruncate apically; mandibles with a distinct inner subapical tooth, overlapping about one-fourth; pubescence of head, thorax and legs entirely pale ochraceous; scutum somewhat shining, punctures deep and rather coarse, quite close over anterior half, becoming somewhat more sparse near center posteriorly, those on scutellum somewhat more coarse and close, the surface dull; pleura coarsely rugose; dorsal area of propodeum oblique, triangle short and broad, coarsely and rather regularly striate; all basitarsi slender and elongate, considerably narrower than their respective tibiae; 2nd submarginal cell much shorter than 3rd, receiving 1st recurrent slightly beyond middle, abdominal terga smooth and shining between fine, but deep and distinct punctures, punctures quite close, apical impressed areas rather shallow but distinct, occupying medially about one-half length of disc, discal pubescence very short, thin, erect, entirely pale, terga, 2-4 with narrow, whitish, apical fasciae evident laterally, but widely interrupted medially; apical portion of sternum 8 slender and elongate, sides parallel, apex narrowly truncate, clothed beneath with rather dense pale pubescence; penis valves slender apically, somewhat broadened basally, sides deeply excavated, gonocoxites abruptly dilated apically to form subtriangular lobes which are somewhat concave above, gonocoxal lobes strongly and narrowly rounded, tips nearly attaining apical lobes (similar to hippotes, fig. 37).
TYPES. — Holotype: Male, Raleigh, N. C., Mar. 16, 1945 (Mitchell, on Salix) [author's coll.]. Paratypes: NORTH CAROLINA: 3 MM, topotypical (on Salix); 3 MM, topotypical, Apr. 7, 1934 (on Pyrus and Sassafras); 1 M, topotypical, Mar. 29, 1949 (R. L. Rabb); 4 MM, topotypical, Apr. 7, 8 and 23, 1942; 3 MM, Faison, Apr. 2, 1952 (H. F. Howden, on Symplocos); 1 M, White Lake, Mar. 14, 1953 (Mitchell, on Amelanchier). MARYLAND: 1 M, Takoma Pk., Apr. 30, 1944 (H. & M. Townes). NEW YORK: 1 M, Ithaca, June 6, 1935 (H. K. Townes). CONNECTICUT: 1 M, Colebrook, June 13, 1926 (W. M. Wheeler). MAINE: 2 MM, Saco, June 13 & 16, 1951 (Mitchell). MICHIGAN: 1 M, Jackson Co., Apr. 13, 1951; 1 M, Gladwin Co., June 10-16, 1951; 1 M, Livingston Co., June 3, 1950 (all Dreisbach); 2 MM, E. Lansing, May 3, 1955 and May 15, 1954 (1 M on Prunus) (R. L. Fischer). DISTRICT of COLUMBIA: 1 M, Washington, May 15, 1944 (Bohart). INDIANA: 1 M, Tippecanoe Co., Apr. 19, 1954 (Montgomery, on Pyrus).
Paratypes are located in the Museum of Comparative Zoology, the University of Michigan, Purdue University, in collections of H. K. Townes, R. R. Dreisbach, R. M. Bohart, and the author. It was at first thought that this species represented the male of obscura, but the flight records and distribution of each of these does not suggest such a relationship. The females (obscura) are in flight during July and August, while the males (pseudobscura) start the flight in March in North Carolina, and the latest records are for June, in New York, Connecticut and Maine. No females of obscura have been collected in the eastern part of North Carolina or in the vicinity of Raleigh.