Reprinted with permission of the American Entomological Society from:
LaBerge, W. E. 1987. A revision of the bees of the genus Andrena of the Western Hemisphere. Part XII. Subgenera Leucandrena, Ptilandrena, Scoliandrena and Melandrena. Transactions of the American Entomological Society 112: 191-248.
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Andrena flexa and the following two species (macra and/ace/a) differ from other members of the subgenus Leucandrena by the posterior hind tibial spur being flexed in the outer third, the distinctly punctate metasomal terga, and the relatively tall vertex. In addition the female has the propodeal corbiculum incomplete anteriorly and both sexes have terga 2-4 with complete or almost complete pale fasciae as described below. This species, together with the two following sister species, are placed provisionally in the subgenus Leucandrena, rather than in Thysandrena as previous authors have done, since a majority of characters are typical of this subgenus, especially the well-formed pronotal angles and dorsoventral ridges and the black male clypeus. It is possible that a new subgenus will be recognized for this small group in the future, based on the hind tibial spur shape.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 11-12 mm; width, about 3.5 mm; wing length, M = 4.23 ± 0.147 mm; FL/FW, M = 0.92 ± 0.003; FOVL/FOVW, M = 3.06 ± 0.40.
INTEGUMENTAL COLOR. — Black except as follows: mandible with apical half or lest dark rufescent; wing membranes hyaline, infumate, yellowish brown, veins reddish brown; tibial spurs dark reddish brown; metasomal terga 2-4 with apical areas narrowly hyaline, colorless apically (on tergum 2 hyaline area equals one-third or more of apical area); tarsi dark reddish brown.
STRUCTURE. — Antennal scape length equals slightly less than first four flagellar segments; flagellar segment 1 as long as following two and one-half segments; segment 2 broader than long and slightly .shorter than segment 3 which is broader than long and shorter than 4; segments 4-10 quadrate to longer than broad. Eyes as in barbilabris but inner margins parallel. Mandibles, malar space, and galea as in barbilabris . Maxillary palpus as in barbilabris but segmental ratio about as 1,0:1.0:1.0:1.0:0.7:0.7. Labial palpus as in barbilabris but segmental ratio about as 1.0:0.6:0.5:0.5. labral process trapezoidal, three times as broad as long, usually gently emarginate apically, flat, shiny; labrum below process with a median and two lateral cristae, shiny sulcus between cristae. Clypeus gently rounded with small punctures separated mostly by half a puncture width except in narrow longitudinal median line, surface moderately shiny, shagreened. Supraclypeal area with small contiguous punctures and reticular shagreening moderately dulling surface. Face above antennal fossae with coarse longitudinal rugulae reaching ocelli. Facial fovea broad, shallow, long as in barbilabris . Vertex tall, above lateral ocellus equal to almost one and one-half ocellar diameters; surface opaque, tessellate with obscure punctures. Genal area in profile broader than eye, surface coarsely reticularly shagreened with minute punctures especially near eye margin.
Pronotum laterally with distinct humeral angle and dorsoventral ridge but ridge blunt and poorly formed in lower half; surface opaque, tessellate. Mesoscutum moderately shiny posteromedially where punctures separated mostly by one puncture width or more, dull anteriorly and peripherally, reticularly shagreened with crowded punctures, Scutellum shiny, medially large punctures separated by half to one puncture width, crowded peripherally where interpunctural spaces shagreened. Propodeum with dorsal enclosure opaque, roughened basally by obscure irregular rugulae, tessellate; outside of enclosure dulled by coarse tessellation and obscure punctures. Mesepisternum sculptured as in propodeum outside of enclosure. Fore wing with vein 1st m-cu meeting second .submarginal cell near or at middle of cell, Posterior hind tibial spur bent and somewhat S-shaped in oilier third.
Metasomal tergum 1 with basal area punctures distinct, separated by half to one puncture width, apical area punctures smaller and more crowded except in impunctate apical third. Terga 2-4 as in tergum 1 but basal area punctures more crowded in tergum 2 and less so in tergum 4. Terga 1-4 with surfaces shiny, shagreening weak or absent. Pygidial plate large, apex rounded, internal raise area lacking. Sterna 2-5 with basal area punctures separated mostly by two to three puncture widths, apical areas impunctate; surfaces dulled by reticular shagreened.
VESTITURE. — Pale ochraceous except as follows: ochraceous on vertex and thoracic dorsum; hind tibial plate and below with brown hairs; middle tibia with outer surface usually brown at least medially; terga 2-4 with apical pubescent fasciae white, that on tergum 2 interrupted medially by one-third or less of tergal width, (hat on tergum 3 narrowly interrupted medially, that on tergum 4 complete or almost so; terga 5 and 6 ochraceous to pale brown medially. Propodeal corbiculum incomplete anteriorly with long simple internal hairs; trochanteral flocculus weak, incomplete at extreme base.
MALE. MEASUREMENTS AND RATIOS. — N = 2; length, about 10 mm; width, about 2.5 mm; wing length, 3.70-3.75 mm; FL/FW, 0.85-0.86; FS1/FS2, 2.14-2.31.
INTEGUMENTAL COLOR. — Black except as follows: mandible with apical fourth rufescent; flagellar segments 3-11 dark reddish brown below; wing membranes hyaline, veins yellow to brown; metasomal terga 1-5 with apical areas broadly hyaline apically, rufescent basad; sterna 2-5 with apical areas hyaline, colorless to yellow; tibial spurs testaceous.
STRUCTURE. — Antennae in repose barely reaching scutellum; scape length equals first two and three-fourths flagellar segments; flagellar segment 1 more than twice as long as segment 2 and longer than 3; segment 2 broader than long; segments 3-11 longer than broad. Eyes each almost three and one-half times as long as broad, inner margins parallel. Galea, malar space, and labral process as in female. Clypeus with distinct round punctures separated mostly by half a puncture width or less, surface moderately dulled by fine shagreening, not opaque. Supraclypeal area, face above antennal fossae and vertex as in female. Genal area in profile broader than eye, broadest just above level of middle of eye; sculptured as in female.
Pronotum laterally with distinct humeral angle; dorsoventral ridge not evident in lower half; surface dull, tessellate. Thoracic sculpture and wing venation as in female (mesoscutum dulled by reticular shagreening). Posterior hind tibial spurs flexed as in female but only weakly so.
Metasomal terga 1-5 as in female terga 1-4 but punctures slightly sparser and apical area punctures minute; surfaces shiny, unshagreened. Tergum 7 without pygidium-like area. Sterna 2-5 with basal area punctures separated by three to five puncture widths; apical areas impunctate; surfaces dull, with coarse reticular shagreening. Sternum 6 flat, not reflexed apically. Penis valves extremely narrow apically; dorsal lobe of gonocoxite short, almost forming a right angle. Sternum 7 distinctly bidentate. Sternum 8 with tip entire, moderately hairy (Figs. 31-35).
VESTITURE. — Generally white but inner surfaces tarsi pale yellow. Terga 2-4 with distinct pale apical fasciae narrowly interrupted medially; tergum 5 with weak fascia of sparse hairs. Sterna 2-5 with subapical fimbriae of long white hairs.
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 11 mm.; eyes about parallel; foveae broad, occupying above most of space between eyes and ocelli, covered with whitish tomentum; vertex not very broad, lateral ocelli separated from its hind margin by a space only slightly exceeding their diameter; cheeks somewhat broader than eyes; vertex and cheeks quite smooth, rather dull, punctures exceeding minute and vague; clypeus rather flat, somewhat shining between the deep, distinct and close, but rather fine punctures, with a narrow, rather vague, impunctate, median line; malar space very short; process of labrum broadly subtriangular, with a narrow, shallowly emarginate apex; basal segment of flagellum somewhat longer than 2nd and 3rd combined, these hardly as long as broad, median segments with length and breadth about equal; pubescence of head and thorax rather short and dense, entirely ochraceous, somewhat more whitish below; scutum and scutellum quite closely, finely, deeply and distinctly punctate, but punctures becoming obscured anteriorly; pleura dull, densely tessellate, punctures hardly evident; dorsal area of propodeum tessellate, not noticeably rugose; propodeal corbicula well developed, but dorsal hairs rather short, without an anterior fringe and with a few scattered interior hairs; trochanteral floccus imperfect; legs black; hind tibial scopa and pubescence generally pale ochraceous; inner apical spur of hind tibia strongly flexed near middle; wings lightly infuscated, veins and stigma ferruginous, 2nd submarginal cell considerably shorter than 3rd, receiving 1st recurrent near middle; tegulae pale testaceous posteriorly, more fuscous anteriorly; abdominal terga deeply, distinctly, closely and finely punctate, punctures invading the impressed apical areas where they are somewhat finer, these areas very shallow and obscure, discal pubescence very short, entirely pale, segments 2-4 with dense, white and conspicuous, apical fasciae, these very slightly interrupted on 2 and 3, apical fimbria more whitish.
DISTRIBUTION. — Illinois to Oklahoma and Texas; April.
Andrena flexa and A. macra are closely related but seemingly distinct. In macra the pubescence is somewhat more deeply ochraceous, the clypeus lacks any evidence of a median impunctate line, and the abdominal terga at most are subfasciate toward the extreme sides. Lanham (1949), having no male by which to judge its position more accurately, suggested that flexa probably belongs in Cryptandrena or Thysandrena. With the male of macra available, it is the opinion of this writer that these two species are more properly placed in Gymnandrena, but this is open to debate.