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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This species is very close to A. aurihirta, but it is a little smaller, especially in the males, and can be distinguished by the clypeus being more protuberant and nearly naked in the lower median area, the propodeal enclosure without a longitudinal, median depression, and the lateral areas of metasomal tergum 2 anteriorly to the apical fascia with all hairs short and appressed. A. citrinihirta is found in the Central Valley of California and as far north as southern Oregon, and A. aurihirta is found in the Santa Barbara Mountains of southern California, north to the Tehachapi Mountains, and for a short distance north of the Tehachapis along the Sierra Nevada. The two species are allopatric but nearly meet in the Tehachapi region (map 11). An original parent population probably extended throughout California, but may have been exterminated in the Sierra by climatic changes, with two populations surviving in refuges, one in the San Francisco Bay area and one in the higher, non-glaciated areas of southern California. Amelioration of the climate since the last Ice Age would have permitted the two now distinct species to reinvade much of the former range and to almost meet in at least one area. These two species are separable from other species in the Citrinihirta group by their citrus yellow vestiture. Metasomal vestiture links these two species to both A. ramaleyi and A. sulcata, and more distantly to A. bendensis.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 6.6-7.9 mm; width, 1.9-2.5 mm; wing length, M = 2.22 ± 0.097 mm; FL/FW, M = 1.03 ± 0.096; FOVL/FOVW, M = 3.23 ± 0.328.
INTEGUMENTAL COLOR. — Black except as follows: last several segments of antenna lighter than remainder; mandible with apical half red; tibial spurs nearly white; tarsi, except basitarsi, yellow-brown; tarsal claws with basal half light yellow, apical half red; tegula shining brown, wing veins red-brown, pterostigma yellow-brown, wing membrane nearly black apically in anterior half, remainder of apical area lightly clouded; metasomal terga and sterna broadly hyaline apically, pygidium dark red.
STRUCTURE. — Scape equal in length to flagellar segments 1 to 3; flagellar segments 1 and 2 equal in length. Eye 4 times longer than wide with inner margin diverging slightly above except upper end inwardly curved. Malar space 7 times as wide as long. Mandible in repose extends for one-fifth its length beyond middle of labrum; notch of mandible tooth less than one-half distance between middle of labrum and mandible apex. Galea moderately tessellate, lateral surface as wide as dorsal surface. Maxillary palpus long, with at least apical segment projecting beyond apex of galea, segmental ratio 0.7:0.8 :0.7:0.6:0.5:0.5. Labial palpal basal segment flattened laterally, curved, with apical half twisted exposing inner flattened face from above, apical segment attached subapically, segmental ratio 0.9:0.5 :0.4:0.5. Labral process moderately reflexed, twice as wide as long, median emargination shallow, depth one-fourth length of labral process. Clypeus protuberant, most protuberant medially; extending for more than one-third its length below eyes; median, longitudinal third smooth, lateral thirds with large punctures separated near median margin by 1 diameter, smaller, more crowded dorsolaterally, dorsolateral periphery shagreened. Supraclypeal area with small punctures laterally, shagreened medially. Genal area more than 1.3 times as wide as eye, with medium-sized punctures separated by 2 to 4 diameters, area near eye margin one-third width of genal area, surface shiny, remainder shagreened. Vertex above lateral ocellus slightly wider than 1 ocellar diameter, with reticular shagreening obscuring punctures. Supra-antennal area with distinct, longitudinal rugulae and obscure punctures in interrugal spaces. Facial fovea more than 3 times longer than wide, wider above than below, rounded above and below, upper limits indistinct, ending above at a line above dorsal limit of median ocellus, ending below slightly below antennal fossa.
Pronotum with humeral angle and ridge moderately developed except humeral ridge almost lacking in upper half; pronotal suture weak; pronotum shagreened throughout. Scutum in anterior half with moderate reticular shagreening, with irregular punctures separated by 1 to 3 diameters; dorsomedian area of posterior half smooth, shiny. Scutellum smooth, polished, except for posterior margin shagreened with medium-sized punctures separated by 2 diameters. Metanotum irregularly tessellate with obscure punctures separated by 2 diameters. Propodeal enclosure with light, reticular shagreening except anterior third with irregular, transverse rugulae; dorsoposterior surface with reticular shagreening and small punctures separated by 2 diameters; corbicular areas moderately shagreened with a few, scattered, prominent punctures in anterodorsal fourth, surface shiny. Mesepisternum with moderate shagreening, surface shiny, and moderate punctures separated by 3 to 4 diameters. Metepisternum weakly shagreened, with median three-fifths impunctate, shiny; upper and lower areas with small punctures separated by 2 to 3 diameters. Mesobasitarsus widest medially, 2.6 times longer than wide, somewhat wider than metabasitarsus. Metabasitarsus widest just above middle, one-fourth longer than mesobasitarsus. Metatibia wider than mesobasitarsus, 1.3 times as long as metabasitarsus. Vein 1st m-cu meets second submarginal cell at middle; pterostigma 4 times as wide as long.
Metasomal terga 1 to 5 with reticular shagreening on disc except for smooth posterior margin; apical areas smooth. Tergum 1 with scattered punctures medially and laterally on disc, terga 1 to 4 with posterior areas of discs and apical areas except extreme apical edges with punctures at closest separated by less than 1 diameter. Tergum 5 with small punctures on disc separated by 2 diameters, crowded posteriorly. Pygidial plate rounded apically, with edge and narrow median area raised. Sternum 1 with small, median, V-shaped, apical emargination with medium-sized punctures separated by 3 to 4 diameters; sterna 1 to 6 moderately shagreened; sterna 2 to 6 with small punctures separated by 3 diameters.
VESTITURE. — Pubescence citrus yellow throughout but slightly less colored beneath. Clypeus with median third naked. Scutum with short, thick, posteriorly directed hairs. Propodeal corbicula with widely spaced hairs in anterior fourth; trochanteral floccus imperfect.
Metasomal terga 1 to 4 with complete apical fasciae of short, dense, appressed hairs obscuring more than half of terga. Tergum 1 with a small, lateral, naked area just anterior to the apical fascia, remainder of disc covered with long, nearly erect hairs. Tergum 2 with disc with very short, appressed hairs in narrow median area and laterally; remainder of disc and discs of terga 3 and 4 with very short, exceedingly fine, sparse, erect hairs. Tergum 5 covered with appressed hairs. Sternum 1 with long, sparse, erect hairs; sterna 2 to 6 with weak, apical fimbriae, poorly developed in median thirds, remaining areas with short, fine, sparse, erect hairs. Sterna 1 to 5 with apical fringes of short, white hairs, well developed on sternum 1, poorly developed on sterna 2 to 5.
MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 6.5-5.8 mm; width, 1.4-1.7 mm; wing length, M = 2.56 ± 0.100mm;FL/FW, M = 1.02 ± 0.010; FS1/FS2, M = 1.16 ± 0.072. INTEGUMENTAL COLOR. — Black except as follows: antenna light brown ventrally beyond scape; mandible with apical half clear bright red; tarsi light yellow-brown, tarsal claws with apical half dark red; tegulae shining light brown except narrow edge hyaline; wing veins and pterostigma red-brown, wing membrane hyaline except for apical area moderately darkened.
Metasomal terga 1 to 5 widely hyaline apically; sterna 1 to 6 narrowly hyaline apically.
STRUCTURE. — Scape short, equal in length to pedicel plus flagellar segments 1 and 2; flagellar segment 1 a little longer than flagellar segment 2, as long as flagellar segment 3. Eye a little more than 3 times as long as wide with inner margin diverging slightly above except upper end somewhat incurved. Malar space extremely short, 12 times wider than long. Mandible in repose extends for almost one-third its length beyond middle of labrum; notch of mandible tooth less than half distance between middle of labrum and mandible apex from mandible apex. Galea as in female. Maxillary palpus with last two segments projecting beyond apex of galea; segmental ratio 0.6:0.7:0.6:0.6:0.5:0.6. Labial palpus with basal segment strongly flattened laterally and curved, apical segment attached subapically, segmental ratio 0.8:0.4:0.4:0.5. Labral process strongly reflexed, wider than long, median emargination depth one-third length of labral process. Clypeus slightly protuberant; extending for one-fourth its length below eyes; whole surface with medium-sized punctures separated by 1 diameter except for lower median area where punctures separated widely; surface shiny throughout. Supraclypeal, supra-antennal areas as in female. Genal area nearly twice as wide as eye, weakly produced opposite midpoint of eye to a blunt projection, with small punctures separated by 3 to 5 diameters, lightly shagreened. Parocular area below upper limit of antennal fossa with large punctures separated by less than 1 diameter, shiny; above as for supra-antennal area. Vertex as in female.
Pronotum with humeral angle and ridge well developed, shagreened with weak, vertical rugulae above indistinct pronotal suture; remainder of thorax as in female. Wings as in female except membrane less clouded apically.
Metasomal terga 1 to 5 with some weak shagreening on basal areas of discs; otherwise smooth, shiny, with small punctures separated by 4 diameters. Sternum 1 broadly emarginate medially; sterna 1 to 6 with moderate shagreening. Sternum 7 (fig. 78) with basal apodemes narrowing anteriorly; shallowly emarginate apically, processes on each side of emargination truncate with numerous hairs. Sternum 8 (fig. 79) with apex and neck region longer than basal region; apex truncate; neck region with abundant, long hairs. Gonoforceps (figs. 75 to 77) in dorsal view flattened, expanded apically. Penis valves strongly bent downwards, projecting well below gonoforceps, weakly expanded laterally, lateral expansions smoothly rounded, penis slightly wider medially than basally.
VESTITURE. — Pubescence yellow throughout except slightly less colored ventrally and sternal apical fringe white. Terga 1 to 5 with apical fasciae obscuring one-third of terga; fasciae of short, nearly erect hairs inclined laterally in lateral thirds. Disc of tergum 1 with long, erect hairs, disc of tergum 2 with medium length erect hairs in small anteromedian area, with much shorter, erect hairs laterally; short, erect hairs on discs of terga 3 to 5. Sterna 1 to 6 with apical fringes of short, dense hairs, with longer, erect hairs on remaining areas.
VARIATION. — In both sexes the integument may be brown or brown-yellow. The smooth, shiny area on the scutum and scutellum varies slightly in size. The amount and intensity of sculpture on the metasomal terga varies, becoming almost finely tessellate basally in some specimens. Vein 1st m-cu meets the second submarginal cell slightly before or well beyond the middle in about one-fourth of the specimens. Some variation may be found in individuals. One male from Clear Creek, San Benito Co., California, has the second submarginal cell in both wings about half as wide as normal.