Reprinted by permission of the Regents of the University of California from:
Thorp, R. W. 1969. Systematics and ecology of bees of the subgenus Diandrena (Hymenoptera: Andrenidae). University of California Publications in Entomology 52: 1-146.
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This species appears to be distinct at the level of species groups and to have its closest affinities with A. cyanosoma. It is distinguished from that species by the narrower jugal lobe of the hind wing, which lacks an incision between it and the vannal lobe, and by the noncontiguous punctures on the anterior portion of the mesoscutum.
Andrena macswaini has a restricted distribution in the southern part of the Central Valley and adjacent foothills of the Sierra Nevada. It is an oligolege of morning-opening, yellow-flowered species of Camissonia (in section Camissonia) and shows a preference for deep, sandy soil for its deep burrows. This is the only known species of Diandrena in which the nests are aggregated and associated with depressions.
FEMALE. — Integument gray-green with pleura bluish; antenna uniformly dark brownish-black clypeus with large dark subapical triangle with violaceous reflections, forewing with stigma dark brownish-black; pubescence pale, white except laterally on face, antennal scape above, and vertex black, episternum 2 with black and white intermixed on upper portion, outer surface of tibial scopa white anteriorly, rust-brown posteriorly, anal fimbria rust-brown; facial fovea with sheen black, tomentum chocolate-brown above, white below; apices of metasomal terga 2 to 4 with distinct white hair bands. Head shiny, tessellate, densely, coarsely punctate; clypeus, latero- and supraclypeal areas with punctures separated by less than one diameter, clypeal punctures increasing in size apically; facial fovea extending from summit of eye to bottom of antennal base; eye slightly arcuate medially; antenna with segments 1 to 3 of flagellum as 14:5:6; labrum with process emarginate, apices broadly rounded, polished (fig. 37); subgenal coronet short, about 5 teeth showing posteriorly; gena moderately coarsely punctate with moderately shiny, tessellate interspaces, punctures separated by 1 to 2 diameters, moderately coarsely, longitudinally striate posterolaterally; pubescence of clypeus moderately long, sparse, suberect. Mesosoma dull, rugose-punctate with tessellate interspaces; pronotum finely, sparsely punctate with tessellate interspaces, punctures separated by 1 to 2 diameters, dorsolateral angle absent, without lateral fold, posterior margin of pronotum nearly transverse; mesoscutum with punctures coarse anteriorly and extending posteriorly along mid-mesoscutal line and parapsidal lines, punctures separated by about one diameter, becoming contiguous lateroposteriorly, M-shaped posterior half dull, finely, nearly contiguously tessellate-punctate, notaulus short, distinct; scutellum moderately shiny, rugose-punctate with punctures coarse and contiguous; metanotum moderately shiny, more coarsely rugose-punctate with punctures contiguous; propodeum rugose-punctate, enclosure somewhat longitudinally rugose with median longitudinal line, apical tip finely, transversely striate; episternum 2 rugose-punctate anteriorly, tessellate-finely punctate posteriorly; wing lightly infuscated, submarginals 1:2 (33:34.5), stigma : rest of marginal cell (15:21), hind wing with jugal lobe narrow and without incision between it and vannal, not reaching level of cu-v; posterior trochanter with long, curved, white, perfect floccus; tibial scopa long, loose, simple except for posterior band of plumose hairs, posterior hairs of scopa about one and one-half times as long as width of tibia at apex; pubescence of mesoscutum with few long hairs intermixed with numerous moderately short hairs. Metasoma dull, coarsely tessellate, finely, moderately densely punctate, punctures of first tergum moderately coarse, with interior edges raised like tilted craters, separated by 1 to 3 diameters, punctures of terga 2 to 4 finer, indistinct, separated by 1 to 2 diameters; pubescence of tergum 1 long, terga 2 to 4 moderately long, subdepressed, with distinct hair bands on terga 2 to 4. Length 9 to 9.5 mm, forewing 6.5 mm.
MALE. — Integument gray-green with bluish reflections on pleura; antenna dark brownish-black, forewing with stigma mahogany; pubescence pale, white except few hairs laterally on face pale coppery. Head moderately shiny, tessellate, densely punctate; clypeus, latero- and supraclypeal areas with punctures separated by less than one diameter; parocular depression short, linear; eyes slightly convergent below; antenna with segments 1 to 3 of flagellum as 11:6.5:8.5; labrum with process short, broad, shallowly emarginate apically, strongly recurved (fig. 38); mandibles short; gena moderately coarsely punctate, punctures separated by about 2 diameters, with shiny, tessellate interspaces, finely, longitudinally striate ventrally; pubescence of clypeus long, dense, subdepressed. Mesosoma dull, coarsely punctate with tessellate interspaces;: pronotum finely, sparsely punctate, dorsolateral angle absent, without lateral fold, posterior margin of pronotum nearly transverse; mesoscutum with punctures coarse anteriorly and laterally, separated by about 2 diameters, becoming finer posteriorly in an M-shaped area, notaulus short, distinct; scutellum and metanotum coarsely rugose-punctate with punctures contiguous and moderately shiny; propodeum coarsely punctate with tessellate interspaces, punctures separated by about one diameter, enclosure more or less longitudinally rugose with median longitudinal line, apical tip finely, transversely striate; episternum 2 anteriorly coarsely punctate with tessellate interspaces, punctures separated by one diameter or less, posteriorly finely tessellate-punctate; wing pale, submarginals 1:2 (32:33), stigma : rest of marginal cell (14:22), hind wing with jugal lobe narrow and without incision between it, and vannal, not reaching level of cu-v; pubescence of mesoscutum long, moderately dense. Metasoma dull, moderately coarsely, moderately sparsely punctate with tessellate interspaces, punctures separated by 1 to 2 diameters or more, punctures with anterior edges raised like tilted craters; sternum 8 (fig. 78); genital capsule (fig. 66); pubescence long, erect, that of tergum 2 almost as long as that of tergum 1, slightly shorter on succeeding segments. Length 7.5 to 8 mm, forewing 6 to 6.5 mm.