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 is most closely related to A. nothocalaidis and more distantly to A. subchalybea. From the latter it is distinguished by the more deeply and densely punctate mesoscutum and scutellum. From A. nothocalaidis it is distinguished by the feely emarginate apex of the labral process. However, considerable variation between populations of A. chlorosoma calls for caution in the use of this character. In coastal populations from Marin and San Francisco counties the labral process is more deeply emarginate (figs. 43, 44), but the apicolateral teeth are broader and not recurved, an in the females the dark blue mesosoma contrasts with the lighter greenish metasoma. These characters will serve to separate these populations from A. nothocalaidis.
Despite the restricted distribution of this species, the variation between populations is greater than in any other species of Diandrena. The differences between coastal populations from Marin and San Francisco and those from Alameda County would be considered to be of specific value were it not for intermediate populations to the north, south and east of the coast in which the characters grade toward the Berkeley populations. This variation at present appears to be clinal, but much more material is needed to determine the taxonomic significance of this variation. The amount of population variation in this species indicates that it is recently derived and undergoing rapid evolution.
Andrena chlorosoma was originally thought to be a subspecies of A. subchalybea, but it has subsequently been found that these two have a considerable area of sympatry in the San Francisco Bay area with no evidence of intergradation. It is possible that A. chlorosoma might better be regarded as a subspecies of its closest relative, A. nothocalaidis. Two females labeled Trinity County have a long, narrow labral process with a shallow apical emargination. Because of this character and the contrasting colors of the meso- and metasoma, I have tentatively assigned the to A. chlorosoma rather than A. nothocalaidis. Until more material from the area between Mendocino and Shasta counties becomes available, it seems more convenient to treat these two taxa as species.
FEMALE. — Integument olive-green; antenna basally and above apically dark brownish-black, apical 7 to 8 flagellar segments below brown, forewing with stigma yellow-brown, clypeus with narrow, transverse, subapical, dark band with violaceous reflections; pubescence black except tibial scopa white anteriorly, dark brown posteriorly, mesoscutum white and black intermixed, metasoma white, anal fimbria gray-brown; facial fovea with black sheen, tomentum gray. Head moderately shiny, coarsely, closely punctate with tessellate interspaces; clypeus, latero- and supraclypeal areas with punctures separated by one diameter or less; facial fovea extending from summit of eye to middle of antennal base; eye slightly arcuate medially; antenna with segments 1 to 3 of flagellum as 16:5:5.5; labrum with process moderately narrow, flat, shallowly emarginate apically with outer median groove (fig. 41); subgenal coronet moderately long, well developed; gena moderately shiny, with moderately coarse, sparse punctures, interspaces tessellate with fine, moderately long, vertical striations associated with punctures, punctures separated by 1 to 2 diameters; pubescence of clypeus moderately long, moderately sparse, suberect. Mesosoma dull, coarsely, closely punctate with tessellate-granular interspaces; pronotum with punctures shallow, separated by 1 to 2 diameters, interspaces transversely tessellate, dorsolateral angles absent, without lateral fold; mesoscutum with punctures separated by one diameter, notaulus; somewhat indistinct; scutellum with punctures separated by less than one diameter; metanotum rugose-punctate; propodeum rugose-punctate with punctures separated by one diameter, enclosure with inner basal triangular area irregularly rugulose and blue, laterally finely reticulate, apically finely, transversely tessellate and greenish; episternum 2 rugose-punctate; wing very lightly infuscated, submarginals 1: 2 (20: 20.5), stigma : rest of marginal cell (19: 24), hind wing with jugal lobe extremely narrow without incision between it and vannal, reaching beyond level of cu-v; posterior trochanter with long, curved, white, perfect floccus; tibial scopa long, dense with hairs of posterior three-fourths of outer face and posterior face branched; posterior scopal hairs about one and two-thirds as long as width of tibia at apex; pubescence of mesoscutum moderately long to moderately short black and white intermixed, moderately sparse. Metasoma dull, moderately coarsely, sparsely punctate with tessellate-granular interspaces; first tergum with punctures separated by 2 diameters, terga 2 to 4 with punctures finer, separated by 2 diameters or slightly less; pubescence moderately long, erect on basal elevation of tergum 1, moderately short, erect on basal elevation of tergum 2, short, suberect on basal elevations of terga 3 and 4; short, subdepressed on apical depressed bands of terga 2 to 4 with spatulate hairs laterally forming weak medially interrupted hair bands on terga 1 to 3, hair band complete on tergum 4. Length 8 to 10.5 mm, forewing 6.5 to 7.5 mm.
MALE. — Integument gunmetal green with bluish reflections; antenna uniformly dark brownish-black, forewing with stigma yellow-brown, clypeus with narrow, transverse, subapical, dark band with violaceous reflections; pubescence pale, white except anal fimbria golden, laterally on face, above and behind eye black. Head moderately shiny, coarsely, closely punctate with tessellate interspaces; clypeus, latero- and supraclypeal areas with punctures separated by less than one diameter; parocular depression short, linear; eyes convergent below; antenna with segments 1 to 3 of flagellum as 12:6:8; labrum with process strongly recurved, usually shallowly emarginate apically with longitudinally grooved outer face and teeth appearing fused (fig. 42); mandibles short; gena moderately shiny, moderately coarsely punctate with tessellate interspaces, short, fine striae associated with punctures, punctures separated by slightly more than one diameter; pubescence of clypeus moderately long, moderately dense, subdepressed. Mesosoma dull, coarsely, shallowly punctate with tessellate-granular interspaces; pronotum with punctures separated by 1 to 2 diameters, Interspaces transversely tessellate, dorsolateral angle absent, without lateral fold; mesoscutum with notaulus somewhat indistinct and punctures separated by one diameter; scutellum with punctures separated by one diameter or slightly less; metanotum somewhat rugose-punctate; propodeum rugose-punctate with punctures separated by one diameter, enclosure with inner basal triangular area irregularly rugulose and blue with median longitudinal carinula, laterally and apically finely reticulate and green; episternum 2 somewhat rugose-punctate; wing pale, submarginals 1:2 (28.5:31), stigma : rest of marginal cell (30: 40), hind wing with jugal lobe very narrow and without incision between it and vannal, reaching beyond level of cu-v; pubescence long, sparse. Metasoma moderately dull, moderately finely, sparsely punctate with tessellate-granular interspaces; punctures separated by 3 to 4 diameters on terga 1 to 5; pubescence of tergum 1 long, erect, tergum 2 moderately long, suberect, terga 2 to 5 moderately short, suberect, apicolateral hairs spatulate and forming weak, medially interrupted hair bands on terga 1 to 3, more or less complete hair bands on terga 4 and 5. Length 7 to 9.5 mm, forewing 5.5 to 7 mm.