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. parachalybea and more I distantly to A. cuneilabris and A. foxii. The males may be distinguished from A. parachalybea by their greener integument; weakly, apically emarginate labral process (compare figs. 4 and 6); and more coarsely imbricate interspaces on metasomal tergum 2. From A. cuneilabris males they are easily recognized by the; rugose-punctate scutellum with contiguous punctures. The females are distinguished from those of A. parachalybea by their greener integument; the larger, more widely separated punctures of metasomal tergum 2; and the predominance of dark pubescence on tho face. From femaless of A. cuneilabris they are readily recognized by the contiguously, rugose-punctate mesoscutum and scutellum, the dark face pubescence, and broader labral process (compare figs. 3 and 5). Both sexes are distinguished from A. foxii by a number of characters, but most readily by the integumental color of the head and mesosoma which is black in A. foxii.
A. chalybaea and A. parachalybea can be distinguished on morphological and ecological grounds, although the structural characters used are primarily quantitative. They are completely allopatric, with the closest known populations being separated by about 25 air miles (map 1). Thus, there is no direct evidence that they are reproductively isolated in the physiological and genetic sense.
Some of the structural characters which separate the two species are variable within populations of A. chalybaea. Individuals of both sexes are found with bluer integumental color and slight emarginations in the apices of their labral processes; females with varying degrees of pale facial pubescence are not uncommon. Although these characters vary in the direction of A. parachalybea no individuals of A. chalybaea show all the variant characters in combination. These variations show no geographic trends, and may even be met more commonly in populations which are farthest geographically from those of A. parachalybea. Although both species are oligolectic on morning-opening, yellow-flowered species of Camissonia, they are ecologically separated. A. chalybaea collects pollen only from C. ovata, while A. parachalybea, appears less specific in its pollen-gathering habits since it has been found collecting pollen from C. campestris subsp. campestris, C. bistorta and C. cheiranthifolia subsp. suffruticosa. There are also differences in the edaphic situations of the nest sites. A. chalybaea constructs its nests in heavy clay-loam soils where C. ovata grows, while A. parachalybea shows a preference for loose, sandy soils whore all its pollen sources are found. Adaptations to different climates may also partially explain why those two species remain allopatric. A. chalybaea inhabits the cooler, more moist northern coastal areas, while A. parachalybea is found in the warmer, drier areas of southern coastal California and the western edge of the Mojave Desert.
Despite the lack of direct evidence for reproductive isolation between A. chalybaea and A. parachalybea, it is my opinion that the two names represent valid species because they are morphologically distinct although the characters used are subtle, their ranges are mutually exclusive, and they show ecological differences.
FEMALE. — Integument blue-green; antenna uniformly dark brownish-black, clypeus with a short, median, subapical, triangular dark area with violaceous reflections, forewing with stigma mahogany; pubescence pale, white on vertex and lower two-thirds of gena, pale gray on antennal scape and sparsely on clypeus, dark brown laterally on face, above antennal base, and upper third of gena, white on mesosoma, outer surface of tibial scopa white anteriorly, dark purplish-brown posteriorly, white on metasoma, rust-brown on anal fimbria; facial foveae with black sheen, tomentum brown above, white below. Head tessellate, densely punctate; clypeus, latero- and supraclypeal areas coarsely, contiguously punctate with dorsal rim of punctures raised as a small rugosity, interspaces shiny; facial foveae extending from summit of eye to below antennal base; eyes slightly arcuate medially; antenna with segments 1 to 3 of flagellum as 17:7:7; labrum with process broad, rounded apically, not emarginate at apex (fig. 3); subgenal coronet long, well developed; gena finely, obliquely striate laterally becoming more coarsely, longitudinally striate ventroposteriorly; pubescence of clypeus suberect. Mesosoma closely, coarsely rugose-punctate with moderately shining, tessellate interspaces; pronotum transversely tessellate with punctures coarse, separated by one diameter, dorsolateral angle obtusely angulate, not elevated, with thickened lateral fold which does not project anteriorly; mesoscutum with punctures usually separated by less than one diameter, notaulus somewhat distinct depression; punctures of scutellum and metanotum contiguous; propodeum shiny, rugose-punctate, enclosure irregularly rugose with distinct median longitudinal carina; episternum 2 coarsely rugose punctate; wing lightly infuscated, submarginals 1:2 (23.5:23.5), stigma : rest of marginal cell (20.5:31.5), hind wing with jugal lobe broad and with incision between it and vannal, reaching beyond level of cu-v (fig. 86); posterior trochanter with long, curved, white, perfect floccus; tibial scopa with long, loose, simple hairs except for narrow band of plumose hairs along inner posterior margin, posterior hairs of scopa nearly twice as long as width of tibia at apex; pubescence of mesoscutum long, pale. Metasoma moderately shiny, interspaces tessellate; first tergum with numerous irregularly spaced, large punctures with anterior margin elevated like tilted craters; terga 2 to 4 with punctures smaller and more regularly spaced, separated by about one diameter on basal elevations, punctures fewer and more scattered on depressed apical margins, with fine transverse striae; pubescence long, erect, sparse, successively shorter on succeeding segments, that of tergum 1 twice as long as that of tergum 2. Length 10.5 to 12 mm, forewing 8.5 to 9.5 mm.
MALE. — Integument, blue-green; antenna uniformly dark brownish-black, clypeus with short median, subapical triangular, dark area with violaceous reflections, forewing with stigma mahogany; pubescence pale, white on clypeus, frons, antennal scape, vertex, and lower three-fourths of gena, black on face laterally, in wide band along inner margin of eye, on dorsal one-fourth of gena, and thin bands along outer margins of eyes, white on meso- and metasoma, yellow-brown on tergum 7. Head tessellate, densely punctate; clypeus, latero- and supraclypeal areas coarsely, contiguously punctate with shiny interspaces; parocular depression short, linear; eye slightly arcuate medially; antenna with segments 1 to 3 of flagellum as 16: 11: 12; labrum with process broad, somewhat parallel-sided, slightly longer than width at apex (fig. 4); mandibles long, decussate; gena somewhat coarsely, transversely striate laterally, becoming more coarsely striate ventrally; pubescence of clypeus long, dense, and subdepressed. Mesosoma coarsely, closely, deeply punctate with edges of punctures raised and moderately shiny, tessellate interspaces; pronotum tessellate with sparse punctures, dorsolateral angle right-angled, somewhat elevated with thickened lateral fold not, projecting anteriorly; mesoscutum with punctures usually separated by less than one diameter, notaulus somewhat distinct depression; scutellum and metanotum with punctures contiguous; propodeum moderately shiny, finely rugulose, enclosure irregularly rugose with distinct median, longitudinal carina; episternum 2 coarsely rugose-punctate; wing pale, submarginals 1:2 (19.5:20.5), stigma : rest of marginal cell (20:27.5), hind wing with jugal lobe broad and with incision between it and vannal, reaching beyond level of cu-v; pubescence of mesoscutum long, pale. Metasoma moderately shiny, with tessellate-granular interspaces; first tergum with numerous irregularly spaced, large punctures with anterior margin elevated like tilted craters; terga 2 to 4 with punctures smaller and more regularly spaced, separated by about one diameter on basal elevations, punctures fewer and more scattered on depressed apical margins, with fine, transverse striae; sternum 8 (fig. 69); genital capsule (figs. 57 and 58); pubescence pale, long, erect on tergum 1, half as long, erect on tergum 2, on terga 3 to 5 half as long as on tergum 2, erect on disks, suberect on apical margins. Length 9.5 to 10 mm, forewing 8.5 to 9 mm.
Pupa. — Shape and form essentially as adult. Spines and processes not present in adults as follows: mandible with large tubercle on ventral surface near apex; posterior lobe of pronotum produced as spine; scutellum with a pair of large, erect protuberances; metanotum with broad median protuberance; tegula with large protuberance; forewing with small anteromedian tubercle and small basal tubercle; fore, mid, and hind coxae each with long inner apical spine; fore, mid, and hind trochanters each with long posterior apical spine, that of hind trochanter of female very long and recurved toward base of femur; fore and mid femora each with posterior basal protuberance; hind tibia with small basal protuberance near position of apex of basitibial plate; metasomal terga 2 to 4 in female and 2 to 5 in male each with transverse subapical row of large spicules.
Postdefecating larva (fig. 55). — Somewhat C-shaped, moderately robust, with distinct intersegmental furrows and prominent, transverse, dorsolateral tubercles which reach downward almost to level of spiracles; tubercles most prominent on thorax, high and rounded with depressed dorsal connecting ridges on abdominal segments 1 to 8, becoming less conspicuous on succeeding segments, inconspicuous on segment 9, absent on anal segment. Head naked, broader than long (6.5: 5.5), vertex with moderately large convexity on either side of cleavage line, frons with large rounded elevation above antenna and with antenna arising from rounded prominence. Marginal thickening of head capsule weak and inconspicuous; posterior tentorial pit large, distinct; epistomal suture indicated by a weak line; cleavage line weak; antenna represented by small convexity; labroclypeal suture weak; labrum with two moderately large lateral tubercles; mandible with apex attenuate and sharply pointed, upper margin apically with 4 or 5 conspicu¬ous tooth, cusp finely, densely toothed; maxilla with apex broadly rounded, maxillary palp longer than broad; labial lobe short of maxilla, labial palp minute, much smaller than maxillary palp; salivary opening a curved slit. Body without setae; spiracular atrium projecting slightly above body surface, peritreme flat, atrium simple, without internal ridges or spines, collar around primary tracheal opening present, diameter of collar opening equal to diameter of atrial opening; anus a transverse slit, slightly below midline.