Reprinted with permission of the American Entomological Society from:
LaBerge, W. E. 1977. A revision of the bees of the genus Andrena of the Western Hemisphere. Part VIII. Subgenera Thysandrena, Dasyandrena, Psammandrena, Rhacandrena, Euandrena, Oxyandrena. Transactions of the American Entomological Society 103: 1-144.
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It is unfortunate that Robertson did not recognize both of the common eastern species of this subgenus and thus avoid the confusion in names that has resulted. Without doubt many specimens previously determined as robertsonii are in reality brevipalpis. Most of the citations in the synonymy given above refer to brevipalpis at least in part.
Andrena robertsonii is closely related and very similar to A. brevipalpis. The female of robertsonii can be recognized by its shorter vertex, dull and virtually impunctate terga and usually dull scutellum. The male of robertsonii has the first flagellar segment about as long as the second segment or only slightly longer, the flagellum dark below, a short vertex as in the female, and usually dull metasomal terga as in the female.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 8-10 mm width, 2.0-2.5 mm; wing length, M = 3.08 ± 0.111 mm; FL/FW, M = 1.07 ± 0.006; FOVL/FOVW, M = 4.93 ± 0.080.
INTEGUMENTAL COLOR. — As in brevipalpis except flagellum below dark brown to dark reddish-brown and metasomal terga not rufescent basally.
STRUCTURE. — Antennae, eyes, malar space, mandible and galea as in brevipalpis but galea usually dull, finely shagreened. Maxillary palpus as brevipalpis but segmental ratio about as 0.9:1.0:0.6:0.5:0.5:0.5. Labial palpus as in brevipalpis but ratio about as 1.0:0.4:0.4:0.4. Labrum, clypeus, supraclypeal area and genal areas as in brevipalpis. Vertex short, above lateral ocellus equal to about three-fourths an ocellar diameter; structure as in brevipalpis.
Thoracic form and sculpturing as in brevipalpis except as follows: scutellum usually dull, reticularly shagreened; propodeal dorsal enclosure with irregular rugulae somewhat finer. Wing venation as in brevipalpis.
Metasomal terga 1-4 dulled by dense, fine, reticular shagreening, punctures absent or obscure on discs. Pygidial plate and sterna as in brevipalpis.
VESTITURE. — Color and distribution of hairs as in brevipalpis except as follows: metasomal tergum 3 with pale apical band interrupted medially by one-fourth to two-thirds width or more; tibial scopal hairs dense.
MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 7-9 mm; width 1.5-2.0 mm; wing length, M = 2.90 ± 0.118 mm; FL/FW, M = 1.17 ± 0.006; FS1/FS2, M = 1.03 ± 0.017.
INTEGUMENTAL COLOR. — As in brevipalpis except as follows: Clypeus usually pale yellow; flagellum dark brown to reddish-brown below; metasomal terga not rufescent basally.
STRUCTURE. — Antenna moderately long, in repose reaching metanotum; scape length equal to about first two and one-third flagellar segments; flagellar segment 1 equal in length to segment 2 or slightly longer (never more than one and one-fourth times as long), rarely slightly shorter; remaining segments longer than broad. Eyes, malar space and galea as in female. Maxillary palpus as in brevipalpis but segmental ratio about as 1.0:1.0:0.8:0.8:0.7:0.8. Labial palpus as in brevipalpis but ratio about as 1.0:0.5:0.5:0.5. Labrum, clypeus, supraclypeal area and genal area as in brevipalpis. Vertex as in brevipalpis but short, above lateral ocellus equal to about three-fourths as ocellar diameter. Face as in brevipalpis.
Thoracic form and sculpturing as in brevipalpis but mesoscutum and scutellum often completely dulled by fine reticular shagreening and propodeum with dorsal enclosure slightly more finely sculptured. Wing venation and legs as in brevipalpis.
Metasomal terga much as in female, discs dulled by reticular shagreening and punctures often absent to obscure, but less often as dull as in female. Sterna and terminalia as in brevipalpis.
VESTITURE. — Generally as in brevipalpis except as follows: tergal discs(especially 3-5) with suberect hairs usually white, more dense and longer than in brevipalpis.
TYPE MATERIAL. — The lectotype (here designated) female of serotina (INHS) was collected at Carlinville, Macoupin Co., Illinois, June 4, 1886, on Pastinaca sativa, by Charles Robertson. The holotype female (USNM) of dreisbachi was collected in Roscommon County, Michigan, June 5, 1955, by R. R. Dreisbach.
DISTRIBUTION. — A. robertsonii ranges from Oregon, Idaho and Utah east to Ontario in Canada and North Carolina and Connecticut in the United States (Fig. 13). It has been collected from April 26 into August but chiefly during May and June. In addition to the types listed above a total of 192 FF and 66 MM were examined from the localities listed below (only verified localities reported in the literature are included).
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 9 mm.; face slightly longer than broad; clypeus slightly convex, projecting slightly less than one-half below suborbital line, microscopically tessellate but somewhat shining, punctures very fine, quite sparse medially, becoming rather close at extreme sides; facial foveae rather narrow, occupying above only slightly more than half of space between eyes and ocelli, covered with silvery tomentum; space between margin of vertex and lateral ocelli subequal to their diameter; cheeks very slightly broader than eyes, rounded posteriorly, rather dull, punctures exceedingly minute and obscure; malar space extremely short; basal segment of flagellum subequal to 2nd and 3rd combined; process of labrum about twice as broad as long, narrowed to the rather broadly truncate apex; mandibles very slightly dilated beneath toward base; pubescence of head, thorax and legs rather thin, quite short, entirely whitish; thoracic integument dull, finely tessellate, punctures of scutum rather deep and distinct, but fine and well separated, becoming sparse toward center posteriorly, surface somewhat shining, those on scutellum more minute, more irregularly scattered, quite sparse; pleura without visible punctures; dorsal area of propodeum nearly horizontal, rather broad, triangle finely subrugose toward basal margin; propodeal corbicula short, rather poorly developed, whitish, without an anterior fringe; trochanteral floccus rather poorly developed, but hairs rather elongate, whitish; hind tibiae slender and elongate, apex but very slightly broader than basitarsi, scopa rather thin, hairs elongate, simple, entirely whitish; front and middle basitarsi quite slender, slightly narrower than their respective tibiae; 2nd submarginal cell considerably shorter than 3rd, receiving 1st recurrent beyond middle; abdominal terga smooth, shining, very finely and rather closely punctate, except for the somewhat more sparse punctures on basal tergum, apical impressed areas quite shallow, occupying medially about one-third length of disc, becoming yellowish-hyaline along rims, discal pubescence extremely short, thin and obscure, apparently pale in color, terga 2-4 with narrow, white, apical fasciae, that on tergum 2 more or less interrupted medially, tergum 5 with a brownish, apical fimbria.
MALE. — Length 7 mm.; face very slightly longer than broad; clypeus slightly convex, projecting but very slightly below suborbital line, yellow, except for two small black spots and the dark apical rim, smooth and shining, punctures fine but distinct, well separated medially but not sparse, becoming close at extreme sides; space between margin of vertex and lateral ocelli subequal to their diameter; cheeks subequal to eves in width. rounded posteriorly, rather dull, punctures exceedingly minute, obscure and close; malar space extremely short; basal segment of flagellum slightly longer than 2nd segment, but shorter than 2nd and 3rd combined; process of labrum subtriangular, with a rather broadly truncate apex; mandibles rather short, with a small but distinct, inner, subapical tooth, overlapping hardly one-third; pubescence entirely pale ochraceous on head and thorax above, more whitish below and on legs; thoracic integument dull, rather densely tessellate, punctures of scutum fine but rather deep and distinct, well separated anteriorly, becoming somewhat more sparse in center posteriorly, surface somewhat more shining, those on scutellum more minute and obscure, surface anteriorly shining, becoming dull posteriorly; pleura anteriorly with a few very minute, obscure punctures, hardly visible; dorsal area of propodeum more oblique, rather extensive, triangle finely subrugose; basitarsi slender and elongate, considerably narrower than their respective tibiae; 2nd submarginal cell considerably shorter than 3rd, receiving 1st recurrent just beyond middle; abdominal terga smooth and shining, finely and closely punctate except for the more sparse and minute punctures on basal tergum, apical impressed areas shallow and rather narrow, becoming obscurely brownish-hyaline along rims, discal pubescence extremely short, thin, erect and entirely pale, forming very narrow, thin and inconspicuous, ochraceous, apical fasciae at sides of terga 2-4; apical margin of sternum 6 quite strongly reflexed; apical portion of sternum 8 slender, rather short, sides nearly parallel, apex very slightly broadened, truncate, clothed beneath with rather short pubescence; penis valves slender apically, somewhat dilated basally, the dilated portion rather deeply grooved laterally, gonocoxites rather abruptly dilated toward apex, the resulting lobe narrowly rounded at tip, gonocoxal lobes quite strongly produced, narrowly rounded apically.
DISTRIBUTION. — Colorado, Nebraska and Minnesota, east to the New England states and Nova Scotia, south to Arkansas and Georgia; April to September.
FLOWER RECORDS. — Apocynum, Aronia, Brassica, Ceanothus, Pyracantha, Rhus, and Rubus. Recorded by Robertson (1929, as A. serotina) on Aruncus, Cryptotaenia, Pastinaca, Ptelea, Taenidia and Viburnum.
Described using the synonymous name: Andrena dreisbachi Mitchell
FEMALE. — Length 9 mm.; face somewhat longer than distance between eyes; eyes about parallel; foveae quite narrow, occupying hardly more than half of space between eyes and ocelli above (as in robertsonii, fig. 49), extending slightly below antennal line, covered with whitish tomentum: lateral ocelli separated from margin of vertex by somewhat less than their own diameter; cheeks about equal to eyes in width; clypeus moderately convex, projecting about one-third below suborbital line, rather dull and microscopically tessellate, with scattered, irregular, very minute and obscure punctures over median area, with the extreme lateral angles rather closely, deeply and distinctly punctate; face below ocelli finely striate and dull, vertex smooth but dull, with no evident punctures, cheeks smooth, somewhat shining toward margin of eye, without evident punctures; malar space hardly evident; process of labrum very broad, evenly rounded, median length hardly one-half basal width; basal segment of flagellum about equal to segments 2 and 3 combined, 2nd considerably shorter than broad, median segments about as long as broad; pubescence of head and thorax entirely pale, rather short and erect, quite dense on either side of antennae and on cheeks below, quite thin in general on thorax; scutum and scutellum smooth but rather dull, with scattered, exceedingly minute and obscure, well separated punctures: pleura quite smooth but dull and finely tessellate; dorsal area of propodeum very finely granular, surface on each side of this finely tessellate and dull, propodeal corbicula rather well developed dorsally, hairs rather short, with few if any hairs on interior and without an anterior fringe; trochanteral floccus complete; legs dark, pubescence entirely pale, basitarsi quite slender and parallel-sided, tibiae quite slender, tibial scopa of whitish, rather elongate hairs, spurs pale-testaceous; wings slightly yellowish, veins and stigma pale testaceous, 2nd submarginal cell about half length of 3rd, receiving 1st recurrent toward apex; tegulae piceous anteriorly, yellowish-hyaline posteriorly; abdominal terga smooth but dull, with exceedingly minute and barely visible punctures, segments 2-4 narrowly impressed apically, these areas more shining, becoming narrowly hyaline along rims, apical fasciae narrow, white, evident only towards sides of segments 2-4, apical fimbria pale-brownish.
TYPES. — Holotype: Female, Roscommon Co., Mich., June 5, 1955 (R. R. Dreisbach) [Dreisbach]. Paratypes: MICHIGAN: 2 FF, topotypical; 1 F, Missaukee Co., June 5, 1955 (Dreisbach); 1 F, Agr. Coll. June 20, 1888; 1 F, 13 miles north of Lapeer, May 30, 1937 (C. Sabrosky).
Paratypes are in the University of Michigan, in the collection of R. R. Dreisbach, and in the author's collection.