Reprinted with permission from the University of Nebraska State Museum from:
Ribble, D. W. 1968. Revisions of two subgenera of Andrena, Micrandrena Ashmead and Derandrena new subgenus (Hymenoptera: Apoidea). Bulletin of the University of Nebraska State Museum 8: 1-124.
Please report text errors to: leah at discoverlife dot org.
This species has been much confused with Andrena nigrae and A. salictaria. A very few specimens of illinoiensis bear salictaria determination labels, but many specimens of salictaria and nigrae have been misidentified as illinoiensis. Robertson (1910) states that he had earlier mixed salictaria with illinoiensis. All three species can occur on the same flower at the same locality on the same date as they do in Nebraska and in other areas. Therefore, unless literature refers to particular specimens (such as types) or to localities where only one species is found (which it rarely does) one cannot place with certainty the references in the synonymy under the correct species.
The males of illinoiensis have a unique tuft of hairs on the turned down margin of sternum six. The genital capsule is also distinctive (figs. 59-61). The females of nigrae, salictaria and illinoiensis are more difficult to separate, especially if the specimens are not in good condition. All the characters used to separate the females may break down occasionally, but by using a combination of characters nearly all specimens can be placed with certainty. The females of illinoiensis have luxuriant apical abdominal fasciae on terga 2-4, and the band on tergum three is not interrupted medially. Both sexes have a small pterostigma (for Micrandrena) and light-colored tarsi.
The descriptions below are based mainly on a male from Lincoln, Nebraska, April 30, 1964, D. W. Ribble, on Salix nigra and a female from Jamaica (10 mi. S. Lincoln), Nebraska, May 13, 1964, 0. W. Isakson. These specimens are typical of illinoiensis and were collected near the center of the range of the species. A total of 2,293 bees of this species were examined.
FEMALE. MEASUREMENTS AND RATIOS. — Length, 7.9 mm; width of mesothorax, 2.4 mm; wing length from tegula, 6.0 mm; facial length/width, 1.03; foveal length/width, 3.33.
INTEGUMENTAL COLOR. — Deep red-brown to black except: head and thorax with deep blue-black or few deep purple metallic reflections; tip of mandible deep red; flagellum orange-brown below; wings light amber, veins and pterostigma darker amber; tegula amber except at base; terga and sterna with amber apices; tips of fore- and mid-tibiae, hind tibia and tarsi deep yellow; tibial spurs light amber; claws red-amber.
STRUCTURE. — Antenna reaching just beyond tegula; scape reaching to one ocellar diameter below medium ocellus, nearly as long as flagellar segments 1-5; flagellar segment 1 about as long as 2 and 3 together, tapered toward base; segment 2 slightly shorter than 3, both slightly tapered; segments 3 and 4 of equal length; middle segments slightly wider than long; ultimate segment rounded in dorsal view, pointed in lateral view, half again as long as broad. Eye about four times as long as broad in anterior view, inner eye margins converging slightly below. Malar space about five times as wide as long. Mandibles decussate in repose, extending just past midline; apex rounded; inner rounded subapical tooth present. Galea with outer margin below palpus expanded into a large lobe; both margins curving downward, tapering to a narrowly rounded apex; surface shiny, with fine reticular shagreening which form shallow, flat bottomed pits. Maxillary palpus with segments in ratio of about 1.0:1.3:1.0:1.1:1.1:1.3; segments tapering toward bases; segment 6 slender, flattened; segments 5 and 6 extending beyond galea. Labial palpus with segments in ratio of about 1.5:1.2:1.0:1.2; segments tapering towards bases; segment 1 curved, segment 4 slender, flattened; segments 3 and 4 attached subapically. Labrum about two and a half times as wide as long, outer margin broadly rounded from side to side; process almost half as wide and almost half as long as entire labrum, raised, shiny, triangular, apicolaterally sinuate. Clypeus half again as broad as long, protruding beyond lower margin of eye by half width of eye in lateral view, shiny, punctate; punctures large, far apart, edges indistinct, becoming smaller and closer together laterally and basally; surface shagreened much like galea, except pits larger, coarser shagreening obscuring punctures at base of clypeus, center of clypeus without shagreening. Supraclypeal area with distinct rugae, otherwise sculptured like base of clypeus. Genal area in lateral view slightly more than half as wide as eye, surface with reticular shagreening. Vertex elevated above eyes, extending past lateral ocellus by one ocellar width; surface between ocelli very rough with irregular shagreening; punctures indistinct; surface above fovea smoother, with reticular shagreening. Face above antennal fossae with indistinct punctures, pronounced vertical rugae, irregular shagreening; frontal line between middle ocellus and supraclypeal area distinct, becoming carinate on lower part. Facial fovea reaching dorsal margin of eye, two-thirds width of eye, rounded dorsally, lateral margins tapering two-thirds distance of eye to rounded point; inner margin distinctly separated from eye margin, lower half markedly separated.
Pronotum evenly rounded from side to side, without humeral angle, sutures extending from pit at base of pronotal lobe to dorsum and to mesad on anterior margin, surface with reticular shagreening. Mesoscutum with indistinct punctures, surface with coarse reticular shagreening; parapsidal lines distinct. Tegula oval, with weak reticular shagreening. Scutellar surface smooth with distinct, widely separated punctures, reticular shagreening minute; scutellum faintly depressed in center. Metanotal surface with indistinct punctures, roughened, with irregular shagreening. Propodeum with dorsal enclosure concave on anterior margin, posterior margins meeting to form a "V," enclosure sloping gently over anterior two-thirds, posterior third vertical, surface with coarse reticular shagreening, becoming rugose towards base; propodeum with posterior surface divided by deep vertical sulcus, posterior and lateral surfaces divided by an angle, no carina present, posterior and dorsolateral areas on same level and surrounding enclosure, punctures indistinct, shagreening slightly smaller and less regular than posterior part of enclosure; corbicular surface with few indistinct punctures, shagreening less granular and more even than on posterior surface. Mesepisternum with surface similar to mesoscutum, but reticular shagreening more uneven. Metepisternum with surface similar to corbicular surface, shagreening less distinct above. Middle basitarsus nearly parallel-sided. Hind tibia moderately slender, half again as wide as basitarsus. Claws with large tooth on inner margin. Anterior tibial spur bent, with broad lamella along basal half of inner margin, spur serrate along distal half of inner margin; middle tibial spur long, slender, nearly straight, serrate along posterior margin; hind tibial spurs long, slender, nearly straight, spurs of equal length, spurs serrate along posterior margins. Wings with pterostigma moderately large, only half again as wide as prestigma; three submarginal cells; first transverse cubital vein ending three vein widths from pterostigma; first m-cu vein ending near middle of second submarginal cell.
Metasomal terga shiny, with scattered minute punctures, surface with fine reticular shagreening. Pygidial plate triangular, broadly rounded at apex, central portion slightly raised. Sternum 1 emarginate; sterna with many fine punctures, surface with fine reticular shagreening.
VESTITURE. — White. Hairs abundant, long, straight, very plumose except: those of facial fovea short; eye with minute, simple hairs; propodeal corbicular hairs few, simple in center, along dorsal margin hairs numerous, curved, with long weak branches; terga 1-4 hairs (except for apical fasciae) fine, short, weakly plumose; terga 2-4 with dense apical fasciae, interrupted medially on tergum 2, hairs of fasciae extending beyond apex of terga by half their length, nearly half as long as exposed tergal length; hairs of sternum 1, center of sternum 2 and subapical fimbriae on sterna 2-5 more erect, much longer and having longer branches than other sternal hairs, except apical row of short, appressed, plumose hairs on sterna 1-4, row on sternum 5 much longer; trochanteral flocculus greatly curved, hairs with long weak branches. Tibial scopa with long hairs, those of anterior part longest, curved posteriorly, the most anterior and posterior ones with few branches; other leg hairs valuable in structure.
MALE. MEASUREMENTS AND RATIOS. — Length, 6.7 mm; width of mesothorax, 2.1 mm; wing length from tegula, 5.4 mm; facial length/width, 1.0; flagellar segment 1/segment 2, 1.30.
INTEGUMENTAL COLOR. — Black except: head and thorax with deep blue-black metallic reflections; tip of mandible deep red; flagellum yellow-brown below; wings and tegula as in female; terga and exposed sterna with amber apices; sterna otherwise deep red-brown to black; tarsi red-brown; tibial spurs light amber; claws red-amber.
STRUCTURE. — Antenna reaching just past middle of scutellum; scape reaching to one ocellar diameter below medium ocellus, longer than flagellar segments 1-3; segment 1 slightly longer than 3, much longer than 2, tapered towards base; middle segments as long as broad; ultimate segment pointed in lateral view, rounded in dorsal view, about twice as long as broad. Eye three times as long as broad in anterior view, inner eye margins slightly convergent below. Malar space about seven times as wide as long. Mandible as in female. Galea as in female. Maxillary palpus as in female but segments in ratio of about 1.4:1.6:1.3:1.3:1.0:1.3. Labial palpus as in female but segments in ratio of about 2.0:1.2:1.0:1.4. Labrum two and a half times as wide as long, apical margin broadly rounded from side to side; process almost half as long as entire labrum and slightly more than half as wide, process raised, shiny, expanded towards base, apex broadly emarginate. Clypeus half again as wide as long, shiny, protruding beyond lower margin of eye by about half width of eye in lateral view; punctures large, distinct, close, becoming closer at extreme basal and lateral areas; shagreening absent in center, becoming coarse at extreme basal and lateral areas and obscuring punctures there. Supraclypeal area like clypeus only coarser shagreening obscuring punctures. Genal area, vertex and face above antennal fossae as in female, except sculpturing coarser.
Pronotum as in female. Mesoscutum and tegula as in female. Scutellum sculptured as in mesoscutum. Metanotum sculptured as in mesoscutum except reticular shagreening more irregular. Propodeum as in female, but sculpturing inside (except base) and outside enclosure the same, shagreening on lateral surface further apart and more regular than dorsal and posterior surfaces. Mes- and metepisternum as in female. Wings, claws and tibial spurs as in female.
Metasomal terga as in female except with seven exposed terga; 7 with broad point at apex. Pygidial plate absent. Exposed sterna as in female except sternum 6 with medium part of apex bent strongly downward, forming large semicircular emargination surrounded by the reflexed sternal margin, this reflexed margin possesses two anterolateral, rounded, elevated portions.
Sternum 7 emarginate at apex with two large rounded lobes, each bearing numerous long, branched setae (fig. 62). Sternum 8 convex, with base expanded into large plate (fig. 63); apex expanded into large rounded lobe; shaft bent downward and then forward, shaft as long as base; posterior three-fourths of shaft and lobe with long, plumose setae; some setae reaching far beyond apex. Gonocoxite bent downward, bent part narrowed toward apex, apex with small expanded knob, subapical dorsal part with few small setae, dorsal lobes small. Penis valve bent downward, apex tapering to narrowly rounded point, apex not reaching beyond tip of gonocoxite, valve much expanded basally, base with large lateral lobes (figs. 59-61).
VESTITURE. — Color as in female. Hairs as in female except: face, especially clypeus, with many more hairs; facial fovea reduced to a small patch of hair along anterodorsal eye margin; apical fasciae weaker on terga 2-4, interrupted, very weak on terga 1 and 5; sternum 6 with central apical tuft of hairs; hairs specialized for pollen collecting absent.
VARIATION. — All specimens from Arizona and adjacent California and Utah are noticeably smaller in size. The five males examined from Blythe, California, and extreme southwestern Utah have a mean wing length of 4.98 mm. Six females from six different localities in Arizona and southwestern Utah have a mean wing length of 5.34 mm. Five males and six females from the Lincoln, Nebraska vicinity, have mean wing lengths of 5.52 and 5.95 mm respectively. A few small individuals do occur in collections from areas other than the southwest. The smallest female examined (not included in the above measurement) from Arizona (Baker no. 2522) has a wing length of 4.2 mm and possesses especially weak apical fasciae on terga 2-4. Other females with the same collection number are normal for this area. Occasionally females from other areas have weak bands, approaching the condition found in Andrena nigrae and salictaria.
Small specimens from the southwest also have darkened legs and antennae; the distitarsi alone or only the last segment of them are light in color. Populations from other areas also exhibit darkened legs which may or may not be accompanied by darkened antennae. The lower side of female antennae at a given locality are usually darker in color than the lower side of male antennae. In the southwest females have nearly all brown antennae while those of the males are red-brown below. Populations from other areas exhibit darkened antennae but the females are not quite as dark as they are in the southwest. Judging from other Utah material there is probably a continuous gradation between the southwestern specimens and more eastern specimens.
Individual specimens are found with yellowish body hairs rather than the normal white hairs and darker specimens appear to be newly emerged individuals. The margin of the clypeal process varies (more noticeably in the females); it may be evenly curved or rarely sinuate (as in the description of the female above) forming in the female lateral tooth-like lobes and in the male an apical emargination.
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 7 mm.; clypeus broadly convex, projecting about one-third below suborbital line, smooth and somewhat shining, punctures exceedingly minute, well separated medially, becoming close and obscure laterally; facial foveae narrow, occupying above about half of space between eyes and ocelli (as in fragariana, fig. 29), covered with pale ochraceous tomentum; space between margin of vertex and lateral ocelli much narrower than their diameter; cheeks slightly narrower than eyes, rounded posteriorly, somewhat shining beneath rather dense pubescence; malar space lacking; basal segment of flagellum subequal to 2nd and 3rd combined; process of labrum quite small, semicircular, about twice as broad as long; pubescence of head, thorax and legs pale ochraceous to whitish; thoracic integument dull, finely tessellate, somewhat purplish, punctures of scutum extremely minute and obscure, well separated, becoming sparse posteriorly, fine and rather close on the more shining scutellum; pleura without visible punctures; dorsal area of propodeum nearly horizontal, rather extensive, triangle tessellate, not contrasting with adjacent areas; propodeal corbicula rather short, without a well defined anterior fringe, whitish; trochanteral floccus white, quite well developed but rather short; hind tibiae somewhat broadened apically, apex nearly twice the width of basitarsi, scopa quite dense, hairs rather short, simple, entirely white; all tarsi pale ferruginous, front and middle basitarsi slightly narrower than their respective tibiae; 2nd submarginal cell considerably shorter than 3rd, receiving 1st recurrent near middle; abdominal terga smooth, but rather dull, the more basal segments microscopically tessellate, punctures inevident, surface obscurely purplish. apical depressed areas narrow and shallow, yellow-hyaline, discal pubescence extremely short and sparse, entirely pale, terga 2-4 with narrow, white, apical fasciae, interrupted on tergum 2 and more narrowly on 3, tergum 5 with a pale brownish, apical fimbria.
MALE — Length 7 mm.; clypeus only very slightly convex, projecting very slightly below suborbital line, very closely and finely punctate beneath short, dense pubescence; space between margin of vertex and lateral ocelli much narrower than their diameter; cheeks slightly narrower than eyes, rounded posteriorly, densely pubescent; malar space lacking; basal segment of flagellum slightly shorter than 2nd and 3rd combined, 2nd much broader than long, segments beyond 2nd pale ferruginous beneath; process of labrum semicircular, fully twice as broad as long; mandibles short, with a small but distinct, inner, subapical tooth, overlapping hardly at all; pubescence of head, thorax and legs entirely pale ochraceous, rather short but rather dense, thoracic integument dull, finely tessellate, punctures of scutum very minute and obscure, well separated, becoming rather sparse posteriorly, exceedingly minute and quite sparse on scutellum, surface obscurely purplish; pleura not visibly punctate; dorsal area of propodeum quite extensive, nearly horizontal, triangle finely roughened; all basitarsi slender and elongate, considerably narrower than their respective tibiae, pale ferruginous; 2nd submarginal cell much shorter than 3rd, receiving 1st recurrent slightly beyond middle; abdominal terga smooth but rather dull, microscopically tessellate, obscurely purplish or greenish, not visibly punctate, apical depressed areas rather narrow and shallow, becoming yellowish-hyaline along rims, discal pubescence extremely short and sparse, entirely pale, the fasciae very poorly developed; apical portion of sternum 8 very narrow and slender, tip narrowly rounded, covered beneath with rather long, dense pubescence; penis valves bulbous medially, slightly narrowed toward base and produced apically into a sharp, slender, spine-like tip, gonocoxites slender, rather abruptly flexed medially, strongly narrowed apically, gonocoxal lobes not at all produced.
DISTRIBUTION — Transcontinental in southern Canada and the northern United States, reaching South Carolina in the East; April to June.
FLOWER RECORDS — Prunus, Salix and Taraxacum. Robertson (1929) records this species on Antennaria, Geranium, Stellaria and Zizia.