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.
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Lanham (1949) and Linsley (1951) considered trapezoidea and primulifrons as Micrandrena, They are now tentatively retained in Micrandrena and are treated below since they are certainly related to the Micrandrena here included (see discussion under Micrandrena). Specimens, literature and types have been accumulated for taxonomic consideration of these two species which present interesting relationships.
Andrena trapezoidea and primulifrons are closely related and are considered sibling species. They are easily distinguished from other Micrandrena considered here by the distinct punctures on the abdominal terga, abdominal sterna and thorax. The heavy punctures are accompanied by a heavier integument. In other respects trapezoidea and primulifrons are little different from other Micrandrena. They are probably more closely related to micheneri than to any other species considered at this time. Andrena trapezoidea and primulifrons can also be separated from other Micrandrena on the basis of the male terminalia (figs. 85-87). Andrena trapezoidea and primulifrons can be separated from each other by the characters given under the latter species.
The descriptions below are based mainly on a male and a female from Palo Duro Canyon State Park, Randall County, Texas (April 8, 1963, R. B. Roberts and M. G. Naumann). The series to which these specimens belong contains 127 of the 167 specimens (representing 13 different collections) known of this species.
FEMALE. MEASUREMENTS AND RATIOS. — Length, 7.3 mm; width of mesothorax, 2.2 mm; wing length from tegula, 5.8 mm; facial length/width, 1.00; foveal length/width, 3.00.
INTEGUMENTAL COLOR. — Black to dark brown except: body with bluish-black reflections; flagellum orange below; tegula amber; terga with broad amber apices; sterna with narrower amber apices; color otherwise as in piperi, STRUCTURE. — Sculpturing in general finer over entire body than in piperi. Head otherwise as in piperi except: scape reaching to less than one ocellar distance from middle ocellus, distinctly longer than flagellar segments 1-4; flagellar segment 1 much shorter than 2 and 3 together; middle segments as wide as long; eye about four times as long as broad in anterior view; inner eye margins nearly parallel below; maxillary palpus with segments in ratio of about 1.3:1.6:1.4:1.4:1.0:1.3, apical segment nearly round in cross-section; labial palpus with segments in ratio of about 2.5:1.2:1.0:1.5; labral process one-third as wide and half as long as entire labrum, apex evenly rounded from side to side; clypeus with rather coarse reticular shagreening, apically clypeus very shiny, without shagreening; genal area in lateral view as wide as eye; surface between ocelli about as shiny and rough as surf ace above facial fovea; fovea reaching upper eye margin.
Mesosoma as in piperi except: mesoscutum with distinct punctures, punctures partly obscured by reticular shagreening, shagreening weak in center of mesoscutum; parapsidal lines indistinct; scutellar surface more shiny than mesoscutal, shagreening absent in center; metanotal surface more coarsely sculptured than mesoscutal; posterior and dorsolateral areas of propodeum not raised above enclosure, surface sculptured like enclosure; mesepisternum with surface more coarsely sculptured than mesoscutal; hind tibia, middle and hind basitarsi broadened, tibia one-fourth wider than basitarsus; posterior spur of hind tibia much longer than anterior spur; pterostigma medium-sized, half again as wide as prestigma; first transverse cubital vein ending several vein widths from pterostigma.
Metasoma as in piperi except: terga very shiny, punctures distinct, shagreening absent or very weak; sterna with larger punctures than piperi.
VESTITURE. — Hairs as in piperi except: hairs on dorsum of thorax moderate in length, dorsum without moss-like appearance; tarsal hairs white; tergum 1 nearly bare; terga 2-4 hairs (except for apical fasciae) short, plumose, abdomen not having as marked dusty appearance as piperi; apical fasciae interrupted on terga 2 and 3, complete on 4; tibial scopal hairs short, anterior-most weakly curved posteriorly.
MALE. MEASUREMENTS AND RATIOS. — Length, 6.7 mm; width of mesothorax, 2.0 mm; wing length from tegula, 5.0 mm; facial length/width, 1.00; flagellar segment 1/segment 2, 0.68.
INTEGUMENTAL COLOR. — Black to dark brown except: body with bluish-black reflections, dorsum of thorax with some purplish or golden reflections; clypeus and parocular areas cream colored; flagellum orange-brown below; color otherwise as in piperi.
STRUCTURE. — Sculpturing in general finer over entire body than in piperi. Head otherwise as in piperi except: antenna reaching to abdomen; scape much shorter than flagellar segments 1-3; segment 1 two-thirds as long as 2, slightly over half as long as 3; segment 2 not tapered; middle segments much longer than broad; eye three times as long as broad in anterior view; maxillary palpus with segments in ratio of about 1.0:1.6:1.3:1.1:1.1:1.4; labial palpus with segments in ratio of about 2.2:1.5:1.0:1.5; labrum about two and one-half times as wide as long; labral process about two-thirds as wide and two-thirds as long as entire labrum, greatly expanded towards base; clypeus with shagreening very fine apically, surface very shiny apically; vertex slightly more coarsely sculptured than trapezoidea female.
Mesosoma as in trapezoidea female except: mesoscutum with marked reticular shagreening over entire surface, parapsidal lines distinct; metepisternum weakly shagreened, very shiny below, sculpturing much finer than on lateral surface of propodeum; hind tibia and basitarsus unmodified.
Exposed metasoma sculptured as trapezoidea female; otherwise exposed metasoma as in piperi.
Sternum 7 distinctly emarginate at apex, producing two medium-sized, rounded lobes; each lobe bearing few long, branched setae; few simple, small setae on apex of sternum below lobes (fig. 88). Sternum 8 with small basal plate, plate flexed ventrad, sides curving upward; apex expanded, rounded; shaft very long, expanded towards plate, with many long, nearly straight, branched setae, some setae just reaching beyond apex (fig. 89). Gonocoxite bent downward; apex slightly expanded in lateral view, dorsolateral part with many weakly branched setae; dorsal lobes wide, short. Penis valve bent downward, apex narrowly rounded in lateral view, medially moderately expanded (figs. 85-87).
VESTITURE. — Hairs as in piperi except: apical fasciae weak on tergum 1, interrupted on terga 2 and 3, complete on 4; other tergal hairs longer, more erect than in trapezoidea female.
VARIATION. — This species has been collected only a few times in a limited area and as one might expect, shows very little variation. The only significant difference noticed is in the male antenna! color, a few specimens have the flagellum bright orange below rather than orange-brown.