Female.-Length 7 mm, forewing 6 mm. Integument black, except for hyaline amber apical margins of abdominal terga and reddish brown flagella.
Head having width/length ratio 4.8/4.0, measuring between outer eye orbits and from vertex to bottom of clypeus, hairs white.
Clypeus with a few irregular shallow wrinkles, especially above; lower half shining, with a few coarse and irregularly spaced punctures, upper half flattened, reticulate, more regularly punctured. Face above clypeus vertically striate, above ocelli becoming coarsely granular, with polished impunctate area at dorsal ends of compound eyes. Facial foveae with dorsal ends extending slightly above eyes, width here slightly less than 1/2 distance between eye and lateral ocellus, extending below beyond antennal insertions but not as far as upper margin of clypeus, lower third abruptly narrowed to 1/2-1/3 width of upper portion by incurving inner margin of fovea and increasing width of integument between fovea and eye, which becomes more than 1/2 as wide as fovea. Antennae with scape plus pedicel reaching to middle of lower ocellus; 1st segment of flagellum longer then 2 3 outer margins. Process of labrum narrowly triangular. Mouthparts normal for the piperi group, 1st 3 maxillary segments about equal to length of galea.
Thorax. Pubescence on the thorax long for the group, sparse and erect dorsally, denser and decumbent on sides, color white tending to brown on median posterior surfaces of dorsum. Pronotum without shoulders, but with strong groove running anteromedially from base of pronotal lobe. Mesonotum shining but strongly reticulate, punctures small, sparse, 4-5 puncture-widths apart, mesoscutum about the same; metanotum coarsely reticulate; propodeum coarsely beaded, with delicate but distinct ridges on dorsal face, sculpture at edges of enclosure about the same as that of adjacent part of propodeum. Corbicula without anterior fringe, dorsal fringe poorly developed, interior with a few long simple hairs widely scattered over most of surface, integument of interior shining, rather coarsely reticulate. Hind leg with trochanteral floccus complete but sparse; hairs of tibial scopa simple, long, the hairs on posterior margin about as long as width of tibia at its widest point, entire scopa moderately loose and sparse; all hairs white, except for dark tuft at tibio-femoral junction; tarsi claw with tooth fully developed, of size normal for the piperi group. Wing membranes clear, veins amber, 1st transverse cubital vein ending 1 to 3 vein widths distad from pterostigma, basal vein falling well distad of transverse medial nervure.
Abdomen with terga semi-shining, reticulation moderately coarse. Tergum 1 without apical hair band, 2 with widely interrupted weak white hair band, 3 with band narrowly interrupted, 4 with band entire, caudal fimbria entirely brown tinged with orange; terga anterior to fimbria without long hairs dorsally; pygidial plate finely granular, narrowly rounded, with weakly developed raised central triangular area.
Type material. - Holotype, female, 4 miles north Boulder, Colorado, 5500 feet, 23 May 1980, collected at flowers Physaria bellii (U.N. Lanham). Seventeen paratypes, females: 2 with same data as holotype; 4 same except 24 and 25 May 1980 (K. Neff); 8 from 10 miles SW Loveland, Colorado, 26 May 1980, collected at flowers Physaria bellii (U.N. Lanham); 1 from 3 miles east Lyons, Colorado, 7 June 1980 (U.N. Lanham and K. Neff); 2 from 12 miles north Fort Collins, Colorado, 7 June 1980 (U.N. Lanham and K. Neff).
The name is pronounced with the second syllable accented and the “i” as in mile.
All localities named in type description are on or very near the outcrop of Cretaceous Niobrara limestone and shale that lies at the eastern base of the foothills of the Front Range. This habit is described in “Some Colorado Andrena of the subgenus Scaphandrena of presumed hybrid origin ...,” Lanham, 1981.
Of the 11 species of the piperi group of Micrandrena only three, including piperi, show a strong preference for Cruciferae.
The rather remarkable primulifrons group of Micrandrena is apparently oligolectic on crucifers, according to Ribble. The group is distinctive on account of heavy and coarsely punctate integument. The two species of the group, primulifrons Casad and trapezoidea Viereck have previously been known only from the southwest. It is therefore of interest to find a species that matches Ribble’s description of trapezoidea on crucifers in northeastern Colorado. I collected two females and a male at Briggsdale, Weld Co., 19 and 21 May 1979 from flowers of Descuraina and 2 females, 10 miles SW Loveland, 26 May 1980 from Physaria bellii. In his Micrandrena paper Ribble suggests that the primulifrons group is annectant between that subgenus and Scaphandrena. His monograph of Scaphandrena (1974) contains the statement that the group should be transferred to Scaphandrena, apparently as an afterthought, since the group is not in the key to species.
(Lanham, U. N. 1981. Some Colorado Andrena of the subgenus Scaphandrena of presumed hybrid origin, with special reference to the tarsal claws (Hymenoptera: Apoidea). J. Kans. Entomol. Soc., 54:537-546.
Ribble, D. W. 1968. Revisions of two subgenera of Andrena: Micrandrena Ashmead and Derandrena, new species (Hymenoptera: Apoidea). Bull. Univ. Nebr. State Mus., 8:237-394.
--. 1974. A revision of the bees of the genus Andrena of the Western Hemisphere subgenus Scaphandrena. Trans. Am. Entomol. Soc., 100:101-189.)