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.
Please report text errors to: leah at discoverlife dot org.
This is a common western species of Thysandrena which can be recognized in the female sex by the complete apical pale band of the third tergum, the yellow or orange hind basitarsi and wing veins and the black integument. The males can be recognized by the complete pale bands of the third and fourth terga, the yellow or red hind basitarsi and wing veins, the flattened, emarginate sixth sternum, and the well-formed sternal fimbriae of sterna 2 to 5.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 8-10 mm; width, 2-3 mm; wing length, M = 3.31 ± 0.137 mm; FL/FW, M = 1.00 ± 0.009; FOVL/FOVW, M = 3.33 ± 0.059.
INTEGUMENTAL COLOR. — Black except as follows: mandible with apical third rufescent; flagellum dark brown below; wing veins red to orange except subcosta which is darker, membranes yellowish; tegula red or testaceous at least on summit; terga 2-5 narrowly hyaline apically; distitarsi rufescent; hind basitarsi and usually hind femora (at least in part) yellow to red; middle basitarsi often rufescent.
STRUCTURE. — Antennal scape length equals first three and three-fourths flagellar segments; flagellar segment 1 about equal to segments 2 plus 3 which are subequal in length and slightly broader than long; segments 4-7 quadrate; segment 8 slightly longer than broad and segment 9 longer than broad. Eyes each about four and one-third times as long as broad, inner margins parallel or converging extremely slightly towards mandibles. Malar space short, linear. Mandible short, in repose barely extending beyond middle of labrum. Galea broad, no more than twice as long as maximum width; surface shiny, unshagreened or with extremely faint, reticular shagreening. Maxillary palpus extends forward to exceed galea by last two segments or slightly more, segmental ratio about as 1.0:1.0:0.8:0.8:0.7:0.8. Labial palpus short, first segment curved, ratio about as 1.0:0.6:0.5:0.4. Labral process weakly emarginate apically to strongly bidentate; labrum apical to process convex, with a weak median crista and one or more extremely weak lateral cristae often present. Clypeus rounded from side to side or slightly flattened medially, with large round punctures separated mostly by half a puncture width or less, midline narrowly impunctate or more sparsely punctate than laterally; surface usually shiny except peripherally, rarely moderately dulled by transversely reticular shagreening. Supraclypeal area dulled by reticulotransverse shagreening and small, shallow, obscure punctures. Genal area in profile about one and one-third times as broad as eye; surface reticularly shagreened, dulled below and posteriorly becoming shiny near margin of eye, rarely entirely shiny; with small, well-separated punctures. Vertex above lateral ocellus usually equal to about one ocellar diameter; dulled by coarse reticular shagreening. Face above antennal fossae dull, roughened by irregular longitudinal rugulae and elongate punctures which become rounded, smaller and denser near ocelli. Facial fovea shallow, extending down to below margins of antennal fossae separated from lateral ocellus by about one ocellar diameter or slightly more.
Pronotum normal, laterally shiny to slightly dulled, shagreening coarsely reticular, delicate, punctures sparse, minute. Mesoscutum usually shiny posteromedially, unshagreened except in anterior third and peripherally, rarely entirely shagreened and moderately dulled; punctures small, round, irregularly separated by one to three puncture widths or more. Scutellum usually shiny, unshagreened except peripherally, with sparse punctures. Propodeum with dorsal enclosure opaque, finely and densely tessellate, often roughened mediobasally; surface outside of enclosure and posterior surface tessellate with obscure shallow punctures (usually barely visible); lateral surface moderately shiny, with coarse reticular shagreening and small piliferous punctures. Mesepisternum opaque, tessellate with small obscure punctures. Pterostigma large, slightly broader than from inner margin prestigma to wing margin; vein first m-cu usually meets second submarginal cell beyond middle of cell; vein r equal to several (5-8) vein widths. Vannal lobe of hind wing long, broad, separated by distinct incision.
Metasomal tergum 1 dulled by extremely fine tessellation, punctures obscure, extremely minute, sparse. Terga 2-4 similar to tergum 1 but punctures slightly more evident especially on basal part of apical areas, occasionally shinier with more distinct punctures. Pygidial plate V-shaped, apex acute (unless worn); with well-formed internal raised triangular area with dull, closely punctate surface (unless worn smooth). Sterna 2-5 usually dulled by reticular shagreening, occasionally delicately shagreened and surfaces shiny; with small round punctures separated by one or more puncture widths becoming sparser to absent posteriorly on each tergum and absent in narrow apical margins.
VESTITURE. — Generally ochraceous to yellow (occasionally pale ochraceous to white) except as follows: facial fovea with upper half usually with short brown hairs (rarely entirely pale); terga 3-4 and usually 2 with median areas (above pale apical fasciae) with short, erect to depressed, dark brown hairs; terga 5 and 6 usually dark brown except white laterally on tergum 5 (occasionally entirely or almost entirely pale); on and surrounding basitibial plates brown; inner surfaces tarsi yellow. Pollen-collecting hairs normal for subgenus. Tergum 3 with pale apical band complete, tergum 2 with fascia narrowly interrupted medially. Thorax with dorsal hairs usually short, usually absent posteromedially. Clypeus with hairs usually sparse to absent medially or at least not so thick as to hide surface.
MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 6-9 mm; width, 1.5-2.5 mm; wing length, M = 2.99 ± 0.185 mm; FL/FW, M = 1.01 ± 0.006; FS1/FS2, M = 1.18 ± 0.030.
INTEGUMENTAL COLOR. — Black except as follows: mandible with apical third or less rufescent; flagellum dark brown below; wing veins red to orange, membrane hyaline, usually slightly yellowed; terga and sterna narrowly hyaline apically; distitarsi rufescent; hind basitarsi and often hind tibiae at least in part red to orange or yellow.
STRUCTURE. — Antennae short, in repose barely reaching back to metanotum; scape length equals first two flagellar segments; flagellar segment 1 about as long as segment 2 or slightly longer, each segment longer than broad, median segments one and one-fourth to one and one-third times as long as broad. Eyes each about three and one-half times as long as broad, inner margins converging slightly towards mandibles. Malar space, mandible and galea as in female. Maxillary palpus as in female but segmental ratio about as 1.0:0.9:0.7:0.7:0.7:0.7. Labial palpus as in female but ratio about as 1.0:0.4:0.4:0.4. Labral process bidentate; labrum below process flat to slightly convex, without cristae or with a single median weak crista, surface shiny. Clypeus as in female but punctures usually slightly smaller and more crowded medially, rarely shagreened except peripherally. Supraclypeal area, genal area and vertex as in female. Face above antennal fossae usually more punctate than rugulate but otherwise as in female.
Thoracic sculpturing as in female except as follows: mesoscutum usually dulled by fine tessellation, but occasionally shiny posteromedially; propodeum with lateral surfaces tessellate with sparse, minute punctures. Wings as in female.
Metasomal terga dull to moderately shiny, with coarse reticulotransverse shagreening and minute obscure punctures; tergum 1 virtually impunctate. Sterna 2-5 much as in female, punctures often sparser. Sternum 6 virtually flat with an apicomedian, shallow but distinct emargination. Terminalia as in Figures 17-21.
VESTITURE. — Ochraceous to yellow, usually darker on vertex and thoracic dorsum, except as follows: face often with black hairs along inner margins compound eyes especially above, occasionally clypeal hairs all or mostly black and facial hairs black except surrounding antennal bases; genal area occasionally with black hairs above; terga 3-5 and often tergum 2 with discs with short erect to depressed black or brown hairs (often mixed with pale) inner surfaces tarsi yellow. Terga 3-5 apical pale bands complete (unless worn); tergum 2 with pale apical band interrupted medially. Sterna 2-5 with subapical fimbriae complete, thick, moderately long. Sternum 6 with fringe of short plumose hairs often present but not so thick as to hide margin.
REMARKS. — Stylopization is reasonably common in A. medionitens and stylopized females usually have narrow facial foveae, as well as reduced or absent pollen-collecting hairs. These specimens are difficult to identify and a low percentage of misdeterminations may well result from these aberrations.
The populations from the intermontane region of Nevada and Utah are, in general, paler than those from California and Oregon or those from Wyoming and Colorado. Since pale specimens occur at random throughout the range of the species and since at least a few dark specimens occur in Nevada and Utah, no subspecies is recognized.
Described using the synonymous name: Andrena pacta Viereck
The pronotum is rounded, not angulate, a character which at once separates this species from Cnemidandrena. Affinities uncertain. Of uncertain position.
|
