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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Andrena vandykei (male) and solutula (female) were described in the same paper (Cockerell, 1936). Even though the name solutula has precedence of position in the work I choose the name vandykei for this species. This action is taken because the male is more easily distinguished than the female (see Recommendation 24A, International Code of Zoological Nomenclature, 1964). It also seems desirable to retain in use a patronymic name for a famous entomologist (E. C. Van Dyke).
Andrena vandykei is a dark, wide-headed bee with a large pterostigma. The male can be distinguished by the deep suture extending below the humeral angle nearly to the anterior margin of the pronotum. This suture is often present to a lesser extent in the female. The propodeal corbicula lacks long hairs along the anterior margin and the apical abdominal fasciae are weak or absent.
The descriptions below are based mainly upon a female (April 17, 1961) and a male (March 11, 1959) collected at Alpine Lake, Marin County, California, by J. Powell. A total of 215 specimens of vandykei were examined during this study.
FEMALE. MEASUREMENTS AND RATIOS. — Length, 7.6 mm; width of mesothorax, 1.9 mm; wing length from tegula, 5.7 mm; facial length/width, 0.92; foveal length/width, 2.50.
INTEGUMENTAL COLOR. — Black except: tip of mandible deep red; eye grey; flagellum brown below; wing amber; veins, pterostigma and tegula darker amber; terga and sterna with narrow amber apices, sterna otherwise dark brown to black; legs dark brown; tibial spurs light amber; claws amber.
STRUCTURE. — Antenna reaching to scutellum; scape reaching to one and one-half ocellar distances from middle ocellus, slightly longer than flagellar segments 1-4; flagellar segment 1 slightly longer than 2 and 3 together, tapered toward base; segment 2 slightly shorter than 3, each shorter than segment 4, each tapered slightly towards base; middle segments about as wide as long; ultimate segment rounded in lateral view, pointed in dorsal view, twice as long as broad. Eye four times as long as broad in anterior view, inner eye margins nearly parallel below. Malar space about seven times as wide as long. Mandibles decussate in repose, extending to opposite corner of labrum; apex sharply pointed; inner, sharply pointed, subapical tooth present. Galea with outer margin below palpus expanded into long narrow lobe; both margins curving downward, tapering to a narrowly rounded apex; surface very shiny, without shagreening. Maxillary palpus with segments in ratio of about 1.4:1.4:1.1:1.3:1.0:1.4; segments tapering towards bases; segment 6 slender, slightly flattened; segments 5 and 6 extending beyond galea. Labial palpus with segments in ratio of about 1.7:1.0:1.0:1.7; segments tapering towards bases; segment 1 curved; segment 4 slender, scarcely flattened; segments 3 and 4 attached subapically. Labrum about two and one-half times as wide as long, outer margin broadly rounded from side to side; process half as wide and less than half as long as entire labrum, raised, shiny, margin evenly rounded from side to side. Clypeus about twice as broad as long, protruding beyond lower margin of eye by about half width of eye in lateral view, shiny, reticular shagreening very weak in center; punctures large, far apart, edges indistinct, laterally punctures becoming closer, smaller, more distinct. Supraclypeal area shiny; punctures sparse, indistinct; reticular shagreening further apart than at base of clypeus. Genal area in lateral view nearly twice as wide as eye, surface with fine, widely spaced, reticular shagreening. Vertex elevated above eyes, extending past lateral ocellus by one ocellar width; surface between ocelli with close, coarse shagreening, punctures indistinct; surface above fovea sculptured like surface between ocelli except shagreening more even. Face above antennal fossae sculptured like surface between ocelli except fine, vertical rugulae along margin of fovea; frontal line distinct, running from middle ocellus to supraclypeal area, lower two-thirds carinate. Facial fovea rounded dorsally past eye, dorsally as wide as eye; inner margin separated from eye, widely separated below; both margins tapering half distance of eye to broad point below.
Pronotum with weak humeral angle; deep suture crossing base of posterior pronotal lobe, turning anteriorly below humeral angle, becoming very weak before reaching anterior margin of pronotum; surface with reticular shagreening. Mesoscutum with indistinct punctures, surface with close reticular shagreening; parapsidal line distinct, short. Tegula oval, with faint reticular shagreening apically, shagreening much coarser basally. Scutellar surface much like mesoscutal except laterally punctures more distinct, shagreening becoming very close; center nearly devoid of punctures, shagreening less coarse. Metanotum sculptured like margins of scutellum except punctures weak. Propodeum with dorsal enclosure concave on anterior margin, posterior margins meeting to form a "V," enclosure sloping gently over anterior two-thirds, posterior third nearly vertical, surface with fine, even reticular shagreening, becoming granular towards base; propodeum with posterior surface divided by deep vertical sulcus, no carina separating posterior and corbicular surfaces; posterior and dorsolateral areas on same level and surrounding enclosure, punctures indistinct, shagreening like posterior part of enclosure; corbicular surface with few indistinct punctures, shagreening less granular, further apart than on dorsal surface. Mesepisternum with surface similar to anterior mesoscutal. Metepisternum similar to corbicular surface but impunctate below. Middle basitarsus slender, slightly expanded towards middle. Hind tibia very slender, little wider than basitarsus. Claws with large tooth on inner margin. Anterior tibial spur bent, with broad lamella along basal part of inner margin, spur serrate along distal third of inner margin; middle tibial spur long, nearly straight, serrate along inner margin; hind tibial spurs long, slender, nearly straight; posterior spur slightly longer than anterior spur; spurs serrate along posterior margins. Wings with pterostigma very large, twice as wide as prestigma; three submarginal cells; first transverse cubital vein ending one vein width from pterostigma; first m-cu vein ending near apex of second submarginal cell.
Metasomal terga shiny, with minute punctures, surface with fine reticular shagreening. Pygidial plate broadly rounded, edges not upturned, central portion slightly raised. Sterna with many fine punctures, surface with fine, widely spaced, reticular shagreening; sternum 1 emarginate.
VESTITURE. — White except: hairs on facial fovea, some hairs on face along fovea, apex of hind femur, base of hind tibia and tip of abdomen chocolate brown; apex of clypeus, labrum, mandible, tarsi, anterior and middle tibiae with amber hairs. Hairs abundant, long, straight, very plumose except: those of facial fovea short; minute, simple hairs on eye; propodeal corbicular hairs few, simple in center, along dorsal margin hairs curved; tergal hairs fine, mostly short; apical abdominal fasciae indistinct, reduced to a few scattered hairs on terga 2 and 3; sternal hairs fine, short, simple except subapical fimbriae of long, plumose hairs on sterna 2-5; trochanteral flocculus curved. Tibial scopa with long hairs, anterior- and posterior-most hairs with few branches, hairs along anterior margin curved slightly posteriorly; other leg hairs variable in structure.
MALE. MEASUREMENTS AND RATIOS. — Length, 6.3 mm; width of mesothorax, 1.4 mm; wing length from tegula, 5.0 mm; facial length/width, 0.86; flagellar segment 1/segment 2, 1.58.
INTEGUMENTAL COLOR. — Color as in female except: apex of clypeus yellow; terga with broader amber apices, terga otherwise dark brown.
STRUCTURE. — Antenna reaching to abdomen; scape reaching to within one ocellar distance of middle ocellus, as long as Flagellar segments 1-3; segment 1 half again as long as 2, equal to 3 in length, tapered towards base; other segments not noticeably tapered; middle segments much longer than broad; ultimate segment rounded in lateral view, pointed in dorsal view, twice as long as broad. Eye about three times as long as broad in anterior view, inner eye margins nearly parallel. Malar space about six times as wide as long. Mandible long, slender, sharply bent in middle; decussate in repose, extending to opposite corner of clypeus; apex sharply pointed; inner subapical, sharp tooth present; posterior margin with small, rounded lobe at base. Galea as in female. Maxillary palpus as in female but segments in ratio of about 1.7:1.3:1.0:1.3:1.3:1.7. Labial palpus as in female but segments in ratio of about 1.7:1.2:1.0:1.3. Labrum slightly more than twice as wide as long, parallel sided, apex truncate; process reduced to a shiny, bare area. Clypeus three times as broad as long, shiny, protruding beyond lower margin of eye more than two-thirds width of eye in lateral view, shagreening absent except extreme basally and laterally, reticular shagreening weak; punctures distinct, large, far apart, becoming closer laterally. Supraclypeal area with large punctures, partly obscured by reticular shagreening. Genal area in later view half again as wide as eye, posteriorly coming to a rounded point, large fingerlike projection at base of mandible, surface with fine, widely spaced, reticular shagreening. Vertex much elevated along posterior margin behind ocelli, extending past lateral ocellus by much more than one ocellar distance; entire vertex and face above antennal fossae with coarse, close, reticular shagreening; punctures indistinct; frontal line distinct, running from middle ocellus to supraclypeal area, lower half carinate.
Pronotum with strong humeral angle; suture extending vertically from leg base, lying in deep, wide sulcus, suture turning anteriorly below humeral angle and extending to anterior margin of pronotum; surface of pronotum with reticular shagreening. Mesoscutum, tegula, scutellum and metanotum as in female. Propodeum as in female except propodeum narrower, enclosure sloping posteriorly (approaching the condition found in Hesperandrena), lateral area with coarser shagreening. Mes- and metepisterna as in female. Wings, claws and tibial spurs as in female.
Metasomal terga as in female except tergum 7 exposed, pointed; pygidial plate absent. Exposed sterna as in female except sternum 6 with apical margin flexed greatly downward medially.
Sternum 7 slightly emarginate and shagreened at apex, producing two lobes, each bearing several setae (fig. 93). Sternum 8 with apical half convex, base expanded into large, long plate (fig. 94); apex slightly expanded, weakly emarginate; shaft short, bent downward and then posteriorly; sternum with apical half setose, some setae branched, some setae reaching considerably beyond apex. Gonocoxite slender, bent downward; gonoforceps expanded near middle, dorsal surface with several branched setae; dorsal lobes wide, short. Penis valve bent downward, apex slender, only slightly expanded medially (figs. 90-92).
VESTITURE. — Hairs white except some chocolate brown hairs on head and thorax. Otherwise hairs as in female except hairs mostly longer, fringe of long hairs along ventral margin of clypeus, facial fovea absent, apical abdominal fasciae entirely absent, tergum 7 with longitudinal bare area, sternal hairs more plumose basad of subapical fimbriae, hairs specialized for pollen collecting absent.
VARIATION. — There is considerable variation in the male terminalia. Sternum 7 varies from deeply notched to truncate at the apex, and the shape of the apical lobes is highly variable. Sternum 8 may or may not be expanded at the apex, the apical emargination is sometimes lacking, and the basal plate varies in shape. Basally the penis valve may be wider or narrower than shown in figure 91 and the apex of the penis valve in side view is often wider (fig. 92). The tip of the gonostylus may be bent inward in dorsal view and the inner lobe of the volsella can be much reduced. Although these variations in the male terminalia are often striking, the terminalia exhibit much the same basic structure. The variation in this basic structure is such that of the specimens dissected no two were the same in the characters discussed above. There does not seem to be any correspondence between variation in terminalia and external morphology; externally the males are very similar. If there is any north-south geographic variation in the terminalia it is slight and masked by individual and populational variation.
The male clypeus may lack the yellow maculation that is usually present. Male size varies considerably (4.3 to 5.9 mm, wing length from tegula); much of this variation can be found at a single locality. A single female is as small as the smallest male (on the basis of wing length). There are a few other females approaching this small size, however, in general the females are more constant in size than the males. A few females have distinct but weak apical fasciae on abdominal terga 2-4, but usually the fasciae are indistinct as in the female description. The female pterostigmata occasionally may be slightly smaller than in the description. The female humeral angle and the suture extending anteriorly below it may be weak at times (this character and the presence of apical fasciae are typical of, but not restricted to, specimens from the Sierra Nevada Mountains). The female clypeus may be covered with distinct reticular shagreening, but more commonly it has weak shagreening in the center.