Reprinted with permission of the American Entomological Society from:
LaBerge, W. E. 1971b. A revision of the bees of the genus Andrena of the Western Hemisphere. Part IV. Scrapteropsis, Xiphandrena, and Rhaphandrena. Transactions of the American Entomological Society 97: 441-520.
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This is a highly variable species characterized by often having red legs (especially the hind legs) in both sexes. The female of imitatrix can be told from other species of Scrapteropsis by the relatively weak tergal fasciae, the propodeal corbicula almost always having at least a few internal hairs plumose (and the anterior marginal hairs plumose) and rather broad hind tibiae. The males of imitatrix can be most readily recognized by the flat sixth sternum and the hind tibia being somewhat bulbous just below the middle (as described below).
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 9-11 mm; width. 2.5-3.5 mm; wing length, M = 3.38 ± 0.151 mm; FL/FW, M = 0.99: ± 0.002; FOVL/FOVW, M = 3.03 ± 0.049.
INTEGUMENTAL COLOR. — Black except as follows: flagellar segments 2-10 brown below: mandible with apical third rufescent; wing membranes hyaline. veins brown to red or orange, pterostigma usually red; terga 1- or 2-4 usually narrowly hyaline apically; sterna 2-5 narrowly hyaline apically; distitarsi rufescent. basitarsi and hind tibiae often rufescent to bright orange.
STRUCTURE. — Antennal scape length equal to flagellar segments 1-4; flagellar segment 1 longer than succeeding segments but shorter than segments 2 plus 3, segment 2 shorter than 3, 3 about equal to 4; segment 2 broader than long. segments 3-9 about as long as broad. Eyes each slightly less than 4 times as long as broad, inner margins parallel or converging very slightly towards mandibles. Malar space extremely short, linear. Mandible short, in repose extending only slightly beyond middle of labrum. Galea shiny, shagreening absent or fragile, short, broad. Maxillary palpus considerably longer than galea, segmental ratio about 1.0: 1.0: 0.9: 1.0: 0.8: 0.8. Labial palpus short, segment 1 slightly curved along inner margin, ratio about 1.0: 0.6: 0.6: 0.6. Labral process trapezoidal, occasionally feebly emarginate apically. about one-third as wide as labrum; labrum apical to process with a shallow transverse sulcus, without distinct cristae. Clypeus rounded, with distinct, round, deep punctures separated mostly by half a puncture width or slightly more except along raised impunctate median line (which is usually present), surface shiny, slightly shagreened posteriorly. Supraclypeal area with minute punctures and fine shagreening dulling surface. Genal area about as broad as eye in profile, with minute, obscure punctures and fine shagreening dulling surface, with fine longitudinal rugulae at least in lower third: under surface shagreened. with fine longitudinal rugulae turned inwards toward hypostomal carinae. Vertex short, above lateral ocellus equal to slightly less than one ocellar diameter, surface dulled by small punctures and coarse shagreening. Face above antennal fossae with fine longitudinal rugae and obscure interrugal punctures. Facial fovea extends down to a level below antennal fossae, broad, shallow, separated from lateral ocellus by less than one ocellar diameter.
Pronotum normal, dulled by minute punctures separated mostly by half to one puncture width and fine dense reticular shagreening. Mesoscutum with small round punctures separated in posteromedian area by two to four puncture widths and in anterior third by half a puncture width or slightly more, surface dulled by regular reticular shagreening. Scutellum similar but punctures often slightly larger and shagreening absent or delicate, shiny. Metanotum opaque, with close-set small punctures and coarse tessellation. Propodeum with dorsal enclosure with irregular coarse rugae. surface finely tessellate; dorsolateral and posterior surfaces moderately coarsely to finely punctatorugose: lateral surfaces with scattered punctures and fine regular tessellation, irrugate, moderately shiny. Mesepisternum with large, confluent, shallow punctures separated by sharp ridges (punctatorugose). bottoms of punctures moderately dulled by coarse tessellation. Hind femur without ventral ridges; hind tibia broad, broadest at about one-fourth distance from apex towards base. Pterostigma large, much broader than from inner margin prestigma to anterior wing margin: vein 1st m-cu meets second submarginal cell in outer third or less of cell.
Metasomal tergum 1 with round punctures separated by half a puncture width or slightly more and surface shiny varying to punctures separated by one to two puncture widths with surface dulled by fine reticulotransverse shagreening. Terga 2-4 with apical areas equal to about one-third length of each tergum; basal areas with punctures variable as in tergum I but sparsely punctate forms with punctures minute and separated by two to three puncture widths or more, surfaces shiny and unshagreened to dulled by fine reticulotransverse shagreening; apical area punctures variable but similar in spacing to those of basal areas of each tergum or slightly more crowded. Pygidial plate V-shaped with rounded apex, with strongly developed, raised, internal triangular area present, shiny. Sterna 2-5 with crowded punctures basally.
VESTITURE. — Generally white to cinereous, often slightly ochraceous or yellow on thoracic dorsum. Thoracic dorsum with long. barbed hairs; corbicula with long. highly plumose hairs above and anteriorly, internal hairs entirely plumose or at least a few of them plumose. Trochanteral flocculus highly developed; tibial scopal hairs simple except along extreme margins, of moderate length, pale color.
MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 7-10 mm; width, 2-3 mm; wing length, M = 3.08 ± 0.168 mm; FL/FW, M = 1.08 ± 0.008; FS1/FS2, M = 0.82 ± 0.020.
INTEGUMENTAL COLOR. — Black with same exceptions as female but tergal apices often broadly translucent and middle tibiae often red.
STRUCTURE. — Antennae short, in repose rarely reaching back beyond middle of scutellum; scape length equal to first two and one-half flagellar segments; flagellar segment 1 short, distinctly shorter than segment 2, segments 2-10 about equal in length and longer than broad. Eyes each about 3 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 ratio about 0.9: 1.0: 0.9: 0.8: 0.8: 0.8. Labial palpus as in female but ratio about 1.0: 0.7: 0.6: 0.9. Labral process short, about one-third as broad as labrum. slightly emarginate medially: labrum without apical transverse sulcus. Clypeus as in female but punctures smaller. crowded, without median impunctate line (or rarely present). Supraclypeal area. genal area. vertex and face as in female but face above antennal fossae often more punctate than rugulate. Small, narrow, distinct facial foveae present near inner eye margins.
Thoracic sculpturing as in female except as follows: mesoscutal puncture smaller and sparser: propodeum with lateral faces dull, tessellate and finely punctatorugose especially in upper and posterior areas. Wing venation as in female. Hind tibia with apex simple, without apicoposterior spur, slightly but distinctly inflated at about one-third distance from apex to base. distinctly broader at this point than at apex.
Metasomal terga 1-5 sculptured as in female terga 1-4 but punctures usually smaller and sparser, often minute and separated by three to four puncture widths, surface more often dulled by fine reticulotransverse shagreening. Sterna 2-5 with basal area punctures sparse except in a narrow crowded zone just basad of apical area. surface usually dulled or moderately dulled by reticular shagreening. Sternum 6 relatively flat, not reflexed apically, apical margin transverse, not emarginate, surface dulled by fine tessellation and crowded punctures.
Terminalia as in figures 7-11. Note the following: sternum 7 with hairs short and apicomedian notch distinct: sternum 8 with apical narrow part relatively short: gonocoxite with dorsal lobe moderately sharply pointed; penis valve lip relatively blunt.
VESTITURE. — White to cinereous but slightly darker above. Generally disposed as in female but lacking pollen-collecting hairs.
REMARKS. — A. imitatrix is a highly variable species varying in color, sculpture and hair pattern. However, this variation cannot be shown to be correlated strongly with geography. A majority of the specimens examined (79 percent of females and 68 percent of males) have the integument of the tarsi and hind tibiae (and occasionally middle tibiae) entirely or at least in part red to orange in color. Slightly more dark specimens come from the eastern reaches of the range than the western, but this difference is not consistent from area to area and no even clinal change can be shown to occur in the character.
The punctation of the terga varies from deep and close-set to fine and sparse in both sexes and the surfaces of the terga vary from shiny and unshagreened to moderately dulled by fine reticulotransverse shagreening. Again this structural difference does not exhibit a strong even dine but the close-set, shiny terga are more abundant in the prairie and western states than the other extreme type.
Especially the females of imitatrix vary in the density of the apical pale pubescent bands on terga 2-4. These usually consist of extremely sparse hairs not obscuring the surface completely or being reduced to weak lateral fasciae on each tergum. Occasionally the fasciae consist of denser, more plumose pubescence which hides the apices of terga 2-4 and this denser vestiture occurs more commonly among specimens from the western states. Specimens from the eastern parts of the range usually have the thoracic dorsum slightly darker ochraceous than in specimens from the west. Again no strong even clinal trends can be shown to exist in these characters.
Reprinted with permission from: Mitchell, T.B. 1960. Bees of the Eastern United States. North Carolina Agricultural Experiment Station Technical Bulletin No. 141.
Described as the subspecies: Andrena imitatrix imitatrix
FEMALE. — Length 10 mm.; clypeus very slightly convex, projecting about one-third below suborbital line, somewhat shining, closely and rather coarsely and deeply punctate, without a distinct, median, impunctate area; facial foveae quite broad, occupying above most of space between eyes and ocelli, only slightly narrowed below, covered with whitish tomentum; space between margin of vertex and lateral ocelli subequal to their diameter; cheeks subequal to eyes in width, rounded posteriorly, rather dull, punctures very fine and quite close; malar space very short; basal segment of flagellum slightly shorter than 2nd and 3rd combined; process of labrum rather small, subtriangular, apex more or less broadly truncate; pubescence of head, thorax and legs entirely pale ochraceous or whitish; scutum quite closely and deeply punctate anteriorly, becoming sparsely and more shallowly punctate in center posteriorly, surface somewhat shining, punctures of scutellum quite close, rather coarse and deep, surface between punctures shining; pleura finely rugose; dorsal area of propodeum oblique, triangle quite extensive, rather coarsely and evenly striate; propodeal corbicula pale ochraceous, rather short, without a distinct anterior fringe but with numerous, inner, plumose hairs; trochanteral floccus rather long and dense, whitish; hind tibiae somewhat broadened apically, apex nearly twice the width of the basitarsi, scopa rather dense, hairs simple, rather short, pale ochraceous; front and mid basitarsi slightly narrower than their respective tibiae; 2nd submarginal cell considerably shorter than 3rd, receiving 1st recurrent near apex; abdominal terga smooth and shining, closely, finely and rather deeply punctate, apical impressed areas rather shallow, occupying medially about one-third length of disc, sometimes becoming narrowly hyaline along rims, discal pubescence very short, thin, pale, terga 2-4 usually with whitish or pale ochraceous apical fasciae, interrupted on tergum 2, tergum 5 with a brownish apical fimbria.
MALE. — Length 7-8 mm.; clypeus rather flat, densely pubescent, projecting about one-third below suborbital line, very closely and rather finely punctate beneath dense pubescence; space between margin of vertex and lateral ocelli subequal to their diameter; cheeks subequal to eyes in width, rounded posteriorly, dull, roughened or subrugose, punctures obscure; malar space very short, basal segment of flagellum short, length about equal to its apical width, slightly shorter than 2nd segment; process of labrum broad and rather short, slightly narrowed to the rather broadly truncate apex; mandibles quite short, with a distinct, inner, subapical tooth, overlapping about one-third; pubescence of head, thorax and legs entirely pale ochraceous; scutum and scutellum rather dull, punctures shallow and rather fine, quite close anteriorly, becoming sparse in center posteriorly on scutum, those on scutellum somewhat more coarse and irregularly scattered; pleura finely rugose; dorsal area of propodeum oblique, triangle rather coarsely striate; all basitarsi slender and elongate, considerably narrower than their respective tibiae; 2nd submarginal cell considerably shorter than 3rd, receiving 1st recurrent near apex; abdominal terga somewhat shining, very finely and quite closely punctate, apical impressed area rather shallow, occupying medially nearly one-third length of disc, becoming narrowly yellowish-hyaline along rims, discal pubescence very short, thin, erect, entirely pale, terga 2-4 at least subfasciate apically toward sides, fasciae pale ochraceous; apical portion of sternum 8 narrow, parallel-sided, slightly broadened at apex which is broadly truncate, clothed beneath with rather long, pale pubescence; penis valves rather slender apically, very slightly broadened toward base, sides excavated, gonocoxites rather broadly dilated apically, the resulting lobes subtriangular, with narrowly rounded apex, gonocoxal lobes strongly produced, acute apically, nearly reaching apical lobes of gonocoxites.
DISTRIBUTION. — Minnesota, Ontario and the New England states, south to Mississippi and Florida; March to June.
FLOWER RECORDS. — Acer, Aronia, Aruncus, Crataegus, Houstonia, Ilex, Malus, Padus, Prunus, Pyracantha, Pyrus, Salix, Taraxacum and Viburnum.
Described as subspecies: Andrena imitatrix profunda
This form differs from typical imitatrix only in the ferruginous color of the hind tibiae and all of the tarsi in both sexes. No other significant differences are apparent.