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.
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Andrena candida is a small, metallic, extremely abundant species of the West Coast and Mountain areas. The female of candida has a relatively broad, long and shallow facial fovea, much as in medionitens, but the hind basitarsi and wing veins are dark in color. The male of candida, like that of medionitens, has well-formed sternal fimbriae but has only weak tergal fasciae which are usually interrupted medially on terga 2 to 4 and often on tergum 5.
FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 8-10 mm; width, 2.5-3.0 mm; wing length, M = 3.17 ± 0.187 mm; FL/FW, M = 0.95 ± 0.009; FOVL/FOVW, M = 3.22 ± 0.054.
INTEGUMENTAL COLOR. — Black except as follows: generally with dark blue to dark greenish-blue metallic reflections, often with violaceous reflections on clypeus and/or mesoscutum; mandible with apical third rufescent; flagellum often dark brown below; wing veins dark reddish-brown to brownish-black, membranes hyaline to moderately infumate; tegulae piceous; terga 2-5 with narrow apical margins translucent brown; tarsi brown to black.
STRUCTURE. — Antennal scape length equals first four flagellar segments flagellar segment 1 equal in length to segments 2 plus 3 plus one-fourth of 4; segment 2 subequal to 3 in length, each broader than long; segments 4-9 quadrate. Eyes narrow, each four and one-half times as long as broad inner margins converging slightly towards mandibles. Malar space, mandible and galea as in medionitens. Maxillary palpus as in medionitens but segmental ratio about as 0.7:1.0:0.7:0.7:0.6:0.6. Labial palpus as in medionitens but ratio about as 1.0:0.6:0.6:0.6. Labral process bidentate labrum below process shiny, flat, with weak median crista. Clypeus moderately rounded from side to side, with small round punctures separate mostly by about half a puncture width except along narrow impunctate midline (impunctate midline frequently absent); surface usually shiny an unshagreened at least apicomedially, dulled posteriorly and laterally an occasionally mostly shagreened. Supraclypeal area dulled by minute rout punctures and dense reticular shagreening. Genal area in profile slight broader than eye; surface dulled by extremely minute punctures and den shagreening. Vertex above lateral ocellus equal to one ocellar diameter or slightly less; surface dulled by dense tessellation and obscure punctures. Face above antennal fossae with fine, regular, longitudinal rugulae and obscure interrugal punctures. Facial fovea long, broad, shallow, as in medionitens but well-separated from inner margin of compound eye at least in lower three-fourths.
Pronotum as in medionitens. Mesoscutum often shiny posteromedially to entirely dulled by fine reticular shagreening; punctures small, round, separated mostly by one to two puncture widths but sparser posteromedially. Scutellum similar but more often shiny and impunctate except along mid-line. Propodeum as in medionitens but dorsal enclosure rarely roughened at extreme base. Mesepisternum as in medionitens. Wings as in medionitens.
Metasomal terga, pygidial plate and sterna as in medionitens.
VESTITURE. — Generally white to extremely pale ochraceous except as follows: facial fovea with short inner hairs dark brown entirely or in part (rarely only upper fourth with dark hairs); in dark specimens face above antennal fossae, vertex, genal areas (especially near compound eyes), and clypeus in part with dark brown hairs, in pale specimens only hairs of vertex and surrounding upper ends of facial foveae dark; mesoscutum with hairs entirely pale or with admixture of dark brown hairs except peripherally; terga 5 and 6 with hairs mostly dark brown; terga 2-4 or 3-4 with basal areas with short, erect to decumbent, brown to pale hairs, with apical pale fasciae thick, usually interrupted medially (occasionally complete on tergum 4 and rarely so on tergum 3); sternal hairs pale; pollen-collecting hairs normal for subgenus; scopae white except hairs on and surrounding basitibial plates and often distad of plates along posterior margins of tibiae.
MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 6-9 mm; width, 1.5-2.5 mm; wing length, M = 2.75 ± 0.155 mm; FL/FW, M = 0.94 ± 0.007; FS1/FS2, M = 0.95 ± 0.018.
INTEGUMENTAL COLOR. — Black except as follows: with dark blue to greenish-blue metallic and violaceous reflections as in female; mandible, antennae, wing veins and membranes, tegulae, and legs as in female; terga with apical areas translucent, clear to smoky-brown; clypeus rarely yellow apicomedially (less than 1% of specimens).
STRUCTURE. — Antennae short, in repose reaching metascutum; scape length equals first two and one-third to two and one-half flagellar segments; flagellar segment 1 almost or quite as long as segment 2, segments all longer than broad, median segments one and one-fourth to one and one-third times along as broad. Eyes in facial view narrow, each about three and one-half times as long as broad or slightly less, inner margins parallel or (lightly converged towards mandibles. Malar space, mandible and galea as in female. Maxillary palpus as in female but segmental ratio about as 1.0:0.8:0.8:0.7:0.7:0.8. Labial palpus as in female but ratio about as 11.0;0.7:0.7:0.7. Labral process strongly bidentate; surface below process shiny, without cristae. Clypeus as in female but punctures smaller and median impunctate line often absent. Genal area, supraclypeal area, vertex, and face above antennal fossae sculptured as in female but face with rugulae irregular and small and punctures and shagreening dulling surface.
Thoracic sculpturing as in female but mesoscutum with punctures usually minute and surface more often shiny posteromedially and propodeal dorsal enclosure more often minutely roughened. Wings as in female.
Metasomal terga dull to shiny, sculptured as in female. Sterna 2-5 as in female but punctures less dense. Sternum 6 flat, weakly but distinctly emarginate apically. Terminalia as in Figures 22-26.
VESTITURE. — Generally as in female but head more commonly with black or dark brown hairs, these present at least on vertex and along margins of compound eyes and often head hairs dark except on face above and surrounding antennal fossae. Mesoscutum often with dark hairs posteromedially. Metasomal terga as in female except as follows: terga 2-5 with apical pale fasciae narrow, interrupted medially (occasionally complete on tergum 5), terga 5 and 6 often pale. Leg hairs pale. Sterna 2-5 with distinct subapical fimbriae of long, curved, pale hairs. Sternum 6 normally hairy, not densely so.
REMARKS. — This is a rather variable species, especially in the color of the vestiture (degree of melanism) and in the intensity of shagreening. A densely shagreened, dark specimen looks quite different from a shiny, pale specimen and, without seeing all of the intergrades, this difference could lead one to assume specific distinctness. However, all types occur between these extremes, and the two types of characters are not necessarily correlated. That is, dark-shiny specimens and pale-dull specimens are common in collections.
Linsley (1937) and Youssef and Bohart (1968) report that A. candida is bivoltine and that there are morphological difference between the two broods. That is, the second brood males seem to have paler facial hairs than those of the first brood (Linsley, 1937^ and the second brood seems to be less shagreened, shinier and less metallic than the first brood (Youssef and Bohart, 1968). I have not been able to verify either of these contentions in looking a specimens grouped by area. However, these differences could obtain in a single nesting population (or populations more narrowly grouped than in the present study). Local variations in temperature and/or moisture during development would tend to obscure these relationships when populations are more broadly grouped. However, the characters reported by Linsley and Youssef and Bohart are not correlated in collections, which one would expect if these were differences between broods.
Youssef and Bohart (1968) give a detailed account of the biology of A. candida as studied by them in northern Utah. Stylopization is quite common in A. candida (Pierce, 1918) and affected females are, as usual, rather difficult to distinguish as to species. Frequently stylopized females lack the characteristic metallic luster and have narrow facial foveae, thus becoming rather like normal females of A. chlorura. The presence of stylopid parasites means that the specimen cannot be identified with the use of the keys given above, but must be determined by comparison and by subjective judgments on the effects of the parasite.
Although considerable variation exists in A. candida, as expressed above no distinct geographical trends appear. Arizona specimens are often more distinctly punctate and less metallic, but in view of the statement by Youssef and Bohart (1968), this may be a function of which brood was collected most frequently. Rarely specimens have been collected very late in the season (August near Yuma, Arizona, and October 10 at Oroville, California) or very early (January 18 at Riverside, California). These data suggest that a third brood may emerge under special conditions in some areas, or perhaps only a few stragglers emerged out-of-season and a few of these were collected.
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