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Andrena amphibola (Viereck, 1904)
Trachandrena amphibola Viereck, 1904; Trachandrena crassihirta Viereck, 1904; Trachandrena perdensa Viereck, 1904; Trachandrena hadra Viereck, 1904; Trachandrena limarea Viereck, 1904; Andrena (Trachandrena) eriogoni Cockerell, 1927; Andrena (Trachandrena) seneciophila Cockerell, 1928

Life   Insecta   Hymenoptera   Apoidea   Andrenidae   Andrena
Subgenus: Trachandrena

Andrena amphibola FEM mm .x f
© Copyright Laurence Packer 2014 · 7
Andrena amphibola FEM mm .x f

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Andrena amphibola MALE mm .x ZS PMax
© Copyright Laurence Packer 2014 · 7
Andrena amphibola MALE mm .x ZS PMax
Overview
Reprinted with permission of the American Entomological Society from: LaBerge, W. E. 1973. A revision of the bees of the genus Andrena of the Western Hemisphere. Part VI. Subgenus Trachandrena. Transactions of the American Entomological Society 99: 235-371.

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This northwestern species is related both to A. miranda and A. quintiliformis. Both sexes have moderately high vertices as in miranda, but usually not as high as in quintiliformis. The female facial fovea is relatively narrow above and moderately broad below as in quintiliformis. The female also has the angulate base of the front femur as in miranda and quintiliformis. Both sexes of amphibola can be separated from those of miranda by the relatively finely sculptured propodeum outside of the enclosure. The female of amphibola differs from that of quintiliformis by the thoracic dorsal hairs being erect and at least slightly longer and by terga 2 and 3 having the apical areas considerably longer than the basal areas. The male of amphibola can be told from that of quintiliformis by the longer first flagellar segment in relation to the second segment, by the usually more densely punctate first tergum and the usually longer apical areas of terga 2 to 5.

FEMALE. MEASUREMENTS AND RATIOS. — N = 20; length, 9-12 mm; width, 3.0-3.5 mm; wing length, M = 4.06 ± 0.233 mm; FL/FW, M = 1.05 ± 0.007; FOVL/FOVW, M = 3.47 ± 0.069.

INTEGUMENTAL COLOR. — Black except as follows: mandible with at least apical half rufescent; flagellar segments 3-10 dark reddish-brown below; tegula rufescent; wing membranes moderately infumate, yellowish-brown; veins reddish-brown; distitarsi and tibial spurs rufescent.

STRUCTURE. — Antennal scape as in sigmundi; flagellar segment 1 as long as segments 2 plus 3 or slightly shorter; segment 2 broader than long, segments 3-8 quadrate, 9 and 10 longer than broad. Eyes each about four times as long as broad or slightly narrower, inner margins parallel. Malar space, mandible and galea as in sigmundi. Maxillary palpus as in sigmundi but segmental ratio about as 1.0:1.0:0.7:0.7:0.6:0.5. Labial palpus as in sigmundi but ratio about as 1.0:0.5:0.4:0.4. Labrum and process as in sigmundi but weak apical cristae may be present as in quintiliformis. Clypeus and supraclypeal area sculptured as in sigmundi. Genal area as in quintiliformis. Vertex as in quintiliformis but slightly shorter (vertex height above lateral ocellus to diameter of ocellus about as 12:9 or 10). Face above antennal fossae with coarse contiguous punctures, moderately dulled by fine shagreening. Facial fovea relatively narrow above, separated from lateral ocellus by three-fourths to one ocellar diameter (inner upper margin indistinct); lower portion relatively broad, usually broader than distance from outer margin to inner eye margin.

Pronotum with punctures distinct, surface shiny to moderately shiny. Mesoscutum with large round punctures separated by distinctly less than half a puncture width except in small posteromedian area where separated mostly by about half a puncture width; surface dull, finely and reticularly shagreened. Scutellum similar but punctures usually larger. Metanotum opaque, densely and finely punctate and shagreened. Propodeum as in sigmundi. Mesepisternum coarsely punctatorugose except lower posterior corner where punctures somewhat separated; surface and bottoms of punctures dulled by fine dense shagreening. Posterior hind tibial spur normal. Anterior femur with inner basal angle angulate as in quintiliformis. Pterostigma and wing venation as in sigmundi but second submarginal cell receives vein 1st m-cu near middle or only slightly beyond.

Metasomal tergum 1 with deep round punctures separated mostly by half a puncture width or less or by half to one puncture width in basal area; surface shiny, unshagreened. Tergum 2 medially with basal area half as long as apical area or somewhat longer, but always shorter than apical area. Terga 2-4 with apical areas either densely punctate with little distinction from densely punctate basal area or apical area punctures separated by half to one puncture width or more; surfaces shiny, weakly or not at all shagreened. Pygidial plate as in sigmundi. Sterna sculptured as in sigmundi but shinier, reticular shagreening fine.

VESTITURE. — Highly variable. Pale specimens generally ochraceous. Darkest specimens with head, pleurae, legs including scopal hairs, propodeum and abdomen with hairs dark brown to black; thoracic dorsum with hairs often bright fox-red. Form and distribution of hairs as in sigmundi except as follows: thoracic dorsum with hairs relatively short to extremely short, thick (base of hair fills three-fourths or more of large mesoscutal puncture), erect; terga without apical pale fasciae; sterna without subapical fimbriae.

MALE. MEASUREMENTS AND RATIOS. — N = 20; length, 8-11 mm; width, 2-3 mm; wing length, M = 3.74 ± 0.168 mm; FL/FW, M = l.ll ± 0.007; FS1/FS2, M = 0.83 ± 0.016.

INTEGUMENTAL COLOR. — Black with same exceptions as in female but flagellar segments 2-11 dark brown below, wing membranes often only slightly infumate and terga occasionally slightly reddened apically.

STRUCTURE. — Antennae in repose barely reaching metanotum or shorter; scape length equals first two flagellar segments or slightly more; flagellar segment 1 two-thirds as long to equal in length to segment 2; first segment quadrate or slightly longer than broad, remaining segments longer than broad. Eyes each about three and one-third times as long as broad, inner margins converging slightly towards mandibles. Malar space, mandible and galea as in. sigmundi. Maxillary palpus as in sigmundi but segmental ratio about as 0.8:1.0:0.7:0.7:0.7:0.5. Labial palpus as in sigmundi but ratio about as 1.0:0.6:0.5:0.6. Labrum as in sigmundi. Clypeus as in sigmundi but median impunctate line usually present. Supraclypeal area as in sigmundi. Vertex, face above antennal fossae, and genal area as in female.

Pronotum as in female. Mesoscutum and scutellum coarsely punctate as in female but often shinier, moderately shiny to dull (scutellum usually dull). Propodeum sculptured as in female but lateral surface punctatorugose. Mesepisternum, wing venation and tibial spurs as in female.

Metasomal terga 1-5 sculptured as in female terga 1-4 but apical areas of terga 2-5 narrower, usually half total length medially or slightly less, and apical area punctures often separated by half to one puncture width or more (occasionally crowded). Sterna 2-5 as in sigmundi but basal area punctures larger, separated mostly by half to one puncture width or more. Sternum 6 deeply emarginate apically. Terminalia as in sigmundi; see figures 34-35; sternum 7 with apical lobes often more flattened apically than drawn and in one specimen slightly more pointed.

VESTITURE. — Generally ochraceous, occasionally pale ochraceous and often with head, abdomen and leg hairs black or partially black. Intermediate forms may have inner surfaces of legs, apical segments of abdomen and clypeal hairs dark brown. Terga without pale apical fasciae; sterna without pale subapical fimbriae.

VARIATION. — The females of A. amphibola. vary in color of the vestiture from entirely pale ochraceous to specimens in which the head, pleurae, propodeum, metasoma and legs are black and the thoracic dorsum bright fox-red. The pale specimens generally are less intensely punctate, especially in the apical areas of the terga, and the thoracic dorsum has hairs moderately long. The dark specimens are densely punctate and have short erect hairs on the thorax. All combinations of intermediate conditions exist between these two extremes. The hind legs may have dark hairs on the inner surfaces and the last two tergites dark brown in paler intermediates. In dark intermediates the scopal hairs are entirely brown or almost so, but the pleural and propodeal hairs remain pale. Males are, in general, much paler than females. However, a few dark males occur in which head, pleurae, propodeum, metasoma and legs have dark brown to black hairs.

This variation is distributed geographically in an odd manner. Specimens from eastern California north to Plumas County and from Nevada and southeastern Oregon are nearly entirely of the darkest form, although a few intermediates occur in these areas and a few specimens are less intensely punctate than usual for dark individuals. The largest concentration of the palest specimens is along the west coast from northern California (Humboldt and Del Norte counties) north to Washington. More than half of the specimens from this area are of the palest, least punctate type and most of the remaining are pale intermediates. Northeastern Washington (Puget Sound area) and southeastern British Columbia has specimens almost as pale as further south. From north-central California (Trinity, Butte, Plumas and Lassen counties) north through the central part of Oregon most specimens are pale intermediates and about one-fourth of the palest type. Further inland in the northeastern Oregon and adjacent areas of Washington and Idaho and also the central part of British Columbia about half of the specimens are of the dark type and the remaining almost entirely intermediates (largely dark intermediates). Montana and Alberta south to southern Colorado and Utah is a large area from which the large majority of specimens are dark intermediates with one-fourth or less of pale intermediates and a few of each extreme type (although more dark than pale specimens).

This distribution of color variation as expressed in the females is shown on the map (Fig. 7) by use of clock-graphs in which the black area represents the percentage of the darkest type of individuals from that area, the hatched section represents dark intermediates, the stippled section pale intermediates and the white section the palest type. Males were not graphed in this manner because too few specimens were available. These graphs also do not represent information concerning the sculpturing of the integument, although this is correlated with the color of the vestiture as was explained above.

The distribution discussed above and shown on the map (Fig. 7) does not seem amenable to explanation by hypothesizing subspeciation with local selective pressures maintaining the observed mixtures of types in each locality. It seems to the author that an hypothesis of two former species hybridizing is simpler and probably correct. The hybrid populations apparently are highly successful and have spread eastward from a center of origin which was probably in central Oregon-Washington-northern California area.

If one looks at the dates on labels of the few hundred females available for study, one notices that after 1940 few entirely pale specimens were collected. Most of the pale females were, in fact, collected before 1900, although they remain relatively abundant in collections through 1929. This may indicate that the hybridization hypothesized took place chiefly during the past 80 or 90 years, although a few hybrids are among our earliest records. It also suggests that the dark form is swamping out the paler forms at least in the Rocky Mountains. Perhaps man has altered the environment enough not only to provide niches in which the hybrid populations can maintain themselves, but also have been able to spread to the east. What factors man has changed can only be surmised. However, considering the large number of specimens collected from dandelions (Taraxacum officinale) it may be that the introduction of this plant and others has bridged the gap between two formerly largely allopatric species.

It is unfortunate that our early records of these bees are so fragmentary that we cannot document this variation in a more explicit manner. Except for a few long series, most collection records consist of one or two specimens. The data can be grouped, but not very logically, and the time factor cannot be studied in detail.

Names
Scientific source:

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Hosts · map
FamilyScientific name @ source (records)
Asteraceae  Erigeron nematophyllus @ BBSL (2)

Taraxacum officinale @ BBSL (1)
Brassicaceae  Erysimum capitatum @ BBSL (1)

Lesquerella montana @ BBSL (2)

Lesquerella sp @ BBSL (1)
Caryophyllaceae  Arenaria hookeri @ BBSL (1)
Crassulaceae  Sedum lanceolatum @ BBSL (1)
Euphorbiaceae  Euphorbia sp @ BBSL (2)
Fabaceae  Cercidium sp @ BBSL (1)

Medicago sativa @ BBSL (2)

Melilotus officinalis @ AMNH_BEE (1)
Liliaceae  Allium geyeri @ BBSL (2)

Zigadenus vaginatus @ BBSL (4)

Zigadenus venenosus @ BBSL (1)
Polycitoridae  Salix sp @ BBSL (1)
Polygonaceae  Eriogonum subalpinum @ BBSL (1)

Eriogonum umbellatum @ BBSL (1)
Rosaceae  Cercocarpus montanus @ BBSL (2)

Potentilla fruticosa @ BBSL (1)

Potentilla glandulosa @ BBSL (1)

Prunus virginiana @ BBSL (5)

Purshia tridentata @ BBSL (1)

Rosa woodsii @ RMBL_ENT (1)
Salicaceae  Salix interior @ RMBL_ENT (1)
_  Withheld @ BBSL (7); BBSL__ZION (10)

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Updated: 2024-03-29 05:20:31 gmt
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