Apis (Trachandrena), Robertson, 1902

Sheffield, Cory S., 2020, A new species of Andrena (Trachandrena) from the Southwestern United States (Hymenoptera, Andrenidae), Journal of Hymenoptera Research 77, pp. 87-103 : 87

Subgenus Trachandrena Robertson, 1902

Trachandrena Robertson, 1902: 187, 189.

Type species.

Andrena rugosa Robertson, 1891, by original designation.

Diagnosis.

Trachandrena , particularly the females, are relatively easy to recognize among most other subgenera of Andrena in the Nearctic region based on the combination of the coarsely rugose metapostnotum (i.e., propodeal triangle) (Fig. 1 ) and the generally coarse body sculpturing (being less strongly sculptured in most other subgenera), the structure of the metasomal terga, especially T2, which have broad apical marginal zones that usually extend ½ the median length of the tergum (Fig. 2B ) or more (Fig. 2A, C, D ) (other subgenera in the Nearctic have narrower marginal zones), and the characteristic structure of the facial fovea, which is typically much narrower in the lower half (Fig. 3 ) (more parallel-sided for entire length in other Nearctic subgenera). As indicated above, in the Nearctic region Trachandrena is most similar to Plastandrena and Scrapteropsis . In addition to both of these subgenera having terga with much narrower marginal zones (Fig. 4 ), both sexes of Plastandrena usually have weakly to strongly curved inner hind tibial spurs (Fig. 5A ) whereas these are straight in Trachandrena (Fig. 5B ), and the facial fovea of females of both subgenera are typically broad throughout. Males of Scrapteropsis are difficult to distinguish from Trachandrena ( Viereck 1924), though each has unique genital capsules ( LaBerge 1971, 1973), the marginal zone of T2 is longer in Trachandrena , the antenna usually being slightly longer. Male Trachandrena also have S6 usually flat, not with a reflexed apical margin or with apicolateral teeth as in some Plastandrena (i.e., A. crataegi ; LaBerge 1969; Michener 2007). In addition, most Plastandrena in North America, excluding A. crataegi , have the clypeus yellow or otherwise maculated ( LaBerge 1969), not black as in Trachandrena .

Figures

Figure 1. Dorsal enclosure of propodeum (i. e., propodeal triangle) of a female Andrena rugosa Robertson, the type species of Trachandrena Robertson.

Figure 2. Dorsal surface of metasoma of female Trachandrena. A Andrena rugosa, the type species of the subgenus, with relatively wide apical impressed area of T 2; B A. hippotes Robertson, with a relatively narrow apical impressed area of T 2 (but still wider than basal area); C A. cleodora (Viereck); D A. hadfieldi, nov. sp. Both of the latter species have broad apical impressed areas of T 2 which are impunctate.

Figure 3. Facial fovea of Andrena rugosa. The lower half of the facial fovea in Trachandrena is usually much narrower than the upper portion, though this species is the most extreme example.

Figure 4. Dorsal surface of metasoma of female A Plastandrena Hedicke, Andrena crataegi Robertson, and B Scrapteropsis Viereck, A. kalmiae Atwood. Both subgenera differ from Trachandrena Robertson in having the apical impressed area of T 2 narrower than the basal area.

Figure 5. Inner hind tibial spur of A Plastandrena, Andrena crataegi, and B Trachandrena, A. hippotes.