Ctenoplectrellini Engel

Tribe Ctenoplectrellini Engel

The tribe Ctenoplectrellini includes superficially osmiine-like bees, so much so that the group was originally assigned as a subtribe of Osmiini ( Engel, 2001) before elevation to a distinct tribe ( Engel, 2005; Engel and Perkovsky, 2006). Ctenoplectrellines have been found as amber inclusions from the Baltic (including Bitterfeld), Rovno, and Oise deposits ( Cockerell, 1909a; Engel, 2001, 2008; Engel and Perkovsky, 2006; Gonzalez and Engel, 2011; Engel and Davis, 2021), and as compression fossils from Messel in Germany and the Green River Formation of Colorado, all from the Eocene ( Wedmann et al., 2009; M.S.E., unpubl. data). There are also compressions of Ctenoplectrellini from the Paleocene of Menat, France ( Nel and Petrulevičius, 2003; M.S.E., unpubl. data). Subsequently, the extant sub-Saharan Aspidosmia was discovered to be nested among the ctenoplectrelline genera ( Gonzalez et al., 2012, 2019), confirming the prediction of Gonzalez and Engel (2011) and documenting a surviving relict of this clade hitherto known only from Eocene occurrences. The tribe Aspidosmiini was established for Aspidosmia and separate from the Ctenoplectrellini ( Gonzalez et al., 2012) , although its recognition renders the latter paraphyletic and obscures the significance of the relationship of Aspidosmia and the various fossil genera ( Gonzalez et al., 2019). In fact, Gonzalez and Engel (2011) noted the shared characters between Aspidosmia and Ctenoplectrella , suggesting that the former could be a surviving relict of ctenoplectrellines, a conclusion later supported by the analysis of Gonzalez et al. (2019). The linkage between Aspidosmia and Ctenoplectrella is further emphasized by the male terminalia, with both genera having a characteristically trilobate apical margin to hidden sternum VII (see below). Accordingly, the tribe Aspidosmiini is considered a junior synonym of Ctenoplectrellini (new synonymy), thereby removing the paraphyly of the group.

DIAGNOSIS: Integument with or without maculation (maculation present on face of males of Aspidosmia ) and either nonmetallic or weakly dark metallic green (fig. 8).

FEMALE. Mandible tridentate; frimbrial ridge absent (known for Ctenoplectrella and Aspidosmia ); interdental laminae lacking. Malar space linear (figs. 8A, 9B, C, 10A, C). Maxillary palpus tetramerous. Labial palpus tetramerous; palpomeres I and II flattened, elongate, palpomere I 0.5–0.9× length of palpomere II; palpomere III projecting obliquely from axis of palpomere II. Clypeus somewhat flattened, not or only slightly extending below lower tangent of compound eyes (figs. 8A, 9C, 10A); clypeus apical margin covering (figs. 8A, 10A) or not convering labral base ( Aspidosmia ), thus labroclypeal articulation either obscured or not (variable among genera, refer to key, below). Single subantennal sulcus directed to outer margin of antennal torulus (fig. 10A). Juxtantennal carina absent. Compound eyes bare (fig. 8A). Posterior margin of vertex gently concave; preoccipital ridge rounded, sometimes sharply angled dorsally.

Pronotal collar virtually absent, with posterior border blending uninterrupted onto dorsal surface without ridge medially (in profile slope continuous and without anterior ridge demarcating dorsal-facing surface comprising collar relative to lower anterior neck), with dorsal transverse ridge effaced or rounded, without dorsolateral angle, without dorsolateral ridge extending vertically across lateral surface.

Mesoscutum broadly rounded anteriorly (fig. 8B, 9A), raised above pronotal posterior margin, sculpturing variable, generally smooth to imbricate with scattered small to minute punctures (fig. 9A); parapsidal lines linear; preaxilla sloping with setae (as in Megachilini ); mesoscutal-mesoscutellar sulcus impressed, without V-shaped notch on mesoscutellum; mesoscutellum low, rounded, posterior margin meeting metanotum and not extending over metanotum (fig. 9); axillae simple (figs. 8B, 9); metanotum sloping, without medial tubercles or spines; basal area of propodeum sloping, asetose, smooth to faintly imbricate (fig. 9); omaular ridge rounded (fig. 9B, D); scrobal sulcus absent; preepisternal sulcus absent; mesepisternum smooth to faintly imbricate, sometimes with scattered punctures (fig. 9B, D); dorsal lamella of metepisternum absent.

Forewing (fig. 8B; refer also to Engel, 2001; Gonzalez and Engel, 2011) with pterostigma proximal to r-rs about as long as or slightly longer than pterostigmal width; pterostigmal length 1.75× or more its basal width; prestigma more than 2× as long as broad; basal vein (1M) arched, thus orthogonal to 1Cu (as in Glyptapini and the new tribe described below); marginal cell apex rounded, slightly offset from anterior wing margin; two submarginal cells; 1m-cu and 2m-cu entering second submarginal cell, i.e., 2rs-m proximal to 2rs-m; hind wing with 6–13 distal hamuli (6–7 hamuli in Ctenoplectrella , 7 in Aspidosmiella , 10 in Glaesosmia , 11–13 in Aspidosmia ).

Protibial calcar with or without anterior ridge on rachis bordering velum, malus simple, short, less than 0.5× length of velum, apical margin of velum simple; tibiae not spiculate; pro- and mesotibiae with apical outer spine, spine less prominent on protibia; mesotibial spur long, slender, minutely ciliate to serrate; metabasitibial plate absent; metatibial scopa present (fig. 8A) (as in Glyptapini and the new tribe described below; absent in other megachiline tribes); metatibial spurs long, slender (fig. 8A), minutely serrate to minutely ciliate; pretarsal claws with short inner ramus; arolium present.

Metasomal scopa present; sting and associated structures well developed (vestigial in Dioxyini ).

MALE (known only for Aspidosmia and Ctenoplectrella ). Mandible bidentate (fig. 9C, 10A) to quadridentate. Metasomal tergum VI without preapical carina; tergum VII exposed, directed posteriorly, without pygidial plate (fig. 11B–D); sternum VI with apical margin simple ( Aspidosmia ) or with lateral notches for reception of gonostyli (fig. 11F) ( Ctenoplectrella ); sternum VII well sclerotized, not divided medially, apical margin trilobate (fig. 11G) (medial lobe large in Ctenoplectrella : fig. 11G; medial lobe formed as short point in Aspidosmia : refer to Peters, 1972); volsella present (fig. 12) (particularly large in Ctenoplectrella ), with or without differentiated digitus and cuspis (differentiated in Ctenoplectrella : fig. 12A; not differentiated in Aspidosmia ).

REMARKS: A new key is provided to the genera of living and fossil Ctenoplectrellini . The subtribe Glaesosmiina Engel (new subtribe; type genus: Glaesosmia Engel, 2001 ; diagnosed by combination of subantennal sulcus as long as torular diameter, interocular distance greater than compound eye length, and forewing 2Rs oblique to 2M, forming acute apical angle) is here recognized to remove paraphyly of Ctenoplectrellina relative to Aspidosmiina and allow for retaining a group for Aspidosmia and its visible labroclypeal articulation and shorter pterostigmal form relative to the fossils. In addition, Ctenoplectrella phaeton Gonzalez and Engel is removed to a separate genus given its peculiarly sparse pubescence and rather discomfited inclusion in Ctenoplectrella .