Scaura Schwarz, 1938

Engel, Michael S., 2022, Notes on the stingless bee genera Scaura and Geotrigona (Hymenoptera: Apidae), Journal of Melittology 2022 (108), pp. 1-4 : 1-2

Genus Scaura Schwarz

The genus Scaura Schwarz is a distinctive group of small to minute stingless bees (3–6 mm in total length), particularly noteworthy for the expanded metabasitarsus, a trait shared with the species of Schwarzula Moure. While Schwarzula is sometimes treated as a separate genus sister to Scaura (e.g., Silveira et al., 2002; Camargo & Pedro, 2002a), it has more recently been classified as a subgenus or synonym of Scaura (e.g., Engel et al., 2021). The genus superficially resembles Plebeia Schwarz , which led Michener (1990, 2007, 2013) to consider Scaura as a subgenus of the former (and Schwarzula as a synonym of Scaura ). Nonetheless, Scaura does not appear to be immediately related to Plebeia ( Rasmussen & Cameron, 2010) , and its inclusion therein is unwarranted.

The phylogeny of Rasmussen & Cameron (2010) suggested that Scaura was paraphyletic with respect to Schwarzula . In their phylogeny, species of the former “ latitarsis ” complex were more closely related to Schwarzula than to Scaura longula (Lepeletier) and S. tenuis (Ducke) . Note, however, that in their phylogeny S. latitarsis (Friese) , the type species of Scaura , was represented by its junior synonym S. tenuis (vide Nogueira et al., 2017, 2019), and that the species identified as “ S. latitarsis ” was instead likely S. amazonica Nogueira et al. Regarding such paraphyly, an easy solution is the synonymy of Schwarzula under Scaura . However, this classificatory arrangement obscures some interesting biological differences among these groups of bees. For instance, both S. latitarsis and S. longula are distinctive for their elongate, thin metasomas and both have brood cells arranged in either irregular clusters or columns ( Nogueira et al., 2019, in press). By contrast, the remaining species have broader metasomas similar to those of Schwarzula (and are putatively more closely related to this group), and all build brood cells in horizontal discs ( Nogueira et al., 2019, in press). Moreover, Schwarzula is known to have a unique mutualism with scale insects ( Coccidae ) ( Camargo & Pedro, 2002a, 2002b), and it is therefore itself a practical taxonomic unit. To rectify the situation regarding potential paraphyly of Scaura relative to Schwarzula it is simple to consider a third subgenus, as proposed herein. Although finely split, the recognition of this group putatively leaves each group monophyletic and allows each subgenus to be associated with a distinctive morphology and biology. Moreover, as subgenera can be ignored easily, it does not burden the classification as those not wishing to employ subgeneric names can simply leave them out.

Key to Subgenera of Scaura

1. Metabasitarsus as wide as or wider than metatibia; malar space shorter than flagellar diameter; gena in profile narrower than compound eye; mandible virtually edentate ............................................................................................................ 2

—. Metabasitarsus narrower than metatibia; malar space as long as or longer than flagellar diameter; gena in profile broader than compound eye; mandible with two denticles ................................................................ Schwarzula Moure

2(1). Metasoma elongate, length 3× width or more; metasomal tergum VI with dark fuscous or black setae ............................................................ Scaura Schwarz , s.str.

—. Metasoma subtriangular, length 1.5× width; metasomal tergum VI with white setae ............................................................................................ Scauracea , n. subgen.