Taxonomic comments on Megachile subgenus Chrysosarus (Hymenoptera: Megachilidae)

Comments on the phylogenetic relationships and taxonomy of American leafcutter bees of the genus Megachile Latreille subgenus Chrysosarus Mitchell are provided. The South American subgenera Austrosarus Raw, Stelodides Moure, and Zonomegachile Mitchell are newly synonymized under Chrysosarus (new synonymies). 1 Department of Biological Sciences, 100 Campus Drive, Southwestern Oklahoma State University, Weatherford, Oklahoma 73096, USA ([email protected]). 2 Division of Entomology, Natural History Museum, 1501 Crestline Drive – Suite 140, University of Kansas, Lawrence, Kansas 66045, USA. INTRODUCTION Megachilidae is one of the seven extant bee families containing more than 4000 described species in 76 genera worldwide (Michener, 2007; Ascher & Pickering, 2013). This family consists of both solitary and cleptoparasitic species and is noteworthy for its astonishing diversity of nesting habits and floral relationships, which collectively are more diverse than any other bee group (e.g., Müller, 1996; Müller & Bansac, 2004; Michener, 2007; Cane et al., 2007), for being the primary source of invasive bees worldwide (e.g., Cane, 2003; Hinojosa-Díaz et al., 2005; Strange et al., 2011), and for including the majority of non-honey bee managed pollinators [e.g., Megachile (Eutricharaea) rotundata (Fabricius), Osmia (Osmia) lignaria Say] now introduced to many parts of the globe (e.g., Pitts-Singer & Cane, 2011). The higher-level phylogeny and classification of the Megachilidae based on adult morphology of extinct and extant taxa were recently revised by Gonzalez et al. (2012) and nine tribes and four subfamilies are currently recognized. The tribe Megachilini is the most common and diverse of all tribes, accounting for about 50% of the species diversity of the family (Michener, 2007). The more than 2000 species have been traditionally grouped in several genera, particularly those non-parasitic taxa placed by Michener (2007) in Megachile Latreille. Following Michener’s classification, two other genera, Coelioxys Latreille and Radoszkowskiana Popov, both clepJournal of Melittology 2 No. 5 toparasitic, are recognized. The non-parasitic genus Noteriades Cockerell was recently transferred from the Osmiini to Megachilini (Gonzalez et al., 2012). Thus, if adopting Michener’s (2007) classification, four genera are to be recognized in Megachilini. The phylogenetic relationships within Megachilini, excluding Noteriades, were explored by Gonzalez (2008), and the multigeneric classification proposed in that review is adopted herein. The genus Megachile, as here understood, is used in a narrower sense than that of Michener (2000, 2007) and refers to a monophyletic, derived clade within Megachile s.l. that included all subgenera of ‘‘Group 1’’ of Michener (2000, 2007), Creightonella Cockerell (the only subgenus of Michener’s ‘‘Group 3’’), and the subgenera Mitchellapis Michener and Megella Pasteels; the latter two subgenera tentatively included by Michener (2007) in ‘‘Group 2’’. Megachile, as here employed, is characterized by the presence of cutting edges among teeth in the female mandibles, which are generally associated with the use of petal or leaf pieces to build their nest cells. Such leafcutting behavior is unique among bees and it appears to have started as early as the Paleocene, as indicated by fossils of dicotyledonous leafs with distinctive, semi-circular cuts into the margin (Wappler & Engel, 2003; Wedmann et al., 2009). However, cutting edges appear to be secondarily lost in some Megachile (sensu Gonzalez, 2008). In the Americas, these cutting edges are absent in the subgenera Chrysosarus Mitchell, some species of Megachile s.str., and in the monotypic subgenera Schrottkyapis Mitchell and Stelodides Moure, although some still exhibit leafcutting behavior (e.g., Zillikens & Steiner, 2004). As part of ongoing studies on the systematics of leafcutter bees, herein I provide taxonomic comments on the subgenus Chrysosarus and synonymize with this group the South American subgenera Austrosarus Raw, Stelodides, and Zonomegachile Mitchell. This paper is part of a series of recent contributions dealing with the systematics of the Megachilini (i.e., Gonzalez & Griswold, 2007; Gonzalez et al., 2010; Engel & Gonzalez, 2011; Griswold & Gonzalez, 2011; Alqarni et al., 2012; Gonzalez & Engel, 2012; Gonzalez et al. 2012), and centered on providing a revised and robust classification. The relationship of Chrysosarus to Stelodides and Zonomegachile was first indicated by Mitchell (1980). He recognized Chrysosarus at the generic level, with Dactylomegachile Mitchell, Stelodides, and Zonomegachile as subgenera. In Michener’s (2000) classification, in which a large, all-encompassing genus Megachile was recognized, Dactylomegachile was synonymized with Chrysosarus while Stelodides and Zonomegachile were treated as separated subgenera. Such a relationship of Chrysosarus with Dactylomegachile and Stelodides has been supported in the cladistic analysis of Gonzalez (2008) and Durante & Cabrera (2009). The synonyms proposed herein are based on these works and are presented at this time to make them available in a forthcoming, updated phylogenetic analysis and classification of the Megachilini (Gonzalez, in prep.).