Introduction

In Michener’s (Reference Michener1941) treatment of Osmiinae Newman, 1834 (Hymenoptera: Megachilidae), he recognised two tribes, Osmiini Newman, 1834 (type genus Osmia Panzer, 1806) and Heriadini Michener, 1941 (type genus Heriades Spinola, 1808). Heriadini also included Chelostoma Latreille 1809, Chelostomopsis Cockerell, 1925 (now considered a subgenus of Protosmia Ducke, 1900), Formicapis Sladen, 1916 (now a subgenus of Hoplitis Klug, 1807), Prochelostoma Robertson, 1903 (now a subgenus of Chelostoma), and Robertsonella Titus, 1904 (now a subgenus of Hoplitis). In subsequent works, most of these genera were placed in Osmiini (e.g., Michener Reference Michener1944, Reference Michener, Muesebeck, Krombein and Townes1951, Reference Michener2000, Reference Michener2007; Hurd Reference Hurd, Krombein, Hurd, Smith and Burks1979). Griswold (Reference Griswold1985), although not using a subtribal classification, recognised Osmiini and Heriadini as the Osmia and Heriades groups. However, Griswold and Michener (Reference Griswold and Michener1998) subsequently noted that these groups seemingly merge, with Protosmia and Othinosmia Michener, 1943 representing intermediates between the two. Michener (Reference Michener2000, Reference Michener2007) also did not recognise subtribes of Osmiini, although he continued to recognise the Osmia and Heriades groups, with Protosmia and Othinosmia placed in the latter.

In the more recent classifications of Engel (Reference Engel2005), Ungricht et al. (Reference Ungricht, Müller and Dorn2008), Wedmann et al. (Reference Wedmann, Wappler and Engel2009), Özbek (Reference Özbek2013), and Gonzalez et al. (Reference Gonzalez, Gustafson and Engel2019), these family-group names were recognised at the subtribal level. Özbek (Reference Özbek2013) also supported the recognition of subtribe Chelostomina Kirby, 1837, indicating that Chelostoma (the type genus) was the sister group to all other Osmiini and deserved subtribal rank. Although this classification was not supported by Gonzalez et al. (Reference Gonzalez, Griswold, Praz and Danforth2012), who also continued to recognise only the Osmia and Heriades groups (with Chelostoma recovered in the latter but still placed in the former), it was supported by Gonzalez et al. (Reference Gonzalez, Gustafson and Engel2019), albeit in contrast to its previous placement in the Osmia group by Griswold (Reference Griswold1985), Griswold and Michener (Reference Griswold and Michener1998), and Michener (Reference Michener2000, Reference Michener2007). It is important to note that, even though the family-group name Chelostomina is not formed correctly (i.e., as noted by Michener Reference Michener1986, the correct combining stem is Chelostomat-, not Chelostom-), under the International Commission on Zoological Nomenclature (1999), Article 29.5, because this spelling is in prevailing use (unanimous since its original publication), it must be maintained; it cannot be corrected to “Chelostomatina.”

Even though Michener (Reference Michener1941) credited Titus (Reference Titus1904) for proposing the genus Robertsonella, he did not mention Titus’s important, albeit brief, discussion on the genus Heriades on the subsequent page. Titus (Reference Titus1904) was the first both to point out that Latreille (Reference Latreille1810) designated Apis truncorum Linnaeus, 1758 as the type species for Heriades and seemingly to recognise the homonymy of Trypetes Schenck, 1861 (which shares the same type species with Heriades) with Trypetes Schönherr, 1836 (Coleoptera: Curculionidae: Trepetidinae). Although the synonymy of Trypetes under Heriades was recognised as early as Smith (Reference Smith1876), the former name continued to be recognised as a valid genus (e.g., Morawitz Reference Morawitz1867; Cuní Reference Cuní1888; Rudow Reference Rudow1901; Robertson Reference Robertson1905) or as a subgenus of Heriades (e.g., Dalla Torre Reference Dalla Torre1896; Cockerell Reference Cockerell1904; Maidl Reference Maidl1922); Michener (Reference Michener, Muesebeck, Krombein and Townes1951) clarified the status but did not reference Titus (Reference Titus1904).

However, Titus (Reference Titus1904) also recognised a homonym at the family-group level, indicating that Trypetini Robertson, 1903 (type genus Trypetes Schenck, 1861) “will not stand” due to the homonymy with Trypetidae Loew, 1861 (Diptera: Tephritidae) and proposed Heriadini Titus, 1904 as a replacement name. For other cases of Trypetes as the type genus for family-group names, see Sabrosky and Zimmerman (Reference Sabrosky and Zimmerman1966), Melville (Reference Melville1970), and International Commission on Zoological Nomenclature (1974). Thus, Titus (Reference Titus1904) is the correct author for Heriadini, not Michener (Reference Michener1941) as indicated in numerous works (Michener Reference Michener1986; Engel Reference Engel2005; Ungricht et al. Reference Ungricht, Müller and Dorn2008; Wedmann et al. Reference Wedmann, Wappler and Engel2009; Gonzalez et al. Reference Gonzalez, Gustafson and Engel2019).

With respect to family-group names, the yet-to-be resolved placement of Chelostoma poses some challenges to a subtribal classification of Osmiini. If considered a member of the Heriades group (i.e., as suggested in Gonzalez et al. Reference Gonzalez, Griswold, Praz and Danforth2012), then Chelostomina would be the correct subtribal name, whereas its inclusion in subtribe Osmiina (e.g., Griswold Reference Griswold1985; Griswold and Michener Reference Griswold and Michener1998; Engel Reference Engel2005; Michener Reference Michener2007; Ungricht et al. Reference Ungricht, Müller and Dorn2008) would support the recognition of subtribe Heriadina. However, Özbek’s (Reference Özbek2013) and Gonzalez et al.’s (Reference Gonzalez, Gustafson and Engel2019) classifications supported the recognition of Chelostomina as a taxon distinct from Osmiina or Heriadina. Until the status of Chelostoma within Osmiini is clarified, Chelostomatidae and Heriadini should be considered as junior synonyms of Osmiini, but Chelostomina and Heriadina are available as subtribal names if further partitioning is warranted.