Specimens of A. melliventris s. l., including type materials, from several North American collections were examined for morphological comparisons for this study, including [CANADA]: Royal Saskatchewan Museum [RSKM], Regina, Saskatchewan; Royal Alberta Museum [PMAE], Edmonton, Alberta; Royal British Columbia Museum [RBCM], Victoria, British Columbia; Packer Collection at York University [PCYU], Toronto, Ontario; [UNITED STATES]: American Museum of Natural History [AMNH], New York; United States National Museum [USNM], Washington, D.C.; University of Colorado Museum of Natural History [UCMC], Boulder, Colorado; Droege Collection, USGS Bee Inventory and Monitoring Lab [BIML], Laurel, Maryland; The University of Arizona [UAIC], Tucson, Arizona.

In addition to the materials mentioned above, records were also mined from the literature (e.g. Porter (1983)) and GBIF.org (2023)), though identifications were likely based on Roberts (1972) concept of the species.

Additional DNA barcode sequences of material from North American were obtained following previously reported methods (Sheffield et al. 2017), supplementing material already in the Barcodes of Life Data System (BOLD: Ratnasingham and Hebert (2007)) as part of an ongoing campaign to build a comprehensive DNA barcode library for the bee fauna of Canada (Sheffield et al. 2017) and the World (Packer et al. 2010). All data were mapped using SimpleMappr (Shorthouse 2010) with taxa assigned according to morphology as per Crawford (1901) and Sandhouse (1936), as described above. Only specimen data for examined specimens of A. fasciatus are provided for this single taxon treatment; specimens from the AMNH were identifed by Corey Smith using photos and descriptions provided by the author.

In addition to the distinctive morphological characters of both sexes of A. fasciatus described above, which are consistent across all material examined, it also differs from A. melliventris genetically, based on results from the Barcode Gap Analysis tool in BOLD. Agapostemon fasciatus is presently assigned to Barcode Index Number (BIN, after Ratnasingham and Hebert (2013)) BOLD:ACU3900 and differs by 7.99% sequence divergence from other "A. melliventris" in BOLD (currently represented by at least three BINs BOLD:AAJ1185, BOLD:ABY2743 and BOLD:AAN8220, which will be the subject of a subsequent paper on the remaining members of species complex not found in Canada). Amongst these four BINs, the mean distance in sequence divergence averages 8.82%, suggesting multiple additional taxa.

Crawford (1901) mentioned that 18 female and 37 male species formed the type series (i.e. syntypes), though none of these was specifically designated as a lectotype within any subsequent publication by that author. However, Sandhouse (1936) indicated that Crawford selected a lectotype female and lectoallotype male from his syntype series (these also examined by Cockerell (1937) and Roberts (1972)) from material at the USNM (see above).

Roberts (1972) indicated that he also examined the type material of A. fasciatus and A. digueti and believed they were conspecific with A. melliventris, based on variable metasomal colour of the females alone and pointed out that, until he synonymised A. fasciatus with A. melliventris, it had been considered by some authors to be of subspecific rank (e.g. Sandhouse (1936)), though others continued to consider it a valid species (e.g. Cockerell (1937), Fischer (1950)). His (Roberts 1972) argument for the synonymy was also based on his belief that A. fasciatus was sympatric with A. melliventris in the south-western part of the range (namely Arizona) where intermediate forms were "too common" (cf. discussion of variation). However, there is no reason why distinct species cannot have overlapping ranges and it is likely that he made this comment based on female metasomal colour alone (which varies even with A. melliventris s. str.); he may not have examined or noted the other characters indicated above that seem to be consistent within each taxa (i.e. scape maculations in females and leg colouring in males). When these are considered, a differing distribution of the two taxa is observed, with only a small area of sympatry (Fig. 7). Thus, some of the material identifed as A. melliventris from the Great Plains reported recently by Portman et al. (2022) may actually be A. fasciatus.

Roberts (1972) also commented on the nomenclature of A. fasciatus. Vachal (1903) considered Agapostemon a subgenus of Halictus Latreille, 1804, making Crawford’s species a junior secondary homonym of Halictus fasciatus Nylander, 1848 (=Halictus tumulorum (Linnaeus, 1758)), so Vachal (1903) proposed the new name, Halictus (Agapostemon) plurifasciatus Vachal 1903. The same also occurred for A. coloradensis Crawford, 1901, which Vachal (1903) renamed H. (A.) coloradinus Vachal, 1903. These specific epithets were used by Sandhouse (1936), though Cockerell (1937) and Michener (1951) believed Crawford's epithet should be used for A. fasciatus and A. coloradensis; a petition from T.D.A Cockerell to the ICZN regarding Crawford's A. coloradensis caused much debate after his death on the larger issues created by these Agapostemon species (see Hemming (1950)). However, Roberts (1972) indicated, based on the International Code of Zoological Nomenclature (citing ICZN (1964)), "secondary homonyms rejected before 1961 cannot be revived," specifically citing the example of A. coloradinus which has been used as a valid species name since Vachal (1903) (e.g. Sandhouse (1936), Roberts (1972), Hurd (1979), Moure and Hurd (1987)). Roberts (1972) also suggested that, if Crawford’s A. fasciatus were to be recognised as a valid taxon (as is done so here), then A. plurifasciatus should be used, but this is not the case as (from ICZN (1999): 59.3. Secondary homonyms replaced before 1961 but no longer considered congeneric): “A junior secondary homonym replaced before 1961 is permanently invalid unless the substitute name is not in use [applicable to A. plurifasciatus since it was synonymised with A. melliventris by Sandhouse (1936) and Roberts (1972)] and the relevant taxa are no longer considered congeneric, in which case the junior homonym is not to be rejected on grounds of that replacement”. As such, A. fasciatus is resurrected from synonymy with A. melliventris and Crawford’s original species epithet is considered valid. By contrast, as A. coloradinus has remained in use in a number of taxonomic (e.g. Sandhouse (1936), Roberts (1972), Hurd (1979), Moure and Hurd (1987), Janjic and Packer (2003), Scott et al. (2011)) and ecological works (e.g. Lavigne (1976), Berger et al. (1985), Osborn et al. (1988)) since Vachal (1903), it is the appropriate name for that taxon (see ICZN (1999)).

Specimens from at least three additinal BINs are tentatively identified in BOLD as A. melliventris, mostly all matching the general discription of A. melliventris, but suggesting that there are possible additional species in this species group. Members of BOLD:AAJ1185 (seven male specimens) are from one location on the Texas/Mexico border and members assigned to BOLD:ABY2743 are from Arizona (two female, three male specimens). Most interesting are the four specimens of BOLD:AAN8220, also from Arizona, though with the single female having both the clypeus apically and scape maculated, though with a metasoma that is similar to A. fasciatus (based on images available on BOLD). These materials will be covered in a subsequent work on the A. melliventris species complex, which is currently in progress.