Crematogaster opaca, MAYR, 1870

Ward, Philip S. & Blaimer, Bonnie B., 2022, Taxonomy in the phylogenomic era: species boundaries and phylogenetic relationships among North American ants of the Crematogaster scutellaris group (Formicidae: Hymenoptera), Zoological Journal of the Linnean Society 194, pp. 893-937 : 918-919

CREMATOGASTER OPACA MAYR, 1870

Crematogaster opaca Mayr, 1870: 992 . Syntype worker, Tabukaya , Mexico, 1865 (Bilimek) ( NHMW) (examined via AntWeb image: CASENT0919705) and syntype worker, Mexico (Sichel) (BMNH) (examined via AntWeb image: CASENT0902152); latter here designated lectotype .

Crematogaster lineolata subsp. opaca Mayr ; Emery, 1895: 283.

Crematogaster opaca Mayr ; Wheeler, 1919: 111.

Crematogaster (Acrocoelia) lineolata subsp. opaca Mayr ; Emery, 1922: 141.

Crematogaster (Acrocoelia) opaca Mayr ; Wheeler, 1934a: 139.

Crematogaster (Crematogaster) opaca Mayr ; Smith, 1958: 126.

Discussion: Morgan & Mackay (2017) refer to a syntype worker of C. opaca in NHMW ‘collected by Professor Bilimek and Dr Sichel in México’. This statement is misleading because there is no single syntype collected by Bilimek and Sichel; their collections were separate. In the BMNH there is a syntype worker (here designated lectotype) (CASENT0902152) labelled ‘Mex.|Sichel’, while the NHMW syntype (now paralectotype) is labelled ‘ Mexico |Takubaya|Bilim. 65’. However, the important point is that these two specimens are almost certainly not conspecific. The Sichel specimen has the head, mesosoma, petiole and postpetiole densely reticulate-foveolate and opaque, and the gaster finely reticulate and sublucid; the promesonotum is evenly convex in profile and broad in dorsal view (pronotum width/head width ~0.62); the propodeal spine distance is relatively large (SPTD/HW ~0.49); and standing pilosity appears to be sparse (not visibly present on the mesosoma dorsum). The Bilimek specimen is more weakly sculptured with a correspondingly shinier integument, especially on the petiole, postpetiole and gaster; the promesonotum is somewhat flattened in profile and narrower in dorsal view (pronotum width/ head width ~0.53); the propodeal spine tips are less distant (SPTD/HW ~0.44); and standing pilosity is more conspicuous, being present on the mesosoma dorsum on both the pronotal humeri and the mesonotal declivity. Although in this study we are concerned primarily with the Crematogaster of America north of Mexico, we have decided to select a lectotype of C. opaca to assist future work. We designate the BMNH specimen as lectotype because it better matches the original description, which emphasizes the densely reticulate-punctate sculpture and the scarcity of standing pilosity ( Mayr, 1870). Unfortunately the provenance of this specimen – other than Mexico – is unknown. Sichel evidently supplied the specimen to Mayr, but there is no evidence that he visited Mexico or anywhere else outside Europe during his lifetime ( Mulsant, 1869), so the specimen would have been acquired from another collector, possibly de Saussure. The non-conspecific paralectotype is from Takubaya (= Tacubaya), a district of Mexico City, near Bilimek’s place of residence during his stay in Mexico ( Roth, 1965: 346).

There is a confusing array of C. opaca -like forms found in Mexico and Central America, showing considerable variation in sculpture, pilosity, configuration of the promesonotum, size of propodeal spines and petiole shape. More comprehensive sampling and careful study is necessary to determine how many species are present in this complex. These ants just barely enter the United States, in southern Arizona. Because of taxonomic uncertainty, we refer to the Arizona populations as Crematogaster sp. cf. opaca . These specimens are similar to the C. opaca lectotype with respect to integument sculpture, promesonotal shape (pronotum width/head width 0.59–0.62) and propodeal spine distance (SPTD/ HW 0.45–0.51), but they have more abundant standing pilosity (MSC 2–5, A4SC 10–18).