Pseudomyrmex mixtecus

Colonies have been collected from Acacia hindsii and A. collinsii, but little more has been recorded about their biology. Janzen's field notes indicate that this species is monogynous. (Ward 1993)

Identification
Ward (1993) - P. mixtecus is distinguished from all other species, except Pseudomyrmex veneficus and Pseudomyrmex flavicornis, by its laterally rounded median clypeal lobe, broad head, and black (or very dark brown) body. It differs from P. veneficus by the fully opaque head, absence of conspicuous suberect pubescence on the petiole, and larger size. P. mixtecus is evidently closely related to P. flavicornis but averages smaller in size (compare worker HW and LHT values), a difference which is absolute in queens (queen HW 0.96-1.01 (n=8), whereas queen HW > 1.11 in P.flavicornis). In addition the petiole is relatively longer and higher, for a given head width, in both workers and queens of P. mixtecus.

Distribution
Known only from the Mexican states of Guerrero and Oaxaca.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Nomenclature

 *  mixtecus. Pseudomyrmex mixtecus Ward, 1993: 144, figs. 15, 26, 55, 61, 69 (w.q.m.) MEXICO.

Worker
Worker measurements (n=13). —HL 0.94-1.19, HW 0.89-1.03, MFC 0.054-0.073, CI 0.86-0.95, REL 0.42-0.47, REL2 0.46-0.52 OOI 1.22-2.28, VI 0.61-0.73, FCI 0.056-0.073, SI 0.43-0.45, SI2 0.86-0.97, NI 0.60-0.65, PLI 0.60-0.68, PWI 0.60-0.68, PPWI 1.40-1.73.

Similar to P. ferrugineus (q.v.) except as follows. Size smaller (HW < 1.04, LHT < 0.90), head broad (CI > 0.85); frontal carinae separated by about basal scape width or less (FCI2 0.45-0.54). Basal and declivitous faces of propodeum forming a less obtuse angle in profile than typical for P. ferrugineus. Head densely punctulate, opaque. Standing pilosity rather common, usually some setae exceeding 0.12 mm and 0.20 mm in length on mesosoma dorsum and petiole, respectively. Pubescence dense but appressed. Very dark brown to black, appendages lighter.

Type Material
Holotype worker. MEXICO, Guerrero: 25.4 mi. S. Chilpancingo, 10.viii.1966, D. H. Janzen #M008810966 (LACM). HW 0.97, HL 1.07, EL 0.48, PL 0.55, PH 0.35.

Paratypes. Same data as holotype, and three other accession numbers (M007810966, M009810966, M010810966) with same locality, date, and collector: series of 43 workers, 34 queens and 17 males.

References based on Global Ant Biodiversity Informatics

 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Heil, M. 2013. Let the best one stay: screening of ant defenders by Acacia host plants functions independently of partner choice or host sanctions. Journal of Ecology 101: 684-688.
 * Vásquez-Bolaños M. 2011. Lista de especies de hormigas (Hymenoptera: Formicidae) para México. Dugesiana 18: 95-133
 * Ward, P.S. 1993. Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae) Journal of Hymenoptera Research 2(1):117-168