Octostruma reducta, Probst & Brandão, 2022

Probst, Rodolfo Da Silva & Brandão, Carlos Roberto Ferreira, 2022, A taxonomic revision of the dirt ants, Basiceros Schulz, 1906 (Hymenoptera, Formicidae), Zootaxa 5149 (1), pp. 1-75 : 69-70

Basiceros redux ( Donisthorpe 1939) =

Octostruma reducta comb. nov.

( Fig 29 )

Type-material: holotype (male), Donisthorpe 1939: 152, GUYANA .

Type-locality: Guyana (“ British Guiana ”): Kaieteur Savannah, 5.ix.1937 (O.W. Richards) (MNH1014339) (examined). Incertae sedis in Rhopalothrix: Brown & Kempf, 1960: 164 .

Combination in Basiceros : Bolton 1995: 80.

Status as species: Kempf 1972: 227; Bolton 1995: 80.

Comments. Brown & Kempf (1960), while mentioning the taxonomic uncertainty regarding Basiceros -genus group males, added that Rhopalothrix redux could be placed in Eurhopalothrix , Rhopalothrix , Octostruma , or Talaridris . Few are the species from the Basiceros -genus group in which the males are known, making it hard to address intraspecific variation. Despite the holotype conditions, a detailed examination revealed unique features present of Basiceros redux when compared to other “basicerotine” males:

1. Mandibles—shape and dentition: most Basiceros males have mandibles somewhat elongate, with the external margin apically curved and 9-14 teeth on the masticatory margin. In Basiceros redux , the mandibles are triangular, having seven or eight teeth;

2. Head shape: Basiceros males have an anteriorly elongated head (the overall head shape has a piriform to subpiriform aspect) and the occipital margin projected and carinate, forming a neck. In B. redux the head is rounded and the occipital margin lacks a neck;

3. Antennae: antennomeres of B. redux are subequal from A3 to the apical segment, a condition not observed in any Basiceros male examined for this study;

4. Ocelli: in general, Basiceros males have the ocelli arranged on the top of the head, surrounded by a conspicuous cephalic crest. In B. redux , although the ocelli are located on the top of the head, the crest is absent;

5. Mesosoma: in B. redux the posterior face of mesoscutellum is strongly truncated and the metanotal band is extremely reduced, giving the mesoscutum + mesoscutellum set an aspect of plateau. In Basiceros males, the posterior margin of mesoscutellum is rounded and the metanotum, although reduced, is detached from the mesoscutellum;

6. Petiolar node in dorsal view: for Basiceros males is elongated, longitudinally rectangular. In B. redux and the known males of Octostruma , Rhopalothrix , and Eurhopalothrix , the node is transversally rectangular;

7. Postpetiolar node in dorsal view: in Basiceros males is nodiform and subglobular, conditions not observed for B. redux ;

8. Gastral integument: in opposition to the shiny integument and the sparse pilosity found in B. redux , males of Basiceros possess finely punctuate to reticulate integument and a more abundant pilosity;

9. Propodeal projections: Basiceros males have short projections, sometimes angled. In B. redux the propodeum is armed with a well-developed triangular and lamelliform projection, similar to observed for Octostruma males;

10. Forewing venation: in B. redux the vein M+Cu has a spectral basal portion, similarly to observed for Octostruma males, whereas in Basiceros males that vein is invariably complete. Eurhopalothrix males tend to have M+Cu completely spectral;

11. Forewing venation II: submarginal cell 1: known Rhopalothrix males have the submarginal cell 1 open (for Eurhopalothrix males, the Rs+M vein is in general spectral or slightly tubular, and a close observation shows that it closes the submarginal cell 1) and the veins Rs, M, Cu, and A nebular or spectral in their basal half (similar condition observed for examined Eurhopalothrix males). This set of characteristics are absent in B. redux , with the male having a submarginal cell 1 closed, feature shared by Basiceros and Octostruma males. Additionally, B. redux presents another configuration for other veins above cited;

12. Pterostigma: Eurhopalothrix males lack the pterostigma or it is poorly developed. Both Basiceros and Octostruma share a conspicuous pterostigma (for the latter, in some males it can be slightly narrower and not greatly developed);

13. Tegula: in B. redux the tegulae are round, contrasting with other Basiceros males, where they are subrectangular and with the posterior margin convex;

Dietz (2004: 151) also proposed transferring B. redux to Octostruma based on wing features. In addition, Dietz suggested that B. redux could be a male of O. iheringi , based on the pilosities of the petiolar peduncle and ventral face of the postpetiole. However, the current knowledge of Octostruma males is considerably scarce, therefore preventing a correct association of Basiceros redux to a valid Octostruma taxon.

Figures

FIGURE 29. Basiceros redux = Octostruma reducta comb. nov., holotype (CASENT0900942, Guyana: Kaieteur); A. forewing, B. dorsal view, C. full-face view, D. lateral view. Original images by Will Ericson (CAS), edited.