Key to Madagascar Probolomyrmex

This worker key is based on: [[Media:Hita Garcia, F. & Fisher, B.L. 2014. Taxonomic revision of the cryptic ant genus Probolomyrmex in Madagascar.pdf|Hita Garcia, F. & Fisher, B.L. 2014. Taxonomic revision of the cryptic ant genus Probolomyrmex Mayr (Hymenoptera, Formicidae, Proceratiinae) in Madagascar. Dtsch. Entomol. Z. 61, 65–76.]]

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 * Probolomyrmex
 * Ants of Madagascar

The lack of any sutures or grooves on the mesosoma of Probolomyrmex is a widely accepted genus-specific character, but we observed the presence of a small but noticeable metanotal groove in two of the three Malagasy species. Probolomyrmex ants are always easily recognisable from other ants on the basis of their long and slender bodies, almost complete lack of pilosity, the long sting, and especially the frontoclypeal shelf bearing the antennal insertions (Taylor 1965, Agosti 1994). Taylor (1965) pointed out that the structural reduction in Probolomyrmex is extreme, which leaves only a few, useful diagnostic characters, such as dimensions and proportions of head, antennae, petiole, as well as surface sculpture. Based on the material from Madagascar, however, we do not consider surface sculpture to be too important for species diagnostics. We observed some noticeable variation within species. Consequently, we tried to avoid using surface sculpture as primary diagnostic character, and used it only as supporting character.

All three species treated in this study are placed in the P. greavesi species group sensu Eguchi et al. (2006), mostly on the basis of the well-developed ventral process. The two species groups hypothesised by Eguchi et al. (2006) work very well for the Oriental and Indo-Australian regions, and there is no reason to create a new group for the three species from Madagascar. As already pointed out by Fisher (2007) for P. tani, the Afrotropical species, which can also be placed in the P. greavesi species group, appear morphologically close to the three species from Madagascar suggesting a close relationship. At the moment however, it is not possible to assess the phylogenetic relationships of the Malagasy species with the species from other regions in a comprehensive way due to the high morphological uniformity and lack of diagnostic characters. A highly desirable multi-gene molecular phylogenetic analysis might provide insights into the subgeneric relationships within Probolomyrmex.

1

 * Petiole relatively longer, lower, and less arched, in profile (without ventral process) around 1.3 to 1.5 times longer than high (LPNeI 127–150), and in dorsal view around 1.4 to 1.6 times longer than broad (DPeI 63–69) (Fig. 1A) . . . . . Probolomyrmex tani


 * Petiole shorter, higher and stronger arched, in profile (without ventral process) between 1.0 to 1.2 times longer than high (LPNeI 103–116); in dorsal view petiole around 1.2 to 1.3 times longer than broad (DPeI 76–86) (Fig. 1B, C) . . . . . 2

2
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 * Head shorter, in full-face view around 1.4 to 1.5 times longer than broad (CI 67–70); antennal scapes longer (SI 99–102); mesosoma with weak but distinct metanotal groove; surface sculpture much stronger developed throughout whole body; body colour usually darker than above, usually dark, reddish brown (Fig. 2A, B) . . . . . Probolomyrmex zahamena


 * Head longer, in full-face view around 1.5 to 1.6 times longer than broad (CI 62–65); antennal scapes shorter (SI 91–94); mesosomal outline straight without any groove; surface sculpture much weaker developed throughout whole body; body colour light orange brown (Fig. 2C, D) . . . . . Probolomyrmex curculiformis