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The tribe Rhodniini is a monophyletic group composed of 22 species, with 19 in the Rhodnius genus and three in the Psammolestes genus. These insects are morphologically very similar (cryptic species), and new tools are important for investigating the taxonomy of these vectors. Spermiotaxonomy is an important tool in differentiating between related species, and this study analyzed the spermatids of Rhodniini species to elucidate their spermiotaxonomy. All of the Rhodniini species contained two heteropyknotic filaments in the extremities of their cells. Although spermiotaxonomy has been an important tool in differentiating between species of the Triatoma genus, all of the species in the Rhodnius genus exhibited the same characteristics in their male gametes. However, spermatid analysis made it possible to confirm the monophyly of the Rhodniini tribe, because Psammolestes tertius had the same pattern as that described for Rhodnius. The results of this study demonstrate that spermiotaxonomy, in addition to being an important tool for differentiating between related species of Triatoma, can be used as an optimization tool in phylogenetic analyses.

The Triatominae subfamily comprises 6 tribes. The tribe Rhodniini comprises 2 genera and 22 nominal species. Rhodnius montenegrensis (Hemiptera, Triatominae) was recently described as evolutionarily related to R. robustus. Therefore, in order to contribute to karyosystematic study of the tribe Rhodniini, this report describes the number of chromosomes and compares the karyotype of R. montenegrensis to that of all other species in the tribe, in order to determine the karyotypic evolution of the tribe Rhodniini. The seminiferous tubules of adult males, after being removed and fixated on a cover slip, were processed with lacto-aceto-orcein for cytogenetic analysis. R. montenegrensis, as well as all other species of the tribe Rhodniini showed 22 chromosomes (20 autosomes + XY). Thus, we hereby describe the karyotype of the species R. montenegrensis and mainly highlight that the tribe Rhodniini displays karyotypic homogeneity, demonstrating itself as a derived group to a lesser extent when compared to the number of chromosomes of the common ancestors of the subfamily Triatominae.