Odontomachus (Latreille) and Anochetus (Mayr) (Hymenoptera: Formicidae: Ponerinae) are closely related pantropical genera of ponerine ants that share morphological and behavioral characteristics. A comparative study was carried out using conventional Giemsa staining, fluorochrome staining, and fluorescent in situ hybridization. Karyotypes revealed a higher stability in chromosome number among Odontomachus species than among Anochetus species. We observed a higher frequency of metacentric chromosomes in the karyotypes of Anochetus compared with the more common telocentrics of Odontomachus species. Differences in the localization of rDNA genes on chromosomes between the two genera also were verified, rDNA genes were found on telocentric and submetacentric chromosomes in Anochetus and on telocentric chromosomes in Odontomachus. Our cytogenetic results lend support to Brown's hypothesis that Odontomachus has evolved from a lineage of Anochetus. The karyotype divergence of both genera can be explained by a model of evolution in which there is a tendency to the increase of chromosome number by centric fission. Supporting evidence for this hypothesis is discussed.

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Cytogenetic studies in Melipona are scarce with only 24 species analyzed cytogenetically. Of these, six species had the rDNA sites physically mapped and characterized by Fluorescent in situ Hybridization (fish). The aim of this study was to perform karyotype analyzes on Melipona species from different regions of Brazil, with a greater sampling representative of the Amazonian fauna and using conventional, fluorochrome staining and FISH with heterologous rDNA probes. The predominant chromosome number was 2n = 18, however, the subspecies M. seminigra abunensis and M. s. pernigra showed 2n = 22 chromosomes. The karyotypes were symmetrical, however M. bicolor, M. quadrifasciata, M. flavolineata, M. fuscopilosa, M. nebulosa presented the first pair heteromorphic in length. CMA3+ blocks also exhibited heteromorphism of size and in almost all cases coincided with rDNA sites, except for M. crinita and M. nebulosa, which presented additional non-coincident CMA3+ blocks. The CMA/ rDNA sites were terminal and interstitial in species with high heterochromatic content, and pericentromeric in those species with low heterochromatic content. In addition to pointing out cytogenetic features of cytotaxonomic importance, the reorganization of the genome in Melipona is discussed.

The haploid karyotype of Kapala sp. (Eucharitidae), a parasite of the Neotropical ant Dinoponera lucida Emery, 1901 (Hymenoptera, Formicidae), is reported for the first time. It consists of four metacentric chromosomes. Chromosomes in the family Eucharitidae were unknown so far; therefore, our results confirm that multiple parallel chromosomal fusions have taken place in several lineages within the superfamily Chalcidoidea.