Cytogenetic techniques have been improving over the last decades, providing useful information for the systematics and evolution of several groups, such as social insects. On the other hand, karyotypic data are still incipient for most wasp genera. For instance, only five of the 240 species of Polistes have been karyotyped, usually based on obsolete data. Therefore, this study aimed to revisit the karyotype structure of Polistes canadensis, providing unpublished information based on traditional (karyotyping and C-banding) and refined (GC- and AT-rich sites by base-specific fluorochrome staining) cytogenetic methods. Males and females of P. canadensis were characterized by haploid and diploid numbers of n = 28 and 2n = 56, respectively. The karyotype formula was established in 2K = 18M + 22SM + 16A with a predominance of pericentromeric heterochromatin and terminal GC+ sites in 16 chromosome pairs. Our results differ significantly from the previous karyotype reported for this species, probably related to the utilization of suitable methods of obtaining mitotic chromosomes in the present study. In addition, the detailed analysis of chromosomal microstructure provided potential cytotaxonomic markers for systematic inferences in social wasps.

Cytogenetic analyses have been widely used to understand evolutionary processes and to resolve taxonomic uncertainties in insects. In particular, the mapping of specific chromosomal regions might provide insights about the genome organization and interspecific relationships. Considering the importance of this approach and the scarcity of chromosomal data in some groups of Hymenoptera, this study provides the first cytogenetic characterization of the parasitoid wasp Brachymeria (Pseudobrachymeria) vesparum Bouček,1992. This species was characterized by 2n = 10 metacentric chromosomes. The heterochromatin was located at pericentromeric and terminal regions, being particularly conspicuous, occupying a large part of chromosomes from pair 2. In addition, GC+ sites were detected at interstitial region of two chromosomal pairs. The present data was useful to infer the chromosomal rearrangements involved in speciation within Brachymeria besides providing cytotaxonomic markers for further comparative cytogenetic studies.