A karyological study of the genus Pnigalio Schrank (Hymenoptera: Eulophidae): Assessing the taxonomic utility of chromosomes at the species level M. Gebiola 1,2 *, M. Giorgini 2 , P. Navone 3 and U. Bernardo 2 1 Dipartimento di Entomologia e Zoologia Agraria ‘F. Silvestri’, Università degli Studi di Napoli ‘Federico II’, via Università 100, 80055 Portici (NA), Italy: 2 CNR – Istituto per la Protezione delle Piante, sezione di Portici (NA), via Università 133, 80055 Portici (NA), Italy: 3 Di.Va.P.R.A. Entomologia e Zoologia applicate all’Ambiente ‘Carlo Vidano’, Università degli Studi di Torino, Via L. da Vinci 44, 10095 Grugliasco (TO), Italy Abstract We provide a karyological study of 12 species of the genus Pnigalio in an attempt to evaluate the taxonomic utility of karyotypes at the species level. For all species of Pnigalio examined the number of chromosome was 2n = 12. Karyotype formulae presented mainly metacentric and submetacentric chromosomes, although a pair of acrocentrics or subtelocentrics, shorter than biarmed chromosomes, was present in some species. The analysis of karyotypes of Pnigalio showed frequent but not general interspecific variability of the chromosome traits. Although most of the studied species revealed concordance between morphological and karyological characters (centromeric index and relative length), two other categories have been identified: morphologically distinct species without reciprocal differences in karyotype structure, and morphologically similar species that strongly differ in chromosomal characters. Keywords: B chromosome, cytotaxonomy, karyogram, karyotype, morphometrics, NORs (Accepted 7 June 2011; First published online 8 July 2011) Introduction Chalcidoidea are one of the most abundant and taxono- mically complicated groups of insects. Despite their widely recognized practical importance as biological control agents, chalcids are still poorly studied from a morphological and biological point of view. Taxonomy of Chalcidoidea, both at the species and at the genus level, is frequently hampered by a lack of reliable morphological characters to separate different biological entities (Heraty, 2004). Cytogenetic data provide information independent from morphological and biological data, revealing differences or similarities that may not be obvious at the morphological level (Gokhman & Quicke, 1995). Furthermore, karyotypic characters, unlike many morphological features, change rather independently of the environment, so they can be useful in cases where morpho- logical characters fail to provide an unambiguous solution to taxonomic problems (Gokhman, 2006). Within Hymenoptera, data on chromosomal morphology have been successfully used for clarifying taxonomic status and species grouping, as well as for searching and recognizing sibling species. For example, karyotaxonomy has been very successful in ants, revealing groups of sibling species (Imai et al., 1988). Substantial progress in chromosome research for parasitic Hymenoptera has occurred over the last 20–30 years (see *Author for correspondence Fax: + 0817755872 E-mail: marco.gebiola@unina.it Bulletin of Entomological Research (2012) 102, 43–50 doi:10.1017/S0007485311000356 © Cambridge University Press 2011