# The lowest chromosome number in the family Pteromalidae (Hymenoptera: Chalcidoidea): the karyotype and other genetic features of Pachycrepoideus vindemmiae (Rondani, 1875)

## TL;DR

This study reveals that the parasitoid Pachycrepoideus vindemmiae has the lowest chromosome number in its family and provides insights into its genetic features.

## Contribution

The study reports the lowest chromosome number in the Pteromalidae family and confirms the absence of specific endosymbiotic bacteria in a particular strain.

## Key findings

- Pachycrepoideus vindemmiae has n = 4 and 2n = 8 chromosomes, the lowest in the Pteromalidae family.
- All chromosomes in the species are metacentric with distinct size differences.
- The hitman strain lacks endosymbiotic bacteria such as Arsenophonus, Cardinium, Rickettsia, Spiroplasma, and Wolbachia.

## Abstract

Various genetic features of the hitman strain of the widespread parasitoid of Drosophilidae (Diptera), Pachycrepoideus vindemmiae (Rondani, 1875) (Pteromalidae, Pachyneurinae) were studied. This strain was established and is maintained at the Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk, Russia). An analysis of air-dried chromosome preparations from prepupae of this parasitoid showed that it has n = 4 and 2n = 8 in males and females, respectively, which is the lowest known chromosome number in the family Pteromalidae. All chromosomes in the karyotype of this species are metacentric. The first and second chromosomes are of similar size, the remaining ones are substantially shorter. The same results were obtained for an additional strain of this species kept at the Moscow State University (Moscow, Russia). A comparison of the DNA sequence of the barcoding region of the mitochondrial cytochrome c oxidase (COI) gene of the hitman strain of P. vindemmiae with those available from the GenBank and BoLD databases demonstrated that this strain clustered together with conspecifics originating from China, Turkey and Italy. Despite certain endosymbionts being previously reported for the genus Pachycrepoideus Ashmead, 1904 as well as for P. vindemmiae itself, the hitman strain turned out to be free of endosymbiotic bacteria in the genera Arsenophonus Gherna et al., 1991, Cardinium Zchori-Fein et al., 2004, Rickettsia da Rocha-Lima, 1916, Spiroplasma Saglio et al., 1973 and Wolbachia Hertig, 1936. The above-mentioned results improve our knowledge of various genetic features of parasitoids of the family Pteromalidae and those of P. vindemmiae in particular.