Abstract
Diachasmimorpha longicaudata (Hymenoptera: Braconidae) is a parasitoid wasp widely used in the biological control of fruit flies. In this paper, we present a detailed analysis of the karyotype of this species based on the results of classical and molecular cytogenetic techniques. The cytogenetic analysis confirmed the male and female chromosome numbers previously reported (n = 20, 2n = 40). The entire short arm of most chromosomes is made up of a large constitutive heterochromatic segment. The high heterochromatin content differentiates D. longicaudata from other braconid species. Fluorescence in situ hybridization (FISH) using autologous 18S rDNA probes revealed six clusters of rDNA, i.e. six nucleolar organizer regions (NORs), in the heterochromatic short arms of different chromosomes in the haploid male karyotype. This number is exceptionally high for Hymenoptera, which usually have two NORs in the diploid complement. It is noteworthy that these rDNA-FISH experiments represent the first use of this technique on a braconid species using autologous probes. Since Ag-NOR-bands were coincident with C-positive bands on metaphase chromosomes, it was not possible to identify active nucleoli. The physical characteristics of the D. longicaudata karyotype, especially the content and distribution of heterochromatin and the number and location of rDNA clusters, contribute to a better understanding of the structure and organization of braconid chromosomes and provide a basis for genomic and evolutionary studies.
Highlights
Parasitic Hymenoptera constitute one of the most taxonomically complex groups of insects (Rasnitsyn, 1980; Quicke, 1997)
The male karyotype consists of 15 metacentric-submetacentric chromosomes and five acrocentric chromosomes that gradually decrease in size, with the exception of chromosome 20 which is markedly smaller (Fig. 1b–c)
The analysis of chromosome variation in parasitic wasps belonging to the Braconidae revealed that different chromosome numbers prevail in the three main phylogenetic branches of this group: (i) from 14 to 20 in cyclostome Braconidae, (ii) from 3 to 9 in Aphidiinae and (iii) from 5 to 11 in most non-cyclostome Braconidae (Gokhman, 2004)
Summary
Parasitic Hymenoptera constitute one of the most taxonomically complex groups of insects (Rasnitsyn, 1980; Quicke, 1997). Even though they are economically important as biological control agents of agricultural and forestry pests (Viktorov, 1976; Godfray, 1994), their chromosomes remain poorly studied (Gokhman, 2004). Karyological research is often incorporated into molecular studies on parasitic wasps, namely that on entomopathogenic viruses associated with many species of this group (Stoltz & Whitfield, 1992; Belle et al, 2002), the analysis of sex determination (Whiting & Whiting, 1925; De Menten et al, 2003,) and the mapping of particular genes (Matsumoto et al, 2002). The lowest number is found in Aphidius sp. (Nees) (Braconidae), Encarsia protransvena (Viggiani) (Aphelinidae), Brachymeria intermedia (Nees)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
