The taxonomic status of the aphid parasitoid Aphidius colemani Viereck has been questioned, especially in regard to Aphidius transcaspicus Telenga (Hymenoptera: Braconidae). The genetic association between A. colemani and A. transcaspicus was studied by cross mating individuals of A. colemani and A. transcaspicus (A.c.[female] x A.t.[male] and A.c.[male] x A.t.[female]) and applying appropriate molecular methods. The cross mating resulted in offspring (female and males) that were fertile. Therefore, the cross mating assays performed in an artificial environment showed that these two populations are potentially compatible. The mean number of mummies that developed and the sex ratio of the offspring of each cross were similar. Most of the male and female offspring from each cross were assigned to A. transcaspicus. Furthermore, the genetic divergence between the ribosomal internal transcribed spacers (ITS2) of the A. colemani and A. transcaspicus studied was 16%. These results indicate that A. colemani might be a complex of species with different morphological and biological characters attacking different host aphids. BR Systematics. Biochemistry. Reproduction. Reproductive behaviour. Genetics. Evolution. Evolutionary adaptation. Variation. Aphidius colemani (Aphidiidae); Aphidius transcaspicus (Aphidiidae). Aphidius colemani, Aphidius transcaspicus: Nucleic acids, DNA sequence variation, taxonomic implications, Mating, Cross mating experiments, Molecular genetics, Hybridization, Population genetics, Genetic divergence, Divergence, Biochemical variation. ST Animalia, Arthropoda, Insecta, Hymenoptera, Apocrita, Terebrantia, Ichneumonoidea, Aphidiidae. Arthropods; Hymenopterans; Insects; Invertebrates. none