Endoparasitoids can achieve successful development in suitable hosts with the help of polydnavirus (PDV), if it is injected into the host with their eggs at parasitization. It was predicted that different species of endoparasitoids that parasitize the same host successfully use a similar system to avoid the defense reaction from the host. In this study, we identified similar PDVs genes. In two endoparasitoids, Cotesia kariyai (Cky) and Cotesia ruficrus (Crf), which can parasitize the same host species, Pseudaletia separata. The electrophoretic profiles of nondigestive segments of PDV in the two parasitoids were different. However, genomic Southern hybridization using reciprocal probes between the two species indicated a similar sequence of PDV genes. Two cDNA libraries were established and screened by a Cky probe. Cky811 was 695-bp, Crf111 was 690-bp, and the predicted peptide sequences were 162aa and 157aa, respectively. The two transcripts had 72.8% similarity with each other and resembled a C-type lectin2 domain. Clones of Cky811 from C. kariyai and Crf111 from C. ruficrus were expressed in hemocytes of the hosts that were injected with PDV plus venom. The Cky811 gene was expressed in hemocytes and fat body of the Pseudaletia host. Hybridization analysis revealed that the Cky811 gene was expressed 6 hrs after injection of Cky-PDV into nonparasitized hosts with venom, and the hybridization signal declined with time. The genetic distance to the lectin of other insects was closer to P. americana than to Lepidopteran insects.