Abstract
Two differentSpodoptera littoralis(Boisd.) (Lepidoptera: Noctuidae) nucleopolyhedrovirus (SpliNPV) isolates were obtained from natural infectedS. littoralislarvae in Egypt. The phylogenetic analysis of the partial nucleotide sequence of the polyhedrin gene (polh) showed that both isolates, Spli-6 and Spli-7, were closed and had a common ancestor withS. littoralisNPV isolate 1263 polyhedrin gene, partial coding sequence with accession number AGE90003.1 that belongs to group II NPVs. This indicates that the natural host of Spli-6 and Spli-7 must beS. littoralis. The virulence of these isolates was tested againstS. littoralislarvae in a laboratory. The LC50 against 1st instar larvae was significantly different, 3 x 10(4) OBs/ml and 9.5 x 10(4) OBs/ml for Spli-6 and Spli-7, respectively. However, the LC50 for the mixed infection of both isolates was 3.9 x 10(4) OBs/ml. On the other hand, the ST(50)was 96 h for both isolates, while it was 120 h for the mixed infection, which was higher than that observed of each single isolate. Upon digestion of viral DNA with ScaI endonuclease, the restriction profile showed one more fragment of about similar to 25 kbp and 3 fragments of about similar to 19, similar to 5.8, and similar to 5.3 kbp in Spli-7 isolate compared to Spli-6 as well as the reference strain SpliNPV-AN1956. The differences in the fragment size and number suggest the existence of genotypic variants between both isolates. Spli-6 and Spli-7 proved to possess promising insecticidal properties for the development of virus-based biopesticide for the control ofS. littoralis.