| Popis: |
Two natural viral strains belonging to the Parvoridae (Densovirus) and the Picornaviridae (Picornavirus) families were isolated from larvae of the Egyptian cotton leafworm #Spodoptera littoralis$. The strains were sampled from natural infestation of cotton field in Kafr El-Sheikh Governorate in May 1997. Electron microscopy observations revealed the presence of icosahedral particles with 22 nm in diameter for the viral capside related to the Densovirus (DNV), and 29 nm for the second one as a Picornavirus (PV). For the DNV four capsid proteins of 91,63, 53 and 47 KDa have been separated, and were undifferentiated from that of the unique published Densovirus isolate from Egypt, the #Mythimna loreyi$ DNV (MIDNV). PV capsids contain three major structural proteins of 30, 32 and 33 KDa resembling the Drosophila C virus (DCV), a very well known Picornavirus of insect. The DNV genome consists of a single stranded DNA molecule of size 5.95 Kb. It was characterized using 12 restriction endonucleases. The DNA restriction profiles were identical with these of MIDNV. The PV contain a single stranded RNA genome of size 9.4 Kb as the different reported isolates of DCV. Using rabbit antisera, immunological comparison revealed a complete homology between the DNV and IDNV, as well as, the PV isolated from #S. littoralis$ shows a complete serological identity with the DCV. These results suggest that we can register the DNV isolated from #S. littoralis$ as a strain of MIDNV and the small RNA virus as an Egyptian strain of DCV. Larvae of #S. littoralis$ reared on artificial diet in the laboratory were susceptible to these two viruses. (Résumé d'auteur) |
