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Two different Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) nucleopolyhedrovirus (SpliNPV) isolates were obtained from natural infected S. littoralis larvae 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 with S. littoralis NPV 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 be S. littoralis. The virulence of these isolates was tested against S. littoralis larvae in a laboratory. The LC50 against 1st instar larvae was significantly different, 3 × 104 OBs/ml and 9.5 × 104 OBs/ml for Spli-6 and Spli-7, respectively. However, the LC50 for the mixed infection of both isolates was 3.9 × 104 OBs/ml. On the other hand, the ST50 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 ~ 25 kbp and 3 fragments of about ~ 19, ~ 5.8, and ~ 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 of S. littoralis. [ABSTRACT FROM AUTHOR]

Background: In the present study, detection, characterization and virulence analysis of a field collected nucleopolyhedrovirus isolated from the cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) was carried out. The obtained isolate, named SpliNPV-YW, was collected from diseased S. littoralis larvae in El-Menoufia governorate, Egypt. Results: Transmission electron microscopy showed the presence of typical occlusion bodies with average size of (1.06 × 1.19 µm). Upon digestion using two different endonucleases, PstI and ScaI, no clear difference was detected in the collected isolate (SpliNPV-YW) DNA genome pattern compared to the reference strain SpliNPV-AN1956. The evolutionary analysis of the polyhedrin gene's partial nucleotide sequence revealed that SpliNPV-YW isolate was closed and had a genetic origin with the NPV isolate SpliMNPV-A26-5 that belongs to group II NPVs with identity of 99.7%. The median lethal concentration (LC50) and the median lethal time (LT50) values were estimated for second and fourth larval instars of S. littoralis. The LC50 values were 2.8 × 104 OB/ml for second larval instar and 5.2 × 105 OB/ml for fourth larval instar after 10 days of treatment. Regarding the speed of killing of the viral isolate, the results showed that the LT50 value for the second instar larvae (LT50 = 5.5 days) was lower than that of the fourth instar larvae (LT50 = 6.2 days) at concentrations of 4.3 × 1010 (ob/ml) and 1.2 × 1011 (ob/ml) for second and fourth instar larvae, respectively. Conclusions: Host specificity and virulence characteristics make SpliNPV-YW isolate a good potential to be utilized as a candidate biopesticide for the control of S. littoralis population in Egypt. [ABSTRACT FROM AUTHOR]

Background: The genetic diversity is naturally occurring in baculovirus population, which may affect the potency of the bio-agent. The Spodoptera littoralis nucleopolyhedrovirus is a promising bio-control agent that can be used to control the cotton leafworm, S. littoralis in Egypt. This study described the virulence and genetic variability of 3 S. littoralis nucleopolyhedrovirus isolates named Cab2, P2 and P3 previously recovered from diseased S. littoralis larvae of cabbage, pepper and eggplant cultivation fields. Results: The viral genomic DNA restriction analysis using PstI and ScaI endonucleases showed identical Pst1 restriction pattern of 10 fragments in both Cab2 and P3 isolates, while there are 7 extra fragments present in P2 isolate of about 25, 19.8, 15, 14, 11, 9 and 6.7 (kbp). On the other hand, the restriction pattern using ScaI revealed 10 common fragments in all three isolates, in addition to an extra marker fragment of about 25 kb in P3 isolate absent in both P2 and Cab3 isolates. The phylogenetic analysis of the partial nucleotide sequence of the polyhedrin gene confirmed an extensive degree of co-linearity among the genomes of the 3 tested isolates, with pairwise sequence identities of 97.04% with S. littoralis nucleopolyhedrovirus isolate A26-5 (Acc. No. AY706717). The median lethal concentration (LC50) value revealed that Cab2 had the best virulence toward the first instar of S. littoralis larvae with LC50 value of 1.59 × 104 Obs/ml compared to the virulence recorded by P3 and P2 which were 1.23 × 106 and 2.7 × 104 OBs/ml, respectively. The median survival time (LT50) value of Cab2 isolate was the highest speed of treated larval mortality with 120 hpi compared to P2 and P3, which recorded 132 hpi for both isolates. Conclusions: Although all three S. littoralis nucleopolyhedrovirus isolates showed considered genotypic variation and insecticidal activity against S. littoralis larvae, the variant Cab2 showed the highest virulence and speed mortality against the first instar larvae of S. littoralis. The new variant proved to possess promising insecticidal properties for the development of virus-based biopesticide for the control of S. littoralis population in Egypt. [ABSTRACT FROM AUTHOR]