Search

Background: Baculoviruses can be inactivated by ultraviolet (UV) light, which limits their application as an efficient biopesticide. In an attempt to enhance virus resistance to UV inactivation, a photolyase gene, isolated from Spodoptera lituragranulovirus (SpliGV), was expressed in a photolyase deficient Spodoptera littoralisnucleopolyhedrovirus (SpliNPV) and the infectivity of recombinant virus expressing phrgene was determined after exposure to UV irradiation. Results: Expression of the photolyase resulted in a fivefold resistance of virus occlusion bodies of the recombinant virus (vSpli-phr) compared to the wild type SpliNPV upon exposure to UV irradiation as measured by LC50value when fed on S. littoralisneonate. Furthermore, the recombinant virus expressing phrshowed a significant decrease in the time required for lethality than the control virus with about 22 h, as measured by ST50value. Hence, expression of photolyase via vSpli-phr relatively may rescue the viral DNA damage caused by UV irradiation. Conclusions: This study provided the evidence that the generated recombinant virus encoding a functioning photolyase, which may have implications for the development of a new generation of baculoviruses with enhanced insect pest management capabilities.

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. littoralislarvae 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 LC50values were 2.8 × 104OB/ml for second larval instar and 5.2 × 105OB/ml for fourth larval instar after 10 days of treatment. Regarding the speed of killing of the viral isolate, the results showed that the LT50value 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. littoralispopulation in Egypt.

Background: The genetic diversity is naturally occurring in baculovirus population, which may affect the potency of the bio-agent. The Spodoptera littoralisnucleopolyhedrovirus is a promising bio-control agent that can be used to control the cotton leafworm, S. littoralisin Egypt. This study described the virulence and genetic variability of 3 S. littoralisnucleopolyhedrovirus isolates named Cab2, P2 and P3 previously recovered from diseased S. littoralislarvae 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. littoralisnucleopolyhedrovirus 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. littoralislarvae with LC50value of 1.59 × 104Obs/ml compared to the virulence recorded by P3 and P2 which were 1.23 × 106and 2.7 × 104OBs/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. littoralisnucleopolyhedrovirus isolates showed considered genotypic variation and insecticidal activity against S. littoralislarvae, 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. littoralispopulation in Egypt.

Background: Spodoptera littoralisnucleopolyhedrovirus (SpliNPV) is considered a promising biocontrol agent that can be used for the effective control of the cotton leaf worm, Spodoptera littoralis(Boisd.) (Lepidoptera: Noctuidae), which is an economic pest on many cultivated plants and crops in tropical and sub-tropical regions. The genome of the SpliNPV-AN1956 isolate has been fully sequenced, providing a reference strain for comparison of new isolates. In this study, identification, biological activity, and genetic characterization of a field collected SpliNPV isolate were carried out. Results: The examination of viral occlusion bodies (OBs) by TEM showed a typical baculovirus OBs of type nucleopolyhedrovirus (NPV) with polyhedral structures. The phylogenetic analysis of the late expression factor- 5 (lef-5) gene as well as the restriction profile analysis confirmed the identity of SpliNPV as a variant isolate. Digestion with ScaI endonuclease showed that 4 fragments of 50, 35, 27, and 13 kb were detected but 3.2 kb was absent in SpliNPV-Cab3 pattern compared to the reference strain. Meanwhile, upon digestion with PstI and HindIII endonucleases, no differences were observed in both isolates’ pattern. Moreover, the virulence evaluation against S. littoralis1st instar larvae indicated that LC50value of SpliMNPV-Cab3 was higher than that estimated for the reference strain. Also, ST50of SpliNPV-Cab3 (120 h) was significantly different with that of the reference strain (132 h). Conclusion: The host specificity based on virulence parameters make SpliNPV-Cab3 isolate a potential candidate to be involved in the integrated pest management strategies for the control of S. littoralispopulation with a prospect to biopesticide development.

Two different Spodoptera littoralis(Boisd.) (Lepidoptera: Noctuidae) nucleopolyhedrovirus (SpliNPV) isolates were obtained from natural infected S. 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 with S. 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 be S. littoralis. The virulence of these isolates was tested against S. littoralislarvae in a laboratory. The LC50against 1st instar larvae was significantly different, 3 × 104OBs/ml and 9.5 × 104OBs/ml for Spli-6 and Spli-7, respectively. However, the LC50for the mixed infection of both isolates was 3.9 × 104OBs/ml. On the other hand, the ST50was 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.