Baculoviruses have been genetically modified to express foreign genes under powerful promoters in order to accelerate their speed of killing. In this study a truncated form of cry1Ab gene derived from Bacillus thuringinsis (Bt) subsp. aegypti isolate Bt7 was engineered into the genome of the baculovirus Autographa californica multiple nuclearpolyhedrosis wild type virus, in place of the polyhedrin gene by using homologous recombination in Spodoptera frugiperda (Sf) cells between a transfer vector carrying the Bt gene and the wild type virus linearized DNA. Recombinant wild type virus containing the cry1Ab gene was detected as blue occlusion-negative plaques in monolayers of Sf cells grown in the presence of X-Gal. In Sf cells infected with plaque-purified recombinant virus, the cry1Ab gene was expressed to yield a protein of approximately 82-kDa, as determined by immunoblot analysis. The toxicity of the recombinant virus expressing the insecticidal crystal protein (ICP) was compared to that of the wild-type virus. Infected-cell extract was toxic to cotton leaf worm Spodoptera littoralis second instar larvae and the estimated LC50 was 1.7 μg/ml for the recombinant virus compared with that of wild-type virus which was 10 μg/ml.

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.

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.

Serological assays for SARS-CoV-2 are being utilized at an exponential rate for surveillance programs. This enterprise was designed to develop and validate a qualitative immunochromatographic test, via the Lateral Flow Assay (LFA), for detection of immunoglobulins M and G (IgM and IgG) against both nucleocapsid (N) and the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2. Both targeted proteins were cloned and expressed in baculovirus expression system utilizing insect cells Sf9. The recombinant RBD and N proteins were purified and conjugated with gold nanoparticles (AuNPs) to set up the coating antigens pad. Both anti-human IgG and IgM were dispensed on nitrocellulose membrane to capture human antibodies in serum samples. A home-made dispensing system was developed to draw identical test and control lines. The validity of the developed LFA was verified by testing serum samples from 103 convalescent COVID-19 patients who were PCR positive for SARS-CoV-2 along with 28 control serum samples. The developed strips showed distinctive bands for IgM and IgG of both proteins (RBD and N) in positive samples. The sensitivity of RBD-based LFA was 70.9% and 39.8% for IgG and IgM, respectively, with a specificity of 100% for both. The N-based LFA exhibited a sensitivity of 73.8% and 35.9% for IgG and IgM, respectively, while its specificity was 75% and 100% for IgG and IgM, respectively. Our developed LFA could afford a tool for surveillance programs in low-resource countries. Moreover, it might be functional for rapid and inexpensive monitoring of the anti-SARS-CoV-2 antibodies in the sera of vaccinated individuals.

Background: Spodoptera littoralis nucleopolyhedrovirus (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. littoralis 1st instar larvae indicated that LC₅₀ value of SpliMNPV-Cab3 was higher than that estimated for the reference strain. Also, ST₅₀ of 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. littoralis population with a prospect to biopesticide development.