Detection, characterization and virulence analysis of nucleopolyhedrovirus isolated from the cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Abstract 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.