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 (LC ₅₀) and the median lethal time (LT ₅₀) values were estimated for second and fourth larval instars of S. littoralis. The LC ₅₀ values were 2.8 × 10 ⁴ OB/ml for second larval instar and 5.2 × 10 ⁵ 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 LT ₅₀ value for the second instar larvae (LT ₅₀ = 5.5 days) was lower than that of the fourth instar larvae (LT ₅₀ = 6.2 days) at concentrations of 4.3 × 10 ¹⁰ (ob/ml) and 1.2 × 10 ¹¹ (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.