The efficacy of different strains of SpltNPV (Spodoptera litura Nucleopolyhedrovirus) against the armyworm Spodoptera litura (Lepidoptera: Noctuidae) in laboratory

The armyworm, Spodoptera litura (Lepidoptera: Noctuidae), is one of the leading vegetable pests in the Mekong Delta area, and chemical control has been ineffective due to resistance. SpltNPV has been developed as a biopesticide for its applications to control S. litura pest. This study aims to assess the efficacy of the SpltNPV strain in controlling armyworm Spodoptera litura. In this experiment, bioassays were performed, and the LC50 and LT50 were established for first to fifth instar larvae through the droplet feeding method. Further, viral residual activity and pathogenicity in cabbage were identified. The result highlighted the pathogenicity of nine SpltNPV strains on S. litura larvae in laboratory and cage-house environments. The LC50 values were determined to be between (0.15–8.2) × 10³ OBs/ml in first instar larvae and (0.27–5.9) × 10⁸ OBs/ml in fifth instar larvae, citing the fact that susceptibility decreases as the larvae grow. All the LT50 values were increased with the larval age and ranged from 73.25 h PI (hour post-inoculation) to 199.75 h PI. The residual activity of SpltNPV on cabbage reduced in activity from an initial rate of 28.8% on the first day to 98.9% on 7 days. The presented research shows that SpltNPV has the prospects for being used in combined pest control strategies, with a focus on early larval instars. Further research should be conducted with more significant effort towards the stability of the virus as it is applied to the field to increase its defence systems of the older larvae