Expression of a neurotoxin gene improves the insecticidal activity of Spodoptera litura nucleopolyhedrovirus (SpltNPV)

SpltNPV-C3 is a novel nucleopolyhedrovirus (NPV) screened from 189 wild Spodoptera litura nucleopolyhedrovirus (SpltNPV) clones collected throughout Japan and has high potential insecticidal activity against S. litura. In this study, we constructed two recombinant SpltNPVs, SpltNPV-Δegt and SpltNPV-Δegt-BmK, which were characterized by the disruption of the UDP-glucosyltransferase gene (egt) only and by replacing the egt locus with the Buthus martensi insect-specific toxin gene (BmK ITa1), respectively. The insecticidal activity of these two recombinant viruses was evaluated by 50% lethal time (LT50) and 50% lethal concentration (LC50) using third instar S. litura larvae. Bioassays showed that the LT50 of SpltNPV-Δegt was reduced by 25% at a dose of 109 Occlusion bodies (OBs)/ml compared to the wild-type SpltNPV. However, the LC50 values did not change. The SpltNPV-Δegt-BmK reduced LT50 by 28% at the highest dose of OBs (109 OBs/ml) compared to the wild-type SpltNPV, and the LC50 was nearly an order of magnitude lower than those of the wild-type SpltNPV and SpltNPV-Δegt. However, there was no discernable difference in the LT50 between SpltNPV-Δegt-BmK and SpltNPV-Δegt when the 3rd instars of S. litura were fed a dose of 108 or 109 OBs/ml. The results suggest that these two recombinant forms of SpltNPV provide further opportunities to develop these viruses into commercially viable products to control S. litura populations.