Biological activity of recombinant Spodoptera exigua multicapsid nucleopolyhedrovirus against Spodoptera exigua larvae

In this study the potency and efficacy of recombinant Spodoptera exigua multicapsid nucleopolyhedrovirus (SeXD1) were compared with that of the wild-type S. exigua virus (wt-SeMNPV). Time-dose-mortality bioassays of SeXD1 and wt-SeMNPV were conducted on 2nd to 5th instars of S. exiuga larvae. The results show that the recombinant SeXD1 killed insects significantly faster than wt-SeMNPV. At high dosages, the LT50 values for SeXD1-infected 2nd to 5th instars were 1.3, 1.3, 1.0 and 0.4 days shorter than those for wt-SeMNPV, respectively. LD50 values also decreased with increases in infection time. LD50 of SeXD1 occurred 1 day earlier than that of wt-SeMNPV at the same instar, but no significant difference between those for SeXD1 and wt-SeMNPV was observed. In addition, the effect of SeXD1 on feeding was evaluated in 5th instar S. exigua larvae. While nutritional indices, such as consumption index (CI) and relative growth rate (RGR), were significantly reduced by SeXD1 infection, digestibility and food conversion efficiency showed a slight increase. As a 50% overall reduction in consumption and lower CI and RGR values were found for larvae infected with the recombinant SeXD1 virus, these findings show that SeXD1 may provide better protection than wt-SeMNPV. (C) 2010 Elsevier Inc. All rights reserved.