The Individual and Combined Entomopathogenic Activity of a Spodoptera frugiperda Multiple Nucleopolyhedrovirus and a Type I Spodoptera frugiperda Granulovirus on S. frugiperda Larvae

The bioinsecticidal activity of several doses of a <i>Spodoptera frugiperda</i> multiple nucleopolyhedrovirus (SfMNPV-CH-32; LD₁₀, LD₅₀, and LD₉₀) and a Type I <i>Spodoptera frugiperda</i> granulovirus (SfGV-CH13; LD₅₀ and LD₉₀), alone and in co-infection, was evaluated on <i>S. frugiperda</i> larvae. In the co-infection assays, one virus was applied at 0 h, and then the second virus was supplied at different times (0, 12, and 24 h) in order to test the effect of the co-infection time on the insecticidal activity of the viruses. The symptoms observed in the co-infected larvae depended on the viral dose supplied at 0 h. The larvae treated with the highest dose (LD₉₀) of SfMNPV-CH32 and co-infected with SfGV-CH13 at LD₅₀ showed symptoms of nucleopolyhedrovirus infection at 14 days post-infection. The larvae initially infected with the highest dose of SfGV-CH13 (LD₉₀) and subsequently co-infected with SfMNPV-CH32 (LD₅₀ and LD₁₀) showed infection symptoms characteristic of both viruses. The insecticidal activity of SfGV-CH13 and SfMNPV-CH32 alone or in combination depended on the viral doses and the time elapsed between the first and second inoculation. An antagonistic effect was observed for most of the treatments tested. A synergistic effect was observed only in treatment 10, where the larvae were first infected with SfMNPV-CH32 at a high dose (LD₉₀) and inoculated 24 h later with SfGV-CH13 (LD₅₀).