Biological Activity of Two Mexican Nucleopolyhedrovirus Isolates and Sublethal Infection Effects on Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

The biological activity of 2 isolates of Spodoptera frugiperda multiple nucleopolyhedrovirus (Sf-YUC and Sf-CHI) obtained from the states of Yucatan and Chiapas, Mexico, on second instar fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) from Michoacan State, Mexico, was determined and compared with that of a Nicaraguan isolate (Sf-NIC). Response of third and fourth instar S. frugiperda to the most active isolate, Sf-YUC, also was determined. Sublethal effects caused by this isolate and its intergenerational persistence were evaluated. The most pathogenic isolates on second instar S. frugiperda were Sf-NIC and Sf-YUC. No significant differences were detected in the speed of kill between the Sf-NIC (146 h) and Sf-YUC (149 h) isolates, whereas that of the Sf-CHI (158 h) isolate was slower significantly. The lethal concentration that kills 50% of the insects (LC50) values of the Sf-YUC isolate increased with larval stage from 9.45 x 10(4) to 1.25 x 10(6) occlusion bodies per mL. Statistically significant reductions in pupal weight, fecundity, fertility, and adult longevity were associated in individuals derived from third instar (generation F-0) treated with 4.8 x 10(4 )occlusion bodies per mL of the Sf-YUC isolate. A viral mortality of 15.83 +/- 1.43% in larvae as well as a significant reduction in pupal weight of generation F1 was recorded. In conclusion, the Mexican isolates may prove suitable as the basis for biological insecticides for regional control of S. frugiperda. Sublethal infections that persist between generations could incur developmental costs and decrease reproductive capacity of the host insect.