Biological activity of two Mexican nucleopolyhedrovirus isolates and sublethal infection effects on Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)
Abstract
The biological activity of 2 isolates of Spodoptera frugiperda multiple nucleopolyhedrovirus (Sf-YUC and Sf-CHI) obtained from the states of Yucatán and Chiapas, Mexico, on second instar fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) from Michoacán 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 × 104 to 1.25 × 106 occlusion bodies per mL. Statistically significant reductions in pupal weight, fecundity, fertility, and adult longevity were associated in individuals derived from third instar (generation F0) treated with 4.8 × 104 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.
Resumen
En el presente estudio, se determinó la actividad biológica de dos aislados mexicanos del nucleopolyhedrovirus múltiple de Spodoptera frugiperda (Sf-YUC y Sf-CHI) sobre larvas de segundo instar del gusano cogollero, Spodptera frugiperda (J. E. Smith), y se compararon con un aislado nicaragüense (Sf-NIC). También se determinó la respuesta de tercer y cuarto instar de S. frugiperda al aislado mexicano más activo, Sf-YUC. Finalmente, se evaluaron los efectos subletales causados por este aislado y su persistencia intrageneracional. Los aislados más patogénicos sobre el segundo instar de S. frugiperda fueron Sf-NIC y Sf-YUC. No se detectaron diferencias significativas en la velocidad de muerte entre los aislados Sf-NIC (146 h) y Sf-YUC (149 h), mientras que la del aislado Sf-CHI (158 h) fue significativamente mayor. Los valores de la concentración letal que matan el 50% de los insectos (CL50) se incrementaron con el estado larval desde 9.45 × 104 a 1.25 × 106 cuerpos de oclusión por mL del segundo al cuarto instar. Reducciones estadísticamente significativas en el peso pupal, la fecundidad, la fertilidad y la longevidad de adultos se asociaron con individuos derivados de tercer estadio (generación F0 ) tratados con 4,8 × 104 cuerpos de oclusión por mL del aislado Sf-YUC. observó una reducción significativa en el peso pupal. En conclusión, los aislados mexicanos pueden ser adecuados como la base de insecticidas biológicos para el control de S. frugiperda. Las infecciones subletales que persisten entre generaciones pueden generar costos de desarrollo y disminuir la capacidad reproductiva del insecto huésped.
Keys Words: baculoviruses; virus persistence; sublethal effects; fall armyworm
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