Effect of four multiple nucleopolyhedrovirus isolates on the larval mortality and development of Spodoptera exigua (Lepidoptera: Noctuidae): determination of virus production and mean time to death
Keywords:
baculovirus, SeMNPV, biological activity, lethal and sublethal effectsAbstract
The biological activity of 4 Mexican isolates (SeSIN6, SeSIN8, SeSLP6, and SeSLP8) of the homologous multiple nucleopolyhedrovirus SeMNPV and their effects on the development of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), were studied. An exotic isolate of SeMNPV from the United States (SeUS2) was used as a reference. Early third-instar larvae were inoculated with 5 × 106 occlusion bodies per mL, resulting in 78% mortality for SeUS2 and approximately 90% mortality for each of the 4 Mexican isolates at 144 h post-inoculation. At 168 h postinoculation, 100% mortality was obtained in all cases. All of the isolates, including SeUS2, significantly reduced the body weights of S. exigua larvae compared with the control larvae; however, at 120 h post-inoculation, the differences among isolates were not significant. All of the isolates reduced the development time of third-instar S. exigua larvae (range: 1.2– to 1.6–fold) compared with the control larvae. An independent experiment was performed to determine production of occlusion bodies and mean time to death. Third-instar S. exigua larvae (15 h after molting) were inoculated with each isolate using the same concentration mentioned above. The occlusion body production rate was similar among all isolates. The isolates SeUS2, SeSLP6, and SeSLP8 yielded the fastest mortality (range: 187–191 h). Thus, the biological activities of the Mexican SeMNPV isolates were similar to the activity of the exotic isolate, indicating that these indigenous viruses are promising for the biological control of S. exigua in Mexico.
Resumen
Se estudió la actividad biológica y los efectos sobre el desarrollo del gusano soldado Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) de 4 aislados mexicanos (SeSIN6, SeSIN8, SeSLP6 y SeSLP8) de su nucleopoliedrovirus múltiple homólogo (SeMNPV). Se usó como referencia un aislado exótico, originario de Estados Unidos (SeUS2). La inoculación de larvas recién mudadas de tercer estadio con 1 × 106 cuerpos de inclusión per mL resultó en 78% de mortalidad para SeUS2 y aproximadamente 90% para 4 aislados mexicanos a las 144 h post inoculación. A las 168 h post inoculación se observó una mortalidad del 100% en todos los casos. Todos los aislamientos, incluyendo el SeUS2, provocaron un efecto significativo en la reducción del peso corporal promedio de las larvas de S. exigua en comparación con el control; sin embargo, a 120 h post inoculación las diferencias entre aislados no fueron significativas. Todos los aislados redujeron el tiempo de desarrollo de las larvas de tercer instar (rango: 1.2–1.6 veces) en comparación con el control. Se realizó un experimento independiente para determinar la producción de cuerpos de inclusión y el tiempo medio de muerte. Para ello, las larvas de tercer estadio de S. exigua (15 h después de la muda) se inocularon con cada aislado utilizado la misma concentración descrita arriba. La tasa de producción de cuerpos de inclusión fue similar entre todos los aislados probados. Los aislados SeUS2, SeSLP6, y SeSLP8 causaron una mortalidad más rápida (rango: 187–191 h). Se concluyó que la actividad biológica de los aislados mexicanos del SeMNPV fue similar a la observada en el aislado exótico, indicando que estos virus son prometedores para el control de S. exigua en México.
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