Relación dosis-respuesta de la azadiractina en Spodoptera frugiperda (J. E. Smith): un estudio por instares larvales, bajo condiciones de laboratorio.

Abstract

This study evaluated the effect of Median Lethal Concentration (MLC₅₀) and Median Lethal Time (ML₅₀) of neem oil, Azadirachta indica A. Juss, on the six larval instars of Spodoptera frugiperda (J. E. Smith) under laboratory conditions. ML₅₀ values progressively increased from 579.67 μL/L at the first instar to 921.36 μL/L at the sixth, indicating a decrease in larval susceptibility with development. Coefficients of determination (R²) ranged from 0.94 to 0.95, confirming a robust predictive model. The average pooled ML₅₀ concentration was 740.4 μL/L, sufficient to induce 50% mortality in mixed populations. Regarding TL₅₀, young instars presented shorter lethality times (52.39 h in the first instar and 37.88 h in the third), while advanced instars showed progressive resistance, reaching extreme values of up to 409.85 h, this difference represents an increase of 271.3% between the first and last instars, which is equivalent to an approximate three-fold increase compared to the initial stages. Regression analysis and three-way ANOVA confirmed that the efficacy of neem oil is dose-dependent and highly influenced by the larval instar and exposure time. These results highlight the importance of applying neem oil at early stages of the larval cycle to maximize its effectiveness and prevent the development of resistance.