Effects of Bacillus thuringiensis on egg viability and neonate survival in Spodoptera frugiperda

The control of Spodoptera frugiperda using Bacillus thuringiensis (Bt) has traditionally focused on the larval stage, whereas its effects on eggs remain poorly explored. Considering the agricultural importance of this pest and the need for more sustainable management strategies, this study evaluated the insecticidal activity of the Bt aizawai HD-68 strain and the commercial product Xentari® against S. frugiperda eggs and the survival of neonate larvae hatched from treated eggs. Three concentrations of Xentari® (3.00, 4.25, and 5.00 g L^-1) and one concentration of the HD-68 strain (3 × 10⁸ spores mL^-1) were tested. After egg immersion in Bt suspensions, embryonic inviability ranged from 27% to 41%. Neonate larvae emerging from treated eggs showed an initial mortality rate exceeding 70% after 72 h, which increased to more than 90% after 7 days. Histochemical and microscopic analyses revealed pronounced damage to the larval midgut epithelium, including cytoplasmic vacuolization and cellular degeneration, in all Bt treatments. The results showed that the Bt aizawai HD-68 strain and Xentari® reduced egg viability and were associated with high mortality of neonate larvae hatched from treated eggs. This study expands current knowledge of the effects of B. thuringiensis on the early developmental stages of S. frugiperda, highlighting its potential for reducing egg viability and early larval survival.