Biocontrol Effect of <i>Bacillus subtilis</i> against <i>Cnaphalocrocis medinalis</i> (Guenèe) (Lepidoptera: Pyralidae): A Sustainable Approach to Rice Pest Management
Muthusamy Janaki | Pavana K. Sivadasan Unni | Vethamonickam Stanley-Raja | Sengottayan Senthil-Nathan | Bader O. Almutairi | Ahmed Abdel-Megeed
Agricultural pests can be effectively controlled using microbes, providing an eco-friendly alternative to available synthetic pesticides. Suitable entomopathogenic bacterial strains were collected from agricultural fields and evaluated for their insecticidal potential against <i>Cnaphalocrocis medinalis</i>. In the four tested entomopathogenic bacteria (W1, Yc1, S1, EB01), the larval mortality ranged from 38 to 74%. Among these isolates, <i>Bacillus subtilis</i> (EB01) induced the highest mortality (74%). In greenhouse conditions, the tests confirm that the results were dosage-dependent: <i>B. subtilis</i> infection considerably delayed the overall development period, reduced pupal conversion, and decreased adult emergence with induced morphological deformities. Larvae fed <i>B. subtilis</i>-treated leaves initiate bacterial infection and broadly damage the midgut tissue, including the epithelial and peritrophic layers. The bacterial growth in the <i>C. medinalis</i> hemolymph considerably increases the activity of enzymes like α and β esterase (85.14 and 44% at 96 h) compared to the control. The isolate <i>B. subtilis</i>-treated diet significantly reduced the larval digestive α and β galactosidase enzyme activity (88.17 and 91.88% at 96 h). Furthermore, germination bioassay with strain EB01 in rice varieties (TN1 and ASD16) significantly increased both varieties’ germination and biomass index. This study shows that the <i>B. subtilis</i> EB01 strain potentially inhibited the biological activity of <i>C. medinalis</i> and improved the rice seeds’ germination index. It can be a potential biocontrol agent in sustainable pest-management strategies.
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