Biocontrol Effect of Bacillus subtilis against Cnaphalocrocis medinalis (Guenèe) (Lepidoptera: Pyralidae): A Sustainable Approach to Rice Pest Management

Abstract

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 Cnaphalocrocis medinalis. In the four tested entomopathogenic bacteria (W1, Yc1, S1, EB01), the larval mortality ranged from 38 to 74%. Among these isolates, Bacillus subtilis (EB01) induced the highest mortality (74%). In greenhouse conditions, the tests confirm that the results were dosage-dependent: B. subtilis infection considerably delayed the overall development period, reduced pupal conversion, and decreased adult emergence with induced morphological deformities. Larvae fed B. subtilis-treated leaves initiate bacterial infection and broadly damage the midgut tissue, including the epithelial and peritrophic layers. The bacterial growth in the C. medinalis 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 B. subtilis-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 B. subtilis EB01 strain potentially inhibited the biological activity of C. medinalis and improved the rice seeds’ germination index. It can be a potential biocontrol agent in sustainable pest-management strategies.