Maize-Derived Endophytic Bacillus subtilis Induces Lethal and Sublethal Effects in the Fall Armyworm, Spodoptera frugiperda

Abstract

Aims: To assess the lethal and sublethal effects of maize-associated bacterial endophytes against Spodoptera frugiperda under laboratory conditions and to identify the most effective isolate through molecular characterization for its potential in biological control. Study Design: Completely randomized laboratory experiment with eight endophytic isolates and an untreated control. Place and Duration of Study: MRC, ARI, Department of Plant Pathology, PJTAU during 2025. Methodology: Eight maize endophytic bacterial isolates (ESB-1 to ESB-8) were tested on second-instar larvae of S. frugiperda using in vitro bioassays. Observations included larval mortality, relative growth rate, efficiency of conversion of ingested food, feeding deterrence index, pupation, adult emergence, and developmental duration. Data were subjected to one-way ANOVA and compared with control. The superior isolate was identified by 16S rRNA sequencing and BLAST analysis. Results: Treatments differed significantly for all parameters (p < 0.05). Isolate ESB-8 caused maximum larval mortality (50.88 ± 0.57%) over control (5.00 ± 0.14%). It recorded the lowest growth rate (0.15 ± 0.005) and food conversion efficiency (8.58 ± 0.52) with highest feeding deterrence (42.96 ± 1.69%). ESB-8 markedly reduced pupation (52.93 ± 4.14%) and adult emergence (55.96 ± 6.61%) and extended larval (17.20 ± 1.47 days) and pupal periods (9.43 ± 0.69 days). Isolates ESB-1, ESB-2 and ESB-6 showed negligible effects. The effective isolate ESB-8 was identified as Bacillus subtilis (GenBank: PV876730). Conclusion: The endophytic isolate Bacillus subtilis (ESB-8) demonstrated pronounced toxic and growth-disrupting effects on S. frugiperda and represents a viable biopesticide for development of eco-friendly pest management strategies in maize.