| Summary: | Nanotechnology has clear potential in the development of innovative insecticidal products for the biorational management of major insect pests. Metal-based nanoparticles of different microbial pest control agents have been effective against several pests. Synthesis of <i>Beauveria brongniartii</i> based Fe<sup>0</sup> nanoparticles (Fe<sup>0</sup>NPs) and their bio-efficacy against <i>Spodoptera litura</i> was observed during this study. <i>Beauveria brongniartii</i> conidia were coated with Fe<sup>0</sup>NPs and characterized by applying a selection of different analytical techniques. Ultraviolet (UV) spectroscopy showed the characteristic band of surface plasmon at 430 nm; Scanning electron microscopy (SEM) images showed spherical shaped nanoparticles with a size ranging between 0.41 to 0.80 µm; Energy-dispersive X-ray (EDX) spectral analysis revealed characteristic Fe peaks at 6.5 and 7.1 Kev; the X-ray diffractogram showed three strong peaks at 2<i>θ</i> values of 45.72°, 64.47°, and 84.05°. The bioassay studies demonstrated that mortality of 2nd instar <i>S. litura</i> larvae following Fe<sup>0</sup>NPs treatment increased with increasing concentrations of Fe<sup>0</sup>NPs at different time intervals. The median lethal concentration (LC<sub>50</sub>) values of Fe<sup>0</sup>NPs against <i>S. litura</i> after seven days of fungal treatment was 59 ppm, whereas median survival time (LT<sub>50</sub>) values for 200 and 500 ppm concentrations of Fe<sup>0</sup>NPs against <i>S. litura</i> seven days post-treatment were 5.1 and 2.29 days, respectively. <i>Beauveria brongniartii</i>-Fe<sup>0</sup>NPs caused significant reductions in feeding and growth parameters (relative growth rate, relative consumption rate, and efficiency of conversion of ingested food) of <i>S. litura</i>. <i>Beauveria brongniartii</i> Fe<sup>0</sup>NPs induced reduction in glutathione-S-transferase activities throughout the infection period whereas activities of antioxidant enzymes decreased during later periods of infection. These findings suggest that <i>B. brongniartii</i> Fe<sup>0</sup>NPs can potentially be used in biorational <i>S. litura</i> management programs.
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