Toxicity and Biological Effects of <i>Beauveria brongniartii</i> Fe⁰ Nanoparticles against <i>Spodoptera litura</i> (Fabricius)

Abstract

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 Beauveria brongniartii based Fe0 nanoparticles (Fe0NPs) and their bio-efficacy against Spodoptera litura was observed during this study. Beauveria brongniartii conidia were coated with Fe0NPs 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 2θ values of 45.72°, 64.47°, and 84.05°. The bioassay studies demonstrated that mortality of 2nd instar S. litura larvae following Fe0NPs treatment increased with increasing concentrations of Fe0NPs at different time intervals. The median lethal concentration (LC50) values of Fe0NPs against S. litura after seven days of fungal treatment was 59 ppm, whereas median survival time (LT50) values for 200 and 500 ppm concentrations of Fe0NPs against S. litura seven days post-treatment were 5.1 and 2.29 days, respectively. Beauveria brongniartii-Fe0NPs caused significant reductions in feeding and growth parameters (relative growth rate, relative consumption rate, and efficiency of conversion of ingested food) of S. litura. Beauveria brongniartii Fe0NPs 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 B. brongniartii Fe0NPs can potentially be used in biorational S. litura management programs.

Keywords

• biological control
• entomopathogenic fungus
• feeding
• growth
• toxicity