Nanoemulsified formulation of cell-free supernatant from Photorhabdus luminescens as a sustainable biopesticide against Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

Abstract

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), presents a significant threat to global agricultural production. While chemical pesticides have traditionally been effective in controlling such pests, the increasing demand for organic products has spurred the search for environmentally friendly alternatives. Biopesticides have emerged as a promising solution, offering efficacy while minimizing health and environmental risks associated with synthetic chemicals. In the present study, the insecticidal potential of the cell-free supernatant (CFS) from Photorhabdus luminescens, sourced from Heterorhabditis indica, was evaluated against third-instar S. frugiperda larvae through in vitro bioassays. Gas chromatography-mass spectrometry (GC-MS) analysis identified key biomolecules in the CFS, which were further studied for their interaction with S. frugiperda protein targets using in silico methods. Additionally, a nanoemulsified formulation of the CFS was developed via., ultrasonication, demonstrating stability with droplet diameters <200 nm over 90 days. Characterization through dynamic light scattering (DLS) and transmission electron microscopy (TEM) confirmed the nanoformulation's regular distribution and spherical shape, with an average diameter of 115.9 ± 5.1 nm and a zeta potential of 65 ± 1.8 mV. The CFS exhibited significant insecticidal activity, resulting in 80% mortality with a half-maximal lethal concentration (LC₅₀) of 593.62 ppm. Furthermore, the nanoformulation displayed strong control efficacy against third-instar S. frugiperda larvae, achieving an LC₅₀ of 578.77 ppm after 48 h of treatment. These findings highlight the potential of utilizing CFS from P. luminescens and its nanoformulation as sustainable and effective insecticide with reduced environmental impact, sustained release properties, and enhanced pest control capabilities.