Insecticidal Effects of Trichoderma yunnanense Cell-Free Supernatants Against Spodoptera frugiperda

Abstract

The fall armyworm, Spodoptera frugiperda (Order: Lepidoptera; Family: Noctuidae) (J.E. Smith), is a highly destructive lepidopteran pest responsible for severe yield losses worldwide. Its management relies predominantly on chemical insecticides, which pose significant risks to human health and the environment, thereby necessitating the development of sustainable and eco-friendly control strategies. In this study, the insecticidal activity of cell-free supernatants (CFS) produced by Trichoderma yunnanense (Order: Hypocreales; Family: Hypocreaceae) against different larval instars of FAW with particular emphasis on mortality, developmental disruption, and histopathological alterations. Bioassays revealed pronounced instar-dependent susceptibility, with second-instar larvae exhibiting a significantly lower median lethal concentration (LC₅₀) than fourth-instar larvae. Exposure of both instars to their respective LC₅₀ values resulted in elevated larval and pupal mortality, significant prolongation of larval development, and reduced adult emergence, indicating both acute and chronic effects of CFS. Histopathological analyses demonstrated extensive tissue damage in treated larvae, including severe disruption of the integument, degeneration of midgut epithelium and peritrophic membrane, fragmentation of muscle fibres, vacuolization of fat body cells, and pronounced nuclear pyknosis in multiple tissues. Additional pathological alterations were observed in the silk glands, Malpighian tubules, and male reproductive tissues, suggesting systemic toxicity. Collectively, these results demonstrate that T. yunnanense CFS acts through a multi-target mechanism and underscore its potential as a biopesticide for management of FAW.