Toxicity Evaluation of a Methanolic Extract from Beauveria bassiana against Spodoptera exigua and Spodoptera frugiperda Larvae

Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Sordariomycetes: Hypocreales) is an entomopathogenic fungus that produces secondary metabolites associated as virulence factors in the pathogenic process of insects. The objective of this work was to evaluate the toxic activity of a methanolic extract obtained from the mycelium of a pathogenic B. bassiana strain in Spodoptera exigua (Hubner) and Spodoptera frugiperda (Hubner) (Lepidoptera: Noctuidae) neonates to determine its insecticidal potential and estimate its participation in the fungal pathogenic process. Conidia bioassays were conducted in both insect species to select the most pathogenic strain, and from the selected strain a methanolic extract was obtained from mycelium by column chromatography. The methanolic extract was administered to the larvae by ingestion to evaluate its activity and was also subjected to functional groups analysis by infrared spectrometry. The results indicated that the methanolic extract caused higher mortality than the conidia in both insects and the functional groups present in the extract is associated with bassianolide, beauvericin, and oosporein, which are fungal secondary metabolites with different biological functions. The methanolic extract has potential to be used in biological control practices because mortality percentage in both species at the highest concentration indicates that it is sufficiently high to reduce pest to population thresholds that are harmless to crops.