Laboratory-Scale Design of a Submerged Fermentation Process Using Agroindustrial Waste for Producing Metarhizium robertsii Mt008 Metabolites and Resistance Structures to Control Anastrepha obliqua

Fruit flies are a major constraint in mango production in Colombia. To address this, the entomopathogenic fungus Metarhizium robertsii Mt008 was selected for biocontrol development due to being shown to be effective against Anastrepha obliqua. This study evaluated the use of agroindustrial waste as a carbon and a complex nitrogen source to optimize both fungal biomass and dextrusin production. A central composite design with 11 treatments was used to assess their effects on biomass, destruxin A and B production, and insecticidal activity against both preimaginal and adult stages of A. obliqua. Fermentations were conducted at 28 °C and 300 rpm. Optimal production was achieved using 6 g/L of the carbon source and 10 g/L of the nitrogen source, resulting in 2×10⁵ conidia/mL, 1.7×10⁵ blastospores/mL, 160 pellets/mL, and destruxin concentrations of 4 ppm (dxt A) and 15 ppm (dxt B). After 18 days of fermentation, the fungal biomass caused 78% mortality in the preimaginal stages, while the metabolites in the extracts achieved 30% adult mortality. These results suggest that submerged fermentation using agroindustrial residues is a promising strategy for the cost-effective production of fungal biocontrol agents targeting A. obliqua, with potential application in sustainable mango pest management programs in Colombia.