Production of spores of the fungus Metarhizium anisopliae using agro-industrial residues as substrates

Industrial production of Metarhizium anisopliae conidia for biological pest control typically relies on solid-state cultivation using rice as substrate, which is more costly than agro-industrial residues and competes with food resources. This study investigated agro-industrial residues as alternatives to rice for conidial production and analyzed the associated economic impacts. Corn bran, corn grits, rice bran, and wheat bran were initially screened, using rice as control and sugarcane bagasse (SB) as an inert support to improve bed porosity. Wheat bran showed the best performance among the by-products, achieving conidial concentrations on the order of 109 spores to gram of dry solid. Its cultivation was further investigated by varying moisture content and the substrate ratio. Lower moisture content and higher substrate proportions favoured spore production, although no definitive optimum was identified within the tested range. Sporulation kinetics showed comparable patterns between wheat bran and rice, with conidial production stabilising after 11 days. Although conidia produced on wheat bran maintained germination rates above 85%, both germination and virulence were significantly lower than those obtained with rice, indicating that comparable production did not result in comparable biological quality. Replacing rice with wheat bran reduced raw material costs by 43.1% and total operating costs by 14.5%, while increasing net present value by 55.5% and internal rate of return by 31.4%. Wheat bran is therefore a promising lower-cost substrate for M. anisopliae production; however, optimisation of conidial virulence and validation under scale-up conditions are still required.