Insecticidal potential of fungal microsclerotia and metabolites produced during its formation

Currently, microsclerotia (MS) are considered the most promising fungal propagules to be used as the active ingredient in mycoinsecticide due to their potential to produce infective conidia under suitable growth conditions and tolerate biotic and abiotic stress. However, the role of metabolites produced during MS formation has not been studied. In this work, MS were produced by liquid fermentation with three entomopathogenic fungi: Metarhizium robertsii, M. novozealandicum, and Beauveria pseudobassiana. MS production reached yields up to 103 MS/mL for the three isolates. MS-derived conidia from M. robertsii caused 77.9% mortality of Diatraea saccharalis larvae and MS-derived conidia from M. novozealandicum and B. pseudobassiana caused 45.7% and 100% mortality of Plutella xylostella larvae respectively. The fungus-free supernatant from M. novozealandicum and B. pseudobassiana did not cause mortality of P. xylostella larvae but the fungus-free supernatant from M. robertsii caused 48% mortality of D. saccharalis larvae and was selected to continue its chemical analysis. This supernatant was extracted with organic solvents (EtOAc:DCM 1:1) and different fractions were evaluated in a bioassay and analysed by HPLC-MS/MS. The data obtained from the mass spectroscopy analysis of the organic fraction were used to build molecular networks using the GNPS platform. The majority of compounds in the organic fraction were from the cyclodepsipeptide family, suggesting the presence of 24 destruxins, including destruxin A, A2 and B, all recognized for their insecticidal activity. Therefore, the MS and the metabolites released during their formation are valuable resources that can be exploited to develop new microbial products for pest control.