Endophytic Metarhizium strains against herbivorous insect pests: development of novel fermentation and formulation strategies

Abstract: Biocontrol of insect pests with entomopathogenic fungi is challenging because of the lower efficacy, difficult handling and limited shelf life of these organisms compared to synthetic pesticides. However, recent studies have provided evidence that some of these fungi can grow endophytically in plant tissues, paving the way for novel plant protection measures. One strategy could be the use of the endophytic entomopathogenic fungus Metarhizium brunneum isolate F52. For application as a commercial biocontrol agent, the fungus has to be mass-produced. M. brunneum was cultivated in shake flasks in media based on agricultural residues to produce submerged spores to a maximum of 1.15 ± 0.06×107 spores/ml. By the use of UV protectants, the viability of submerged spores was significantly increased by 71.6 ± 12.1% after a UV-B radiation of 120 min. Submerged spores were formulated in a novel spray that delivered the fungus on tomato leaves and allowed penetration of the leaves verified by a polyphasic approach using light microscopy and PCR.