Toxic Secondary Metabolites and Virulence Factors Expression by Entomopathogenic Fungi during Insect Infection and Potential Impact as a Tool for Pest Management

Abstract

Entomopathogenic fungi interact with their insect hosts by infecting and colonizing their bodies as part of their life cycle. After breaching the host cuticle, a variety of toxic secondary metabolites is secreted into the hemocoel facilitating a successful invasion and colonization. The production of fungal toxins, e.g. beauvericin and destruxin in some model fungi such as Beauveria bassiana and Metarhizium anisopliae, represents a powerful defense tool system for the fungal species but also an opportunity to exploit its efficacy against prejudicial insects. Most of these compounds, such as non-ribosomal peptides, alkaloids, terpenes, and polyketides, are referred to as virulence factors and their synthesis and secretion regulation is tightly controlled. In the last decade few informations were available on how these metabolites work when secreted, and how to harness their potential regarding biological control applications. In recent years, with the advent of nextgeneration sequencing techniques and the advances in genetic manipulation of fungal species, vast information became available on the genes involved in the interaction between host and entomopathogenic fungi, including those involved in the synthesis and regulation of toxic secondary metabolite production. The design and application of transgenic entomopathogens with enhanced virulence factors are currently being addressed as a more effective alternative in traditional biological control strategies. The ecological importance of fungal secondary metabolites and virulence factors, and their role in the effectiveness of different species relying on toxins production, are key to enhance control of detrimental insect population, in an environmentally friendly and sustainable manner.