Assessment of Beauveria bassiana Virulence Across Diverse Insect Hosts and Understanding the Role of Genes Contributing to Insect Virulence

Abstract

Beauveria is an entomopathogenic fungus known to infect and kill wide range of insects through cuticle penetration and release of variety of toxins. The major focus of this study is to evaluate the efficacy of nine Beauveria isolates against diverse insect hosts and identify highly virulent isolates. In Chapter 2, conducting virulence assay with nine Beauveria isolates against diverse insect hosts, several highly virulent isolates among insects tested were identified. ARSEF 2597 displayed the highest virulence across all the insects in the orders Lepidoptera, Coleoptera, and Blattodea. The isolates exhibited varying degrees of efficacy with most isolates not displaying host specificity. However, with Aedes aegyptii larvae, host specificity was observed, with isolate ARSEF 8028 demonstrating significantly high level of virulence. Some isolates demonstrated virulence across several orders suggesting wide host range, while some exhibited higher level of virulence against specific insect suggesting narrow host range and host specificity. In Chapter 3, a phylogenetic comparison between the seven Cry-like genes of B. bassiana ARSEF 2860 and 71 Cry genes from various species and subspecies of Bacillus thuringiensis (Bt) revealed a strong phylogenetic relationship with Cry 2, Cry 11, and Cry 18 families indicating the Cry-like genes may have a conserved function for virulence. Mutants were generated for all the seven Cry-like genes using CRISPR/Cas9 to evaluate their roles in insect virulence. Virulence assay conducted with mutants of each of the seven different Cry-like genes with the G. mellonella and H. zea larvae demonstrated reduced virulence for mutants of the two Cry-like genes, BBA_03803 and BBA_08516 suggesting their potential role in insect virulence.