Enhancing the Efficacy of Fungal Biocontrol Agents for Matsumuratettix hiroglyphicus, the Vector of Sugarcane White Leaf Disease, Through Serial Passaging

The leafhopper Matsumuratettix hiroglyphicus is the vector of the phytoplasma associated with sugarcane white leaf disease in Asia. However, highly virulent strains of entomopathogenic fungi to control this vector are lacking. To select effective fungal strains, serial passaging through the leafhopper and the phenotypic properties and virulence of four strains were evaluated and compared to those of their initial stock. The influence of fungal passaging through the insect varied according to the fungal genus, strain, and passage number. The third and fifth passages of all fungal strains improved the examined parameters and showed virulence enhancement compared to those of the initial stock; however, a decrease in the parameters was observed after the seventh passage. The fifth passage of Beauveria bassiana SUTTU01 exhibited phenotypic changes resulting in significantly higher pathogenicity (80% mortality) than its corresponding initial stock. When the effect of fungal treatment on the transmission capacity of M. hiroglyphicus was tested, no significant difference was found in white leaf disease-related phytoplasma infection between untreated and fungi-treated leafhoppers. However, the fifth passage of B. bassiana SUTTU01-treated leafhoppers exhibited the lowest titer of the phytoplasma, resulting in a reduced transmission rate and fewer infected plants. This is the first report on the influence of B. bassiana on leafhopper vector capacity. The results obtained constitute a basis for future research on effective fungal strains able to reduce the phytoplasma transmission rate of this leafhopper vector.