Technical Abstract: The glassy-winged sharpshooter, Homalodisca coagulata (Say), is an important pest on grapes, citrus, almonds and other commercial crops in California as it is a vector of Xylella fastidiosa Wells, a bacterium that causes Pierce¿s disease in grapes, citrus variegated chlorosis, almond leaf scorch and other plant diseases. Various entomopathogenic fungi isolated from natural infections of H. coagulata, its habitats and other insect hosts were evaluated for their potential for suppression of this insect vector. Assays were conducted using the hyphomycetous fungi, Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin, Hirsutella sp. and an unidentified fungus against adult H. coagulata. In addition, three isolates of B. bassiana were selected for further evaluation. Two of these were California isolates, one each from the three-cornered alfalfa hopper, Spissistilus festinus (Say) and soil from H. coagulata habitat, and the third was a Texas isolate from natural infections of H. coagulata. All three isolates were similar in their virulence to H. coagulata under laboratory conditions. The genetic relatedness of the B. bassiana isolates was also compared using single sequence repeat (SSR) markers which showed genetic diversity of this species based on the source of the isolate. Some isolates were four times more infectious than others demonstrating that virulence of B. bassiana is not necessarily associated with their genetic relatedness.