The pathogenicity of the newly discovered entomopathogenic fungus species Isaria poprawskii, found during epizootics on Bemisia tabaci (Gennadius) in the Lower Rio Grande Valley of Texas, was tested against the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) Takiya, under laboratory conditions (27 +/- 1 degrees C; 75 +/- 5% RH; photoperiod of 14:10 (L:D) h. Exposures of nymphs and adults to 500, 1000, and 2000 conidia/mm(2) on cowpea, Vigna unguiculata (L.) Walp, leaves resulted in insect mortality. Median lethal concentrations for second- (685 conidia/mm(2)) and fourth-instar nymphs (771 conidia/mm2) were similar to those for adults (855 conidia/mm(2)). Virulence, as measured as mean time to death of the GWSS by survival analysis, was different between concentrations within each insect stage. For example, for the second-instar, I. poprawskii was more virulent at high concentrations (4.6 days) than medium (5.4 days) or low (5.5 days) concentrations. Mycosis in sharpshooters occurred at 3-4 days and continued for 8-10 days after spray. This fungus has the ability to immobilize and stop feeding on infected GWSS, which could potentially slow the spread of Pierce's disease. These results indicate that I. poprawskii is pathogenic to H. vitripennis nymphs and adults. Its pathogenicity and virulence against H. vitripennis show that this fungus is a promising biocontrol agent to control the glassy-winged sharpshooter. (C) 2013 Elsevier Ltd. All rights reserved.