The small poplar longhorn beetle, Saperda populnea is an important pest of Lombardy poplars (Populus nigra L.) in Turkey. A survey for natural entomopathogenic fungi of S. populnea larvae was made in Erzurum, Turkey, during the period 2004-2005. Larvae (13.5%) infected with a strain of the fungus Beauveria bassiana were found. The pathogenicity of B. bassiana strain 46 was conducted with different concentrations of conidia (10(6), 10(7) and 10(8) conidia/ml) of this isolate on S. populnea larvae. The lowest concentration (10(6) conidia/ml) caused about 56% mortality within 6 days. One hundred percent mortality was achieved after median lethal time (LT50) of 4.6 and 4.4 days for 10(7) and 10(8) conidia/ml, respectively. There were no significant differences between median lethal times. This is the first record of natural infection of S. populnea larvae by B. bassiana.