Corythucha arcuata (Say) (Hemiptera: Tingidae) is a pest of oaks that is highly distributed in several regions of the world, including North America, the Balkan Peninsula, Europe, and Turkey. In the present study, ten entomopathogenic fungi belonging to four different genera (Metarhizium (x4), Beauveria (x4), Isaria (x1), and Myriodontium (x1)) were tested against nymphs and adults of C. arcuata under laboratory conditions. Based on the initial screening studies, it was shown that all isolates were able to infect both nymph and adult individuals of the pest after application of 1 x 10(7) mL(-1) conidial concentration. Among the tested isolates, Beauveria bassiana KTU-24 caused the highest mortality against both nymphs and adults within 14 days, with 80% and 90% mortality, respectively. This isolate also produced the highest mycosis values on both nymphs and adults, with 77% and 83% mycosis, respectively. Therefore, this isolate (B. bassiana KTU-24) was selected for concentration-mortality response tests for further characterization. The concentration-mortality response tests showed that the conidial concentrations of 1 x 10(8) and 1 x 10(9) mL(-1) of B. bassiana KTU-24 produced 100% mortality against nymphs and the conidial concentration of 1 x 10(9) mL(-1) of this isolate caused 100% mortality against adults. Based on probit analysis, the LC50 values of the isolate B. bassiana KTU-24 were calculated as 1.17 x 10(7) and 6.44 x 10(6) conidia mL(-1) against nymphs and adults, respectively. This study indicates that B. bassiana KTU-24 has a significant potential for further investigation as biological control agent against C. arcuata.