Ips sexdentatus (Boerner) and I. typographus (Linnaeus) (Coleoptera: Curculionidae) are considered to be important destructive pests of coniferous forests in Europe and Asia. In this study, the efficacy of Beauveria pseudobassiana strain ARSEF 9271 isolated from Dendroctonus micans (Kugelann) (Coleoptera: Curculionidae) was evaluated against I. sexdentatus and I. typographus adults. Insects were treated with different conidial concentrations of the fungus to determine the virulence. A conidial suspension of 1 x 10(8) conidia mL(-1) caused 100% mortality in both I. sexdentatus and I. typographus within 5 and 7 days, respectively. Additionally, 100% mycosis was obtained in the concentration-response experiments for both insects. LC50 values of the fungus were calculated as 3.94 x 10(4) conidia mL(-1) and 1.32 x 10(4) conidia mL(-1) for I. sexdentatus and I. typographus, respectively. I. sexdentatus and I. typographus adults were also inoculated with a conidial suspension of 1 x 10(6) conidia mL(-1) at inoculation rates of 0% (control), 25%, 50%, 75%, and 100% to determine the horizontal transmission of the fungus. Mortality values from horizontal transmission experiments were determined as 100% at all rates after 15 days at 20 degrees C under laboratory conditions. Our results indicate that B. pseudobassiana ARSEF 9271 is a promising microbial control agent against the tested Ips species and can horizontally spread among a population of both I. sexdentatus and I. typographus.