This work aimed to assess the virulence of Beauveria bassiana isolates in different concentrations on Thaumastocoris peregrinus (Hemiptera, Thaumastocoridae) and select them to control this insect pest. Suspensions of IBCB35, IBCB66, IBCB18, IBCB01 and JAB06 isolates were tested in the concentrations of zero, 1 × 104, 1 × 106, 1 × 108 conidia/ml, applied on the eucalyptus leaves used to feed the insects. Dead insects were disinfested daily and placed in a humid chamber to confirm the death by fungus. Mortality at the end of the experiment ranged from 12% for IBCB66 to 48% for IBCB18 at a concentration of 1 × 104 conidia/ml, between 32% for IBCB66 and 68% for JAB06 at a concentration of 1 × 106 conidia/ml, and between 60% for IBCB01 and 84% for JAB06 at the concentration 1 × 108 conidia/ml. The assessed isolates were efficient in controlling the insect, especially JAB06.
