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The UV-A and UV-B wavelengths of solar radiation may seriously reduce viability of Metarhizium anisopliaeconidia,a fungus used extensively in Brazil for insect pest control. The conidial tolerances to UV-A and UV-B radiation werestudied for one isolate (IBCB 425) commercially available product produced on rice grains. Aqueous or oil emulsion conidialsuspensions were irradiated for O (control), 2, or 3 h using the solar simulator filtered with diacetate filter to remove UV-Cradiation which afforded 652 mW.m-2 in the spectral range of 280～370 nm. The UV tolerance was based on conidial germi-nation (viability) and virulence to Diatraea saccharalis larvae. Conidia formulated with oil emulsion had higher survival after3 h of UV exposure, but the virulence of the eonidia previously exposed to 2 h of UV radiation were similar when oil formula-ted or not. The mortality of D. saccharalis caterpillars exposed to non-UV-irradiated conidia was greater than that of larvae ex-posed to irradiated conidia, and the LT50values were lower for the non-irradiated suspensions than for those irradiated. Thisapparent reduction in virulence was directly related reduction in viability or delay of germination of UV-irradiated conidia.