Microsclerotia (MS), overwintering structures produced by many plant pathogenic fungi, have not been described for Beauveria bassiana.Two strains of B.bassiana, RSB and SZ21, formed MS in shake flask cultures using media with different nitrogen sources.Both strains produced MS in addition to typical blastospores and mycelia.Strain SZ21 (17.9×10⁵ and 7.4×10⁵ L^-1 in media with soybean powder and corn flour, respectively) produced higher concentrations of MS than strain RSB (14.8×10⁵ and 6.2×10⁵ L^-1 in media with soybean powder and corn flour, respectively) of B.bassiana. Microsclerotial preparations of B.bassiana containing diatomaceous earth survived vacuumdrying (to <5 % moisture) with no significant loss in viability.Rehydration and incubation of vacuum-dried MS granules on water agar plates resulted in hyphal germination and sporogenic germination to produce high concentrations of conidia.Bioassays using soil-incorporated, vacuum-dried MS preparations resulted in significant infection and mortality in soil-dwelling stages of the western flower thrip, Frankliniella occidentalis (Pergande).This is the first report of the production of sclerotial bodies by B.bassiana and provides a novel approach for the control of soil-dwelling insects with this entomopathogenic fungus.