Abstract: There has been a debate on whether the release of pine caterpillar isolates of Beauveria bassiana causes or enhances white muscardine of the silkworm, Bombyx mori. In order to scientifically investing pathogenic risk of pine caterpillar isolates against silkworms, with high representativeness and great accuracy, 64 pine caterpillar isolates from 8 provinces and 12 silkworm isolates from 4 provinces were used against the 3rd instars of the silkworm in pathogenicity tests in 3 batches. The results showed that either pine caterpillar isolates (except for one of them) or silkworm isolates showed some pathogenicity to silkworm, but with great different virulences. At the concentration of 3×10⁷ conidia/mL and 1.5×10⁸ conidia/mL, the average infection rate of pine caterpillar isolates was 10.2% and 36.4% respectively, significantly lower than that of silkworm isolates (89.6% and 90.6%); the average infection rate of the pine caterpillar isolates at 1.5×10⁸ conidia/mL was significantly higher than that at 3×10⁷ conidia/mL, while in silkworm isolates, the average infection rate were almost the same under the same concentrations. The average values of LT₅₀ of 4 pine caterpillar isolates with comparatively more pathogenic to silkworms at 1.5×10⁸ conidia/mL were 7.83 d, longer than that of 6 silkworm isolates (3.62 d). The lethal concentrations of the least virulent silkworm isolates B1 and B5 were 132—15733 times higher than those of the most virulent pine caterpillar isolate D26, D22. The lethal dosages of B1, B5 were 43—2201 times as high as D26, D22. The poignant contrast suggested that although different pine caterpillar isolates had different virulence on silkworms, all pine caterpillar isolates showed obvious host specificity. A comprehensive analysis indicated that the risk of an epizootic induction of white muscardine in silkworms by application of B. bassiana insecticides against pine caterpillars was low.