Beauveria bassiana (Bals. -Criv.) Vuill. is widely valued as an entomopathogenic biocontrol agent in agriculture and forestry, yet it is also the causal agent of white muscardine, one of the most contagious and destructive diseases of the domesticated silkworm, Bombyx mori L. This short review integrates classical experimental evidence with recent molecular, microbiome and epidemiological studies to summarise how the fungus harms sericulture. Infection proceeds through cuticular penetration and gut invasion, and kills larvae within days; all developmental stages are susceptible, but late-instar larvae are the most vulnerable, with experimental larval mortality approaching 100% and median lethal concentrations falling from about 1,600 spores mL-1 in first-instar larvae to about 435 spores mL-1 in fifth-instar larvae. Cool (15-18 oC), humid (90-100% relative humidity) and poorly ventilated rearing conditions favour outbreaks, and infected moths produce far fewer eggs. Silkworm strains differ markedly in susceptibility, and host defences (cuticular proteins, serine protease inhibitors, antimicrobial peptides and mulberry-derived cuticular bacteria) offer routes to resistance. Population-genetic tracing in China found no link between silkworm outbreaks and released biopesticide strains, so the risk from agricultural use of B. bassiana near sericultural areas remains plausible but poorly quantified. We outline diagnostic and management options and identify priorities for research and policy.