A novel protease inhibitor in Bombyx mori is involved in defense against Beauveria bassiana

► We cloned and expressed a novel TIL-type protease inhibitor from the silkworm, Bombyx mori, BmSPI38. ► BmSPI38 had high stability at temperatures as high as 99 °C and stability in a wide range of pH conditions (2-11.8). ► BmSPI38 might suppress penetration by entomopathogenic fungi via the inhibition of its cuticle-degrading proteases. ► Our study identified an alternative route for reducing damage to silkworms by blocking the harmful melanization.