Background: Silkworm is the typical model organism of Lepidoptera.As its gene experission in silk gland owns timeliness and spatiality, the increasing number of researchers devote to using it as the bioreactor to produce recombinant protein.Mutant in natural conditions with the phenotype of naked pupa or forming sericin cocoon is the suitable materical for investigating silk protein synthesis and secrete mechanism of silkworm.