The body color of insect is varied,of which the melanism is a common form.The mechanism of insect melanism has long attracted biologists and ecologists.In silkworm,Bombyx mori,black pupa (bp) is a unique pupal-stage melanic mutant.Its molecular basis,however,remains unclear.In the present study,we identified the aspartate decarboxylase gene which is responsible for bp mutant using positional cloning.In the bp mutant,a 493 bp SINE transposon was inserted 2.3 kb upstream of the transcription start site of BmADC.Further,we observed the dramatic reduction of BmADC expression levels in bp mutant,resulting in the deficiency of β-alanine,NBAD and the accumulation of Dopamine.Injection of β-alanine into bp mutant rescued its color pattern to wild-type,and knockdown of BmADC gene obtained melanic pupae in the wild-type.All the results showed that BmADC plays an important role in melanin metabolism during pupa stage in silkworm.This may contribute to a better understanding of the pigmentation mechanism of pupal cuticle in Lepidopteran.