RESUMEN
The observation statistics suggested that the haemolymph melanization speed of larvae became fast and the growth inhibition of Escherichia coli was strong as the quantities of feeding on mulberry leaves increased. The RT-PCR result showed that the mRNA expressions of melanin biosynthesis enzyme BmTan, BmPo-1, BmYellow-f and BmDdc were high in the haemolyph of 5 L 3 d larvae. The qPCR analysis showed Bmtan, Bmddc, Bmyellow, Bmebony and Bmblack, especially Bmddc expression were significantly higher in black disease larvae than in normal larvae. Compared with control, Ddc inhibitors drastically inhibited the lipopolysaccharide-induced haemolymph melanization. In addition, the content of Dopa and Dopamine markedly rose after E. coli injection. These indicated that haemolymph melanization was linked to immune defenses and Bmddc may play a role in melanization response of haemolymph immune in silkworm.