Abstract: Prothoracicostatic peptide is one of insect brain neuropeptides, which was observed to inhibit the prothoracic glands of the silkworms, Bombyx mori, at active stage of ecdysone biosynthesis, in the experiments in vitro. In the present paper, prothoracicostatic peptide was injected into the silkworms in different dosages with different methods, single or strengthened injection, and hemolyms were taken thereafter in different intervals. By using ³H-ecdysteriod radioimmunoassay, a remarkable in vivo activity of prothoracicostatic peptide and developmental changes of ecdysteroid titer in the silkworm in vivo, caused by prothoracicostatic peptide treatment were gained. This is the first evidence that prothoracicostatic peptide significantly inhibits ecdysteroidogenesis in an insect in vivo.

Key words: Bombyx mori, prothoracicostatic peptide, ecdysteroid, in vivo activity