Localization of myoinhibitory peptide immunoreactivity in Manduca sexta and Bombyx mori, with indications that the peptide has a role in molting and ecdysis.

For normal development of Manduca sexta larvae, the ecdysteroid titer must drop following its sudden rise at the start of the molting cycle; this sudden decline in titer may be due to myoinhibitory peptide I (MIP I), which has an inhibitory effect on the release of ecdysone by the prothoracic glands of Bombyx mori in vitro. Using an antiserum to MIP, we have demonstrated secretion of an MIP-like peptide by the epiproctodeal glands of Manduca sexta, which are located on each proctodeal nerve, just anterior to the rectum. These MIP-immunoreactive glands are also present in B.