Control of ommochrome synthesisby both juvenile hormone and melanization hormone in the cabbage armyworm,Mamestra brassicae

Pigmentation of last instar larvae of the cabbage armyworm,Mamestra brassicae is of two types: melanin in the cuticle and ommochrome in the epidermis. The latter was found to be primarily xanthommatin. When allatectomy was performed 8 h before head capsule slippage (HCS) in the last larval molt, later ommochrome synthesis was inhibited. Application of juvenile hormone (JH) up to 12 h after HCS (9 h before ecdysis) (activity: methoprene≧JH I>JH II>JH III) restored ommochrome synthesis. After that time it has less and less effect.

Removal of the suboesophageal ganglion from the larvae 8 h before HCS prevented both later ommochrome synthesis and melanization. Melanization of isolated abdomens was restored by implantation of 3 suboesophageal ganglia or injection of melanization and reddish coloration hormone (MRCH) 18 h after HCS. Restoration of ommochrome synthesis required exogenous JH in addition to melanization hormone from suboesophageal ganglion or MRCH. Therefore, melanization appears to be critical for the later onset of ommochrome synthesis even in a larva which has been exposed to JH during the critical period.