Endocrine Regulation of Melanization in Late Larvae of the Oleander Hawk Moth, Deilephila nerii12

Abstract

Approximately 78–104 h prior to larval-pupal ecdysis, the last (5th) instar of the oleander hawk moth, Deilephila nerii (L.), undergoes a color change from green to black on the dorsum of all abdominal segments. The color change involves a melanization process whose initiation appears to be under the control of a blood-borne factor. A series of ligation and hormone injection experiments have pinpointed the source of the factor to be the prothorax and the factor to be ecdysone. The head appears not to be necessary for the triggering of melanization. However, the role of the head may be of ensuring that secretion of ecdysone is synchronized with a period of sensitivity during which the epidermal cells are competent to initiate melanization when exposed to ecdysone. The finding that high levels of juvenile hormone or ecdysterone administered to larvae during the precritical period (in respect to melanization) can effectively block melanization but not pupation supports a model involving a critical ratio of ecdysone/juvenile hormone which may be involved in establishing epidermal cell competency for melanization.