Neuroendocrine regulation of seasonal morph development in a bivoltine race (Daizo) of the silkmoth, Bombyx mori L.

We investigated the neuroendocrine regulation of the development of seasona l morphs in a bivoltine race (Daizo) of the silkmoth, Bombyx mori, by decer ebration, the transplantation of brain-suboesophageal ganglion (Br-SG) comp lexes and the injection of active neuropeptides. When brains were removed f rom fresh pupae destined to develop into summer morphs (SD pupae) by embryo nic and larval exposures to short days at low temperature, the pupae develo ped into autumn or intermediate morphs. However, in pupae destined to devel op into autumn morphs (LD pupae), the operation did not show an effect on s easonal morph development. Br-SG complexes were excised from fifth-instar L D and fifth-instar SD larvae 2 days after larval ecdysis and were transplan ted into the abdomen of SD larvae of the same age. The Br-SG complexes of L D larvae, but not the Br-SG complexes of SD larvae, shifted the host's seas onal morph development toward the autumn morph. Furthermore, when treated w ith crude pupal SGs extract and diapause hormone (DH), fresh SD pupae devel oped into autumn or intermediate morphs, respectively. Possibly the develop ment of seasonal morphs in the silkmoth, B. mori, is regulated by a novel f unction of DH. Alternatively, DH may act on the imaginal wing disks at an e arlier stage than on the ovaries. (C) 2000 Elsevier Science Ltd. All rights reserved.