STUDIES ON THE ROLE OF THE CORPUS ALLATUM IN THE ERI-SILKWORM, PHILOSAMIA CYNTHIA RICINI

Abstract

1. Pupae of Philosamia cynthia ricini in which diapause had been artificially induced by the removal of the brain, served as test animals for the effects of corpus allatum implants. Four to six corpora allata from donors in different stages induced molting in hosts which otherwise would have remained pupae. It was concluded that in Philosamia the corpus allatum, in addition to producing juvenile hormone, contains an appreciable amount of molt-inducing hormone furnished by neurosecretory cells of the brain. The interpretation is supported by the existence, in Philosamia as well as other insect species, of a neurosecretory pathway which links the secretory part of the brain with the corpora cardiaca-allata and which permits the storage of hormones produced in the brain at some distance from the cells of origin. While in most species studied so far the main storage center is the corpus cardiacum, this role may have been taken over by the corpus allatum in Philosamia. 2. As might be expected, the molt induced may or may not be coupled with adult differentiation depending on the stage of the donor. Implants of corpora allata from adult or fourth instar larval donors caused an additional pupal molt because, in addition to molt-inducing hormone, they also supplied juvenile hormone to the host. By contrast, implants from pupal donors contained no appreciable amount of juvenile hormone with the result that they brought about an imaginal molt. Some of the fifth instar implants had the same effect as those from pupae, while others acted like tissues from fourth instars. It seems that during the fifth larval stage the change from activity to temporary inactivity of the corpus allatum cells occurs gradually. Thus implants of larval and adult corpora allata furnish two hormones controlling post-embryonic development, while pupal corpora allata contain only one, namely, the neurosecretory material derived from the protocerebrum. 3. Even though the presence of corpus allatum hormone has been demonstrated in glands from adult donors in the present experiments, the role normally played by this hormone in the adult moth is still unknown. Extirpation of corpora allata from female pupae of Philosamia did not prevent egg maturation in the resulting moths.