Rôle des organes perisympathiques et dynamique de la secretion de la bursicon chez Tenebrio molitor

Abstract

Light and electron microscope observations have been made on the perisympathetic organs (P.O.) situated on the dorsal somatic abdominal nerves in pupae of Tenebrio molitor. Tests carried out with extracts of P.O. using a bioassay method on pupae of Tenebrio at various developmental stages indicate that these organs have an important role in the storage and release of the tanning hormone, bursicon. The P.O. extracts from the abdominal segments (2 to 5) of 5-day-old pupae were found effective but not those from pharate adult (2 days before ecdysis). The storage and release of bursicon occur later from the P.O. of the posterior abdominal segments (6 to 8). The activity of the blood begins to be effective in the pharate adult 2 days before ecdysis, reaches a maximum 1 hr after the adult ecdysis, and decreases thereafter. This study carried out on the various parts of the nervous system shows that all these parts are effective at a certain stage of the pupal and adult development following an antero-posterior gradient. In the cephalic region, this activity is early and long-lasting, but it appears at later stages and only for a short time in the thorax and abdomen. This phenomenon indicates that bursicon is either passed along the ventral nervous chain or it is synthesized in different parts of the nervous system at successive developmental stages. In the present paper, we have tried to give a comprehensive summary of the dynamics of bursicon in insects.