ECDYSTEROID TITERS IN A TENEBRIONID BEETLE, ZOPHOBAS-ATRATUS - EFFECTS OF GROUPING AND ISOLATION

Metamorphosis in Zophobas atratus is dependent on isolation: when kept in grouped conditions, larvae undergo numerous supernumerary moults? growing in size, without pupating, This beetle thus represents an inte resting model for the analysis of possible differences in the endocrin e regulation of normal vs, supernumerary larval moults, In this study, the ecdysteroid titres have been analysed in this species, using enzy me immunoassay, The hormonal variations of larvae undergoing normal or supernumerary larval cycles were particularly examined, in either gro uped or isolated conditions, Normal larval cycles presented very simil ar ecdysteroid variations in grouped as well as isolated conditions, s howing a single hormonal peak (at about 1000 pg/mu l). Supplementary l arval cycles, occurring in grouped conditions, also showed a similar s ingle ecdysteroid peak, but after a longer period of basal levels, Iso lation of such larvae triggered their larval-pupal transformation, whi ch was characterized by more complex hormonal fluctuations, including a small ecdysteroid peak before the main one, Interestingly, the isola tion of big larvae during a large part of their cycle induced this pec uliar hormonal pattern synchronously, confirming the involvement of a complex neuroendocrine control between external conditions and ecdyste roid titres. (C) 1997 Elsevier Science Ltd.