Neuroendocrine control of ecdysteroid titres and gonadotrophs cycles in the insectLabidura ripariafemales

Abstract

Summary Neuroendocrine controls of vitellogenesis, gonadotrophic cycles and ecdysteroid levels were examined in Labidura riparia using microsurgical manipulations, hormonal treatments, enzyme immunoassay (EIA) and high performance liquid chromatography (HPLC). In normal females high levels of ecdysteroids occur both in ovaries and hemolymph at the end of each vitellogenic cycle. In allatectomized (CA−) and pars intercerebralis cauterized females (PI−) vitellogenesis is suppressed, and ovarian ecdysteroids are at a low level. Juvenile hormone (JH) treatments restore vitellogenesis and high ecdysteroid levels in both experimental cases. Pars lateralis cauterized females (PL−) display a continuous vitellogenesis; however, ecdysteroid levels are lower in ovaries and higher in hemolymph than in normal females. HPLC/EIA analysis of ovarian ecdysteroids was performed, and the effects of different hormonal treatments are described. Discussing the interactions between JH, ecdysteroids, gonadotrophic activity and neurosecretory centers, we point out the role of the pars lateralis in the regulation of ecdysteroid levels. Besides, we suggest that ecdysteroids exert a feed-back control on Labidura gonadotrophic cycles.