IN-VIVO INHIBITION OF VITELLOGENESIS IN THE DERMAPTERAN LABIDURA-RIPARIA BY 20-HYDROXYECDYSONE

In previous studies we have described the existence of cyclical change s in ecdysteroid levels during the female reproductive life of the ear wig Labidura riparia. High levels of ecdysteroids are observed at the end of each vitellogenic period just before follicle degeneration, in coincidence with the beginning of each non-vitellogenic period. In the present work, using in vivo [(35)]methionine incorporation, electroph oresis and electron microscopy, we study the effects on fat body and o varies of 20-hydroxyecdysone (20E) injections into young vitellogenic females. This resulted in a reduction of proteosynthetic organelles (s carce Golgi complexes and fragmented RER cisternae), inhibition of vit ellogenin synthesis in adipocytes, vitellogenesis arrest and premature follicular atresy. All these effects are suppressed when juvenile hor mone treatment is associated with 20E injections. 20E does not inhibit vitellogenesis when applied to pars lateralis deprived females, which display continuous vitellogenesis. Thus, 20E does not act directly on ovaries nor on corpus allatum: the presence of the pars lateralis cel ls is required for 20E to inhibit vitellogenesis. These findings are e xplained in terms of the existence of a 20E feed back loop. This hormo ne acts via lateral neurosecretory cells of the brain which probably h ave an allatostatic effect.