LOM OMP, A PUTATIVE ECDYSIOTROPIC FACTOR FOR THE OVARY IN LOCUSTA-MIGRATORIA

The primary target of the gonadotropic neurohormone of Locusta migrato ria (Lom OMP) was investigated in locust fifth instar larvae (last lar val instar) and adult females by analysing the effect of Lom OMP and 2 0-hydroxyecdysone (20-HE) on the appearance of vitellogenin (Vg) in th e haemolymph and on ovarian growth, Detection of Vg was carried out us ing 7.5% polyacrylamide gel electrophoresis of haemolymph while ovaria n growth was estimated by measuring the mean length of basal oocytes. Injections of 20-HE had no effect in larvae but induced, in adults, a precocious occurrence of Vg and precocious ovarian maturation similar to injections of Lom OMP, Moreover, injections of 20-HE counterbalance d the endogenous Lom OMP inactivated by its immune serum, Finally, Lom GRIP did not induce the appearance of Vg when it was injected in ovar iectomized fifth instar larvae, These results demonstrate, in contrast to the prevailing concept, that ecdysone is a gonadotropic hormone in Locusta and strongly suggest that Lom OMP induces ovarian ecdysone pr oduction, The possibility that not only the ovary but also the fat bod y could be a target organ of Lom OMP is discussed.