The relations of the pars intercerebralis, corpora allata, and juvenile hormone to oocyte development and oviposition in the African migratory locust

Electrocoagulation of the median neurosecretory cells (MNSC) of the pars intercerebralis (PI) performed 1 or 3 days after fledging in adult females of Locusta migratoria migratorioides resulted in the absence of oviposition. In the majority of the females the oocytes developed up to the early vitellogenetic state (length, 0.8-2.0 mm), and then continuous alternating cycles of oocyte resorption and growth occured. Implantation of three pairs of corpora allata (CA) to PI-coagulated females resulted in oocyte development up to the late vitellogenetic state (oocyte length, 2-6 mm) in most recipients. Slight overdoses of juvenile hormone (JH) I (60-100 μg per locust) injected into PI-coagulated females led to completion of the oocyte development in almost all females. In some instances more than one generation of the oocytes reached maturation (chorionated eggs), but no laying occurred. In some females the oviduct ruptured, presumably because of the pressure exerted by the large number of the eggs and the eggs passed to the hemocoel. Nevertheless, no egg was found to leave the body through the natural way of the gonopore; oviposition was completely blocked. In contrast to certain claims in the literature, the MNSC do not exert a specific direct effect on oocyte growth; their role in this process seems to be limited to the regulation of CA activity. Some further factors, however, perhaps outside of the MNSC, may also be involved in the control of oocyte growth and/or CA activity, since individual variations among similarly treated females were considerable. The act of laying is under complete control of the PI; probably a neurosecretory factor is responsible for this effect, but a possible role of ordinary neurons (in the PI) cannot be ruled out.