Nervous and humoral inhibition of C16 juvenile hormone synthesis in last instar females of the viviparous cockroach, Diploptera punctata.

The control of the decline in C16 juvenile hormone (C16JH) synthesis in the final larval stadium of the viviparous cockroach Diploptera punctata Eschscholtz was investigated to establish how nervous and humoral signals affect the activity of the corpora allata (CA) before metamorphosis. Denervation of the CA in young last instars caused an increase in the rate of JH biosynthesis as monitored by an in vitro radiochemical assay and resulted in a supernumerary larval form at the following ecdysis. However, when larval CA were transplanted into corpus allatectomized adults, they exhibited a further 5- to 10-fold stimulation in synthetic rate and supported host oocyte development at near normal rates. Conversely, adult CA implanted into young and old last instars were inhibited in comparison to those implanted into penultimate instars and adults. These experiments suggest that in D. punctata, an unfavorable humoral environment as well as nervously transmitted inhibitory signals maintain low rates of JH synthesis prior to the imaginal molt.