Decay in juvenile hormone biosynthesis by insect corpus allatum after nerve transection

Abstract

THE ability of the insect corpus allatum (CA) to synthesise and release juvenile hormone (JH) is believed to be controlled by various neural and humoral influences of both stimulatory and inhibitory nature¹. In last instar Galleria mellonella, a CA stimulatory neurohormone (allatotropin) originating in the medial neurosecretory cells of the brain and operating during the early part of the instar has been proposed^2,4. In the later part of the instar the synthesis and/or release of JH is inhibited by nervous impulses originating in the brain and reaching the CA through nervous connections². A similar nervous inhibition of JH synthesis is thought to operate in adult Pyrrhocoris apterus⁵ and in the cockroaches Leucophaea maderae⁶ and Diploptera punctata⁷, because section of the nervi corporis allati 1 (NCA 1) seems to activate the CA. A neurohormonal factor from the medial neurosecretory cells of the pars intercerebralis which causes the activation of the CA has also been proposed in the orthopterans, Anacridium aegyptium and Locusta migratoria⁸. In still other Orthoptera, Schistocerca sp., the necessity for intact NCA 1 for activation of the CA has been suggested, indicating a direct stimulatory neural influence rather than an inhibitory influence or a humoral stimulation^9,10. Thus the factors controlling JH biosynthesis in different insect species are not clear. We show here that disruption of the NCA 1 by section during the first gonotrophic cycle of the desert locust Schistocerca gregaria results in a rapid and predictable decline in the ability of the CA to synthesise JH. The effect of section of the NCA 1 on JH biosynthesis is detectable within 3 h.