Interaction between Manduca sexta allatotropin and Manduca sexta allatostatin in the fall armyworm Spodoptera frugiperda

A peptide that strongly stimulates juvenile hormone (JH) biosynthesis in vi tro by the corpora allata (CA) was purified from methanolic brain extracts of adult Spodoptera frugiperda. Using HPLC separation followed by Edman deg radation and mass spectrometry, the peptide was identified as Manduca sexta allatotropin (Mas-AT). Treating the CA from adult S.frugiperda with synthe tic Mas-AT (at 10(-6) M) caused an up to sevenfold increase in JH biosynthe sis. The stimulation of JH synthesis was dose-dependent and reversible. Syn thetic M. sexta allatostatin (Mas-AS) (10(-6) M) did not affect the spontan eous rare of JH secretion from CA of adult S. frugiperda, nor did any of th e allatostatins of the Phe-Gly-Leu-amide peptide family tested. However, wh en CA had been activated by Mas-AT (10(-6) M), addition of synthetic Mas-AS (10(-6) M) reduced JH synthesis by about 70%. This allatostatic effect of Mas-AS on allatotropin-activated glands was also reversible. When CA were i ncubated in the presence of both Mas-AT (10(-6) M) and various concentratio ns of Mas-AS (from 10(-8) to 10(-5) M), the stimulation of JH-biosynthesis observed was inhibited in a dose-dependent manner. The experiments demonstr ate a novel mechanism of allatostatin action. In S.frugiperda JH synthesis was inhibited only in those glands which had previously been activated by a n allatotropin. (C) 2000 Elsevier Science Ltd. All rights reserved.