FACTORS AFFECTING THE BIOSYNTHESIS AND RELEASE OF JUVENILE-HORMONE BISEPOXIDE IN THE ADULT BLOWFLY CALLIPHORA-VOMITORIA

The principal juvenile hormone produced by the corpus allatum of the adult blowfly Calliphora vomitoria has been identified as juvenile hormone bisepoxide. The precursor compounds, methyl farnesoate and juvenile hormone III are also synthesized and released from the isolated gland in vitro, but in small amounts (approx. 1% of the total radiolabelled products of the gland). In females given unrestricted access to sugar, water and meat immediately after eclosion, the rate of juvenile hormone bisepoxide production rises with the initiation of oocyte development, reaches high levels early in the first gonadotropic cycle and remains consistently high through successive cycles. Mature males on the same diet also produce juvenile hormone bisepoxide at high rates. Flies restricted to a sugar-and-water-only diet synthesize much lower levels of juvenile hormone bisepoxide (less than 50% of meat-fed flies). Partially-purified brain extracts of C. vomitoria contain material that is immunoreactive in an ELISA against the inhibitory neuropeptide, allatostatin 1, of the cockroach Diploptera punctata. This material is able to inhibit significantly the biosynthesis of juvenile hormone bisepoxide in flies, and also has strong inhibitory effects on juvenile hormone III biosynthesis by cockroach corpora allata in vitro. Cockroach allatostatins 1-4 at concentrations of 10(-4)-10(-7) M have no significant effect on juvenile hormone bisepoxide release in the blowfly. Also tested at the same concentrations, and shown to have no significant effects on the synthesis and release of juvenile hormone-related compounds in either the blowfly or the cockroach were the vertebrate peptide Met5-enkephalin-Arg6-Gly7-Leu8 (YGGFMRGL) and its carboxyamidated analogue (YGGFMRGL-NH2). Similarly, the FMRFamide-related peptides, calliFMRFamides 1 and 5 and their non-amidated analogues, at concentrations of 10(-4)-10(-6) M, had no effect on juvenile hormone bisepoxide biosynthesis and release. Forskolin (5 x 10(-5) M) and 8-bromo-cAMP (10(-4) M) appeared not to have an inhibitory influence on juvenile hormone bisepoxide release in the blowfly, suggesting that cAMP may not be the intracellular second messenger in this species. A presumed precursor of juvenile hormone bisepoxide, farnesoic acid, did not stimulate an increased production of juvenile hormone bisepoxide, but resulted in an increase in juvenile hormone III production.