Biosynthesis and degradation of juvenile hormone in corpora allata and imaginal wing discs of Galleria mellonella (L.)

Abstract

The rate of juvenile hormone (JH) biosynthesis by corpora allata-corpora cardiaca complex (CA/CC) during two last larval instars of Galleria mellonella was analysed. The rate of biosynthesis reaches maxima at the beginning of the VIth and VIIth instars. It is markedly reduced before the last larval ecdysis and after the first day of the last larval instar. After passing the second day of the last larval instar CA/CC exhibits again an increased ability for the biosynthesis of JH. The JH esterase activity in CA/CC is very low at the beginning of last larval instar and rapidly increases after the first day of this instar. Beginning on the second day of last larval instar the rate of JH hydrolysis is always higher than the rate of JH synthesis in CA/CC. It is concluded that the secretion of JH by CA/CC is possible until the second day of the last larval instar. After this, JH-acid can be supplied by CA/CC to peripheral tissues. The imaginal wing discs of mobile prepupa exhibit the ability to methylate JH-acid. It is concluded that some elevations of JH titre in G. mellonella haemolymph after the second day of VIIth instar are due in part to JH-acid methyltransferase activity in the imaginal discs.