Age dependent changes in the binding and hydrolysis of juvenile hormone in the haemolymph of last instar larvae of Galleria mellonella

Abstract

Binding and hydrolysis of juvenile hormone I (JH) and cleavage of four 1-naphthyl esters were determined in the haemolymph of Galleria mellonella throughout the last larval instar. JH binding per ml haemolymph parallels changes in the protein content with a maximum at the onset of spinning at 120 hr (152 mg protein/ml; binding of 20 n-mole JH/ml) and a drop at the pupal ecdysis. Activity of JH esterase(s) exhibits two maxima: first between cessation of feeding and the start of spinning at 96–120 hr (hydrolysis of 65 n-mole JH/ml/min) and second just before pupal ecdysis at 168 hr (52 n-mole JH/ml/min). Correlations between these changes and available data on the JH content in caterpillars indicate that JH binding protein and JH esterase(s) may play a role in clearing JH from its target tissues rather than in regulating its amounts. Fluctuations in the hydrolysis of 1-naphthyl esters of acetate (max. 4.5 μ-mole/ml/min), butyrate (max. 21 μ-mole/ml/min), palmitate (max. 0.5 μ-mole/ml/min), and laurate (max. 0.4 μ-mole/ml/min) reflect primarily the feeding activity of caterpillars and follow a very different course than changes in the potential to hydrolyze JH.