Age dependency and regulatory properties of juvenile hormone III biosynthesis in adult male crickets, Gryllus bimaculatus

Abstract

The in vitro rate of juvenile hormone III (JH III) biosynthesis by corpora cardiaca-corpora allata complexes from paired and unpaired adult males of Gryllus bimaculatus is age-dependent. Both groups display a peak of juvenile hormone III production on day 2 after the imaginal moult, with the peak rate in paired males reaching about double that of unpaired animals. The juvenile hormone III synthesis then declines steadily in unpaired males, while in paired males additional phases of elevated rates occur. The juvenile hormone III titre in the haemolymph (as measured by radioimmunoassay) parallels the biosynthesis rate of juvenile hormone III for the first 4 days of adult life. Stimulation of the corpora allata with 200 μM farnesol in vitro produces no increase in juvenile hormone III production, but methyl farnesoate accumulates by a factor of 17 times over control values. Elevated Ca 2+ concentrations in the incubation medium stimulate the juvenile hormone III synthesis in vitro in a dose-dependent manner, while increased K + concentrations inhibit synthesis almost completely. Combined treatment with elevated Ca 2+ and exogenous application of 20 μM farnesol indicates no synergistic increase in methyl farnesoate accumulation, even when free calcium is increased 20-fold. Elevated K + combined with 200 μM farnesol leads to a stimulation of juvenile hormone III biosynthesis and especially methyl farnesoate accumulation. Male corpora allata, completely deprived of nervous connections during incubation or incubated together with detached brain or as intact brain-endocrine complexes, always show lower biosynthetic activity compared to control CC-CA complexes.