AGE DEPENDENCY AND REGULATORY PROPERTIES OF JUVENILE HORMONE-III BIOSYNTHESIS IN ADULT MALE CRICKETS, GRYLLUS-BIMACULATUS

The in vitro rate of juvenile hormone III (JH III) biosynthesis by cor pora cardiaca-corpora allata complexes from paired and unpaired adult males of Gryllus bimaculatus is age-dependent. Both groups display a p eak of juvenile hormone III production on day 2 after the imaginal mou lt, with the peak rate in paired males reaching about double that of u npaired animals. The juvenile hormone III synthesis then declines stea dily in unpaired males, while in paired males additional phases of ele vated rates occur. The juvenile hormone III titre in the haemolymph (a s measured by radioimmunoassay) parallels the biosynthesis rate of juv enile hormone III for the first 4 days of adult life. Stimulation of t he corpora allata with 200 muM 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 Ca2+ concentrati ons in the incubation medium stimulate the juvenile hormone III synthe sis in vitro in a dose-dependent manner, while increased K+ concentrat ions inhibit synthesis almost completely. Combined treatment with elev ated Ca2+ and exogenous application of 20 muM farnesol indicates no sy nergistic increase in methyl farnesoate accumulation, even when free c alcium is increased 20-fold. Elevated K+ combined with 200 muM farneso l leads to a stimulation of juvenile hormone III biosynthesis and espe cially methyl farnesoate accumulation. Male corpora allata, completely deprived of nervous connections during incubation or incubated togeth er with detached brain or as intact brain-endocrine complexes, always show lower biosynthetic activity compared to control CC-CA complexes.