L'action differentielle des hormones juveniles sur la metamorphose chez Locusta migratoria

The morphogenetic effect on metamorphosis of the three juvenile hormones is studied under experimental conditions that permit accurate conclusions in Locusta migratoria. Injections are made at the beginning on the last larval instar, which is the best time for action at the optimum level on the control of metamorphosis. Racemic hormones in stereochemical form comparable to that of natural compounds were used. Doses were chosen between 5 and 50 μg in order to give clear morphogenetic effects and give effects at a physiological level.A chronological study showed that juvenile hormones have the most important morphogenetic effect when injected in the first 40 hr of the last larval instar. Oiled solutions, stored at 4°C, lost only a small part of their morphogenetic activity after 9 months.Among the three hormones, JH-III presented the weaker morphogenetic effect, very significantly different from that of JH-I and JH-II. It has been possible to dissociate the effects of JH-I and JH-II on metamorphosis, JH-I giving a more potent action.