Induction of rhythmic modulation of haemolymph ecdysteroids in the insect Rhodnius prolixus by treatments which elicit rhythmic ecdysis.

The titer of moulting hormones (ecdysteroids) in fifth instar male Rhodnius displays a gradual decline throughout the week preceding ecdysis when animals are maintained in constant light (LL). Multiple sampling of haemolymph from the same animal reveals a constant rate of decline with no increases in titer observed. However, 20-hydroxyecdysone (20HE) provokes increases in the titer of ecdysteroids which occur between 18 and 27 hr after injection. Multiple injections of 20HE provoke regular changes in the rate of decline of the titer. When 20HE is injected into animals reared in LL, a rhythm in the titer of ecdysteroids with an initial periodicity of approximately 28 hr is provoked which is reduced to 24 hr by 72-96 hr after injection. Injection of antiserum to ecdysteroids elicits an immediate rapid oscillation in titer similar to that observed in light/dark (L/D) cycles. Therefore injections of 20HE or antiserum to ecdysteroids can provoke a rhythm in the titer of ecdysteroids in animals reared in LL. Rhythms in ecdysteroid titer would appear to result from the interactions of synthetic and catabolic systems, both of which would appear to be able to act in a timed fashion. Such rhythmic modulation of ecdysteroid titer may provide time cues to the circadian system timing ecdysis. Thus the gated ecdysis rhythm observed after 20HE or antiserum injections may be a response to induced modulation of the ecdysteroid titer.