Circadian control of a daily rhythm in hemolymph ecdysteroid titer in the insect Rhodnius prolixus (Hemiptera).

The hemolymph levels of the insect molting hormone (ecdysteroid) during the week preceding ecdysis in fifth-instar male Rhodnius prolixus have been determined using a radioimmunoassay. When animals are kept on light-dark cycles, the titer displays massive daily increases and decreases producing a daily rhythm. This rhythm is maintained with a period of approximately 24 hr in continuous darkness. The free-running period of the rhythm was determined at 24 and 28 degrees and found to be temperature compensated. Therefore the titer of ecdysteroids is modulated by a circadian system. Since ecdysteroids are known to influence a wide variety of developmental events ranging from chromosome puffing to cuticle deposition, circadian modulation of the titer will provide information concerning time to all ecdysteroid sensitive tissues hence could function as a pacemaker for imposing developmental synchrony.