Haemolymph ecdysteroid titres controlled by a circadian clock mechanism in larvae of the wax moth, Galleria mellonella

Abstract

The underlying mechanism of circadian rhythmicity of ecdysteroid titres in the haemolymph of the last-instar Galleria mellonella larvae was investigated. It was found that brain removal or head-ligature of larvae in which developmental processes were synchronized by transfer from 18 to 30°C, did not abolish daily rhythms of ecdysteroid titres in the haemolymph. Daily rhythms of ecdysteroid titres were also found in larvae ligated behind the thorax. The observed rhythms persisted 5 days after treatment, and transfer from 18 to 30°C, which suggests that the circadian clock driving these rhythms is not located within the brain. In further experiments it was shown that the prothoracic glands taken from temperature-synchronized larvae exhibit a daily rhythm of ecdysteroid synthesis with maximal activity coinciding with the peak of ecdysteroid titre found in the controls. It is therefore suggested that the circadian rhythm of ecdysteroid titres in Galleria larvae is regulated by a clock that probably is located within the prothoracic glands.