Growth and respiratory enzyme activity in the prothoracic glands of Galleria

In the penultimate-larval instar, the total volume of the prothoracic gland and the activities of some oxidative mitochondrial enzymes (cytochrome oxidase, NADH: cytochrome c oxidoreductase, succinate: cytochrome c oxidoreductase) undergo cyclic variations associated with larval growth. These specifically larval-larval growth cycles are absent in the prothoracic glands of normal last-instar larvae. Here the cycles can be induced artificially by implantation of brain or corpora cardiaca-allata complexes or, by exogenous application of juvenile hormone. The smallest size of the prothoracic gland in relation to the size of the body, as well as the minimal activity of all the three mitochondrial enzymes in the gland, have been found exactly at the moment of the pre-pupal peak of ecdysteroid in the body. The possibility that the prothoracic glands alone can synthetize ecdysteroid during the peak is questioned.