Physiology of larval diapause in the wax moth, Galleria mellonella: An utrastructural analysis

Abstract

1. 1. The wax moth, Galleria metionella enters larval diapause when 1-day-old last instar larvae are transferred from an optimal rearing temperature of 30 to 18°C. In the haemolymph of diapausing larvae very low ecdysteroid titres exist which are due to synthetic inactivity of the prothoracic glands and not due to a reduction in prothoracic gland cell numbers. Ultrastructural analysis of the prothoracic glands taken from diapause-committed 8-day-old last instar larvae, show all the signs of inactivity as far as the development of the endoplasmic reticulum and mitochondrial system are concerned. Whereas in the same age last instar non-diapausing larvae, the glands are extremely active as judged by their ultrastructure. 2. 2. Paraldehyde-fuchsin staining and ultrastructural studies have revealed that in diapause-committed 8-day-old last instar larvae of Galleria mellonella, neurosecretory cells of the protocerebrum accumulate the neurosecretory vesicles in their perikaria. The protocerebral cells of control (non-diapausing) larvae of the same age contain only a small amount of neurosecretory vesicles. 3. 3. The corpora allata of diapause-committed larvae seems to be inactive despite the high titre of juvenile hormone found in their haemolymph. The endoplasmic reticulum and mitochondrial system, organellae involved in the juvenile hormone biosynthesis, are reduced. 4. 4. The possible mechanism controlling larval diapause of Galleria mellonella is discussed.