Tissue distribution of the ice-nucleating agents in larvae of the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Abstract

To investigate the tissue distribution of ice-nucleating agents in the rice stem borer, Chilo suppressalis Walker, the crystallization temperatures of the whole bodies and individual tissues of nondiapausing and diapausing larvae were measured. In nondiapausing mature larvae the crystallization temperature of the gut with its contents was the highest, being about − 8 °C, showing that a freezing site is present in the gut. As food particles in the alimentary canal of hibernating larvae were excreted in autumn, the larval supercooling capacity increased with lowering crystallization temperature of the gut. In diapausing larvae the crystallization temperatures of the muscle and epidermis were the highest, being above − 15 °C, which is similar to that of the whole larvae, and the hemolymph crystallization temperature was the lowest, being below − 25 °C. Furthermore, the crystallization temperatures of the nervous system, trachea, silk gland, salivary gland, and ovary were below − 20 °C, which was equivalent to those of 0.9% NaCl solution. Consequently, in diapausing larvae a primary site of freezing is present in the muscle and epidermis, indicating that the potent ice-nucleating agents exist in these tissues. However, since the epidermis could not be completely divided from the muscle, it was not concluded whether the potent ice-nucleating agents existed in the epidermis or not.