Studies on the venomous spicules and spines of moth caterpillars. I. Fine structure and development of the venomous spicules of the Euproctis caterpillars.

Scanning and transmission electron microscopy (SEM and TEM) revealed unique structures and development of the venomous spicules of tussock moth caterpillars of the genus Euproctis: (1) Flower-like structure at the distal end and a longitudinal minute depression on the proximal subapical wall of these spicules were observed by SEM. This depression was revealed to be a small hole by TEM. (2) During molting, observed were cytoplasmic processes of several trichogen cells penetrating the cytoplasm of a tormogen cell to form the spicules with the holes at their subapical portions. A papilla was formed by a tormogen and several epidermal cells. (3) After the molting, the cytoplasmic process in a spicule disappeared and the spicule cavity was replaced by electron-dense materials secreted apparently from the trichogen cell. (4) It was considered that the electron-dense materials were the main toxic or precursory substances in the Euproctis spicules.