A HISTOLOGICAL STUDY OF THE DEVELOPMENT OF THE URTICATING SPICULES OF THE FAR EASTERN URTICATING MOTH, EUPROCTIS FLAVA BREMER (LEPIDOPTERA: LYMANTRIIDAE)

Abstract

In the summer of 1955, about two hundred thousand inhabitants in the vicinity of Nagoya City were affected with an accidental dermatitis caused by contact with the yellowish moths, which were attracted by light and invaded into house rooms. These moths were identified as the Far Eastern urticating moth, Euproctis flava Bremer, which is very common from southern Hokkaido to Kyushu, and is known for some fifty years as a medical pest mainly in Tohoku and Hokuriku District. This rash has been ascribed to the minute barbed spicules attached mainly on the anal tuft of the female moth. Observations have affirmed that these urticating spicules are carried by the adult moth from the cocoon into which the caterpillar deposited them. The spicules are, therefore, originally a product of the larval insects. Clinical studies have shown the possibility that the dermatitis is caused by a poisonous substance originated from the urticating spicules. Therefore it is most interesting to know the fine structure of the subcutaneous tissue of the larva and the detailed process of the development of the urticating spicules.
Histological investigations were made in the past by a number of authors, such as Tyzzer (1907), Eltringham (1913), Kephart (1914), Gilmer (1925), and Pawlowsky and Stein (1927) . Kephart (1914) was the first to show two kinds of specialized hypodermal cells, viz., the poison-secreting cells and the hair formative cells, in the subdorsal tubercles of a larva of the brown tail moth. Gilmer (1925), on the contrary, had the opinion that poisonous substance was secreted through small chitinous intracellular ducts of one poinson gland cell just beneath each papilla, in spite of the fact that both authors used the same material and the same slide specimens. Pawlowsky and Stein (1927) illustrated the strongly pigmented hypodermal cells, the large gland cells and small trichogen cells from the thickened hypodermal tissue of the brown tail moth. It was in 1933 that the developmental process was first described in detail by Tonkes, who observed three kinds of cells ; the small papilla formative cells, the large gland cells and the small trichogen cells. Tonkes' conclusion is entirely different from Gilmer's, which is quoted in several text books. Weidner (1937) compared the tissue of the larvae of the urticating moth of the genus Euproctis with that of the procession caterpillar, Tliaumetopoea pityocampa Schiff, and hypothesized that the large gland cell of the brown tail moth might be a membrane cell. Recently Morishita (1957) stated that the large cells of the uppermost layer secrete the urticating spicules. Various interpretations have thus been presented, but it appears still worthy to add an another investigation of the fine structure of the larval epidermis and a histological observation concerning the development of the spicule formative epidermis.