Abnormal cell proliferation in the epidermis of the fall webworm, Hyphantria cunea, induced by the infection of a nuclear-polyhedrosis virus

Abstract

Histopathological studies of the larval integument of the fall webworm, Hyphantria cunea, infected with a nuclear-polyhedrosis virus were carried out. It was found that in the early stage of the disease most regions of the epidermis swelled to form multilayered structures as the result of the abnormal proliferation of the epidermal cells. During the multiplication period, different phases of amitotic figures were always found in the epidermis. After the amitosis, the resulting cells enlarged markedly with an initiation of polyhedral formation in their hypertrophied nuclei. Thus, the diseased epidermis in the middle stage of infection consisted of several layers of the cells packed with a large number of polyhedra. In the later stages of the disease, multilayered epidermis was completely disintegrated; the constituent cells were separated from each other and were released from the integument into the body cavity. About this time, darkly pigmented spots were occasionally observed on the body surface of moribund larvae. Histologically, these spots were cuticular projections containing muscle tissue, blood cells, fat-body tissue, and disintegrated epidermal cells, with necrotic and melanized scabs covering the outside.