Cytopathology of the soybean looper,Pseudoplusia includens,infected with the Pseudoplusia includens icosahedral virus

Ultrastructural responses of soybean looper cells of various tissues infected with Pseudoplusia includens icosahedral virus (PIIV), a newly characterized RNA virus [Y. C. Chao, H. A. Scott, and S. Y. Young (1983)J. Gen. Virol.64, 1835–1838], were studied in situ. Most cells of fat body and epidermis consistently contained virus particles and associated cytopathic structures. Virus particles, corresponding to those of purified PIIV in morphology and size, always occurred in the cytoplasm either in membrane-bound virogenic stroma and/or freely in the ground cytoplasm. Virogenic stroma, which appeared to be distinct from those induced by other insect viruses, consisted of electron-dense matrix material, in which virus particles were embedded, and membranous vesicles, 70 or 80 nm in diameter, containing nucleic acid-like fibrils. Virus particles in virogenic stroma occurred as hexagonally arranged crystalline arrays made up primarily of homogeneously dense particles, while those in the ground cytoplasm were dispersed randomly and had an electron-lucent central core. Extremely large numbers of virus particles were also located in noncellular cuticle layers of the integument.