Ultrastructure of a cytoplasmic polyhedrosis virus affecting the monarch butterfly, Danaus plexippus: I. Development of virus and normal polyhedra in the larva

Abstract

An account is given of the replication cycle of the virus and the development of normal polyhedra, as contrasted with a cubic mutation, in a cytoplasmic polyhedrosis affecting the larvae of Danaus plexippus, the monarch butterfly. The polyhedra are somewhat unusual being almost spherical and varying in size from very small to 5 μ in diameter. Two general lattice patterns were observed in the polyhedra, a dot pattern and a line pattern which are two views of the same crystal lattice. In the early stages of the disease a virogenic stroma forms in the cytoplasm in which the virus particles appear to develop. At a later stage what has been termed a crystallogenic matrix is produced which surrounds the developing polyhedra. Both contain virus particles but no normal cellular components. The crystallogenic matrix has many complete virus particles in it while the virogenic stroma has few complete, but many incomplete, particles present. The virus particle itself consists of a central electron-opaque core surrounded by a less dense capsid. The particle measures about 670 A in diameter, and the core, which may be hexagonal or pentagonal, measures about 350 A. There are 12 projections on the surface of the capsid measuring about 170 A in length, in section often six projections are visible forming a six-pointed star. An unusual feature is the presence of a “tail” extending from a vertex of the hexagon; the length of the tail is almost that of the diameter of the virus particle and is much longer than the regular projections. There is circumstantial evidence that the virus is transovarially transmitted.