The Iridescent Virus Group

Abstract

In this chapter, the iridescent virus group will be considered to consist of three viruses of insects, Chilo iridescent virus (CIV), Sericesthis iridescent virus (SIV), and Tipula iridescent virus (TIV). The iridescent viruses contain deoxyribonucleic acid (DNA) but no detectable ribonucleic acid (RNA). The particles of SIV and TIV have lxen shown to be icosahedral by shadowing them in two directions, and comparing the shadows of the particles in the electron niicroscopc with those of models of regular polyhedral. The faces of TIV particles are approximately equilateral and triangular. Knowledge of the internal structure of iridescent viruses is even less certain. The core has been described as consisting of 42 “large knobs” forming an icosahedron but similar structures are found in uninfected insects, and there may be an internal component consisting of 12 subunits. Pellets or crystals of iridescent viruses appear blue-violet and green when viewed with oblique illumination. Crystals of these viruses have such large lattice constants that they diffract light of visible wavelengths just as ordinary crystals diffract X-rays, and light of selectively reflected wavelengths is seen as iridescence in the iridescent pellets. The optimum temperature for the replication of iridescent viruses is 20° to 25°, depending on the host and experimental conditions. Two diseases of mosquitoes appear to be caused by viruses with some resemblance to the iridescent viruses. One of these viruses, found in Aedes taeniorrhynchus , has been named “mosquito iridescent virus.”