Chapter M 



The Insect Viruses 



Kenneth M. Smith 



Agricultural Research Council, Virus Research Unit, 



Cambridge, England 



I. Introduction 369 



II. Different Types of Insect Viruses and the Diseases Caused 370 



A. Polyhedral Viruses 370 



1. Nuclear Viruses 370 



2. Cytoplasmic Viruses 375 



B. Granulosis Viruses 378 



C. Viruses without Intracellular Inclusions 379 



III. Morphology of Insect Viruses and their Associated Membranes 380 



A. Nuclear Polyhedral Viruses 380 



B. Cytoplasmic Polyhedral Viruses 381 



C. Granulosis Viruses 382 



D. Viruses without Intracellular Inclusions 383 



E. The Ultimate Infective Unit 384 



IV. Pathological Changes in the Infected Cell and the Development of the Virus 



Particles 384 



V. Latent Infection in Insects and its Bearing on the Cross -Transmission of 



Viruses 380 



VI. Methods of Transmission of Insect Viruses 388 



References 390 



I. Introduction 



The early work on the viruses affecting insects was devoted exclusively to 

 the polyhedral virus diseases, so called because of the presence in certain 

 tissues of polyhedra, the many-sided crystalline inclusions associated with this 

 type of virus. The reason for this exclusive study is obvious enough since the 

 polyhedra are easily visible on the optical microscope, thus making diagnosis 

 easy. Although intensive study of the insect viruses is only of recent origin, 

 we know that there are at least three types and of these, the polyhedral 

 viruses are divisible into two quite distinct groups. 



The kinds of insect viruses, then, which are known so far, are the polyhedral 

 virus diseases or polyhedroses; these consist of the nuclear and cytoplasmic 

 diseases according to the site of virus multiplication. Secondly, there are the 

 granular diseases, or granuloses, in which the intracellular inclusions are 

 extremely small crystals — the granules from which the disease takes its name. 

 Thirdly, there are those diseases in which no intracellular inclusions have been 

 observed. 



vol. in— 24 369 



