INSECT VIRUSES 



G. H. Bergold 



Department of Agriculture, Laboratory of Insect Pathology, 



Sault Ste. Marie, Ontario, Canada 



Characteristic for one type of virus disease of insect larvee are 

 polyhedral shaped inclusion bodies. These polyhedra develop in great 

 numbers and very rapidly in the nuclei of most organs, shortly before 

 the death of lepidopterous larvae (Bergold, 1943) and in the mid-gut 

 nuclei of sawfly larvae (Bird, 1950). Finally the nucleus and cell mem- 

 branes burst and enormous numbers of polyhedral bodies are released 

 into the serum. 



They can be purified by centrifugation and are finally obtained as 

 a white powder of considerable purity. Their size and crystal shape 

 vary with the insect species. The polyhedral bodies from silkworms 

 are about 5 microns in diameter and are rhombical-dodecahedra. 



The polyhedral bodies are insoluble in water, but dissolve rapidly 

 in weak alkali, a condition which exists in the gut of susceptible insect 

 larvae. Some years ago I was able to demonstrate (Bergold, 1947) that 

 about 95% of the weight of the polyhedral bodies consists of the very 

 homogenous, but not infectious, polyhedral protein, with very little or 

 no nucleic acid and a molecular weight of 275,000 to 375,000, depend- 

 ing on the insect species. Only about 3 to 5% of the polyhedral bodies 

 consist of the active virus particles which are occluded in the polyhedral 

 bodies. These active virus particles are liberated when the polyhedral 

 bodies are dissolved in weak alkali. 



The nature of the polyhedron-virus union is unknown. The poly- 

 hedral protein and the virus particles from silkworms are serologically 

 unrelated, they have also no relationship to silkworm serum (Bergold 

 and Friedrich-Freksa 1947). 



The virus particles are rod-shaped with dimensions of about 30 to 50 

 millimicrons in diameter and 260 to 360 millimicrons in length, depend- 

 ing on the insect species. About io~^^ gm. or about 100-1000 of these 

 rods are necessary for the L.D. 50. Infectivity tests combined with sedi- 

 mentation experiments in the ultracentrifuge and serological examina- 

 tions give very strong evidence that these rods are identical with the 

 infective principle (Bergold, 1947, Bergold and Friedrich-Freksa, 1947). 

 The virus rods contain about 14% desoxyribonucleic acid. Acid hydrol- 

 ysis and paper chromatography (Wellington, 1950) indicate the 

 presence of the following amino acids: cyst(e)ine (small), aspartic, 



