THE DEVELOPMENT OF A CYTOPLASMIC POLYHEDROSIS VIRUS IN THE SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA (CLEMENS)

Virus particles and polyhedra develop in patches of viroplasm in the cytoplasm of mid-gut cells of larvae of the spruce bud worm, Choristoneura fumiferana (Clemens). Normal components of the cell disintegrate as the disease spreads, and either they completely disappear or mitochondria, ribosomes, and other components form rings in the outer regions of the cell.Polyhedra develop from dense material which appears to attract and envelop virus particles. Only complete particles with large prominent cores are incorporated into growing polyhedra. As the polyhedra mature, they assume a smooth outline and polyhedral shape and either cease to attract virus particles, or their size is limited by the amount of polyhedron protein and numbers of complete virus particles produced in the cell. Although most of the virus particles not incorporated into polyhedra appear incomplete, the large masses of incomplete particles formed in a similar type of disease of another insect were not found in bud worm larvae.