The Size and Variability of Cytoplasmic Polyhedra in the Silkworm, Bombyx mori L. : (Lepidoptera : Bombycidae)

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In the case of inoculation, the polyhedra produced in the anterior part of midgut were larger than those in the posterior part, and those in the middle part were intermediate in size. The polyhedra appeared 48 hr after inoculation of the virus. At this time they were observed with difficulty in the cytoplasm around the cell nucleus of the midgut epithelium. The mean size of the polyhedra increased during the course of cytoplasmic-polyhedrosis. The growth rate of polyhedra was faster in the anterior part than in the posterior part, the middle part assuming the intermediate. On the variation of the size of polyhedra formed, the longer the time after the virus inoculation, the larger and more variable was the size of the polyhedra, and 120 hr after the inoculation the variability in the anterior part was larger than that in the posterior part. When the larvae were inoculated per os with larger polyhedra obtained from anterior part, and smaller ones obtained from posterior part, there was no difference in the size of the polyhedra formed between anterior and posterior parts, which indicated that the size of polyhedra is solely dependent on their position in the host midgut.