Changes of the susceptibility of mid-gut epitherium in the silkworm larvae treated with low temperature, to the nuclear polyhedrosis virus, were studied by microscopical observation.
When the larvae were chilled at 5°C for 24hr just after the moulting without any feeding and inoculated with the polyhedra, the posterior portion of mid-gut in these larvae was heavily affected with virus, specific C. P. E. and polyhedra were formed in both cylindrical cells and goblet cells (Figs. 1 and 2), but in anterior portion of mid-gut, infected cells could hardly be seen as shown in Fig. 3. And most of larval body in these insect became shorter and died within 24-48hr after the inoculation of polyhedra.
In larvae which were chilled after the feeding following the moulting, and non-chilled larvae, polyhedral bodies could not be seen in both cylindrical cells and goblet cells as shown in Fig. 4. And most of these larvae died over of 72hr after the inoculation of polyhedra, showing the swelling of segmental membrane.
From these results, it was concluded that, usually cylindrical cells and goblet cells of mid-gut epitherium in the silkworm are not so susceptible to the nuclear polyhedrosis virus, but if the larvae are chilled at 5°C after the moulting without any feeding, the susceptibility of both cylindrical cells and goblet cells become higher.