Abstract
Some observations have been made on the infectious agent, the histopathology, and the incubation period of a polyhedrosis in western hemlock looper larvae. External and internal symptoms are generally similar to nuclear polyhedrosis in other Lepidoptera. Infection is first detectable in fat body nuclei, other susceptible tissues being blood, hypodermis, and tracheal matrix. Larvae subjected to a short period of starvation just prior to oral infection show a shorter incubation period than non-starved larvae. The polyhedral inclusion bodies range from 0.5 μ to 5.0 μ in diameter. Electron micrographs of dissolved polyhedra show their contents to be largely rod-shaped viruses measuring approximately 40 mμ × 290 mμ.