Abstract
Hyalophora cecropia (Linnaeus) is susceptible to infection by a cytoplasmic polyhedrosis virus. Electron microscope studies showed spherical viral particles known as "cores" which remain in groups of 12 to 17 subunits. The virus particles were embedded in a protein mass located in craters of the polyhedra. Larvae of the first, second, and third instars were more susceptible to viral infection than later instars. However, up to 50% of the larvae of later instars sometimes survived. The larvae of subsequent instars and the pupa were very resistant and periodic injections of strong dosages of virus material produced no ill effect. In general, larvae infected by this cytoplasmic virus shrank to less than half normal size before death.