Stressor Effects of High Relative Humidity and a High Moisture Diet on Appearance of Disease from Nuclear Polyhedrosis Virus in Larvae of Porthetria Dispar (L.)

Pauline A. Thomas, Yale University


High relative humidity (R.H.) and a high moisture diet were tested as stressors in the incidence of nuclear polyhidrosis virus (NPV) disease of larvae of Porthetria dispar (L.). Relative humidity was shown to have no effect on the appearance of NPV disease in larvae reared in the laboratory. However, a high mortality from other causes was sustained by a group of larvae subjected to both high R.H. and a high moisture diet. The absence of NPV disease during the first larval instar period confirmed earlier findings that effective egg sanitization virtually eliminates NPV disease. This supports current disfavor with the theory of transovarial transmission of P. dispar NPV. One case of NPV disease was found in a late instar larva. This may be attributed to incomplete sanitization of its egg, or to later contamination. The problems encountered here in studying latent viral disease , and in pinpointing the roles of certain environmental conditions as stressors, parallel similar obstacles to the study of stressor action and latency in human disease. The nature of insect nuclear polyhidrosis virus is discussed, as well as the potential effects on public and environmental health of its use as a viral insecticide .