A NUCLEOPOLYHEDROSIS VIRUS IN POPULATIONS OF DOUGLAS-FIR TUSSOCK MOTH HEMEROCAMPA PSEUDOTSUGATA IN CALIFORNIA

A nuclear-polyhedrosis virus of the Douglas-fir tussock moth, Hemerocampa pseudotsugata, was found in the white fir forests of California for the first time. Tussockmoth populations declined in 1965, and this virus may be one of the important mortality factors. Egg masses were collected in selected study areas and the larvae reared in petri dishes on artificial diet. Larvae were also collected in several instars during the course of the summer and reared individually in petri dishes. An attempt was made to design a survey technique that would indicate the rate of decline, due to virus, of tussock-moth populations in the field. Further refinement will be necessary before egg-mass collections can be used as a survey tool but these studies indicate a good potential for such use. Evidence from this study shows the rate of dying in sample dishes in the laboratory to be related to the rate of larval mortality in the field. The primary use of such a survey would be an indicator to those involved in pest control decisions. © 1969.