Long-Term Persistence of the Nuclear Polyhedrosis Virus of the Douglas-Fir Tussock Moth, Orgyia pseudotsugata (Lepidoptera: Lymantriidae), in Forest Soil

Abstract

The long-term persistence of the nuclear polyhedrosis virus of the Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), in forest soil has been established by bioassaying soil and duff samples from an area in which the last tussock moth outbreak took place in 1936–38. Samples were taken from beneath each of 75 white fir, Abies concolor (Gord. and Glend.) Lindl., trees selected within 17 clusters in a study area in the Inyo National Forest, California. Virus was present in 15 soil samples from 9 of the clusters. Although present concentrations of active virus are low (<45 PIB/cm3), enough remains in the mineral soil from sheltered locations to infect tussock moth larvae. Absence of active nuclear polyhedrosis virus in the duff layers above the positive soil samples indicates the duff has accumulated since the last epizootic of tussock moth nuclear polyhedrosis.