The objective of this report is to describe the current increase in Douglas-fir tussock moth (Orgyia pseudotsugata McDunnough) activity in northern Idaho and Montana. The report also relates current conditions to historical and future trends and larger scale increasing tussock moth activity in surrounding western states.
Mortality from various causes was recorded in a Douglas-fir tussock moth, Orgyia pseudotsugata McD., outbreak southeast of Coeur d'Alene, Idaho, in 1974. Observations began June 27 when about 50 percent of the larvae were second instars and continued until pupation. Within a 35-day period, there was a 93 percent average...
An epidemic of Douglas-fir tussock moth was detected in northern Idaho
in 1972. In 1973, aerial surveys showed that nearly 100,000 acres contained
various degrees of visible defoliation. An egg mass survey of
five reporting units made in the fall of 1973 determined potential for
damage in 1974. Based on...
The last outbreak of the Douglas-fir tussock moth, Hemerocampa pseudotsugata McD., in the Northern Region subsided in 1965. Tussock moth populations were not detected again until 1970 when ornamental spruce were defoliated in Spokane, Washington, and Poison and Missoula, Montana.
A practical demonstration of a method for
rating forest stands as to their probability of
defoliation by the Douglas-fir tussock moth
using aerial photographs and available cruise
data was done in the Palouse Ranger District,
Clearwater National Forest, Idaho.
A nonlinear computer program, RISK, was used to
identify significant independent...
Douglas-fir tussock moth populations are monitored annually in northern Idaho and western Montana to insure early detection of changes from endemic to outbreak population levels. Adult moth trapping in 1982 was intensified and expanded into additional areas from 1981 because of concern that with each passing year the probability of...
The sinuous flight behavior of male Douglas-fir tussock
moths, Orgyia pseudotsugata, (McD.), is characterized by
positive anemotaxis and positive chemoklinotaxis and varies
depending on distance from the pheromone source, population
density, and time of day. Visual cues play a minor role
in close-range orientation to a pheromone source, but
males...
The young larvae of the Douglas-fir tussock moth (Orgyia pseudotsugata (McDunnough) (DFTM) are dependent on the new foliage of its ho'sts (Doug1as-fir, grand fir, white fir) for their food supply. The phenology of the DFTM and its hosts are synchronized, with
egg hatch and dispersal occurring one to three weeks...
Loss of early instar Douglas-fir tussock moth (Orgyia pseudotsugata McDunnough) (DFTM) has been found to constitute 66-92% of intra-generation mortality and to be a key factor in inter-generation population change. This death has been attributed to dispersal and to arthropod predation, two factors previously judged more important to an endemic...
Published July 1974. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalog
In 1973, two centers of defoliation by Douglas-fir tussock moth totaling 350 acres were detected near Missoula, Montana. Egg mass surveys showed two sections south of Frenchtown and one section northwest of Lolo 41, contain sufficient egg mass population to cause heavy defoliation in 1974.
Douglas-fir tussock moth egg mass studies during winter 1974 indicate that natural factors such as low egg viability, egg parasitism, and virus do not alter the potential for heavy defoliation in two sections south of Frenchtown and one section northwest of Lolo, Montana.
The genome of the multicapsid nuclear polyhedrosis virus of
Orgyia pseudotsugata (OpMNPV) was mapped by examining overlapping
Hindlll fragments from cosmid clones which had been constructed
from partial Hindlll digests of viral DNA. Five OpMNPV cosmid
clones containing fragments encompassing the entire OpMNPV genome
were hybridized to blots of DNA...
An aerial survey during 1974 revealed approximately 5,000 acres of various degrees of Douglas-fir tussock moth, Orgyia pseudotsugata McD., defoliation in the lower Flathead Valley. An egg mass survey was made in September to determine the potential for damage in 1975. Based on new egg mass densities, significant defoliation may...
A supplemental Douglas-fir tussock moth egg mass evaluation was made within three quarter sections north of Poison, Montana, during April 1975. These areas were being considered for a pilot control project of a nucleopolyhedrosis virus spray. Results from the April evaluation showed these areas no longer qualified as sites for...
In conjunction with a proposed suppression project against the Douglas-fir tussock moth in northern Idaho, more than 1,000 larvae were collected from sample plots throughout the 32,000-acre treatment area. We had hoped to determine naturally occurring mortality factors which may have contributed to lower than anticipated population levels. Reared on...
The Douglas-fir tussock moth, Orgyia pseudotsugata McD., periodically
defoliates Douglas-fir, true firs, and other host trees in forests of
the western United States. In the Northern Region, these infestations
occur about once every decade.
This history covers the earliest recorded outbreak in northeastern
Washington from 1928 to 1930 and includes...
Evaluation of Douglas-fir tussock moth, Orgyia pseudotsugata, egg masses collected from an outbreak area in the lower Flathead Valley indicated that overall egg viability was relatively high, egg parasitism was low, and virus infestation averaged 7.1 percent northwest of Polson, 17.9 percent south of St. Ignatius, and 57.0 percent west...