DOUGLAS-FIR TUSSOCK MOTH (HEMEROCAMPA PSEUDOTSUGATA) EGG-MASS DISTRIBUTION ON WHITE FIR IN NORTHEASTERN CALIFORNIA

1967 ◽  
Vol 99 (11) ◽  
pp. 1193-1203 ◽  
Author(s):  
Robert F. Luck ◽  
Donald L. Dahlsten
Keyword(s):  
Sampling Method ◽  
Douglas Fir ◽  
Egg Mass ◽  
Egg Masses ◽  
Sample Unit ◽  
Tussock Moth ◽  
White Fir ◽  
Cardinal Direction ◽  
Sources Of Variation ◽  
Cardinal Directions

AbstractThe distribution of Douglas-fir tussock moth (Hemerocampa pseudotsugata McD.) egg-masses on white fir (Abies concolor (Gord. and Glend.) Lindl.) was studied in three areas of northern California. In each area 100 trees between 4.5 and 8.4 in. in diameter were stratified into five defoliation classes and four crown classes, giving a total of 20 classes per study area with five trees per class. Trees were divided into four crown levels and samples were taken at each of the cardinal directions at each level. Two branches comprised n sample unit in the top half of the tree (eight branches per level) and one branch the sample unit in the bottom half of the tree (four branches per level). Egg masses were recorded per 10 sq. ft of foliage or branch area. Eighty per cent or more of the egg masses were found in the bottom half of the crown. This percentage in the bottom half of the crown increased on trees with heavy defoliation or with increased exposure of the crown. Of the four possible sources of variation considered in this study, crown level, defoliation class, and crown class were significant while cardinal direction was not. A sampling method is proposed on the basis of the information gathered in this investigation.

PEST MANAGEMENT OF DOUGLAS-FIR TUSSOCK MOTH (LEPIDOPTERA: LYMANTRIIDAE): A SEQUENTIAL SAMPLING METHOD TO DETERMINE EGG MASS DENSITY

1984 ◽  
Vol 116 (7) ◽  
pp. 1041-1049 ◽  
Author(s):  
R. F. Shepherd ◽  
I. S. Otvos ◽  
R. J. Chorney
Keyword(s):  
Sampling Method ◽  
Mass Density ◽  
Sequential Sampling ◽  
Douglas Fir ◽  
Egg Mass ◽  
Tussock Moth ◽  
Incipient Stage ◽  
Orgyia Pseudotsugata ◽  
Detection Tool ◽  
Variability Data

AbstractA sequential egg-mass sample system for Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough (Lepidoptera: Lymantriidae), was designed, based on visual scanning of the lower branches of Douglas-fir trees, Pseudotsuga menziesii (Mirb.) Franco. A branch was removed from each quadrant from the upper, middle and lower crown level, and from the lowest whorl of a total of 59 non-defoliated trees in 10 areas. No consistent trend in egg-mass density per branch could be found between crown levels and no level proved superior as a representative of the tree. Therefore, the lower whorl of branches was selected for survey purposes because of sampling efficiency. Sample stop lines were determined from egg-mass density and variability data collected on 55 sites and subsequent defoliation estimates were related to these densities. The system is designed as an early detection tool to be used only in non-defoliated stands at the incipient stage of an impending outbreak.

PARASITOIDS AND PREDATORS OF THE DOUGLAS-FIR TUSSOCK MOTH, ORGYIA PSEUDOTSUGATA (LEPIDOPTERA: LYMANTRIDAE), IN LOW TO MODERATE POPULATIONS IN CENTRAL CALIFORNIA

1977 ◽  
Vol 109 (5) ◽  
pp. 727-746 ◽  
Author(s):  
D. L. Dahlsten ◽  
R. F. Luck ◽  
E. I. Schlinger ◽  
J. M. Wenz ◽  
W. A. Copper
Keyword(s):  
Sierra Nevada ◽  
Egg Parasitoid ◽  
Host Population ◽  
Douglas Fir ◽  
Egg Mass ◽  
Moth Population ◽  
Tussock Moth ◽  
Orgyia Pseudotsugata ◽  
White Fir ◽  
Pupal Parasitoids

AbstractDouglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), populations were studied on white fir at four areas in central Sierra Nevada mountains of California during 1971–73. Life tables were constructed for four populations in El Dorado County. The number of eggs per egg mass decreased and the percentage eggs parasitized doubled with declining moth populations. Hymenopterous parasitoids were collected from all immature stages of the moth: one egg parasitoid, Telenomus californicus Ashmead, six species of larval parasitoids, principally, Hyposoter sp., and 13 species of larval–pupal parasitoids. Tachinids were predominant and accounted for 73% of the parasitoidism of the cocoons in 1971. The apparent mortality of female pupae due to the parasitoid complex was greater than 97% in 1971 and 75% in 1972. One population in Placer County collapsed in 1971 apparently due to a combination of heat exhaustion and low levels of virus infection. Other defoliators, spiders, and several predatory insect species were collected from the foliage samples simultaneously with the tussock moth during larval sampling. Twelve species of "free living" spiders which could be capable of preying on the defoliator complex of white fir were collected. Parasitoids and predators appear to be potentially important biotic factors at low to moderate host population levels. This is the first recorded case where an agent other than the nucleopolyhedrosis virus has been responsible for the collapse of a Douglas-fir tussock moth population.

REGRESSION FOR ESTIMATING NUMBER OF DOUGLAS-FIR TUSSOCK MOTH EGGS RELATIVE TO EGG MASS WEIGHT

1978 ◽  
Vol 110 (2) ◽  
pp. 131-134
Author(s):  
Roy C. Beckwith ◽  
R. R. Mason ◽  
H. G. Paul
Keyword(s):  
Douglas Fir ◽  
Regression Equation ◽  
Sampling Scheme ◽  
Egg Mass ◽  
Tussock Moth ◽  
Early Instar

AbstractA common regression equation, representing data collected from four widely separated areas, was constructed to determine number of eggs of the Douglas-fir tussock moth based on individual egg mass weights. The regression is designed for use in any egg mass sampling scheme where a knowledge of the potential early instar population is required. The regression equation is also given for each area.

WITHIN AND BETWEEN TREE VARIATION OF LIVE AND PARASITIZED DOUGLAS-FIR TUSSOCK MOTH, ORYGIA PSEUDOTSUGATA (LEPIDOPTERA: LYMANTRIIDAE), COCOONS ON WHITE FIR IN CENTRAL CALIFORNIA AND ITS IMPLICATIONS FOR SAMPLING

1980 ◽  
Vol 112 (3) ◽  
pp. 231-238 ◽  
Author(s):  
Robert F. Luck ◽  
Donald L. Dahlsten
Keyword(s):  
Sierra Nevada ◽  
Douglas Fir ◽  
The Other ◽  
Central California ◽  
Tree Distribution ◽  
Tussock Moth ◽  
Orgyia Pseudotsugata ◽  
White Fir ◽  
Sierra Nevada Mountains ◽  
Total Parasitism

AbstractThe distribution of Douglas-fir tussock moth, Orgyia pseudotsugata (McD.), cocoons was studied within and between the crowns of white fir, Abies concolor ((Gord. and Glend.) Lindl.), at six locations in the central Sierra Nevada Mountains of California. The within tree, between tree, and between plot distribution of cocoons in the crown, categorized by sex, mortality (including parasitization), and stage (larva or pupa) were analyzed. Only cocoons containing female pupae varied in their distribution within the tree and they were concentrated in the bottom third of the live crown but their densities at any one level bore little relation to those in the other levels within the crown. Cocoon density varied significantly between plots and between trees within plots. Total parasitism did not vary significantly between plots. The variable within tree distribution of cocoons containing female pupae and their increased percentage parasitism relative to those containing male pupae, suggested that the live crown should be stratified. A sample unit consisting of two branches selected from the midpoint of each of the three crown levels (total: 6 branches) sampled approximately 5% of the live crown of white fir. The relation between the number of sample trees and mean cocoon density at three levels of precision is provided.

MORTALITY OF LARVAE IN STOCKED COHORTS OF THE DOUGLAS-FIR TUSSOCK MOTH, ORGYIA PSEUDOTSUGATA (LEPIDOPTERA: LYMANTRIIDAE)

1983 ◽  
Vol 115 (9) ◽  
pp. 1119-1127 ◽  
Author(s):  
R. R. Mason ◽  
T. R. Torgersen
Keyword(s):  
Douglas Fir ◽  
Total Loss ◽  
Abies Concolor ◽  
Bird Predation ◽  
Tussock Moth ◽  
Orgyia Pseudotsugata ◽  
White Fir ◽  
Arthropod Predation ◽  
Early Larvae

AbstractCohorts of instar I larvae of the Douglas-fir tussock moth, Orgyia pseudotsugata, were stocked on branches of white fir, Abies concolor. Branches were either exposed naturally over drop-trays or protected with cages of nylon netting. Only 8.7% of the larvae in exposed cohorts survived to pupate, compared with 68.0% survival in caged cohorts where dispersal and predation were prevented. Losses from the exposed cohorts were caused mostly by arthropod predation, disappearance, and non-replaced dispersal. Disappearance of early larvae was attributed primarily to predation by spiders and insects while disappearance of late larvae was suspected to be due mostly to bird predation. In an analysis of k-values, actual or suspected predation accounted for 47.2% and dispersal 40.5% of the total loss.

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