Multicentury, Regional‐Scale Patterns of Western Spruce Budworm Outbreaks

1993 ◽  
Vol 63 (4) ◽  
pp. 399-424 ◽  
Author(s):  
Thomas W. Swetnam ◽  
Ann M. Lynch
Keyword(s):  
Regional Scale ◽  
Spruce Budworm ◽  
Western Spruce Budworm

A tree-ring reconstruction of western spruce budworm outbreaks in the San Juan Mountains, Colorado, U.S.A.

2003 ◽  
Vol 33 (6) ◽  
pp. 1010-1028 ◽  
Author(s):  
Daniel E Ryerson ◽  
Thomas W Swetnam ◽  
Ann M Lynch
Keyword(s):  
Tree Ring ◽  
Regional Scale ◽  
Spruce Budworm ◽  
Western Spruce Budworm ◽  
Spatial And Temporal Patterns ◽  
Control Series ◽  
Increment Core ◽  
San Juan Mountains ◽  
Mixed Conifer Forests ◽  
Tree Ring Reconstruction

Tree-ring records were used to reconstruct spatial and temporal patterns of western spruce budworm (Choristoneura occidentalis Freeman) outbreaks in mixed conifer forests of southern Colorado. Reconstructions in 11 host stands showed a regionally synchronous pattern of at least 14 outbreaks during the past 350 years. Intervals between outbreaks were highly variable within stands, but at the regional scale outbreak intervals were more consistent. Spectral analyses of regional outbreak time series confirmed periodicities at about 25, 37, and 83 years. Comparison with an independent drought reconstruction indicated that outbreaks typically corresponded to increased moisture, while relatively little budworm activity occurred during dry periods. In contrast to other published reconstructions in Colorado and New Mexico, reconstructions from this study area did not exhibit significant 20th-century changes in the frequency of outbreak occurrence or magnitude of growth reduction. Sharply reduced growth during outbreaks was not clearly visible on the increment core samples, and budworm-induced reductions in tree-ring growth were usually detectable only after comparison with nonhost tree-ring series. This finding emphasizes that defoliation effects on ring growth can be highly relativistic. Hence, caution should be exercised in reconstructing insect outbreak histories based only on visual detection approaches, or without comparison with nonhost or nondefoliated tree-ring control series.

A method for sampling western spruce budworm pupae.

1981 ◽  
Author(s):  
Nilima Srivastava ◽  
Roy C. Beckwith ◽  
Robert W. Campbell ◽  
Torolf R. Torgersen
Keyword(s):  
Spruce Budworm ◽  
Western Spruce Budworm

Chemistry and field evaluation of the sex pheromone of western spruce budworm,Choristoneura occidentalis, Freeman

1982 ◽  
Vol 8 (2) ◽  
pp. 339-350 ◽  
Author(s):  
H. T. Cory ◽  
G. E. Daterman ◽  
G. D. Daves ◽  
L. L. Sower ◽  
R. F. Shepherd ◽  
...  
Keyword(s):  
Sex Pheromone ◽  
Spruce Budworm ◽  
Field Evaluation ◽  
Choristoneura Occidentalis ◽  
Western Spruce Budworm

Baculoviruses in populations of western spruce budworm

2015 ◽  
Vol 127 ◽  
pp. 76-80 ◽  
Author(s):  
V.G. Nealis ◽  
R. Turnquist ◽  
B. Morin ◽  
R.I. Graham ◽  
C.J. Lucarotti
Keyword(s):  
Spruce Budworm ◽  
Western Spruce Budworm

RELATIONSHIPS BETWEEN ATTACK RATES AND SURVIVAL OF WESTERN SPRUCE BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN (LEPIDOPTERA: TORTRICIDAE), AND BUD DEVELOPMENT OF DOUGLAS-FIR, PSEUDOTSUGA MENZIESII (MIRB.) FRANCO

1992 ◽  
Vol 124 (2) ◽  
pp. 347-358 ◽  
Author(s):  
Roy F. Shepherd
Keyword(s):  
Close Association ◽  
Spruce Budworm ◽  
Larval Survival ◽  
Douglas Fir ◽  
Choristoneura Occidentalis ◽  
Western Spruce Budworm ◽  
Bud Development ◽  
Feeding Sites ◽  
Vegetative Buds ◽  
Wide Range

AbstractIndividual larvae of western spruce budworm (Choristoneura occidentalis Freeman) were observed from overwintering emergence to pupation at six locations spread over a wide range of altitudes and thus climate. A weekly census of 100 lower-crown buds per plot indicated large differences in rates of bud development and larval survival among locations.Emerging second-instar larvae attempted to mine swelling buds of Douglas-fir. If the buds were hard and tight, larvae mined 1-year-old needles until penetrable buds were available. Larvae dispersed over the crowns with only one larva becoming established in each bud; thus, many early-emerging and surplus larvae could not find suitable feeding sites and disappeared. Within the protective bud, survival was high. After buds flushed and larvae became exposed, densities dropped, probably due to increased predation and decreased food quality. Correlations indicated a close association between larval survival for the exposed period between bud flush and pupation, and overall larval survival.Douglas-fir trees responded to initial bud removal, but not to needle removal, by inducing latent buds in the axils of needles to grow into active vegetative buds ready to develop and flush the next spring. The number of these new vegetative buds formed was greatest when the initial buds were removed early in the season before flush, and decreased thereafter. Trees with vigorous crowns had the greatest response to defoliation by inducing the largest number of latent buds into becoming active vegetative buds; these were found mainly on the 2- and 3-year-old internodes.

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