Western Spruce Budworm Research Articles

Oviposition Deterrence, Stimulation, and Effect on Clutch Size of Choristoneura (Lepidoptera: Tortricidae) Species by Extract Fractions of Host and Nonhost Foliage

Homogenated ethanol extracts of balsam fir, Abies balsamea (L.) Miller, white spruce, Picea glauca (Moench) Voss, and jack pine, Pinus banksiana Lambert, were fractionated sequentially into 4 solvent fractions (hexane, butanol, postbutanol water, and an ethanol extract of the residue). Their effect on oviposition was evaluated in screen cage arenas containing a mated female and filter paper substrate, half of which was treated with extract and the other half with solvent. Tests were conducted mainly against spruce budworm, Choristoneura fumiferana (Clemens) and jack pine budworm, C. pinus Freeman, but some fractions were also evaluated against western spruce budworm, C. occidentalis Freeman. Oviposition by the spruce budworm and jack pine budworm was stimulated by filter paper substrates treated with hexane fractions and uniformly deterred by substrates treated with the postbutanol water fraction of both host and nonhost extracts. Significant deterrent activity also occurred with some butanol extract fractions of the respective nonhosts of these budworm species. Western spruce budworm was deterred by the postbutanol water fraction of 1 of the white spruce extracts. To the best of our knowledge, these results are the first evidence for a lepidopteran oviposition deterrent from coniferous foliage. Clutch size of the spruce budworm was not affected by any of the active fractions from host and nonhost extracts, but clutch size of the jack pine budworm was significantly increased by the stimulating extract fraction of its host and decreased by the deterrent extract fraction of its host.

Oral exudate as a mediator of behavior in larval eastern and western spruce budworms (Lepidoptera: Tortricidae)

The production of oral exudate by larval eastern and western spruce budworms,Choristoneura fumiferana (Clem.) andChoristoneura occidentalis Free., respectively, was investigated in the laboratory. All larvae except those entering into a molt exhibited aggressive behavior and produced exudate in response to handling or intraspecific encounters. Larvae could be induced to produce exudate up to four times over 2–3 min and produced an average of 1.92±0.04 µl (X ± SE) per induction. Larvae on foliage spent much of their time maintaining their silken feeding tunnel, including spinning and combing silk and removing frass. Exposure to conspecific oral exudate deposited inside the tunnel, or released by agitated larvae inside the tunnel, increased the proportion of larvae that dispersed away from the tunnels and, apparently, increased the larval sensitivity to disturbances. The behavior induced by the oral exudate indicates that it acts as an epideictic (spacing) pheromone.

No Long-Term Impact of Carbaryl Treatment on Western Spruce Budworm Populations and Host Trees in the Malheur National Forest, Oregon

Abstract The effects of a single application of carbaryl on western spruce budworm (Choristoneura occidentalis Freeman) populations on the Malheur National Forest in northeastern Oregon were examined for 7 consecutive years beginning in 1983. Budworm control was evident only in the treatment year, 1983, and the next, 1984. There was little difference in the pattern of budworm population behavior between treated and untreated sites during the 7 yr study. Defoliation of Douglas-fir and true firs was reduced slightly by the carbaryl treatment, but did not translate into increased radial growth. On the contrary, there was a general decline in annual radial increment among host trees in both treated and untreated areas from 1980 to 1987, presumably because of chronic defoliation. For. Sci. 41(4):851-863.

Aerial and Satellite Sensor Detection and Classification of Western Spruce Budworm Defoliation in a Subalpine Forest

RÉSUMÉLa détection et la classification des patrons de défoliation par la tordeuse occidentale de l'épinette (Choristoneura occidentalis, Freeman) dans une forêt subalpine de l'ouest de l'Oregon ont été réalisées à l'aide d'images vidéo acquises à deux altitudes à partir d'un aéronef ultra léger et à l'aide d'images numériques multibandes acquises par le capteur thématique de Landsat.L'analyse de texture des images vidéo a donné lieu à une précision de classification de l'ordre de 78 % en référence avec un relevé de terrain de la défoliation et de l'interception de lumière du couvert forestier effectué sur 21 parcelles en septembre 1994. Les données acquises par le capteur thématique en 1993, à elles seules, ont permis d'obtenir des résultats de classification satisfaisants dans une proportion de 75 % pour quatre classes de dommages (aucun, léger, modéré et sévère) dans ces mêmes parcelles. La précision cartographique était de l'ordre de 67 % d'après les résultats d'une classification (K-moyennes) non dirigée modifiée. À partir d'une série de données diachroniques acquises par le capteur thématique de Landsat, une comparaison a été effectuée entre une structure forestière telle qu'elle apparaissait avant l'épidémie en 1988 et cette structure en état de défiolation à la suite de la chute de la population d'insectes en 1993, ce qui a permis d'atteindre une précision de 86 % dans la discrimination de trois classes de dommages (aucun, léger/modéré, sévère).L'analyse texturale et spectrale combinée des données vidéo peut constituer une méthode complémentaire aux photographies aériennes et aux relevés de terrain classiques pour évaluer le niveau de défoliation ainsi qu'une solution de rechange à la tâche complexe que constitue la sélection des sites d'entraînement pour les classifications effectuées à l'aide d'images satellites.

Assessment of Trichogramma species for biological control of forest lepidopteran defoliators

AbstractIn a laboratory study, we determined the potential of three Trichogramma (Hymenoptera: Trichogrammatidae) species, T. brassicae Bezdenko, T. minutum Riley and T. nr. sibiricum Sorokina, for biological control against six species of forest lepidopteran pests, black army cutworm, hemlock looper, eastern spruce budworm, western spruce budworm, white‐marked tussock moth, and gypsy moth. Females of each parasitoid species were offered eggs from each of the six host species. Parasitization and the effect of the host species on the emerging progeny were examined and recorded. Trichogramma minutum had the broadest host range and successfully parasitized four host species out of the six offered. Trichogramma nr. sibiricum had the narrowest host range and parasitized only two species of hosts. Of the six host species, black army cutworm was the most preferred by all three Trichogramma species; white‐marked tussock moth and gypsy moth were not parasitized by any parasitoids. There was a positive correlation between the size of female offspring and their corresponding egg complement in all three parasitoid species. The developmental time of parasitoids from egg to adult was influenced by both the parasitoid and host species. Our results suggest that T. minutum has the greatest potential for biological control against various forest lepidopteran pests and that the black army cutworm may be the best target candidate for further study.

A dendroecological reconstruction of western spruce budworm outbreaks (Choristoneura occidentalis) in the Front Range, Colorado, from 1720 to 1986

Radial increment cores from Douglas-fir (Pseudotsuga menziesii) and blue spruce (Picea pungens), defoliated by western spruce budworm (Choristoneura occidentalis), were analyzed by means of dendrochronological methods and compared with cores from undefoliated ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta) growing on the same sites in the Front Range, Colorado. Extensive deforestation during the gold and silver booms in the second part of the nineteenth century led to dense and almost pure stands of shadetolerant budworm host species. By using the skeleton plot method, the number of trees with clear growth reductions is obtained, thus representing an exact record of forest insect attacks. The analysis of abrupt growth reductions revealed at least nine outbreaks of western spruce budworm between 1720 and 1986, the majority occurring in the nineteenth century. The outbreaks were graphically compared with periods of attack in New Mexico and Colorado which were detected by other scientists employing tree-ring measurement techniques. No increase in the frequency of severe outbreaks during the twentieth century was observed, yet there is some evidence that the most recent outbreak might be the most severe ever recorded. Open Douglas-fir stands on higher sites were more susceptible to heavy budworm attack than dense stands on lower sites. Blue spruce was less frequently and less severely attacked than Douglas-fir. The spatial pattern of historical outbreaks generally was very patchy.

Toxicity of Bacillus thuringiensis var. kurstaki to Three Nontarget Lepidoptera in Field Studies

Bacillus thuringiensis Berliner val. kurstaki is used extensively in aerial sprays for control of forest defoliators such as gypsy moth, Lymantria dispar (L.), and western spruce budworm, Choristoneura occidentalis Freeman. Although the short half–life of B. thuringiensis in the field is believed to minimize its impact on nontarget Lepidoptera, there is increasing concern over the immediate and long-term effects of the widespread aerial application of this microbial insecticide. We examined the toxicity and persistence of B. thuringiensis toward larvae of tree-feeding swallowtail butterflies ( papilio glaucus L. and p. canadensis Rothschild & Jordan) and the promethea moth, Callosamia promethea (Drury), on seven of their natural host plants. B. thuringiensis applied to trees at a rate of 40 BIU/ha with a backpack sprayer equipped with a rotary atomizer nozzle (Micronair) was toxic to early and later (fourth) instars, regardless of the host the larvae were feeding on. Long–term persistence of B. thuringiensis on potted tulip trees placed in exposed or below–canopy locations was monitored at 0, 10, 20, 30, and 40 d after the spray. Toxicity toward early–instar p. glaucus persisted for up to 30 d in 1992 and 1993 field studies. Survival on trees sprayed with B. thuringiensis tended to be lower in below–canopy locations, but differences were not always significant. The results of these studies indicate that B. thuringiensis sprays are toxic to some nontarget lepidopterans for at least 30 d after the spray.

Natural Variation: A Complicating Factor in Bioassays with Chemical and Microbial Pesticides

Our investigation of responses of Colorado potato beetle, Leptinotarsa decemlineata (Say), to Bacillus thuringiensis subsp. tenebrionis over 83 wk; diamondback moth, Plutella xylostello (L.), to B. thuringiensis subsp. kurstaki (cloned into Pseudomonas florescens ) over 37 wk; and western spruce budworm, Choristoneura occidentalis Freeman, to pyrethrins and DDT over 91 generations indicated that ratios at LC50, LC90, and LC99 varied among pesticides tested on the same species and among insect species tested with the same pesticide. Frequencies with which LCs were significantly different (based on bracketing of the value 1.0 by 95% CI of each ratio) compared with the standard (the lowest LC in the data set) were extremely high (>95%) in all tests except those with pyrethrins on western spruce budworm. For example, toxicity ratios for Colorado potato beetle larvae fed B. thuringiensis subsp. tenebrionis were as high as 12.8 at LC50, 37.0 at LC90, and 155 at LC99 over 83 wk; the maximum upper 95% CL for a ratio were 18.6, 168, and 1,000, respectively, at these LCs. We conclude that the extent of natural variation must be investigated before biologically important changes can be identified with any certainty. The conventional practice of using ratios of one LC to another in studies to detect resistance and other biological changes may lead to erroneous conclusions if natural variation in cohorts of a population and subsequent generations of the same genetic strain are unknown.

Forest Defoliators and Climatic Change: Potential Changes in Spatial Distribution of Outbreaks of Western Spruce Budworm (Lepidoptera: Tortricidae) and Gypsy Moth (Lepidoptera: Lymantriidae)

Changes in geographical ranges and spatial extent of outbreaks of pest species are likely consequences of climatic change. We investigated potential changes in spatial distribution of outbreaks of western spmce budworm, Choristoneura occidentalis Freeman, and gypsy moth, Lynumtria dispar (L.), in Oregon and Pennsylvania, respectively, using maps of historical defoliation, climate, and forest type in a geographic information system. Maps of defoliation frequency at a resolution of 2 × 2 km were assembled from historical aerial survey data. Weather maps for mean monthly temperature maxima and minima and precipitation over 30 yr were developed by interpolation. Relationships between defoliation status and environmental variables were estimated using linear discriminant analysis. Five climatic change scenarios were investigated: an increase of 2°C, a 2°C increase with a small increase and a small decrease in precipitation, and projections of two general circulation models (GCMs) after 100 yr at doubled carbon dioxide. With an increase in temperature alone, the projected defoliated area decreased relative to ambient conditions for budworm and increased slightly for gypsy moth. With an increase in temperature and precipitation, defoliated area increased for both species. Conversely, defoliated area decreased for both when temperature increased and precipitation decreased. Results for the GCM scenarios contrasted sharply. For the other, defoliation by budworm was projected to cover Oregon completely, whereas no defoliation was projected by gypsy moth in Pennsylvania. For the other, defoliation disappeared completely for budworm and slightly exceeded that under ambient conditions for gypsy moth. The results are discussed in terms of current forest composition and its potential changes.

Relationship Between Lower-Crown Sampling and Midcrown Sampling for Choristoneura occidentalis (Lepidoptera: Tortricidae) After Treatment with Bacillus thuringiensis

We found no change in the relation between densities of western spruce budworm, Choristoneura occidentalis Freeman, determined by lower-crown sampling and densities determined by conventional midcrown sampling on host trees in a suppression project with Bacillus thuringiensis Berliner. The relationship was tested on units treated with B. thuringiensis and on untreated units. We present an equation that provides an improved means to predict midcrown densities based on lower-crown population estimates. Analysis of larval densities before treatment and densities 1 yr after treatment broadens application of the equation to include the full range of fourth to final instars for natural, untreated budworm populations, as well as for sampling before treatment and sampling after treatment with B. thuringiensis .

Role of Douglas fir (Pseudotsuga menziesii) carbohydrates in resistance to budworm (Choristoneura occidentalis)

The current year's growth of Douglas fir contains galactose, unusual in that this carbohydrate makes up 78.7% of the total carbohydrate fraction. An agar diet study was undertaken to determine the effects of galactose, other carbohydrates, and terpenes on western spruce budworm larval mortality, growth rate, and adult biomas production. All concentrations of the carbohydrates and terpenes tested, as well as other mineral elements not tested, were typical of the current year's foliage of Douglas fir. In experiment I, the diet containing 5.61% total carbohydrate did not significantly affect larval mortality when compared to the control diet. However, diets containing 9.45% and 15% total carbohydrate concentrations significantly increased larval mortality 64% and 96.1%, respectively, when compared to the control. Also in experiment I, terpenes alone (78.9% morality) and terpenes in combination with 9.45% and 15% total carbohydrates significantly increased larval mortality (97.2% and 100%, respectively) when compared to mortality on the control diet (44%). To determine which carbohydrate was causing the adverse effect, 6% glucose, 6% fructose, and 6% galactose were placed individually and in combination with terpenes in diets in experiment II. The 6% galactose diet significantly increased larval mortality and reduced growth rate when compared to the control, glucose, and fructose diets. Glucose resulted in 16% less larval mortality, significantly enhanced female larval growth rate and pupal weight, but did not affect male larval growth rate and pupal weight, when compared to the control. Fructose resulted in a significant decrease in larval mortality and a general trend of enhanced female and male larval growth rate and pupal weight. Larval mortality on terpenes alone was not significantly different from the control, but terpenes with 6% galactose increased larval mortality and decreased female and male growth rate and pupal weight significantly when compared to glucose-terpene and fructose-terpene diets. No significant interactions were found between carbohydrates and terpenes in either experiment.

Multi-century regional western spruce budworm outbreak patterns

Multi-century regional western spruce budworm outbreak patterns

Multicentury, Regional‐Scale Patterns of Western Spruce Budworm Outbreaks

Tree ring chronologies from 24 mixed—conifer stands were used to reconstruct the long—term history of western spruce budworm (Choristoneura occidentalis) in northern New Mexico. Temporal and spatial patterns of budworm infestations (within—stand occurrences) and outbreaks (more—or—less synchronous infestations across many stands) were investigated to identify local—scale to regional—scale forest disturbance patterns. Nine regional—scale outbreaks were identified from 1690 to 1989. One ancient stand of Douglas—fir trees (Pseudotsuga menziesii) exceeding 700 yr in age revealed that budworms and overstory trees can coexist for extraordinary lengths of time. Using spectral analysis we found that the regional outbreak record contained important cyclical components with periods varying from ≈20 to 33 yr. The statistically significant (P < .05) but variable periodicity of regional outbreaks suggests the forest—budworm dynamic is pseudoperiodic (i.e., a stable limit cycle or damped oscillator perturbed by noise). Duration of infestations within stands was ≈11 yr and has not obviously changed in the 20th century; however, infestations tended to be more synchronous among stands in this century than during earlier centuries. Regional budworm activity was low from the mid—1920s to late 1930s and mid—1960s to late 1970s, and the most recent outbreak, beginning in the late 1970s, was unusually severe. These results, and contrasting infestation patterns in mountain ranges with different land use histories, generally support a hypothesis that human—induced changes in Southwestern forests have led to more widespread and intense budworm outbreaks in the late 20th century. Despite human—induced changes in the 20th century, climate variation also appears to have been important to budworm regimes in this century as well as in earlier times. Regional outbreaks in the 20th century tended to occur during years of increased spring precipitation, and decreased budworm activity coincided with decreased spring precipitation. No clear association with temperature was identified. Comparisons of regional outbreak history since AD 1600 with a reconstruction of spring precipitation from limber pine (Pinus flexilis) ring width chronologies also shows that periods of increased and decreased budworm activity coincided with wetter and drier periods, respectively. This finding contrasts with results from shorter time—scale studies conducted in northwestern U.S. and Canada (western spruce budworm) and eastern Canada (spruce budworm C. fumiferana), where low precipitation and/or warmer temperatures were generally associated with outbreaks. Different patterns of budworm population response to changing moisture regimes might be due to differences in regional forest—budworm systems, or to differences in the spatial and temporal scales of observation. We conclude that changes in forest structure in the southwestern U.S. may have shifted the spatial and temporal pattern of budworm outbreaks. The dynamic behavior and statistically significant association between multicentury, regional budworm and climate time series also suggest that complex budworm dynamics are driven by a combination of internal and external factors.

Influence of Dwarf Mistletoe and Western Spruce Budworm on Growth and Mortality of Douglas-Fir in Unmanaged Stands

Abstract Permanent inventory plots in 94 unmanaged stands of primarily Douglas-fir (Pseudotsuga menziesii) on three national forests in Oregon and Washington were examined for growth suppression caused by dwarf mistletoe (Arceuthobium douglasii) and western spruce budworm (Choristoneura occidentalis). Ten-year increments of diameter and basal area were calculated from measurements in 1977-1987. Severity of dwarf mistletoe was scored using the six-class system. Severity and duration of defoliation were determined from aerial maps drawn over a 20-yr period. Dwarf mistletoe significantly decreased 10-yr diameter increment. Western spruce budworm significantly reduced diameter increment and basal area increment. No significant interactions between defoliation and dwarf mistletoe were found. Ten-year mortality of Douglas-fir due to dwarf mistletoe averaged 5% and 2% of the infected trees and basal area, respectively, for stands with moderate dwarf mistletoe severity and 4% and 3% of the infected trees and basal area, respectively, for stands with severe dwarf mistletoe infestation. Mortality was highest in stands with the most dwarf mistletoe and in stands with the most severe defoliation. There were no significant differences in diameters of dead trees among severity classes for dwarf mistletoe. Dead-tree diameters were significantly smaller in stands with the most severe defoliation during the measurement period. For. Sci. 39(3):465-477.

Patterns of Occurrence and New Sampling Implications for Instar IV Western Spruce Budworm (Lepidoptera: Tortricidae)

Abstract This study examines relations of western spruce budworm (Choristoneura occidentalis Free.) larval distribution on terminal tips, whole branches, among crown strata (vertical crown thirds), and within and among whole trees. Study sites were in Washington, Oregon, Idaho, Montana, and New Mexico and represented 63 plot-yr of data. A range of densities from <1.0 to >600 larvae per m² of foliage on midcrown terminal tips were observed. We validated and expanded on earlier published descriptions of intratree and intertree distribution of larvae as they influenced sampling schemes. Larval density on nominal 45 cm terminal tips in the lower crown-third were slightly better predictors of whole-tree density than were midcrown tips. Therefore, we propose the use of a two-tip sample from the middle of the lower crown-third of each sample tree. Equations are given to determine the number of trees to sample for desired precisions and confidence levels. We provide equations describing relations between larval densities on branch tips and whole branches in vertical crown-thirds, and their relation to whole-tree density. For. Sci. 39(3):573-593.

Bacillus thuringiensis var. kurstaki Affects a Beneficial Insect, the Cinnabar Moth (Lepidoptera: Arctiidae)

The microbial insecticide Bacillus thuringiensis Berliner var. kurstaki is used to control forest pests in regions where tansy ragwort, Senecio jacobaea L., occurs. Biological control of this noxious weed may be compromised if the cinnabar moth, Tyria jacobaeae (L.), is susceptible to B. thuringiensis . In laboratory feeding tests, we found that foliage dipped in B. thuringiensis solutions had very little effect on survival of first, second, and third instars, but fourth and fifth instars were susceptible; LC50s were 0.31 and 0.22 mg formulation per ml (Dipel-hg; potency 4,320 IU/mg), respectively. Field tests were done to test the effect of B. thuringiensis on larval defoliation of potted tansy ragwort plants at five different application rates. The application rate significantly affected percentage of leaves defoliated and mean number of cinnabar moth-days per plant. In both control plants and those treated with B. thuringiensis , defoliation by cinnabar moth did not affect plant biomass within the IQ-d course of’ the experiment. Results of the laboratory and field experiments suggest that the pesticide could interfere with the biological control of tansy ragwort if applied to areas where the weed occurs and when late-instar cinnabar moths are active. However, most applications for western spruce budworm, Choristoneura occidentalis Freeman, and gypsy moth, Lymantria dispar (L.), occur when only early instars of cinnabar moth are present.

Stand response to western spruce budworm and Douglas-fir bark beetle outbreaks, Colorado Front Range

The montane forests (i.e., below ca. 2900 m) of the Colorado Front Range have experienced repeated outbreaks of western spruce budworm (Choristoneuraoccidentalis Free.) and Douglas-fir bark beetle (Dendroctonuspseudotsugae Hopk.), both of which locally attack Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco). In this study we examine the effects of historically documented outbreaks of these insects on succession, stand structure, and radial growth of host and nonhost species in Rocky Mountain National Park. The most recent budworm (1974–1985) and bark beetle (1984–present) outbreaks resulted in the most severe and widespread disturbance of these forests since the late 1800s. Stand response to these outbreaks is primarily a function of stand structure and age characteristics of Douglas-fir prior to an outbreak. Young, vigorous postfire stands show minimal budworm defoliation, and in these stands only remnant trees from the prefire generation appear susceptible to beetle-caused mortality. Dense stands exhibit higher budworm-induced mortality, which hastens the natural thinning process and shifts dominance towards the nonhost species. The stands most severely disturbed by the combined insect agents are multistoried stands with high host densities and a wide range of stem sizes. The stand response to these disturbances include the growth release of shade-intolerant, seral species, and in some cases, a higher survivorship among midsized individuals of the host Douglas-fir. The net result of the combined insect outbreaks is the temporary slowing of the successional trend towards a steady-state Douglas-fir forest. Fire suppression, by increasing the density of suppressed Douglas-fir, has previously been shown to favor increased outbreak severity of western spruce budworm in the northern Rockies. However, in the Front Range, recent increases in outbreak severity and their synchroneity may also be the result of large areas of forest, burned during the late 19th century during European settlement, simultaneously entering structural stages susceptible to insect outbreak.

Defining the Western Spruce Budworm's Nutritional Niche With Response Surface Methodology

A response surface design was used to help define the "nutritional niche" of the western spruce budworm, Choristoneura occidentalis. We evaluated how calcium, magnesium, and phosphorus interacted to influence budworm fitness on artificial diets containing five different levels of the minerals. We quantified survival rates for several life stages using a three—generation bioassay. Data from the bioassay were used to estimate population growth over three complete generations. Performance of the budworm was affected by Mg (linear response for F1 generations; 0.83—1.95 mg/g tested) and P (quadratic response for P1 [parental] and F1 generations; 2.74—4.95 mg/g tested) but was largely unaffected by Ca (0.50—6.81 mg/g tested). Overall, the results suggested budworm performance is best when Mg is at low concentrations and P is at moderate concentrations, and that very high levels of Mg and P are detrimental to the budworm. On average, host trees had too much Mg and too little P for optimal response by budworms. Interactions between Mg and P imply that balances or ratios of minerals are important in budworm nutritional ecology. However, detectable effects from Mg, P, and Ca in the diets diminished as the bioassay continued into the F2 generation, and, consequently, the estimated number of larvae alive at the beginning of the F2 and F3 generations showed no relationship to concentrations of the test minerals. This result probably reflected: (1) the loss of some design points in the second and third generations of the biomass because larvae did not survive on diets that were markedly suboptimal and (2) increased variability in the population growth response as the experiment contributed into the F2 and F3 generations.

Douglas-Fir Needle Anatomy in Relation to Western Spruce Budworm (Lepidoptera: Tortricidae) Herbivory

We compared 23 anatomical characteristics of current-year needles from five pairs of Douglas-fir, Pseudotsuga menziesii var. glauca (Beissner) Franco, trees that were either phenotypically resistant or susceptible to western spruce budworm, Choristoneura occidentalis Freeman, defoliation. The trees were mature (44-101 yr old) and were paired by size and microsite. Repeated-measures analysis of variance indicated needles from resistant trees were Significantly longer, had thinner epidermal layers, and had proportionately more transfusion and less mesophyll tissue than needles from susceptible trees. There was no evidence that needle toughness or resin canal size was associated with resistance to budworm herbivory. It appears unlikely that anatomical features of the needles affect resistance to the budworm. The observed differences in needle anatomy may have resulted from stresses associated with repeated defoliation of the trees that were susceptible for reasons other than their anatomy.

A method to calculate the losses caused by western spruce budworm in uneven-aged Douglas fir forests of British Columbia

A system was designed for projecting the growth of uneven-aged stands of interior Douglas fir ( Pseudotsuga menziesii var. glauca (Beissn.) Franco) of the Kamloops Region of British Columbia after defoliation by the western spruce budworm ( Choristoneura occidentalis (Freeman)). The system reads forest inventory files and simulates infestations of varying severity and duration. The system produces the losses in total stand volume (all trees with a diameter larger than 2.5 cm) and in volume of the harvestable trees (all trees with a diameter larger than 30 cm) for every 10 year interval. In a trial consisting of a 20 year projection on 32 stands, assuming a 7 year infestation in the first decade, the system calculated that at the end of the projection, losses in total volume per hectare averaged 6.2%, 23.3% and 32.8% of the total stand volume, for light, moderate and severe infestations, respectively. Reduction in the 20 year periodic annual increment of the total volume averaged 7.1, 39.3 and 51.6%, for light, moderate, and severe infestations. Losses resulting from infestations lasting 1–9 years are also reported.