Biology of North American spruce budworms

Comparative ecology of conifer-feeding spruce budworms (Lepidoptera: Tortricidae)

Article

May 2015

Vince Nealis

The comparative ecology of conifer-feeding budworms in the genus Choristoneura Lederer (Lepidoptera: Tortricidae) in Canada is reviewed with emphasis on publications since 1980. Systematics and life history are updated and historical outbreak patterns and their current interpretation summarised. Recent evidence is analysed in the context of ecological interactions among three trophic levels; host plant, budworm herbivore, and natural enemies. The influence of weather and climate are viewed as modulating factors. The population behaviour of budworms is interpreted as the result of tri-trophic interactions that vary at different scales. The result of these multi-scale interactions is that despite shared phylogenetic constraints and common adaptations, different budworm species display different population behaviour because of specific ecological relationships with their respective hosts and natural enemies.

Behaviors of Western Spruce Budworm Moths (Choristoneura occidentalis) as Defences Against Bat Predation

Article

Oct 2006

We investigated potential defense behaviors of adult western spruce budworm (Choristoneura occidentalis), a non-auditive lepidopteran, against bat predation. Although western spruce budworm moths started to fly before sunset, earlier than many species of moths, temporal isolation of flying moths from foraging bats was incomplete as moths were most active after sunset once bats were foraging. Flying C. occidentalis were most active close to their host trees, and thus were isolated from some bat activity because vegetation limits foraging by some bats. Moths mostly flew near the tops of trees, an area that may have a high predation pressure from bats. Resting western spruce budworm spent little time fluttering their wings or crawling, behaviors that are used as cues by gleaning bats. The outbreak nature of this species, in which large numbers of moths are active at one time, may allow dilution effects to reduce predation risk.

Defining the window of opportunity for feeding initiation by second instar spruce budworm larvae

Article

Full-text available

Sep 2017

Establishing feeding sites is critical for the survival of neonate Lepidoptera larvae. Rapid foliar quality changes during leaf expansion create a narrow window of opportunity for establishment of early-spring feeders. We examined the effect of phenological synchrony between black spruce (Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) Mill.)) budbreak and spruce budworm (Choristoneura fumiferana (Clemens)) emergence on the feeding behaviour of young larvae and on overall larval growth and survival under laboratory conditions. We correlated these variables with bud development and foliar toughness during the growing season. Our results show that early-emerging second instar larvae were unable to feed on either black spruce or balsam fir buds; budworm on balsam fir mined old foliage and exhibited good survival and performance, but those on black spruce remained on the foliar surface and suffered high mortality and low growth. In the second later-emerging cohort, bud feeding gradually increased on black spruce whereas it was already the predominant behaviour on balsam fir, and no differences in performance were observed between host species. Thus, black spruce budbreak constitutes a strict window of opportunity, since larvae are often unable to mine the old foliage. Our results suggest that mechanical toughness could be the obstacle preventing young larvae from mining old black spruce needles. Our findings confirm the importance of second instar ecology in spruce budworm, suggesting that, if climate warming eventually results in an improvement in phenological synchrony between spruce budworm and black spruce, larval survival may increase.

Effects of tree age and stand thinning related variations in balsam fir secondary compounds on spruce budworm Choristoneura fumiferana development, growth and food utilization

Article

May 2011

• The effect of tannins and monoterpenes on the development, mortality and food utilization of spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) was investigated under laboratory conditions using an artificial diet. Tannins were extracted from balsam fir foliage of thinned and unthinned stands to reproduce stand thinning related variations in tannins. A mixture of synthetic monoterpenes was utilized to simulate the concentration found in young and old balsam fir trees. • Longer development time and lower pupal weight were observed for insects fed on diets with a lower nitrogen concentration and a higher tannin concentration (unthinned treatment). Tannins induced higher insect mortality at a low nitrogen concentration compared with the diet with a higher nitrogen concentration. • Approximate digestibility was higher for larvae fed on diets with high concentrations of nitrogen at both low and high concentrations of tannins. Efficiency of conversion of digested food (ECD) decreased with an increase in tannin concentration. Tannins reduced both the relative consumption and growth rate (RCR and RGR). • Monoterpenes increased spruce budworm mortality and this mortality reached almost 50% under concentrations of monoterpene typical of the young trees compared with 20% under monoterpene concentrations found in old trees. • A higher digestibility was observed for larvae fed on diet with a higher concentration of monoterpenes, whereas efficiency of conversion of ingested food (ECI), ECD, RCR, and RGR decreased with an increase in monoterpenes in the diet. • The results obtained in the present study are consistent with the defensive role of secondary compounds such as tannins and monoterpenes in the spruce budworm–balsam fir system.

Life-History Consequences of Chronic Nutritional Stress in an Outbreaking Insect Defoliator

Article

Full-text available

Feb 2014
PLOS ONE

Food shortage is a common situation in nature but little is known about the strategies animals use to overcome it. This lack of knowledge is especially true for outbreaking insects, which commonly experience nutritional stress for several successive generations when they reach high population densities. The aim of this study is to evaluate the life history consequences of chronic nutritional stress in the outbreaking moth Choristoneura fumiferana. Larvae were reared on two different artificial diets that emulate nutritional conditions larvae face during their natural population density cycle (low and medium quality artificial diets). After four generations, a subset of larvae was fed on the same diet as their parents, and another on the opposite diet. We explored larval life-history strategies to cope with nutritional stress, its associated costs and the influence of nutritional conditions experienced in the parental generation. We found no evidence of nutritional stress in the parental generation increasing offspring ability to feed on low quality diet, but the contrary: compared to offspring from parents that were fed a medium quality diet, larvae from parents fed a low quality diet had increased mortality, reduced growth rate and reduced female reproductive output. Our results support a simple stress hypothesis because the negative effects of malnutrition accumulated over successive generations. Density-dependent deterioration in plant quality is thought to be an important factor governing the population dynamics of outbreaking insects and we hypothesize that chronic nutritional stress can be a driver of outbreak declines of C. fumiferana, and of forest insects in general.

Spruce budworm outbreaks and the incidence of vagrancy in eastern North American wood-warblers

Article

Full-text available

Feb 2011

The Tennessee (Vermivora peregrina), Cape May (Dendroica tigrina), Bay-breasted (D. castanea), and Canada (Wilsonia canadensis) warblers and the Ovenbird (Seiurus aurocapillus) appear to show positive numerical responses to outbreaks of the spruce budworm (Choristoneura fumiferana); the Magnolia (D. magnolia), Black-throated Green (D. virens), and Blackburnian (D. fusca) warblers may occur in lower numbers during outbreaks because of increased competition with these budworm specialists. Thus, we predicted that the number of fall vagrant Tennessee, Cape May, and Bay-breasted warblers and Ovenbirds occurring in California are highly positively associated with budworm population density, positively intercorrelated, and negatively associated with numbers of Magnolia, Black-throated Green, and Blackburnian warblers. A 23-year (1972-1994) data set of budworm population densities and vagrant warbler occurrences in California showed that (i) budworm population density was an excellent predictor (explaining about 50% of the variance) of numbers of occurrences of the Cape May, Bay-breasted, and Canada warblers; (ii) all warbler species tended to co-occur, with numbers of Cape May and Bay-breasted warblers especially highly intercorrelated; and (iii) Magnolia Warbler numbers were negatively associated with those of budworm specialists, but Black-throated Green and Blackburnian warblers showed no association.

Risk of dispersal in western spruce budworm

Article

Dec 2008
AGR FOREST ENTOMOL

1 Western spruce budworm Choristoneura occidentalis Free. larvae emerge in the spring before buds have expanded and spend a variable period of time foraging on branches and mining needles. 2 Losses of dispersing budworms during this needle-mining period are related directly to the severity of defoliation in previous years and inversely related to foliage biomass in the study plot and to temperature and rainfall during the needle-mining period. 3 Losses can be interpreted in terms of risk of dispersal, which is the product of the propensity of early-stage budworms to disperse in search of resources and the consequences of this behaviour for survival under variable ecological conditions. 4 A comparison of the species-specific nature of risk of dispersal in three conifer-feeding budworm systems of North America may elucidate the common nature but variable features of their respective population dynamics.

Diapause disruption with tebufenozide for early-instar control of the spruce budworm, Choristoneura fumiferana

Article

Full-text available

Aug 2007

In North America, the eastern spruce budworm, Choristoneura fumiferana Clem., is an important coniferous pest against which tebufenozide has proven effective as a control product. By acting as an ecdysone agonist, tebufenozide can induce precocious moulting in late (fifth-sixth) instars but can also be carried over to the next generation owing to its persistence on foliage. The authors conducted laboratory experiments on first-instar larvae treated with tebufenozide dissolved in acetone. Larvae exposed to doses equal to or above 0.1 microg cm(-2) displayed precocious moulting in the second instar after hibernaculum spinning, which effectively disrupted diapause. Larger doses induced moulting in first instars. Evidence is provided that this dose-response difference is related to whether or not an effective dose of tebufenozide is ingested by the first instar prior to the peak of moulting hormone (20-hydroxyecdysone) in first instars. Doses ineffective to kill first instars are carried over to the second instar, where they induce a precocious moult. This type of response to tebufenozide is dependent on the presence of a moulting machinery (the EcR-USP receptor complex) that is ready for ecdysone transduction. Interestingly, ecdysone levels are low in second instars, as measured by a radioimmunoassay, which suggests that diapause in spruce budworm is maintained by a suppression of ecdysone production. Thus, diapause disruption by tebufenozide may well provide an alternative control strategy for this important pest.

Complementary roles of two classes of defense chemicals in white spruce against spruce budworm

Article

Full-text available

Mar 2024
PLANTA

Main conclusion Monoterpenes and phenolics play distinct roles in defending white spruce trees from insect defoliators. Monoterpenes contribute to the toxicity of the foliage, deterring herbivory, whereas phenolics impede budworm growth. This study demonstrates the complex interplay between monoterpenes and phenolics and their collective influence on the defense strategy of white spruce trees against a common insect defoliator. Abstract Long-lived coniferous trees display considerable variations in their defensive chemistry. The impact of these defense phenotype variations on insect herbivores of the same species remains to be thoroughly studied, mainly due to challenges in replicating the comprehensive defense profiles of trees under controlled conditions. This study methodically examined the defensive properties of foliar monoterpenes and phenolics across 80 distinct white spruce families. These families were subsequently grouped into two chemotypes based on their foliar monoterpene concentrations. To understand the separate and combined effects of these classes on tree defenses to the eastern spruce budworm, we conducted feeding experiments using actual defense profiles from representative families. Specifically, we assessed budworm response when exposed to substrates amended with phenolics alone or monoterpenes. Our findings indicate that the ratios and amounts of monoterpenes and phenolics present in the white spruce foliage influence the survival of spruce budworms. Phenotypes associated with complete larval mortality exhibited elevated ratios (ranging from 0.4 to 0.6) and concentrations (ranging from 1143 to 1796 ng mg⁻¹) of monoterpenes. Conversely, families characterized by higher phenolic ratios (ranging from 0.62 to 0.77) and lower monoterpene concentrations (ranging from 419 to 985 ng mg⁻¹) were less lethal to the spruce budworm. Both classes of defense compounds contribute significantly to the overall defensive capabilities of white spruce trees. Monoterpenes appear critical in determining the general toxicity of foliage, while phenolics play a role in slowing budworm development, thereby underscoring their collective importance in white spruce defenses.

Physics of Ice Nucleation and Antinucleation: Action of Antifreeze Proteins and Ice Nucleators

Preprint

Full-text available

Sep 2023

Ice-binding proteins are crucial for adaptation of various organisms to low temperatures. Some of these, called antifreeze proteins, are usually thought to inhibit growth and/or recrystallization of ice crystals. However, prior to these events, ice must somehow appear in the organism, either coming from outside or forming inside through the nucleation process. Unlike most other works, our paper is focused on ice nucleation rather than the behavior of the already existing ice. The nucleation kinetics is studied both theoretically, with special attention paid to ice nucleation on ice-binding surfaces, and experimentally. For experimental studies, we use the ice-binding protein mIBP83, a previously constructed mutant of a spruce budworm Choristoneura fumiferana antifreeze protein. We show that mIBP83 does not affect the ice nucleation temperature in the buffer in test tubes, but hinders the impact of potent ice nucleators of various chemical natures, namely CuO powder and ice-nucleating bacteria Pseudomonas syringae. Additional experiments on human cells show that mIBP83 is concentrated in some regions, but only in cooled cells. Thus, the antifreeze protein not only binds to ice, but also blocks various sites that act or can act as ice nucleators. Such ice-preventing binding may be the crucial biological task of antifreeze proteins.

Plasticity of cold hardiness in the eastern spruce budworm, Choristoneura fumiferana

Article

Jun 2021
COMP BIOCHEM PHYS A

High latitude insect populations must cope with extreme conditions, particularly low temperatures. Insects use a variety of cold hardiness mechanisms to withstand this temperature stress, and these can drive geographic distributions through overwintering mortality. The degree of cold hardiness can be altered by two evolved responses: phenotypic plasticity and local adaptation. Phenotypic plasticity can occur within or between generations (transgenerational plasticity; TGP), and local adaptation can evolve through directional selection in response to regional climatic differences. We used the eastern spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae) as a model to explore the role that variable winter temperatures play in inducing two aspects of plasticity in cold hardiness: TGP and local adaptation in phenotypic plasticity. This species is one of the most destructive boreal forest pests in North America, therefore accurately predicting overwintering survival is essential for effective management. While we found no evidence of TGP in cold hardiness, there was a long term fitness cost to larvae that experienced repeated cold exposures. We also found evidence of local adaptation in both seasonal and short-term plasticity of cold hardiness, as our more northerly populations that would experience lower overwintering temperatures had more plastic responses to cold exposure. These findings provide evidence for the importance of phenotypic plasticity and local adaptation when modelling species distributions.

Plasticity of cold hardiness in the eastern spruce budworm, Choristoneura fumiferana

Preprint

Full-text available

Apr 2021

High latitude insect populations must cope with extreme conditions, particularly cold temperatures. Insects use a variety of cold hardiness mechanisms to withstand this temperature stress, and these can drive geographic distributions through overwintering mortality. The degree of cold hardiness can be altered by two evolved responses: phenotypic plasticity and local adaptation. Phenotypic plasticity can occur within or between generations (transgenerational plasticity; TGP), and local adaptation can evolve through directional selection in response to regional climatic differences. We used the eastern spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae) as a model to explore the role that variable winter temperatures play in inducing two aspects of plasticity in cold hardiness: TGP and local adaptation in phenotypic plasticity. This species is one of the most destructive boreal forest pests in North America, therefore accurately predicting overwintering survival is essential for effective management. While we found no evidence of TGP in cold hardiness, there was a long-term fitness cost to larvae that experienced repeated cold exposures. We also found evidence of local adaptation in both seasonal and short-term plasticity of cold hardiness. These findings provide evidence for the importance of phenotypic plasticity and local adaptation when modelling species distributions.

Comparing the efficacy of various aerial spraying scenarios using Bacillus thuringiensis to protect trees from spruce budworm defoliation

Article

Full-text available

Oct 2018
FOREST ECOL MANAG

Large-scale aerial spray operations against the spruce budworm (Choristoneura fumiferana (Clemens)) (SBW) with the biological insecticide Bacillus thuringiensis ssp. kurstaki (Btk) aim at maintaining trees alive during outbreaks. This objective is thought to be achieved when ≥ 50% of current-year foliage is preserved until the end of the outbreak. This protection target is associated with low balsam fir (Abies balsamea [L.] Mill.) mortality. However, it is unknown whether this approach is always needed or whether less frequent interventions could provide similar results at a lower cost. Between 2010 and 2016, we conducted field experiments in Quebec’s Côte-Nord region to determine the efficacy of five different Btk spraying scenarios for protecting balsam fir, white spruce (Picea glauca [Moench] Voss) and black spruce (P. mariana [Mill.] BSP) in mixed stands. We used the residual photosynthetic capacity (RPC) to evaluate the efficacy of the five scenarios. RPC makes it possible to take into account the impact of SBW defoliation on foliage contribution to tree photosynthetic effort over several years, and can be used as a proxy of the risk of tree mortality. We hypothesized that less frequent Btk applications could maintain the required RPC level to keep trees alive. Our results show that areas not protected resulted in great losses of RPC in balsam fir and white spruce. Btk applications every 3 years kept RPC above 50% for 2 years in balsam fir and 4 years in white spruce. RPC losses were above 62% after 4 years in both species. The strategy currently employed in Quebec (spraying every year after a first year of moderate-severe defoliation) and the intensive protection scenario (Btk applications every year) meet the protection goals for these hosts. However, their cost prevents their application at a large scale. Btk applications every 2 years seems a relevant alternative to the current strategy to protect balsam fir and white spruce stands given the adequate level of protection provided (RPC above 39%) and the reduction in the number of Btk applications required (36% fewer applications over 7 years, resulting in 36% lower cost), particularly if the objective is to maintain trees alive. Black spruce maintained at least 54% of its RPC, even without protection. Btk applications every 3 years might be a valid alternative to reduce growth losses in black spruce-dominated stands. The use of different spraying scenarios may allow us to develop cost-efficient treatment strategies to protect Quebec’s forests.

Association genetics of acetophenone defence against spruce budworm in mature white spruce

Article

Full-text available

Oct 2018
BMC PLANT BIOL

Background Outbreaks of spruce budworm (SBW, Choristoneura fumiferana Clem.) cause major recurrent damage in boreal conifers such as white spruce (Picea glauca [Moench] Voss) and large losses of forest biomass in North America. Although defensive phenolic compounds have recently been linked to chemical resistance against SBW, their genetic basis remains poorly understood in forest trees, especially in conifers. Here, we used diverse association genetics approaches to discover genes and their variants that may control the accumulation of acetophenones, and dissect the genetic architecture of these defence compounds against SBW in white spruce mature trees. Results Out of 4747 single nucleotide polymorphisms (SNPs) from 2312 genes genotyped in a population of 211 unrelated individuals, genetic association analyses identified 35 SNPs in 33 different genes that were significantly associated with the defence traits by using single-locus, multi-locus and multi-trait approaches. The multi-locus approach was particularly effective at detecting SNP–trait associations that explained a large fraction of the phenotypic variance (from 20 to 43%). Significant genes were regulatory including the NAC transcription factor, or they were involved in carbohydrate metabolism, falling into the binding, catalytic or transporter activity functional classes. Most of them were highly expressed in foliage. Weak positive phenotypic correlations were observed between defence and growth traits, indicating little or no evidence of defence-growth trade-offs. Conclusions This study provides new insights on the genetic architecture of tree defence traits, contributing to our understanding of the physiology of resistance mechanisms to biotic factors and providing a basis for the genetic improvement of the constitutive defence of white spruce against SBW.

Why western spruce budworms travel so far for the winter: Travelling spruce budworms

Article

Jul 2016

1. Conifer‐feeding budworms ( C horistoneura ) hibernate in sheltered locations on their host trees from late summer of 1 year to spring of the next. During this period, they do not feed but rely on sustenance provided in the egg. Overwinter survival is dependent on the rate of consumption of these limited reserves. 2. A process model was developed that quantifies the relationship between the rate of consumption and survival at variable temperatures and exposure times for western spruce budworm. The model supported physiological evidence that warm weather conditions early in the diapause period have a dominant influence on overwinter survival. Output compared favourably with field observations of poorer budworm survival at lower elevations where late‐summer and autumn temperatures were warmer compared to those overwintering at cooler, higher elevations. 3. Field experiments demonstrated these weather‐dependent rates of survival were modulated significantly by the degree of shelter experienced by hibernating budworms. 4. Dissection of whole trees harbouring overwintering western spruce budworms showed a significant portion of the population had travelled a considerable distance from the periphery of the tree canopy where eggs were laid to overwinter successfully on the tree bole where sheltered niches are common. 5. Thus, budworms will travel relatively long distances and risk increased mortality during this dispersal to find adequate shelter to overwinter.

Forecasting the response to climate change of the major biotic disturbance regime in Ontario’s forests: the spruce budworm

Technical Report

Full-text available

Jan 2008

Forecasting the response of spruce budworm defoliation to climate change in Ontario

Article

Full-text available

Sep 2011

Jean-Noel Candau

Predicting the effect of climate change on insect populations is critical to improve the reliability of forest management plans, wood supply projections, and pest protection programs. In this study, we use an empirical model to relate the spatial distribution of past defoliation by spruce budworm (Choristoneura fumiferana Clem.) in Ontario to bioclimatic variables. We then apply data from six climate change scenarios to this model to project potential changes in the distribution of defoliation for 2011–2040. The spatial distribution of historical defoliation was found to be related to winter maximum and minimum temperatures, forest content in balsam fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss), and spring and summer minimum temperatures. All six climate change scenarios project broadly similar changes in the spatial patterns of defoliation: (i) an extension of the northern limit of defoliation as far as available data go or close to it, (ii) a decrease in the frequency of defoliation in the center of the historical defoliation belt, and (iii) a persistence of the southern limit of defoliation. This leads to a projected increase of the total area defoliated of between 22.8% and 25.5%, while the mean frequency of defoliation, calculated over the whole study area, would slightly increase (+1%) or decrease (–17.7% to –2.9%).

BIO-ECOLOGY OF PSYLLIDS ON EUCALYPTUS: Biological and Ecological Aspects of Cardiaspina (Hemiptera:Psyllidae)

Book

Jun 2011

Nismah Nukmal

Psyllids resemble miniature cicadas and are sometimes called jumping plant lice. Most species have to be considered as pest of agriculture and forests because they feed on plant juices (phloem sup). Considerable attention has been given to the ecology of Australian tree-dwelling psyllids, particularly the genus Cardiaspina (Hemiptera: Psyllidae). Cardiaspina is one of the most important genera of the Australian Psyllidae, owing to the spectacular damage it can cause to Eucalyptus spp in Eucalypt forests of Australia. The population two species of Cardiaspina (C. albitextura and C. retator) reported increase from time to time. The basic knowledge of those pests (biological and ecological) should be known before controling the pest. This book therefore, provides a new information about biology of the pests such as: oviposition, development, phylogenetic, and ecological aspects that influence their life, should be especially useful for success controlong those pest in order to save particularly forests and generally agriculture products.

Pollen cone production in jack pine: Spatial and temporal patterns subject to natural disturbance by the jack pine budworm

Article

Full-text available

Mar 2014
CAN J FOREST RES

Patterns of jack pine (Pinus banksiana Lambert) pollen cone production are of interest because they may help explain jack pine budworm (Choristoneura pinus pinus Freeman) outbreak patterns. We used generalized linear mixed models to analyze pollen cone production in 180 permanent plots in Ontario, Canada between 1992 and 2008. Pollen cone production increased with stand age, and large trees in sparsely-populated stands produced more pollen cones. Defoliation decreased the propensity of trees to produce pollen cones for at least two years. We also identified important patterns that are not explained by defoliation and stand characteristics. Pollen cone production is spatially synchronized among years, trees in central Ontario produced more pollen cones than trees in northwestern Ontario, and background cone production increased over time in the central region but not in more northwestern plots. Synchronized reproduction is common among tree species, but has not previously been noted for jack pine pollen cones. Increasing cone production in central Ontario may be evidence of changing forest and (or) climatic conditions and deserves further investigation. Our model can be used to quantitatively predict pollen cone production and assess the risk of jack pine budworm defoliation.

Spatial variability of spruce budworm defoliation at different scales

Article

Sep 2014
FOREST ECOL MANAG

Aerial survey records of defoliation by spruce budworm (Choristoneura fumiferana (Clem.)) in New Brunswick, Canada taken annually from 1965 to 1992, were analyzed at four scales (66 × 66 km, 10 × 10 km, 2 × 2 km, 1 × 1 km) to determine patterns and spatial variability of defoliation. Spruce budworm defoliated 92% of the 7.4 million ha study area in at least one year. Cluster analysis was used to group similar defoliation patterns, and 51% of the variation in the 28-year record was described by 28 representative defoliation patterns, at 1 × 1 km cell size. Individual defoliation patterns were grouped into five spruce budworm outbreak classes (termed A–E), which each covered 12–27% of the area. These differed substantially in defoliation duration and severity: classes A–B had only 1–3 years of moderate–severe defoliation and 42–75% cumulative defoliation; class C had 8 years and 127% cumulative defoliation; and classes D–E had 13–16 years and 170–208% cumulative defoliation. Given the degree of ‘averaging out’ of high defoliation occurrences that cause the largest impacts, larger 10 × 10 km and 66 × 66 km cells were inappropriate for impact analysis. Defoliation variability was highest at 20–60% mean defoliation than at lower or higher defoliation levels. Distributions of area in each class in 1 × 1 km cells for 66 × 66 km areas throughout the province showed that with the exception of several small coastal areas, four or five of the above outbreak classes occurred in all areas. The wide variation in spruce budworm outbreak patterns is important in making management decisions that differentiate insecticide or salvage treatments based on defoliation severity, and emphasizes the importance of accurate annual aerial survey or remote sensing-based defoliation assessment.

INTUITION-BASED MODELING AND INSIGHTS INTO HOW ANTIFREEZE PROTEINS BIND TO ICE

Article

Nelson Lin

Heritability of life-history traits in the spruce budworm

Article

Jan 2014
ENTOMOL SCI

The heritability of life-history traits is of particular importance for insects that are very dependent on host conditions. Severe defoliation caused by the spruce budworm negatively impacts its food source, which in turn imposes environmental constraints on the insect. The heritability of those traits can help elucidate this species' evolutionary process. Heritability also helps identify which traits exhibit significant additive variance and can be key to understanding natural selection effects. Individuals were reared under laboratory conditions over three generations on an artificial diet. Heritability was estimated by parent–offspring regression. Fertility and fecundity demonstrated significant heritability followed by larval development, while pupal mass showed minimal heritable variation. These results suggest an important percent of additive variance in life-history traits. This study contributes to our understanding of the relationship of this forest pest to its environmental conditions. This study also reveals an important genetic architectural structure of life-history traits in the spruce budworm.

Identification and ecological characterisation of Choristoneura occidentalis (Lepidoptera: Tortricidae) populations in southwestern Alberta, Canada

Article

Full-text available

Oct 2013
CAN ENTOMOL

The western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera: Tortricidae), is an important pest of western North American coniferous forests, where its principal larval host is Rocky Mountain Douglas-fir, Pseudotsuga menziesii subspecies glauca (Beissner) Murray (Pinaceae). In southwestern Alberta, Canada, populations were recently discovered feeding on an unconventional host, an Engelmann spruce, Picea engelmannii Parry ex. Engelmann × white spruce, Picea glauca (Moench) Voss hybrid (Pinaceae), in a transition zone between the two major forest types characterised by these conifer species. We use molecular evidence to verify the species identity of outbreaking Choristoneura populations collected from Douglas-fir and hybrid spruces in southwestern Alberta in 2009, and characterise the larval and male moth phenology. Both mitochondrial and microsatellite markers confirmed these populations as C. occidentalis, but admixture with Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) was detected in some individuals. Few differences associated with separate host trees were evident in the phenology of larvae and the flight period of male moths.

Moths Caught in Traps during a Survey of Choristoneura Fumiferana (Clemens, 1865) – Lepidoptera, Tortricidae – in Lithuania

Article

Jan 2010

A survey for the North American spruce budworm (Choristoneura fumiferana (Clemens, 1865)) was carried out using sticky traps baited with a synthetic sex pheromone blend from 2002 to 2004. The traps were deployed at 90 localities throughout Lithuania: in parks, botanical gardens, forest trees nurseries and forest lots, where non-native coniferous trees were planted. No C. fumiferana were found, but a total of 88 other moth species were trapped and identified. Acleris ferrugana (Denis & Schiffermüller, 1775) was the most frequently found species. Other species of trapped moths revealed new information on the Lithuanian fauna. Merrifieldia leucodactyla (Denis & Schiffermüller, 1775) moths, a new species for the Lithuanian fauna, were caught in six localities. Seven new localities were recorded for the occurrence of the following very rare species: Diplodoma laichartingella Goeze, 1783, Depressaria (Depressaria) sordidatella Tengström, 1848, Elachista (Elachista) consortella Stainton, 1851, Mompha (Mompha) sturnipennella (Treitschke, 1833), Bryotropha senectella (Zeller, 1839), Dichelia histrionana (Frölich, 1828). 63 new localities were recorded for the occurrence of 16 moth species which are rare in Lithuania.

Stochastic simulation of growth loss in thinned balsam fir stands defoliated by the spruce budworm in Newfoundland

Article

Feb 2011
CAN J FOREST RES

Erhard John Dobesberger

A stochastic simulation model was developed to derive a damage function for the spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), and balsam fir, Abies balsamea (L.) Mill., herbivore interaction at the stand level for open-grown trees. Both aggregated and uniform models of attack pattern by late-instar larvae based on k of the negative binomial were evaluated to determine the impact of larval density and attack pattern on the loss in stemwood volume increment of young, thinned balsam fir stands in Newfoundland. Percentage loss in stemwood increment was a nonlinear, negative exponential function of initial larval density. Implementation of control measures to prevent 50% defoliation that is caused by about 14 larvae/branch tip would result in saving 24% of the annual stemwood increment after 1 year of defoliation and about 32% after 2 years of cumulative defoliation. Aggregation of spruce budworm larvae among trees within a forest stand results in less growth loss compared with a uniform pattern of attack. The nonlinear damage function may suggest tolerance and possibly compensatory growth after herbivory by low population levels of the spruce budworm.

Phenolic compounds that confer resistance to spruce budworm

Article

Sep 2011
ENTOMOL EXP APPL

Carry over effects of the entomopathogen Bacillus thuringiensis ssp. Kurstaki on Choristoneura fumiferana (Lepidoptera: Tortricidae) progeny under various stressful …

Article

Full-text available

Feb 2006

In the present study, we documented the lethal and sublethal effects of the entomopathogen Btk on spruce budworm and its progeny under various environmental conditions. We hypothesized that aerial spray of Bacillus thuringiensis ssp. kurstaki ( Btk ) could affect the biological performance of the surviving spruce budworm ( Choristoneura fumiferana Clem.) populations and their progenies and that Btk sublethal effects could be widened by other types of stress (i.e. temperature conditions and changes in food suitability from year to year). The results from a 3‐year field experiment indicated that Btk treatments decreased the fitness of the surviving larvae whatever the prevailing temperature and nutritional conditions. The detrimental Btk effects on the parental generation carried over to the offspring. The percent of egg hatch and first‐instar survival were negatively affected by Btk whatever other stress spruce budworm parents underwent. The present study also highlighted the fact that the effects of temperature and nutritional stress suffered by the parents could carry over to the next generation. Balsam fir flowering, which provided larvae with pollen rich in nitrogen, favoured both the parental generation and the fitness of their offspring. Spruce budworm mothers allocated to their progenies large amounts of energy reserves (triglycerides and glycogen) that greatly enhanced the survival of the early stages. Egg hatch and the survival of first‐instar larval progeny were drastically affected when their parents had reduced larval growth as a result of exposure to cool temperatures that had desynchronized insect and bud phenology. Budworm mothers submitted to negative impacts of previous defoliation allocated low amounts of energy reserves to their progeny. This lack of energy associated with unfavourable temperature conditions (i.e. high temperatures in late summer and in early fall and an extended cool period in spring) drastically reduced survival of diapausing second‐instar larvae. These results highlight the importance of considering the various sources of stress when attempting to evaluate the impact of a control agent on an insect pest population and its progenies.

Ecological mechanisms of population change during outbreaks of the spruce budworm

Article

Oct 2007
ECOL ENTOMOL

Abstract 1. Stage-specific survival and recruitment of spruce budworm were measured by frequent sampling of foliage in four outbreak populations over a 15-year period in Ontario and Quebec, Canada. 2. Patterns of change in population density during the outbreak collapse phase were closely linked to changes in survival of the late immature stages, and were determined largely by the impact of natural enemies. 3. Host-plant feedback also contributed significantly to survival patterns throughout the outbreak: annual defoliation influenced survival of fourth and fifth instars and fecundity while cumulative defoliation influenced survival of the very early larval stages (first and second) via impacts on stand condition. 4. Inclusion of this host-plant feedback reveals spruce budworm population dynamics as a function of density-related trophic interactions that vary in their order and strength of influence over time. This view re-introduces the importance of forest interactions as a component of dynamics of the spruce budworm.

Influences of Climatic Change on Some Ecological Processes of an Insect Outbreak System in Canada's Boreal Forests and the Implications for Biodiversity

Article

Full-text available

Feb 1998

Insect outbreaks are a major disturbance factor in Canadian forests. If global warming occurs, the disturbance patterns caused by insects may change substantially, especially for those insects whose distributions depend largely on climate. In addition, the likelihood of wildfire often increases after insect attack, so the unpredictability of future insect disturbance patterns adds to the general uncertainty of fire regimes. The rates of processes fundamental to energy, nutrient, and biogeochemical cycling are also affected by insect disturbance, and through these effects, potential changes in disturbance patterns indirectly influence biodiversity. A process-level perspective is advanced to describe how the major insect outbreak system in Canadian forests, that of the spruce budworm (Choristoneura fumiferana Clem. [Lepidoptera: Tortricidae]), might react to global warming. The resulting scenarios highlight the possible importance of natural selection, extreme weather, phenological relationships, complex feedbacks, historical conditions, and threshold behavior. That global warming already seems to be affecting the lifecycles of some insects points to the timeliness of this discussion. Some implications of this process-level perspective for managing the effects of global warming on biodiversity are discussed. The value of process-level understanding and high-resolution, long-term monitoring in attacking such problems is emphasized. It is argued that a species-level, preservationist approach may have unwanted side-effects, be cost-ineffective, and ecologically unsustainable.

Effect of temperature and host tree on cold hardiness of hemlock looper eggs along a latitudinal gradient

Article

Feb 2011

The hemlock looper, Lambdina fiscellaria, is an economically important insect pest of Canadian forests which overwinters as eggs. Although the hemlock looper causes extensive damages, no information on the mechanisms related to its cold tolerance is known. The objective of this study was to determine the effect of temperature and exposure duration on hemlock looper winter survival but also to identify seasonal supercooling capacity and cryoprotectant levels of three populations along a latitudinal gradient. As host plant may contribute to offspring overwintering success, cold tolerance of hemlock looper eggs from parents whose larvae were fed on three different tree species was also measured. Mean supercooling point (SCP) of hemlock looper eggs was lower than -30 °C from October through the following spring with values being as low as -47 °C in February. Trehalose was the most abundant sugar found in hemlock looper eggs with a peak concentration of 0.3 μg mg⁻¹ DW⁻¹. Glycerol, a polyol, was more often absent in eggs of the different populations and tree species tested in the study. When exposed to different temperature regimes for various periods of time, significant mortality of hemlock looper eggs occurred at higher temperatures than the mean SCP. Thus, hemlock looper could be considered as a chill tolerant species. No clear pattern of population and host plant effects on SCP and cryoprotectants was detected in this study. However, when exposed to different winter temperatures and exposure duration, hemlock looper from higher latitudes survived better (survival rates ranging between 0 and 89% at -20 °C) than those from lower latitudes (survival rates ranging between 0 and 56% at -20 °C). Our results may contribute to a better understanding of hemlock looper winter biology and thus facilitate predictions of outbreaks and range expansion.

I>Bacillus thuringiensis subsp. kurstaki Aerial Spray Prescriptions for Balsam Fir Stand Protection Against Spruce Budworm (Lepidoptera: Tortricidae)

Article

Full-text available

Oct 2004
J ECON ENTOMOL

Although commercial formulations of Bacillus thuringiensis subsp. kurstaki (Btk) are being widely used in forest protection against lepidopteran defoliators, optimal application prescriptions have often yet to be worked out in detail. We conducted field experiments over a 6-yr period (1996-2001) in southwestern Québec to determine application prescriptions for optimal protection of balsam fir, Abies balsamea (L.), healthy stands against the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). At moderate larval densities (<30 larvae per 45-cm branch tip), similar foliage protection was achieved with one or two Btk applications of 30 billion international units per hectare (BIU/ha). When larval densities exceeded 30 larvae per branch tip, two successive applications of 30 BIU/ha significantly increased foliage protection. Whether the second application took place 5 or 10 d after the first spray did not affect treatment efficacy. Increasing the application dosage from 30 to 50 BIU/ha did not lead to better foliage protection against high larval densities, but the current standard dosage of 30 BIU/ha saved more foliage than 15 BIU/ha against moderate populations. The recommended dosage of 30 BIU can be applied in lower application volumes (1.5 liters/ha) by using a high-potency product (20 BIU/liter), because we did not observe a reduction in efficacy compared with the application of a lower potency product (12.7 BIU/liter) in 2.37 liters/ha. We also demonstrated that Btk can be applied much earlier in the season without compromising spray efficacy: there was no difference in treatment efficacy of double applications at 30 BIU/ha when the first spray was timed for early third, peak third, or early fourth instars.

Physics of Ice Nucleation and Antinucleation: Action of Ice-Binding Proteins

Article

Full-text available

Dec 2023

Ice-binding proteins are crucial for the adaptation of various organisms to low temperatures. Some of these, called antifreeze proteins, are usually thought to inhibit growth and/or recrystallization of ice crystals. However, prior to these events, ice must somehow appear in the organism, either coming from outside or forming inside it through the nucleation process. Unlike most other works, our paper is focused on ice nucleation and not on the behavior of the already-nucleated ice, its growth, etc. The nucleation kinetics is studied both theoretically and experimentally. In the theoretical section, special attention is paid to surfaces that bind ice stronger than water and thus can be “ice nucleators”, potent or relatively weak; but without them, ice cannot be nucleated in any way in calm water at temperatures above −30 °C. For experimental studies, we used: (i) the ice-binding protein mIBP83, which is a previously constructed mutant of a spruce budworm Choristoneura fumiferana antifreeze protein, and (ii) a hyperactive ice-binding antifreeze protein, RmAFP1, from a longhorn beetle Rhagium mordax. We have shown that RmAFP1 (but not mIBP83) definitely decreased the ice nucleation temperature of water in test tubes (where ice originates at much higher temperatures than in bulk water and thus the process is affected by some ice-nucleating surfaces) and, most importantly, that both of the studied ice-binding proteins significantly decreased the ice nucleation temperature that had been significantly raised in the presence of potent ice nucleators (CuO powder and ice-nucleating bacteria Pseudomonas syringae). Additional experiments on human cells have shown that mIBP83 is concentrated in some cell regions of the cooled cells. Thus, the ice-binding protein interacts not only with ice, but also with other sites that act or potentially may act as ice nucleators. Such ice-preventing interaction may be the crucial biological task of ice-binding proteins.

Characterizing eastern spruce budworm’s large-scale dispersal events through flight behavior and stable isotope analyses

Article

Full-text available

Mar 2023

Eastern spruce budworm moth (Choristoneura fumiferana (Clem.)) mass outbreaks have widespread economic and ecological consequences. A key explanation for the large-scale spread and synchronization of these outbreaks is the long-distance dispersal (up to 450 km) of moths from hotspots (high-density populations) to lower-density areas. These events have proved difficult to monitor because dispersal flights occur only a few times a year, have no consistent routes, and commonly used tracking methods (e.g., population genetics, mark-recapture, radio telemetry) are inadequate for this system. Confirming immigration and distinguishing between local and immigrant individuals are crucial steps in identifying the physical and ecological drivers of moth dispersal. Here, we test whether isotopes of hydrogen (i.e., delta notation: δ²H) and strontium (i.e., strontium isotope ratios: ⁸⁷Sr/⁸⁶Sr), known to independently vary in space in a predictable manner, can be used to show that an immigration event occurred and to distinguish between local and immigrant adult spruce budworm moths. We used an automated pheromone trap system to collect individuals at six different sites in eastern Canada within and outside the current outbreak area of budworm moths. We first use moth flight behavior and time of capture, currently the best available tool, to determine putative local vs. immigrant status, and then evaluate whether individual ⁸⁷Sr/⁸⁶Sr and δ²H differ between putative classes. At two sites, we detect immigrant individuals that differ significantly from putative locals and thus confirm immigration has occurred. Saliently, sites where putative locals were sampled before the occurrence of potential immigration events (~10 days) showed the strongest differences between immigrant individuals’ and local ⁸⁷Sr/⁸⁶Sr and δ²H values. Sites where the collection of putative locals was close in time (hours) or following an immigration event (days) had a less-clear distinction between putative immigrants and locals, and showed signs of mixing between these two groups. We speculate that recent immigration could have led to the misclassification of immigrants as putative locals. ⁸⁷Sr/⁸⁶Sr and δ²H data generally support the adequacy of current approaches using capture-time to detect immigration events, and provide enhanced resolution to distinguish between local and immigrant individuals and to confirm an immigration event. We discuss the broader implication of adding isotopes to the toolkit to monitor spruce budworm dispersal and suggest next steps in implementing these tools.

The Impact of Moth Migration on Apparent Fecundity Overwhelms Mating Disruption as a Method to Manage Spruce Budworm Populations

Article

Full-text available

Sep 2019

Aerial applications of a registered formulation of synthetic spruce budworm female sex pheromone were made in 2008, 2013 and 2014 to disrupt mating in populations of this forest insect pest in Quebec, Canada. Each year, the applications resulted in a 90% reduction in captures of male spruce budworm moths in pheromone-baited traps. A commensurate reduction in mating success among virgin females held in individual cages at mid-crown of host trees was also obtained. However, there was no reduction in the populations of eggs or overwintering larvae in the following generation (late summer and fall). The failure of this approach as a viable tactic for spruce budworm population reduction could have resulted from considerable immigration of mated females, as evidenced by high rates of immigration and emigration that caused steep negative relationships between apparent fecundity and the density of locally emerged adults.

A Review Of The Tachinid Parasitoids (Diptera: Tachinidae) Of Nearctic Choristoneura Species (Lepidoptera: Tortricidae), With Keys To Adults And Puparia

Article

Apr 2005
ZOOTAXA

James E. O’Hara

The genus Choristoneura (Lepidoptera: Tortricidae) comprises about 16 species in the Nearctic Region and includes several destructive pests of importance to forestry and agriculture. The following 15 species of Tachinidae (Diptera) are recognized as occasional or common parasitoids of Choristoneura species in this region: Actia diffidens Curran, Actia interrupta Curran, Ceromasia auricaudata Townsend, Compsilura concinnata (Meigen), Cyzenis incrassata (Smith), Eumea caesar (Aldrich), Hemisturmia parva (Bigot), Hyphantrophaga blanda (Osten Sacken), Hyphantrophaga virilis (Aldrich and Webber), Lypha fumipennis Brooks, Madremyia saundersii (Williston), Nemorilla pyste (Walker), Nilea erecta (Coquillett), Phryxe pecosensis (Townsend), and Smidtia fumiferanae (Tothill). Keys to the adults and puparia of these tachinid species are provided. The known distribution, biology, and rates of parasitism are reviewed for each species and published host records from Choristoneura species are listed. Colour habitus images of adults, illustrations of all puparia, and illustrations of features mentioned in the adult key are included. Thirteen other species of Tachinidae recorded from Choristoneura species but excluded from the main text as highly dubious, rare, or accidental records are briefly discussed.

Spruce budworm biological and nutritional performance responses to varying levels of monoterpenes

Article

Full-text available

Jul 2013

Dose effect of six monoterpenes (α-pinene, bornyl acetate, camphene, δ-3- carene, terpinolene, tricyclene) found in the foliage of host trees was tested on sixth-instar spruce budworm (Choristoneura fumiferana (Clem.)) using artificial diet. The larval mortality, growth and food utilization have been observed. Two monoterpenes, α-pinene and δ-3-carene caused 22 and 12% mortality respectively at concentrations found in balsam fir foliage. Bornyl acetate and camphene reduced larval survival when their concentration was higher than the foliage. Terpinolene and tricyclene have no effect on mortality. All six tested monoterpenes reduced larval growth rate. Spruce budworm tried to minimize this negative growth impact by increasing his digestibility in presence of camphene and δ-3-carene, and by increasing his efficiency of conversion of ingested-digested food with α-pinene and bornyl acetate. These results support the traditional theory that monoterpenes are a defense agent against spruce budworm and that each monoterpene has a different mode of action and effects which are not necessarily proportional to its concentration.

The Geography of Spruce Budworm in Eastern North America

Article

Aug 2011

Spruce budworm (Choristoneura fumiferana) is a native insect that defoliates needleleaf trees, especially balsam fir (Abies balsamea) and spruces (Picea spp.), in northern North America. Spruce budworm can defoliate millions of hectares of forest during an infestation, depressing regional economies that depend on the timber industry. Ecosystems, though, can benefit from spruce budworm because outbreaks rejuvenate the forest, maintaining optimal levels of primary production, and thereby carbon sequestration. Although many ecologists, entomologists, geographers, and resource managers have studied the effects of spruce budworm on spruce–fir forests throughout the region, no single explanation of what causes the number of insects in a forest to rise and fall is universally accepted. Spruce budworm populations can reach ‘outbreak’ levels, or densities high enough to defoliate and kill balsam fir and spruce on a landscape scale, on average every 30–40 years. We review the biology of spruce budworm, the processes that scientists follow to reconstruct spruce budworm outbreaks, the leading hypothesis to explain population dynamics and outbreak events, and the complexity of forecasting possible future trends of populations and distributions of spruce budworm. Reconstructions of past outbreaks help us understand their severity, frequency, and spatial synchrony, which might be linked in complex ways to climate, forest, and stand characteristics. Future spruce budworm dynamics are difficult to predict because the insect is part of a complex food web. In the coming decades, spruce budworm probably will survive climate change because it is adapted to a wide range of temperatures and precipitation amounts.

The phenological window for western spruce budworm: Seasonal decline in resource quality

Article

Nov 2012

Vince Nealis

Western spruce budworm Choristoneura occidentalis Free. (Lepidoptera: Tortricidae) emerge in the spring before budburst and then face a rapidly deteriorating host quality each season. Measures of fitness, survival and fecundity, were made on cohorts of final‐instar spruce budworms deployed on host trees at several times during the season in four field locations in coastal and interior British Columbia, Canada. Survival and fecundity were strongly correlated throughout the season and varied as much as four‐fold from maxima at mid‐season to minima at the end of the season. Fitness values overall were greatest in the coastal compared with interior locations. Among interior locations, fitness was greatest at the highest elevation and least at the lowest elevation. Both cohort and sample‐based estimates of survival of wild, final‐instar budworms were relatively high in these outbreak populations. The influence of the phenological window and degree of synchrony with the host plant on herbivore abundance often depends on other processes affecting population rates of change.

The chalcidoid parasitoids and hyperparasitoids (Hymenoptera: Chalcidoidea) of Choristoneura species (Lepidoptera: Tortricidae) in America north of Mexico

Article

Dec 1996
CAN ENTOMOL

An illustrated key is given to 28 genera, representing 10 families of at least 50 chalcidoid parasitoids and hyperparasitoids recorded from Choristoneura species (Tortricidae), or their primary parasitoids, in America north of Mexico. We include species reared throughout a 12-year study of the parasitoids and hyperparasitoids associated with the spruce budworm, Choristoneura fumiferana (Clemens), in New Brunswick, Canada, as well as those listed in various catalogs. Notes are provided for all the chalcidoid species, whether or not they are recorded in the literature. Nine species doubtfully or incorrectly recorded from Choristoneura species are also discussed. Primary parasitoids belonging to the Ichneumonidae, Braconidae, and Tachinidae have been recorded from 10 of the 16 Nearctic Choristoneura species but chalcidoid parasitoids are recorded, usually as hyperparasitoids, from only four of the 16 species. The species of primary parasitoids of Choristoneura checked for records of parasitism by Chalcidoidea are tabulated by host species. Also listed are species of primary parasitoids serving as hosts for each of the chalcidoid species. We report 51 new host records of primary parasitoids and hyperparasitoids from C. fumiferana and its parasitoids collected in New Brunswick. A new generic combination is given: Mesopolobus tortricis (Brues) comb.nov. from Psychophagus (proposed by Z. Boucek).

Insect–host relationships influencing disturbance by the spruce budworm in a boreal mixedwood forest

Article

Full-text available

Sep 2004
CAN J FOREST RES

V.G. Nealis and J. Régnière Abstract: Demographic data from a 15-year outbreak of the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), in a boreal mixedwood forest in Ontario, Canada, are used to interpret stand-level ecological disturbance in terms of susceptibility and vulnerability (mortality) of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP). All three host-tree species are highly susceptible for oviposition by the spruce budworm and all are suitable for completion of the budworm life cy- cle. Host-related differences in susceptibility arise from the degree of synchrony between spruce budworm phenology during the feeding stages and host-tree phenology. Spruce budworm density was highest on white spruce throughout the budworm's life cycle and over the course of the outbreak, but more rapid flushing and growth of current-year buds in white spruce reduced damage relative to that on balsam fir. Conversely, later flushing of current-year buds on black spruce led to a reduction in budworm density early in the season and a corresponding reduction in defoliation. The combination of high budworm densities and severe defoliation caused mortality first on balsam fir. By the end of the outbreak, 89% of the balsam fir component >10 cm DBH was eliminated compared with 49% of the white spruce in the same size class. The lower susceptibility of black spruce resulted in survival of all but the smallest size classes of that species. Nonhost species such as trembling aspen (Populus tremuloides Michx.) nearly doubled their basal area during the outbreak. The results link processes inherent in the insect-host relationship with the population ecology of the insect and the disturbance ecology of the forest.

Glycerol synthesis by diapausing larvae in response to the timing of low temperature exposure, and implications for overwintering survival of the spruce budworm, Choristoneura fumiferana

Article

Nov 1995
J INSECT PHYSIOL

Spruce budworm larvae, Choristoneura fumiferana, were exposed at different times during diapause to a lower temperature regime (from 18 to 2 °C with or without 1-week at − 5 °C in between). A lower temperature clearly elicited a stronger response in glycerol synthesis by the larvae. However, the magnitude and the pattern of increases in glycerol level were associated with the timing of the cold exposures, indicating the existence of a physiological window. These laboratory results were related to those from two experiments conducted outside during the winters of 1992–1993 and 1993–1994. By delaying the starting date of outside exposure in the 1993–1994 winter, larvae failed to produce a significant amount of glycerol and most died. This was most likely due to the effective change of the physiological window together with an “earlier” arrival of extreme cold temperatures. Based on this evidence, we argue that overwintering success of an insect depends not only on temporal changes in external parameters (e.g. temperature) but on internal developmental processes and their interactions. Timing of such events plays a very important role in insect overwintering survival and deserves particular attention in future investigations of insect winter biology.

Effect of starvation on the accumulation of CfDAP and CfDAP-like proteins in post-diapause Choristoneura fumiferana and diapause-free Choristoneura occidentalis

Article

Feb 2011

In 1998, Palli et al. found that in the eastern spruce budworm, Choristoneura fumiferana, two hexameric proteins termed CfDAP1 and CfDAP2 are expressed abundantly before and during diapause. To determine whether the accumulation of these proteins in early instars is a direct consequence of the diapause phenomenon, we assessed the abundance of CfDAP-like proteins in first (L1), second (L2), and third (L3) instars of a diapause-free strain of the closely related western spruce budworm, Choristoneura occidentalis. Using sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western-blot analyses of L2 whole-body proteins, a CfDAP-specific antiserum reacted with two C. occidentalis proteins displaying apparent molecular masses identical with those of CfDAP1 and CfDAP2. Among the three larval stadia examined, CfDAP-like proteins accumulated to significant levels only in the first two, with enhanced accumulation observed in L2s starved from the time of hatching. Accumulation of CfDAP1 and CfDAP2 in post-diapause C. fumiferana L2s was affected similarly by food availability. Thus, the data presented here, combined with those of Palli et al., suggest that expression of CfDAP and CfDAP-like proteins in early larval life is more or less limited to L1 and L2, and is associated with starvation stress imposed either experimentally or by elements of the life cycle (i.e., diapause).

Non-freeze survival of spruce budworm larvae, Choristoneura fumiferana, at sub-zero temperatures during diapause

Article

Apr 2011
ENTOMOL EXP APPL

Spruce budworm larvae, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), in early‐, mid‐ and late‐diapause (maintained at 2 °C), were exposed to various sub‐zero temperatures, above the supercooling point, for different periods to determine the insect's cold‐hardiness in terms of non‐freeze survival. Larvae which were in the middle of diapause showed the highest survival (percentage of larvae emerging from hibernacula after diapause), followed by larvae in late‐ and early‐diapause respectively. When exposed to −23 °C, larvae which were acclimatized to outside air temperatures had a much higher survival than the larvae maintained at 2 °C. This survival was correlated with a glycerol content that was ten times higher and a depressed supercooling point in acclimatized larvae compared to lab‐maintained larvae. Experiments also demonstrated that mortality of the larvae maintained in an extended supercooled state at −23 °C was due to cold injury rather than freezing. The present study supports the hypothesis that glycerol may have a cryoprotective role other than depressing the supercooling point in freeze‐intolerant insects and highlights the importance of investigating non‐freeze mortality during insect diapause. Résumé Des larves de tordeuse des bourgeons de l'épinette, Choristoneura fumiferana (Clem.), en début, milieu et fin de diapause (maintenue à 2 °C) furent soumises à divers régimes de températures supérieures au point de congélation cellulaire, de façon à déterminer la capacité de l'insecte à survivre à ces températures. Les larves en milieu de diapause furent celles ayant le mieux survécu (proportion des larves émergeant de leur hibernacula après la diapause). Elles furent suivies respectivement par celles en fin et en début de diapause. La suivie larvaire, suite à une exposition à −23 °C, fut plus élevée dans le cas des larves préalablement acclimatées aux températures de terrain que dans le cas des larves maintenues à 2 °C. Comparativement aux larves non acclimatées sur le terrain, le point de congélation cellulaire des larves acclimatées était inférieur et leur contenu en glycérol était dix fois plus élevé. Cette étude a aussi montré que la mortalité des larves maintenues durant une longue période à −23 °C ne fut pas causée par un phénomène de congélation cellulaire mais plutôt par d'autres effets létaux du froid. Les résultats de cette étude sont en accord avec l'hypothèse selon laquelle le glycérol jouerait, en tant que cryoprotectant, un rôle autre que celui d'abaisser les points de congélation cellulaire des insectes du type intolérant au gel. De plus, ces résultats montrent l'importance détudier la mortalité induite par les températures situées au‐dessus du point de congélation cellulaire durant la diapause de l'insecte.

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

Article

Nov 1995

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 1.920.04 l (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.

Forecasting the susceptibility and vulnerability of balsam fir stands to insect defoliation with Landsat Thematic Mapper data

Article

May 1997
REMOTE SENS ENVIRON

The potential of remote sensing to aid in the forecast of insect defoliation and the associated impact on forest stands was tested by examining the relationships between i) preoutbreak forest structure and growth characteristics, ii) multispectral values recorded by the Landsat Thematic Mapper (TM) sensor, and iii) subsequent patterns of defoliation and volume loss in the balsam fir (Abies balsamea L. Mill) forests of Western Newfoundland. Forest structure and growth characteristics were measured in the field in 1992–1993 and reconstructed to represent conditions 3 years prior to an infestation of black-headed budworm, Acleris variana (Fern.), which began in 1988. Preoutbreak Landsat TM data were acquired on 8 August 1985. Spectral values were converted to approximate reflectances using PCI atmospheric correction routines and related to the field measurements. Logistic regression techniques were used to develop models for predicting forest susceptibility (probability of attack) and vulnerability (response to attack) and to assess the accuracy of the susceptibility and vulnerability forecasts. In general, susceptible stands were younger and had lower basal area and tree density, but higher leaf area index than stands that were not attacked. Vulnerable stands were older, had lower vigor and growth efficiency indices (stemwood growth per unit of leaf area), and also displayed the highest near infrared spectral values. The best predictions combined selected spectral measurements with provincial forest inventory data. These models produced classifications with accuracies of 81%, 67%, and 78% for predicting susceptibility and pre- and postoutbreak vulnerability, respectively.

The bugs that came in from the cold: molecular adaptations to low temperatures in insects

Article

Feb 2009
CELL MOL LIFE SCI

The widespread distribution of insects over many ecological niches is a testimony to their evolutionary success. The colonization of environments at high latitudes or altitudes required the evolution of biochemical strategies that reduced the impact of cold or freezing stress. This review focuses on our current interests in some of the genes and proteins involved in low temperature survival in insects. Although the most widespread form of protection is the synthesis of low molecular weight polyol cryoprotectants, proteins with intrinsic protective properties, such as the thermal hysteresis or antifreeze proteins are also important. These have been cloned and characterized in certain moths and beetles. Molecular techniques allowing the isolation of genes differentially regulated by low temperatures have revealed that heat shock proteins, cold stress proteins, membrane protectants, as well as ice nucleators and other less well characterized proteins likely also play a role in cold hardiness.

The antifreeze potential of the spruce budworm Thermal hysteresis protein

Article

Oct 1997

Antifreeze proteins (AFP) inhibit ice growth by surface adsorption that results in a depression of the freezing point below the melting point. The maximum level of this thermal hysteresis shown by the four structurally unrelated fish AFP is approximately 1.5 degrees C. In contrast, hemolymph and crude extracts from insects can have 5 degrees to 10 degrees C of thermal hysteresis. Based on the isolation, cloning, and expression of a thermal hysteresis protein (THP) from spruce budworm (Choristoneura fumiferana), the vastly greater activity is attributable to a 9 kDa protein. This novel, threonine- and cysteine-rich THP has striking effects on ice crystal morphology, both before and during freezing. It is also 10 to 30 times more active than any known fish AFP, offering the prospect of superior antifreeze properties in cryoprotective applications.

Crystallization and Preliminary X-Ray Crystallographic Analysis of Spruce Budworm Antifreeze Protein

Article

Jun 1999

Antifreeze proteins have the ability to bind to ice with high affinity and inhibit further crystal growth. The insect antifreeze protein from spruce budworm exhibits very high thermal hysteresis activity and is implicated in the protection of overwintering larvae from freezing. This protein has been crystallized in 20-25% polyethylene glycol (Mr 6000), 0.4 M NaCl, 0.1 M Tris-HCl, pH 8.5, by vapor diffusion using the hanging drop method. The resulting crystals are very thin (typically <0.01 mm in the shortest dimension), and only after repeated seeding could crystals be grown large enough for data collection using synchrotron radiation. The crystals belong to the monoclinic space group C2, with cell dimensions a = 82.28 A, b = 62.29 A, c = 63.63 A, and beta = 113.7 degrees. Molecules in the asymmetric unit are related by a twofold axis of symmetry with two molecules present. Native data to a resolution of 2.6 A have been collected with 90.3% completeness and a Rsym of 6.9%.

Interactions Among White Spruce Tannins, Bacillus thuringiensis subsp. kurstaki , and Spruce Budworm (Lepidoptera: Tortricidae), on Larval Survival, Growth, and Development

Article

Jan 2007
J ECON ENTOMOL

The interactions among white spruce, Picea glauca (Moench) Voss, purified acetone tannin extracts (hydrolyzable and condensed tannin), Bacillus thuringiensis subsp. kurstaki Cry1A(c) delta-endotoxin strain HD-73 (Btk), and spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) on larval survival, growth, and development were investigated over the whole larval feeding period by using artificial diet supplemented with three concentrations of Btk toxins per milliliter of diet (0, 0.021, and 1.72 microg/ml) and three concentrations of foliar tannin extract (0, 8, and 15% dry mass basis). At high Btk concentration, tannin antagonized Btk potency against spruce budworm by lowering Btk-related larval mortality from 83 to 43%. At moderate Btk concentration tannin did not affect Btk potency. Host tree tannins antagonized not only the lethal effects of Btk toxin but also sublethal Btk-related impacts in terms of larval development, pupal weight, relative consumption rate, and growth rate. When alone in the diet, tannin negatively affected larval survival, growth, and development. Maximum potency of tannins against spruce budworm larvae (60% mortality) was reached at dietary concentrations corresponding to what is found in the plant (8% dry mass). The addition of Btk toxin in food containing tannin reduced percentage of larval mortality by one-third, indicating that Btk toxin can antagonize tannin potency against the insect. Development of Btk transgenic spruce trees should consider the antagonistic effect the toxin may have on the resistance conferred by tannins that have evolved naturally in spruce trees.

Biology of North American spruce budworms

Abstract

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