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Effect of climatic factors on post-diapause emergence and survival of spruce budworm larvae (Lepidoptera: Tortricidae)
Abstract
Earlier attempts to correlate spruce budworm, Choristoneura fumiferana (Clem.), outbreaks and weather conditions were usually carried out by comparing seasonal data and spruce budworm outbreak development in broad terms: it was found that warm, dry weather favored outbreak development, while cool, wet weather retarded development. In this paper, laboratory experiments and historical data are examined to determine the effect of temperature and precipitation on second-instar larvae, just prior to and after spring emergence. Results tend to show that prolonged rain and freezing temperatures during and shortly after emergence are detrimental and may, in some cases, have a profound impact on outbreak development.
... The duration of the needle-mining period was defined as delay (in days) between 50% emergence and 50% bud-mining. From these same weather records, total rainfall during the emergence period was calculated because this variable has been implicated in survival of spruce budworm during the spring emergence period ( Lucuik, 1984 ). ...
... A negative effect of maternal infection by N. fumiferanae on spring survival is consistent with the higher mortality of infected, spring-dispersing larvae observed by van Frankenhuyzen et al. (2007) . No evidence was found of direct precipitation effects on survival suggested by Lucuik (1984) but two other weather-related factors had significant impacts on survival between emergence from overwintering sites and establishment in feeding sites. First, duration of the emergence period was positively related to survival. ...
Abstract 1. A lagged, density-dependent relationship between survival of early instars and host-tree condition is revealed during outbreaks of spruce budworm, Choristoneura fumiferana Clem. Persistent damage to hosts leads to deterioration of the stand.
2. Resource limitation affects survival during early-instar dispersal of spruce budworm. Impediments to distinguishing these events with estimates of survival were overcome with a simple model that describes the dispersal and survival processes. The model was used to analyse a recent 15-year population series from Black Sturgeon Lake and two historical datasets from Green River, in Canada.
3. Defoliation-induced damage to the trees resulted in increased losses of spring-emerging larvae that are dispersing in search of feeding sites. Losses were further exacerbated by biotic factors such as maternal fecundity, rates of infection by the pathogen, Nosema fumiferanae, and by weather-related effects on the foraging period.
4. Survival of early-stage budworm larvae in persistent outbreaks declined and the likelihood of other density-related factors such as rate of mortality from natural enemies increased. These results may reconcile outstanding differences in interpretation of the role of the forest resource in spruce budworm population dynamics and point to a common process linking the dynamics of other well-known budworm species.
... In general, populations of plants and animals will likely experience the effect of climate change directly through shifts in their per capita growth rates, and indirectly through feedbacks and interactions with other species and abiotic components of their environment. For instance, although climate can influence spruce budworm survival (Lucuik, 1984) and fecundity (Harvey, 1983b) directly, competitive interactions among individual spruce budworm will probably modify the degree to which climate-caused increases in survival and fecundity lead to increases in per capita growth rate. However, competition among spruce budworm in the same generation is unimportant, except among larvae feeding at very high densities (e.g., Sanders, 1991). ...
... Possible reasons for this are: plants experiencing drought are usually 2-4 C warmer than well-watered plants because stomatal closure reduces transpirational cooling (Mattson and Haack, 1987), and reduced humidity and greater air temperatures are usually aspects of drought conditions. In general, as the temperature of microhabitat of the spruce budworm increases towards optimum, the insect is more fecund (e.g., Sanders et al., 1978), develops faster (e.g., Lysyk, 1989), and has greater early instar survival as the frequency of cool, wet springs declines (e.g., Lucuik, 1984). During droughts, losses to natural enemies may also decrease since the temperature of about 26.6 C (Hudes and Shoemaker, 1988) at which the budworm develops fastest is greater than that of many of its natural enemies [e.g., the solitary endoparasitoid Apanteles fumiferanae (Nealis and Fraser, 1988), the microsporidian parasite Nosema fumiferanae (Wilson, 1974), and the entomophthoralean fungal pathogen Erynia (Zoophthora) radicans (Perry and Fleming, 1988)]. ...
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.
... This is largely consistent with previous research indicating the importance of climatic variables and host phenology in WSB outbreak dynamics. Precipitation in summer, particularly in early months, can be a large source of mortality for young foraging budworm larvae (Lucuik, 1984). Similarly, early fall (eFFP) and Table 2 Ensemble and top performing algorithm evaluations using TSS (true skill statistic) for each model period. ...
Forest disturbances caused by irruptive insect outbreaks have become more frequent due to the non-stationary and warming climate that favours insect development and survival, as well as forest management practices that increase host tree susceptibility. However, predicting and managing the impacts of these highly mobile pests is a challenge due to their uncertain distributions. Dynamic species distribution models (DSDM) acknowledge the non-stationary environment and species' ecological niches and facilitate niche modeling by matching species observational data relative to environmental data, leading to better outcomes and reducing over-prediction in conservation efforts. The western spruce budworm (WSB; Choristoneura freemani Freeman) is a native forest pest with irruptive dynamics characterized by periodic landscape-scale outbreaks. WSB feeds primarily on Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) foliage and can cause extensive defoliation throughout western North American forests. Using decades-long presence and absence records of WSB outbreaks detected via aerial surveys and environmental variables, we developed dynamic outbreak distribution models (DODMs) to predict the distribution of outbreaks over time. Our results showed that DODMs provided robust temporal trends of WSB distributions while generating predictions that support documented northward shifts in epidemic populations. We found that in addition to the environmental variables known to affect WSB survival, phenological synchrony between bud burst and the emergence of larvae in spring was the most important predictor of outbreak distributions. We also identified high-risk areas for future WSB outbreaks and predicted range expansions and contractions under different climate change scenarios. Our study highlights the importance of using presence-absence data and incorporating temporal trends in environmental variables for better assessment of forest pest potential outbreak distributions. These findings have implications for proactive management strategies to prevent outbreaks and mitigate the impacts of WSB on forest ecosystems.
... • Rising air temperatures in winters promote the survival of insects in boreal forests like spruce budworm (Lucuik, 1984), geometrid moth ( Jepsen et al., 2009), Siberian silk moth ( Kharuk et al., 2003), spruce bark beetle (ACIA, 2005) etc. The great abundance and survival of insects causes large scale defoliation. ...
The role and scale of human impact on the global environment is a question of special importance to the scientific community and the world as a whole. This impact has dramatically increased since the beginning of industrialisation, yet its understanding remains patchy. The sub-Arctic plays a central role in forming the global environment due to the vast territory of boreal forest and tundra. Severe climatic conditions make its ecosystems highly sensitive to any natural and human disturbances. In this context, the dynamics of boreal vegetation, and of the forest/tundra interface (the treeline), is the most representative indicator of environmental changes in the sub-Arctic.
For some time now, monitoring land cover and vegetation changes using remote sensing techniques have been a powerful method for studying human impact on environment from landscape to global scales. It is particularly efficient when applied to the sub-Arctic ecosystems. Remote sensing gives access to accurate and specific information about distant and hard-to-reach areas across forest and tundra. Despite all the e orts, there is a lack of uniformity in studying human impact, a shortage of mapping of impact over large territories and a lack of understanding of the relation between human activity and environmental response.
This dissertation develops a systematic approach to monitoring land cover and vegetation changes under human impact over northern Fennoscandia. The study area extends north and south of the treeline and covers around 400,000km2 reaching from Finnmark in Norway, through Norrbotten in Sweden, Lapland in Finland up to the Murmansk region in Russia. This is the most populated and industrially developed region of the whole sub-Arctic and, therefore, suffering most from human impact.
This dissertation identifies industrial atmospheric pollution, reindeer herding, forest logging, forest fires and infrastructure development as the primary types of human impact close to the treeline. For each type characteristic hotspots are identified and human impact is analysed in the context of physical environment as well as cultural, economical and political development of the area.
This dissertation presents an automated workflow enabling large-scale land cover mapping in northern Fennoscandia with high throughput. It starts with automated image pre-processing using image metadata and ends with automated mapping of classification results. A single classifier for multispectral Landsat data is trained on extensive field data collected across the whole region. Open source tools are used extensively to set up the processing scripts enabling rapid and reproducible analysis.
Using the developed advanced remote sensing methodology land cover maps are constructed for all identified hotspots and types of human impact. Changes in vegetation are analysed using three or four historical land cover maps for each hotspot. More than 35 Landsat TM and ETM+ images covering the period from the 1980s until 2011 are processed in an automated manner. A strong correlation between the level of impact and the scale of vegetation change is confirmed and analysed. The structure and dynamics of the local treeline and the quality of environment are analysed and assessed in the context of changing levels of impact at each hotspot and regionally.
... Higher fecundity in A. xanthogaster may be caused by the favorable temperatures in their microhabitat. As the temperature of the microhabitat increases towards optimum, insects become more fecund (Sanders et al. 1978), develop faster (Lysyk 1989), and also have greater early instar survival (Lucuik 1984). ...
The sawfly, Arge xanthogaster (Cameron) (Hymenoptera: Argidae), has recently emerged as a major pest of roses (Rosa spp. L; Rosales: Rosaceae) in Meghalaya and causes around 80% damage to wild and cultivated rose plants. This is a first report of A. xanthogaster as a pest of roses in India. Adults cause ovipositional injuries (split shoots) and larval feeding often results in complete defoliation. The species is multivoltine. Studies on its life history in new habitat are given. Since this species belongs to a species complex of Arge in which species are difficult to distinguish, an attempt was made to develop a DNA barcode based on standard barcoding gene cytochrome oxidase I (COI) of the mitochondrial DNA of this species.
... Both of these elements are likely to be affected by climate change as well as their interrelations, and their interactions with each other, other species and abiotic components of their habitat. For instance, it is expected that the combined effects of climate warming and CO 2 fertilization will directly affect spruce budworm populations through an increase of individual growth rate (Lysyk 1989), survival (Lucuik 1984) and fecundity (Sanders et al.1978). The resulting increase in the population's net per capita growth rate could be reduced by competition among individuals of the same generation and trophic interactions with other species in the food-web. ...
... Both of these elements are likely to be affected by climate change as well as their interrelations, and their interactions with each other, other species and abiotic components of their habitat. For instance, it is expected that the combined effects of climate warming and CO 2 fertilization will directly affect spruce budworm populations through an increase of individual growth rate (Lysyk 1989), survival (Lucuik 1984) and fecundity (Sanders et al.1978). The resulting increase in the population's net per capita growth rate could be reduced by competition among individuals of the same generation and trophic interactions with other species in the food-web. ...
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%).
... Drought creates stress in trees and lowers their defenses, making them less resistant to defoliating insect attacks (the plant-stress hypothesis) (Mattson and Haack 1987; Crois e and Lieutier 1993; Rouault et al. 2006), as well as to attacks by bark-beetles (Caldeira et al. 2002). Early studies of the SBW also suggested an association between the beginning of an outbreak and a series of preceding dry summers (Ives 1974;Lucuik 1984). In contrast, in this study, tree mortality increased with high humidity (high CMI). ...
Forest insects are major disturbances that induce tree mortality in eastern coniferous (or fir-spruce) forests in eastern North America. The spruce budworm (SBW) (Choristoneura fumiferana [Clemens]) is the most devastating insect causing tree mortality. However, the relative importance of insect-caused mortality versus tree mortality caused by other agents and how this relationship will change with climate change is not known. Based on permanent sample plots across eastern Canada, we combined a logistic model with a negative model to estimate tree mortality. The results showed that tree mortality increased mainly due to forest insects. The mean difference in annual tree mortality between plots disturbed by insects and those without insect disturbance was 0.0680 per year (P < 0.0001, T-test), and the carbon sink loss was about 2.87t C ha−1 year−1 larger than in natural forests. We also found that annual tree mortality increased significantly with the annual climate moisture index (CMI) and decreased significantly with annual minimum temperature (Tmin), annual mean temperature (Tmean) and the number of degree days below 0°C (DD0), which was inconsistent with previous studies (Adams et al. ; van Mantgem et al. ; Allen et al. ). Furthermore, the results for the trends in the magnitude of forest insect outbreaks were consistent with those of climate factors for annual tree mortality. Our results demonstrate that forest insects are the dominant cause of the tree mortality in eastern Canada but that tree mortality induced by insect outbreaks will decrease in eastern Canada under warming climate.
... If the slightly colder springs in this zone were to affect outbreaks, then we would have expected them to limit the duration and intensity of spruce budworm outbreaks compared with the other management zones. If there was an effect of the slightly drier beginning of summer, it would be to increase outbreak intensity as early summer moisture affects the beginning of the initial phase of outbreaks (Lucuik 1984). Instead, the most severe outbreaks were observed within northern sites in the coarse-grained zone, an area with higher July precipitation. ...
It is postulated that landscape structure changes connectivity of insect populations by affecting movement and dispersal. Spruce budworm outbreaks that have become more severe than in the past may be due in part to the effects of forest management on landscape structure, although this hypothesis remains to be tested. The main objective of this study was to evaluate the effects of landscape structure resulting from different types of management on spruce budworm outbreaks under similar biophysical conditions. The Border Lakes Landscape, with its contrasting management legacies on each side of the Canada-U.S border, provides an opportunity to study the effect of landscape structure on outbreak dynamics. We compared spruce budworm outbreak characteristics between forests managed at a fine scale (e.g., 10 hectare harvests) in Minnesota, USA, forests managed at a coarse scale (e.g., 100 hectare harvests) in Ontario, Canada, and a conservation zone overlapping the US-Canadian Border (i.e., Boundary Waters Canoe Area Wilderness and Quetico Provincial Park). We sampled sites to minimize the effect of other confounding factors such as climate and host abundance that also have an effect on spruce budworm cycle. Dendrochronological reconstructions of outbreaks in each zone allowed the detection of differences in the periodicity and synchrony of outbreaks. In comparison to the conservation zone where periodicity varied between 15 to 40 years, outbreaks were more frequent within the fine-scale managed zone (6-12 years) in the United States. Managed Canadian forests had an intermediate periodicity of 13 to 30 years. Results are consistent with the hypothesis that fragmentation and reduction of host abundance reduced the synchronization of outbreaks in the fine-scale zone thus explaining the difference in periodicity.
... If the slightly colder springs in this zone were to affect outbreaks, then we would have expected them to limit the duration and intensity of spruce budworm outbreaks compared with the other management zones. If there was an effect of the slightly drier beginning of summer, it would be to increase outbreak intensity as early summer moisture affects the beginning of the initial phase of outbreaks (Lucuik 1984). Instead, the most severe outbreaks were observed within northern sites in the coarse-grained zone, an area with higher July precipitation. ...
The “silvicultural hypothesis” of spruce budworm (Choristoneura fumiferana Clem.) dynamics postulates that increasing severity of spruce budworm outbreaks over the last century resulted from forest conditions created by past management activities. Yet, definitive tests of the hypothesis remain elusive. We examined spruce budworm outbreak dynamics (synchrony, periodicity, and intensity) in the 20th century using historical reconstruction from tree-ring chronologies sampled within 19 sites in a large ecoregion located on the border of Minnesota and Ontario. The study encompassed three areas affected by contrasting management legacies: a fine-grained area (Minnesota, six sites, average cut size = 17 ha), a coarse-grained area (Ontario, six sites, average cut size 10 times that of Minnesota), and a conservation zone (seven sites) with little recent harvest activity overlapping the border. Results suggest important differences in outbreak dynamics between the forest management zones that cannot be explained by differences in climate among sample sites. Budworm outbreaks within the conservation zone were more synchronous, with more trees per site affected and less frequent outbreaks than sites sampled within fine-scale managed areas. Outbreak dynamics within forests managed at coarser scales suggest a mixture of the conservation and fine-scale management zone outbreak patterns. Potential factors affecting differences in the observed outbreak patterns include forest pattern, composition, and age. Our study generally supports the silvicultural hypothesis and emphasizes that management legacy effects on spruce budworm dynamics should be observable at landscape scales, as well as at local scales.
... Temperature and drought have been suggested as one of the triggers for outbreaks (Greenbank 1956) although this has been dismissed by Royama (1978). Lucuik (1984) suggested that precipitation during the period of larval emergence from overwintering may be involved in the early termination of outbreaks. The dispersal of moths, also believed to be one of the triggers of new outbreaks, is strongly influenced by weather conditions such as temperature, precipitation, and wind (Greenbank 1957;Royama 1984;Régnière and Nealis 2007). ...
Much evidence is accumulating that insect distributions are changing. The changing earth’s climate is providing mobile species
with an evolving “hospitability” template, and increasing global commerce expands opportunities for mobile species to colonize
new habitats. Predicting the distribution of insects in the face of accelerating global commerce and climate change is quite
a challenge. Many fruitful approaches are available and are being improved. Some are correlative; some are based on process-level
knowledge. We have focused on an eco-physiological approach based on the known responses of species to specific weather factors
at the physiological level. Of particular importance are developmental responses, of course, as they determine climates under
which an insect can achieve a stable, adaptive seasonality. With this underlying minimal requirement, models can also take
into account other weather influences such as cold tolerance and the deleterious effects of too much heat. In this paper,
we illustrated the use of this approach to predict the change of distribution and potential impacts of the spruce budworm
Choristoneura fumiferana (Clem.), a major native insect pest of conifer forests in North America. Like previous work on the invasive gypsy moth (Lymantria dispar L.) and the native mountain pine beetle (Dendroctonus ponderosae Hopkins), the present work points to the following conclusions concerning the effects of global warming on species distributions:
(1) they will shift towards the poles (and to higher elevations); (2) temperate regions will bear the brunt of these shifts;
and (3) distribution shifts may be good or bad, depending on the species and the regions concerned.
KeywordsDistribution shift-Invasion-Forest insect-
Choristoneura fumiferana
-Climatic suitability-Climate change
Variation in insect herbivory can lead to population structure in plant hosts as indicated by defence traits. In annual herbaceous, defence traits may vary between geographic areas but evidence of such patterns is lacking for long-lived species. This may result from the variety of selection pressures from herbivores, long distance gene flow, genome properties, and lack of research. We investigated the antagonistic interaction between white spruce (Picea glauca) and spruce budworm (SBW, Choristoneura fumiferana) the most devastating forest insect of eastern North America in common garden experiments. White spruces that are able to resist SBW attack were reported to accumulate the acetophenones piceol and pungenol constitutively in their foliage. We show that levels of these acetophenones and transcripts of the gene responsible for their release is highly heritable and that their accumulation is synchronized with the most devastating stage of SBW. Piceol and pungenol concentrations negatively correlate with rate of development in female SBW and follow a non-random geographic variation pattern that is partially explained by historical damage from SBW and temperature. Our results show that accumulation of acetophenones is an efficient resistance mechanism against SBW in white spruce and that insects can affect population structure of a long-lived plant.
Insect populations have a substantial impact on Canada’s forest. They are a dominating disturbance factor and during outbreaks they can cause tree mortality over vast areas of forest. If the predicted climate changes take effect, the damage patterns caused by insects may be drastically altered, especially for the many insects whose occurrence in time and space is severely limited by climatic factors. This possibility substantially increases the uncertainties associated with the long-term planning of pest control requirements, with hazard rating models, with depletion forecasts, and with projections for the sustainability of future timber supplies. Moreover, because insect damage affects the rates of various processes in nutrient and biogeochemical cycling, potential changes in damage patterns can affect ecosystem resilience. This paper presents a number of plausible scenarios that describe how some key processes in the boreal forest’s insect defoliator outbreak systems may respond to climate change. The spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is used as an illustrative case study throughout. The potential importance of phenological synchrony in the dynamical interactions between species is emphasised. It is argued that natural selection may be a particularly important process in the response of insects to climate change and that climate change may already be influencing some insect lifecycles. The importance of threshold effects, rare but extreme events, and transient dynamics is emphasised, and the inadequacy of ‘equilibrium’ models for forest:pest systems noted. We conclude by discussing approaches to developing forecasts of how one of the boreal forest’s insect defoliator-based disturbance regimes, as a whole, might respond to climate change.
A high-resolution macrofossil analysis was conducted to reconstruct spruce budworm abundance in an 8600-year-old mire in Saguenay, Québec, Canada. Abundant spruce budworm (Choristoneura fumiferana [Clem.]) faeces recovered in the peat profile suggested endemic and epidemic presence of the insect in the study site since 8240 cal. BP. Important variations in the abundance of faeces were observed, and two exceptional periods of insect activity were delineated, from 6815 to 6480 cal. BP and during the twentieth century. Lepidoptera head capsules were also found in the Lac des Îlets peat profile. They were less abundant and more altered than spruce budworm faeces, but they offered complementary information on insect activity. The long-term perspective achieved with this macrofossil analysis strongly suggests that intense periods of spruce budworm activity were rare events during the Holocene.
About one third of North America is forested. These forests are of incalculable value to human society in terms of harvested resources and ecosystem services and are sensitive to disturbance regimes. Epidemics of forest insects and diseases are the dominant sources of disturbance to North American forests. Here we review current understanding of climatic effects on the abundance of forest insects and diseases in North America, and of the ecological and socioeconomic impacts of biotic disturbances. We identify 27 insects (6 nonindigenous) and 22 diseases (9 nonindigenous) that are notable agents of disturbance in North American forests. The distribution and abundance of forest insects and pathogens respond rapidly to climatic variation due to their physiological sensitivity to temperature, high mobility, short generation times, and high reproductive potential. Additionally, climate affects tree defenses, tree tolerance, and community interactions involving enemies, competitors, and mutualists of insects and diseases. Recent research affirms the importance of milder winters, warmer growing seasons, and changes in moisture availability to the occurrence of biotic disturbances. Predictions from the first US National Climate Assessment of expansions in forest disturbances from climate change have been upheld - in some cases more rapidly and dramatically than expected. Clear examples are offered by recent epidemics of spruce beetles in Alaska, mountain pine beetle in high-elevation five-needle pine forests of the Rocky Mountains, and southern pine beetle in the New Jersey Pinelands. Pathogens are less studied with respect to climate but some are facilitated by warmer and wetter summer conditions.
Changes in biotic disturbances have broad consequences for forest ecosystems and the services they provide to society. Climatic effects on forest insect and disease outbreaks may foster further changes in climate by influencing the exchange of carbon, water, and energy between forests and the atmosphere. Climate-induced changes in forest productivity and disturbance create opportunities as well as vulnerabilities (e.g., increases in productivity in many areas, and probably decreases in disturbance risks in some areas). There is a critical need to better understand and predict the interactions among climate, forest productivity, forest disturbance, and the socioeconomic relations between forests and people.
Insect populations have a substantial impact on Canada's forest. They are a dominating disturbance factor and during outbreaks they can cause tree mortality over vast areas of forest. If the predicted climate changes take effect, the damage patterns caused by insects may be drastically altered, especially for the many insects whose occurrence in time and space is severely limited by climatic factors. This possibility substantially increases the uncertainties associated with the long-term planning of pest control requirements, with hazard rating models, with depletion forecasts, and with projections for the sustainability of future timber supplies. Moreover, because insect damage affects the rates of various processes in nutrient and biogeochemical cycling, potential changes in damage patterns can affect ecosystem resilience. This paper presents a number of plausible scenarios that describe how some key processes in the boreal forest's insect defoliator outbreak systems may respond to climate change. The spruce budworm,Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is used as an illustrative case study throughout. The potential importance of phonological synchrony in the dynamical interactions between species is emphasised. It is argued that natural selection may be a particularly important process in the response of insects to climate change and that climate change may already be influencing some insect lifecycles. The importance of threshold effects, rare but extreme events, and transient dynamics is emphasised, and the inadequacy of equilibrium models for forest:pest systems noted. We conclude by discussing approaches to developing forecasts of how one of the boreal forest's insect defoliator-based disturbance regimes, as a whole, might respond to climate change.
Diapause termination was examined in field-overwintering populations of the spruce budworm, Choristoneura fumiferana (Clem.). The time required for emergence of overwintering larvae decreased rapidly until the end of December following which photoperiod had no effect on diapause termination. There was no detectable yearly or geographical variation in the duration of postdiapause development, or in its relationship with temperature, when measured in early March. Thus, it is concluded that diapause in this spcies ends before the end of February. Cycling temperatures led to slower development than expected from temperature responses of the overwintering larvae, suggesting developmental inertia to temperature fluctuations. There was a brief but pronounced increase in developmental rate in the first few days after transfer from the field to experimental conditions. Sensitivity of overwintered larvae to warm temperature increased gradually during postdiapause. This is hypothesized as a mechanism by which adequate synchrony is achieved between the emergence of larvae from diapause, the appearance of suitable food, and optimal weather conditions for the establishment of young larvae on host-tree foliage. A method was developed to incorporate age-dependence in mathematical descriptions of relationships between temperature and development rates for the purposes of simulation.
There is no doubt that tree survival, growth, and reproduction in North America's boreal forests would be directly influenced by the projected changes in climate if they occur. The indirect effects of climate change may be of even greater importance, however, because of their potential for altering the intensity, frequency, and perhaps even the very nature of the disturbance regimes which drive boreal forest dynamics. Insect defoliator populations are one of the dominating disturbance factors in North America's boreal forests and during outbreaks trees are often killed over vast forest areas. If the predicted shifts in climate occur, the damage patterns caused by insects may be considerably changed, particularly those of insects whose temporal and spatial distributions are singularly dependent on climatic factors. The ensuing uncertainties directly affect depletion forecasts, pest hazard rating procedures, and long-term planning for pest control requirements. Because the potential for wildfire often increases in stands after insect attack, uncertainties in future insect damage patterns also lead to uncertainties in fire regimes. In addition, because the rates of processes key to biogeochemical and nutrient recycling are influenced by insect damage, potential changes in damage patterns can indirectly affect ecosystem resilience and the sustainability of the multiple uses of the forest resource.
In this paper, a mechanistic perspective is developed based on available information describing how defoliating forest insects might respond to climate warming. Because of its prevalence and long history of study, the spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is used for illustrative purposes in developing this perspective. The scenarios that follow outline the potential importance of threshold behaviour, historical conditions, phenological relationships, infrequent but extreme weather, complex feedbacks, and natural selection. The urgency of such considerations is emphasized by reference to research suggesting that climate warming may already be influencing some insect lifecycles.
We examined vertical transmission of Nosema fumiferanae in the eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), and how it affects overwintering distribution and survival and spring emergence and dispersal of second-instar larvae in outbreak populations. Females containing 5.0 x 10(5) spores or more consistently produced 100% infected progeny. Transmission efficiency was still 50% at burdens as low as 0.2 x 10(5) spores per moth. Infection intensity in offspring increased with maternal spore load but became highly variable above 25 x 10(5) spores per female. Nosema multiplied in second instars for at least 1 month after they entered dormancy, regardless of temperature (2 degrees C versus 21 degrees C). Infection did not affect the distribution of overwintering larvae in a white spruce canopy. Dormancy survival between late-summer and the following spring was lower in families from infected females and was negatively correlated with larval infection intensity. Infection delayed larval emergence from hibernacula in the spring and resulted in delayed dispersal of emerged larvae, at least when parasite prevalence and infection intensities were high. Infected larvae were less successful in establishing feeding sites after dispersal. Our results underscore the potential of Nosema infection to negatively affect processes early in the budworm life cycle.
An absolute requirement for sugar could not be shown but laboratory rearing experiments using artificial diets have demonstrated a definite increase in weight of adult spruce budworm ( Choristoneura fumiferana (Clem.) Freeman) with increasing dietary levels of certain sugars. Males exhibit a threshold of 0.9% soluble sugars above which higher sugar levels produce no further increases in size. Females respond with an increase in size up to 4.0%, the highest level tested. Generally, faster development rates accompany greater mature weights on diets with higher nutrient levels.
Maltose, raffinose, glucose, sorbitol, sucrose, and fructose are all good sugar sources. Galactose and trehalose are only slightly inferior. Lactose, ribose, melibiose, xylose, mannose, arabinose, and melezitose in the diet are little different from the sugarless control. Sorbose is somewhat inhibitory.
Results of transfer experiments confirm the importance of sugar particularly during late larval development. They also indicate that a high protein diet during early instars has a significant effect on development rates. These results suggest that departure from the normal synchrony of development in the insect and its host can affect both rate of development and mature size of the insect.
Larvae are reared on a synthetic diet in 1 oz. ribbed plastic cups. To eliminate the task of placing individual larvae on food, small gauze patches containing 25–40 larvae are placed in the cups prior to emergence from hibernacula. Larvae establish feeding sites between the ribs and are relatively undisturbed by others in the cup until the fifth instar. For maintenance of rearing stock the number of larvae is reduced to six to eight per cup, and they are allowed to pupate in the cups. Up to 100 pairs of pupae are placed in screened cages for adult emergence, mating, and oviposition. When the adults emerge balsam fir foliage is introduced and most of the eggs are deposited on the needles. Needles or twigs with egg clusters are transferred to large dishes the inside of which is painted black. The dish is tightly sealed with parafilm to which small gauze patches are attached and then placed under artificial lighting. The newly-hatched larvae are attracted toward the light and spin hibernacula in the gauze. The parafilm and gauze are sealed in plastic bags for cold storage treatment. By this system up to 10,000 larvae per week are easily produced.A discussion on the selection of rearing stock, rearing conditions, rearing containers, and the use of anti-fungal agents is included in the report.
The spruce budworm, Choristoneura fumiferana (Clemens), was reared on a synthetic diet. Comparison of two successive laboratory generations reared on synthetic diet and on frozen balsam fir buds showed that diet-fed insects had a higher survival, developed faster, were heavier, mated more successfully, and were more fecund.
Nearly all forest regions in the Province of Quebec where balsam fir ( Abies balsamea (L.) Mill.) is an important tree component have been subjected to severe defoliation by the spruce budworm, Choristoneura fumiferana (Clem.), during the past 20 years. These outbreaks have followed an easterly direction beginning near the Ontario-Quebec border in 1939 and ending in the Gaspé Peninsula in 1958.
Potted 3–4-yr-old seedlings of white, red, and jack pine (Pinus strobus L., P. resinosa Ait., and P. banksiana Lamb.), white, black, and Norway spruce (Picea glauca (Moench) Voss, P. mariana (Mill.) B.S.P., and P. abies (L.) Karst.), and Eastern larch or tamarack (Larix laricina (Du Roi) K. Koch) were grown outdoors and subsequently subjected to freezing temperatures in a freezing chamber during the period from September 1968 to November 1969. Each freezing test consisted of five trees per species. Electrical impedance readings were taken on each tree. The frost hardiness was determined by visually assessing damage and measuring subsequent growth. Differences in frost hardiness between species were small. The minimum frost hardiness in the summer was between −3 and −5 C. The maximum frost hardiness in the winter was below −40 C, with the exception of Norway spruce, which had its maximum around −40 C. It is suggested that the processes of hardening and dehardening consist of two stages. Electrical impedanc...
New Brunswick outbreaks of the spruce budworm which began in 1912 and 1949 are considered in relation to the theory of climatic release. Studies on a natural population show that larval development is more rapid in dry and sunny weather than in humid and cloudy weather. Polar air masses bring the favorable conditions, and tropical air masses and cyclones the unfavorable. June precipitation and temperature records, analyzed in conjunction with weather maps, show that climatic changes took place in regions where the outbreaks developed. The outbreaks were preceded by dry and sunny summers during four or five consecutive years. Although direct mortality of the budworm due to adverse weather conditions has not been observed, favorable climatic conditions may have indirectly promoted population increase from the endemic to the outbreak level in the following ways. Flower production became more frequent in periods of dry years and larvae which fed on staminate flowers developed more rapidly. Larvae that developed early in the season gave rise to more fecund females than larvae that developed late. The age of current foliage consumed is also related to fecundity. The rate of development of balsam fir relative to the budworm varies from year to year. It is postulated that the average fecundity of the budworm increases in the pre-outbreak years as the result of favorable climatic conditions and greater than usual flower production. Larval mortality is greater in years with a prolonged developmental period although the increase is not statistically significant. The theory that outbreaks in New Brunswick resulted from the spread of populations from outbreak areas to the west will be considered in the second part of this two-part paper.
Unseasonal temperatures, as low as −6°C, were recorded in western Montana in mid-June 1969, a period when western spruce budworm (Choristoneura occidentalis Freeman) larvae were actively feeding on newly developing foliage of coniferous host trees. Studies in progress at that time provided circumstantial evidence that the freeze reduced: (1) budworm populations on Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), western larch (Larix occidentalis Nutt.), and ponderosa pine (Pinus ponderosa Laws.) over 90%; and (2) budworm damage to young larch 54–71%.
A new sampling technique for spruce budworm
- Miller