Population Dynamics Of Forest Insects Research Articles

On the characterization of patterning in spruce budworm time-series data

I outline the “definitional problem” in forest insect outbreak analytics and show how it is related to the “counting problem” in dendroentomology and the “forecasting problem” in forest insect population dynamics, through the ubiquitous presence of non-stationary complex periodicity. Using real-world examples from the spruce budworm ( Choristoneura fumiferana Clem.) system, I show that regardless how outbreak patterning is characterized—whether by peak impact, cycle frequency, interval duration, or interval severity—the distribution in pattern attributes appears to be extremely variable, regardless how the data are processed through definitional filters. I show that this extreme variability is an unavoidable and key feature of the system’s dynamics and argue that it needs to be viewed as an object of study, instead of a nuisance problem to be swept under the rug. The single biggest opportunity for rapid gains in spruce budworm predictive ecology is determining the environmental and ecological factors that separate high-intensity from low-intensity outbreak cycling.

Spatiotemporal dynamics of forest insect populations under climate change.

Effects of climate on forest insect populations are complex, often involving drivers that are opposing, nonlinear, and nonadditive. Overall, climate change is driving an increase in outbreaks and range shifts. Links between climate and forest insect dynamics are becoming clearer; however, the underlying mechanisms remain less clear. Climate alters forest insect population dynamics directly through life history, physiology, and voltinism, and indirectly through effects on host trees and natural enemies. Climatic effects on bark beetles, wood-boring insects, and sap-suckers are often indirect, through effects on host-tree susceptibility, whereas climatic effects on defoliators are comparatively more direct. We recommend process-based approaches to global distribution mapping and population models to identify theunderlying mechanisms and enable effective management of forest insects.

Landscape predictions of western balsam bark beetle activity implicate warm temperatures, a longer growing season, and drought in widespread irruptions across British Columbia

Warming temperatures and drought are leading to unprecedented irruptions of forest insects worldwide. Altered climatic regimes have the potential to allow native forest insects to express novel behaviors and expand in latitude and elevation beyond their hypothesized thermal tolerances. Yet, disentangling the drivers of novel behaviors and range expansions is difficult due to cross-scalar interactions that dictate forest insect population dynamics. We investigated the irruptive dynamics of western balsam bark beetle (Dryocoetes confusus Swaine), which undergoes intermittent, long-lasting, but low-severity outbreaks in subalpine fir (Abies lasiocarpa Hook) forests. We compiled data from 1998 to 2019 across British Columbia, Canada, at 1 and 16 km2 resolutions to describe the spatiotemporal structure of beetle outbreaks, predict the landscape susceptibility to outbreaks, explain when outbreaks occur based on bioclimatic drivers, explore whether beetle populations exhibit self-driving growth, and determine whether the extent of outbreaks has increased. Overall, we found that outbreaks occur in discrete clusters and are synchronous at distances of 10–25 km. Further, we found that landscape susceptibility to beetle outbreaks was best explained by latitude*elevation (i.e., the product of latitude [m] and elevation [m] Z-standardized) and volume of fir (m3/ha; >17.5 cm size class; >100 yrs.) both within 8 km and each pixel. Meanwhile, a longer growing season, increased growing degree day accumulation, and drought best explained when outbreaks occurred. Further, we did not find evidence to suggest that beetle populations exhibit self-driving population growth. Finally, we found that the extent of beetle outbreaks has increased over the last 20 years and that increases in landscape susceptibility primarily occurred at higher latitude*elevations and were best explained by an increase in the mean growing season and degree day accumulation. In other words, abnormally warm temperatures have facilitated a northward and upward expansion of western balsam bark beetle. Collectively, these results serve as the first quantification of the spatiotemporal dynamics of this understudied insect and support previous modeling efforts to investigate the multi-scale drivers of western balsam bark beetle outbreaks. We propose that future work should identify specific supercooling points, the relationship between temperature and development rate, and how the relatively high within-stand variability in age and size class of subalpine fir affect the irruptive dynamics of this understudied bark beetle.

Field Translocation of Mountain Pine Beetles Suggests Phoretic Mite Communities Are Locally Adapted, and Mite Populations Respond Variably to Climate Warming.

Simple SummaryClimate warming has significant effects on forest insect populations, particularly bark beetles, which cause millions of hectares of forest tree damage. Bark beetles live alongside a diverse host of other organisms which affect the success of beetle attacks on trees and are also affected by climate changes. Here, we explore climate effects on symbiotic mite communities associated with the mountain pine beetle (Dendroctonus ponderosae). We show that warming causes significant shifts in the abundance of mites. These effects were dependent on source population, suggesting mite populations are adapted to their local climates. Understanding beetle–mite patterns is important because mites can directly affect beetle reproduction by feeding on eggs, or indirectly affect beetle health by introducing fungi. Our results provide foundational information for understanding how climate change will affect beetle–mite associations; and serve to help determine how these shifting associations will affect the success of bark beetles in forest ecosystems.Temperature is a key determining factor in the population dynamics of forest insects and their associated biota. Bark beetles, often considered key agents of change in forest ecosystems, are particularly affected by warming in their environment. Beetles associate with various phoretic mite species that have direct/indirect effects on beetle fitness and population dynamics, although there is limited knowledge of how temperature affects these communities. Here, we use a field reciprocal translocation experiment with the addition of a novel “warming” environment to represent future changes in local environment in two populations of a keystone bark beetle species (Dendroctonus ponderosae). We hypothesize that mite community abundances as carried by bark beetles are significantly altered when not in their native environments and when subjected to climate warming. We use multivariate generalized linear models based on species abundance data to show that mite community compositions significantly differ across different field climates; and that these patterns diverge between source populations, indicating local adaptation. Our study offers foundational information on the general effects of simulated climate-warming on the compositional shifts of common and abundant biotic associates of mountain pine beetles and may be used as a model system for other important insect–mite systems.

Impact of Horizontal Edge-Interior and Vertical Canopy-Understory Gradients on the Abundance and Diversity of Bark and Woodboring Beetles in Survey Traps.

Simple SummaryTraps baited with sex attractants and plant odors are used by regulatory agencies to survey for alien invasive forest insects that may arrive via importation of goods from overseas. The performance of these surveys is affected not only by the type of traps and attractants used, but also by where the traps are placed at survey sites. We tested the effect of trap position along horizontal (relative to the forest edge) and vertical (canopy-understory) forest gradients on the diversity and abundance of species of bark and wood boring beetles detected. Both horizontal and vertical trap position affected trap performance, but trends differed among taxa and were context-dependent. For example, jewel beetles were detected mainly in canopy traps regardless of horizontal position, whereas bark and ambrosia beetles were detected mainly in understory traps placed along the forest edge. For optimal early detection of potentially invasive bark and wood boring beetles, surveys should place traps at multiple locations along horizontal and vertical gradients.Semiochemical-baited intercept traps are important tools used to collect information about the presence/absence and population dynamics of forest insects. The performance of these tools is influenced by trap location along both horizontal edge–interior and vertical understory–canopy gradients. Consequently, the development of survey and detection programs requires both the development of effective traps and semiochemical lures but also deployment protocols to guide their use. We used field trapping experiments to examine the impact of both horizontal edge–interior and vertical understory–canopy gradients and their interactions with the species richness and abundance of Buprestidae, Cerambycidae and Curculionidae. Both gradients had significant effects on the diversity and abundance of all three families collected in traps and the pattern of gradient effects differed between the two experiments. In the first experiment, traps were deployed along transects involving large (>100 m) forest gaps and in the second experiment traps transected small (ca. 15 m) forest gaps. These results were consistent with the idea that gradient effects on the abundance and diversity of these three families of forest Coleoptera are context dependent. The results of this study suggest that monitoring programs for bark and woodboring beetles should deploy traps at multiple locations along both vertical understory–canopy and horizontal edge–interior gradients.

Index to Titles and Authors/Editors of Books Reviewed

Index to Titles and Authors/Editors of Books Reviewed

Long-distance dispersal of spruce budworm (Choristoneura fumiferana Clemens) in Minnesota (USA) and Ontario (Canada) via the atmospheric pathway

Dispersal can play an important role in the population dynamics of forest insects, but the role of long-distance immigration and emigration remains unclear due to the difficulty of quantifying dispersal distance and direction. We designed an agent-based spruce budworm flight behavior model that, when interfaced with temperature, wind speed, and precipitation output from a high-resolution atmospheric model, produces detailed flight trajectories and deposition patterns over large landscapes. Rules and relationships describing budworm adult (moth) lift-off, ascent, horizontal flight, and descent were parameterized using a detailed empirical study of budworm dispersal behavior and corresponding meteorological conditions during a 1970s outbreak in New Brunswick, Canada. Simulated moth landings were assumed to be dependent in part on the availability of suitable host tree species. We applied the model to a 6.4million ha landscape at the border between northern Minnesota (USA) and Ontario (Canada) during an eight-day flight window in late June 2007. Specimens collected during and after this flight window indicated moths emerging from an inland source of outbreak populations dispersed over 150km to trap sites near the north shore of Lake Superior, where localized cooling was predicted to have delayed emergence of locally-produced budworm moths. Simulations suggested immigration of moths to lakeshore sites from the outbreak source was plausible on three of eight dates within the flight window, but the relatively narrow deposition footprints implied immigration occurred on different dates across lakeshore sites. Apart from wind speed and direction, precipitation and low temperatures limited dispersal to substantially shorter distances for a few dates within the simulated flight window. Key uncertainties limiting our understanding of atmospheric transport of spruce budworm include behavioral responses to vertical heterogeneity in the air temperature profile, the precipitation threshold required for the forced descent of moths from the air column, and search mechanisms affecting host and/or mate location during long-distance flight.

Spatiotemporal patterns of mountain pine beetle activity in the southern Rocky Mountains

The current mountain pine beetle (MPB; Dendroctonus ponderosae) outbreak in the southern Rocky Mountains has impacted approximately 750 000 ha of forest. Weather and habitat heterogeneity influence forest insect population dynamics at multiple spatial and temporal scales. Comparison of forest insect population dynamics in two principal host species may elucidate the relative contribution of weather and landscape factors in initiating and driving extensive outbreaks. To investigate potential drivers of the current MPB outbreak, we compared broadscale spatiotemporal patterns of MPB activity in lodgepole pine (Pinus contorta) and ponderosa pine (Pinus ponderosa) from 1996 to 2010 in Colorado and southern Wyoming with regional weather fluctuations, and then tracked the annual meso-scale progression of the epidemic in lodgepole pine with respect to weather, topographic, previous MPB activity, and forest stand attributes. MPB activity in lodgepole pine compared to ponderosa pine showed higher magnitude and extent of spatial synchrony. Warm temperatures and low annual precipitation favorable to beetle populations showed high regional synchrony across areas of both pine species, suggesting that habitat interacts with weather in synchronizing MPB populations. Cluster analysis of time series patterns identified multiple, disjunct locations of incipient MPB activity (epicenters) in lodgepole pine, which overlapped an earlier 1980s MPB outbreak, and suggests a regional trigger (drought) across this homogenous forest type. Negative departures from mean annual precipitation played a key role in subsequent spread of MPB outbreak. Development of the outbreak was also associated with lower elevations, greater dominance by lodgepole pine, stands of larger tree size, and stands with higher percentage canopy cover. After epidemic levels of MPB activity were attained, MPB activity was less strongly associated with stand and weather variables. These results emphasize the importance of considering differences in patterns of MPB dynamics for different host pine species even under similar regional-scale weather variation and the nonstationarity of outbreak dynamics over time.

Modelling the spatial population dynamics of the green oak leaf roller ( Tortrix viridana) using density dependent competitive interactions: Effects of herbivore mortality and varying host-plant quality

Cyclic population dynamics of forest insects with periods of more than two generations have been discussed in relation to a variety of extrinsic and intrinsic forces. In the present study, we employed the selection pressure of density dependent competitive interactions according to Witting's equations ( Witting, 2000) as driver for a discrete spatiotemporal model of the green oak leaf roller ( Tortrix viridana). The model was successfully parameterised to rebuild the cyclic population dynamics of an empirical data set of a 30-year leaf roller monitoring in Russia. Our analysis focussed on the role of herbivore mortality and host plant food quality, which have a significant effect on T. viridana population dynamics. An additional egg or larvae mortality lowers population density and can lead to selection pressures that favour individuals with higher growth rate. This increased population growth rate can not only compensate the additional mortality, but also can lead to higher average moth abundances in subsequent generations. Furthermore, we analysed the effect of inter- and intraspecific variation in host plant quality on herbivore population dynamics and the spatial distribution of abundance and defoliation patterns. We found significant effects of the qualitative composition of a trees neighbourhood on the herbivore population of the respective tree. Also, the patchy damage patterns observable in reality have been reproduced by the present model. The applicability of the model approach and the putative genetic processes underlying Witting's model are discussed.

Modeling forest insect population dynamics

Overview of the Special Interdisciplinary Minisymposium at the 2009 meeting of the Society for Mathematical Biology on modeling of forest insect population dynamics.

Modeling forest insect population dynamics

AbstractOverview of the Special Interdisciplinary Minisymposium at the 2009 meeting of the Society for Mathematical Biology on modeling of forest insect population dynamics.

Green oak leaf roller moth dynamics: An application of discrete time mathematical models

Discrete mathematical model is selected for description of green oak leaf roller ( Tortrix viridana L.) population dynamics. Experimental data set from Rubtsov [Rubtsov, V.V., 1992. Models of Oscillation Processes in Forest Ecosystems, Forest Institute, Moscow, Russian Federation, p. 39 (in Russian)] is analyzed from the standpoint of phenomenological theory of forest insect population dynamics [Isaev, A.S., Khlebopros, R.G., Nedorezov, L.V., Kiselev, V.V., Kondakov, Yu. P., 1984. Dynamics of Forest Insects Populations, USSR, Nauka, Novosibirsk, p. 224 (in Russian); Isaev, A.S., Khlebopros, R.G., Nedorezov, L.V., Kiselev, V.V., Kondakov, Yu.P., Soukhovol'sky, V.G., 2001. Population Dynamics of Forest Insects, Russian Federation, Nauka, Moscow, p. 347 (in Russian)]. For checking hypotheses confidence for fitting of experimental time series, Moran–Ricker model, Maynard Smith–Slatkin model, and some others are used. Selection of statistical criteria for estimating parameter's values is discussed. In addition, probabilities of realizations of several dynamical regimes are estimated.

Restoration of phase portrait structure for the dynamics of a forest pest, the pine moth ( Dendrolimus pini L.)

In this paper we consider the method for the restoration of phase portrait structure of population dynamics and apply this method for analysis of experimental data on the population dynamics of Dendrolimus pini L. The method is based on the results of phenomenological theory of forest insect population dynamics (Isaev, A.S., 1979. Lesovedenie 3, 27–42; Isaev, A.S., 1984. Nauka, 74–82.) and includes the elements of statistics, cluster analysis and knowledge of trajectory's behavior of ordinary differential equation's systems. Using the method allows determination of such important features of phase plane as the value of stable level, structure and boundaries of the stable zone, behavior of the threshold curve which separates the stable and outbreak zones and coordinates of ‘point of escape’ etc.

Dynamics of Forest Insect Density: Bifurcation Approach

Six basic phase portraits differing in character and in the number of their equilibrium behaviour regimes were suggested in the classification of forest insect population dynamics. The portraits graphically illustrate six types of dynamic behaviour of numbers of the system “phytophage-entomophage”: two types of stable equilibrium dynamics (stationary and oscillatory) and four types corresponding to outbreaks of mass reproduction—fixed, permanent, reversive and true outbreaks, respectively.In this paper we consider the single parameter model, with its parametric domains realizing a wide spectrum of phase dynamics, both basic and transitional. The changes in the phase portraits are accompanied by the bifurcations in the model.The results of these analyses are in agreement with the “stability principle of mobile ecological systems” and may supply its parameter substantiation at the model level.

Population Dynamics of Forest Insects.

Population Dynamics of Forest Insects.