Dynamics of Forest Insect Populations: Patterns, Causes, Implications
Abstract
Insects multiply. Destruction reigns. There is dismay, followed by outcry, and demands to Authority. Authority remembers its experts or appoints some: they ought to know. The experts advise a Cure. The Cure can be almost anything: holy water from Mecca, a Government Commis sion, a culture of bacteria, poison, prayers denunciatory or tactful, a new god, a trap, a Pied Piper. The Cures have only one thing in common: with a little patience they always work. They have never been known entirely to fail. Likewise they have never been known to prevent the next outbreak. For the cycle of abundance and scarcity has a rhythm of its own, and the Cures are applied just when the plague of insects is going to abate through its own loss of momentum. -Abridged, with insects in place of voles, from C. Elton, 1924, Voles, Mice and Lemmings, with permission of Oxford University Press This book is an enquiry into the "natural rhythms" of insect abundance in forested ecosystems and into the forces that give rise to these rhythms. Forests form unique environ ments for such studies because one can find them growing under relatively natural (pri meval) conditions as well as under the domination of human actions. Also, the slow growth and turnover rates of forested ecosystems enable us to investigate insect popula tion dynamics in a plant environment that remains relatively constant or changes only slowly, this in contrast to agricultural systems, where change is often drastic and frequent.
Chapters (23)
Among the pest species that damage larch cones in Eurasia, the larch cone fly, Lasiomma melania Ackland (Diptera: Anthomyiidae), is undoubtedly one of the most serious. The genus Lasiomma contains at least three closely related species that attack larch cones in the same areas: L. melania, L. laricicola Karl, and L. infrequens Ackland. These three species, previously known under the name of Lasiomma (= Chortophila = Phorbia = Hylemya)laricicola Karl, were separated in 1965 on the basis of male characters1 and later using female characters.34 Thus, much cone damage attributed to the single species, L. laricicola, in Europe and the Soviet Union during the first half of the twentieth century, was probably also attributable to the two other species. For example, L. melania is generally the dominant species in the French Alps, even though it was only discovered in 1975 in this region.34 Today, the presence of L. melania is well established in Western Europe,1,17,34,35 in the Soviet Union from the European part to the Far Eastern regions,8,12,31,48,49 and in China.9 The larch cone fly is restricted to Larix cones but damages various species and subspecies of this genus according to region, including European larch (L. decidua), Siberian larch (L. sibirica), Dahurian larch (L. gmelini), and Japanese larch (L. leptolepis = L. kaempferi). Thus, its geographic range probably covers the major part of the Eurasian natural distribution area of the genus Larix, as well as the western European regions in which these conifers have been introduced.
The development of new practices in agriculture and forestry frequently alters the habitats of herbivorous insects, turning normally nondamaging species into economically significant pests, Seed orchard plantations in Siberia provide an example wherein cultural practices have given rise to problems of protecting larch seed from pests, in particular, the larch gall midge, Dasyneura laricis F. Loew (Diptera: Cecidomylidae).
Two armored scales, Fiorinia externa Ferris and Nuculaspis (formerly Tsugaspidiotus
4) tsugae (Marlatt) (Homoptera: Diaspididae), native to Japan,44,45 were accidentally introduced into the vicinity of New York City at the turn of the nineteenth century,8,42,48 They have since spread into several northeastern states and have become destructive pests of Eastern hemlock, Tsuga canadensis Carriere, their primary host. In addition to Eastern hemlock, these two scales attack many other native and exotic species of conifers.23 A survey that I conducted at two arboretums in Connecticut demonstrated that F. externa can mature and reproduce on Abies (9 species), Cedrus (3 species), Picea (12 species), Pinus (12 species), Pseudotsuga (1 species), Taxus (2 species), and Tsuga (5 species), while N. tsugae matured and reproduced on Abies (2 species), Cedrus (1 species), Picea (3 species), and Tsuga (5 species). The lower number of conifers exploited by N. tsugae probably reflects the much lower abundance of this scale in hemlock forests surrounding the two arboretums, rather than a more restricted host range.23 Both scales were generally more abundant on Abies and Picea than on Tsuga,23 which suggests that the pests may become even more important as they spread farther northward into the natural ranges of these other conifers.
Scale insects are among our most important pests, but relatively few have been studied in detail. These insects are often small and inconspicuous, and identification is usually a highly specialized activity. The beech scale Cryptococcus fagisuga Lindinger is to some extent an exception because the white wax secreted by this insect makes it highly conspicuous and the absence of any similar coccid on beech largely eliminates the chore of identification. Nevertheless, during the nineteenth century, this organism was described as a fungus (Psilonia nivea), the curly wax threads being taken for fungal hyphae.8,20
The balsam woolly adelgid, also known as the balsam woolly aphid, is native to the silver fir (Abies alba) forests of central Europe. The insect was introduced into North America around 1900. Although European firs are not seriously affected by this adelgid, North American firs frequently experience either crown dieback or tree death, or both.
The white lace lerp, Cardiaspina albitextura Taylor (Psylloidea: Spondyliaspididae), causes severe defoliation, branch dieback, and sometimes death of its food plants, Eucalyptus blakelyi Maiden and E. camaldulensis camaldulensis Dehnhardt in southeastern Australia.2,22 Its distribution covers the entire range of E. blakelyi in the montane and riverine zones of southern New South Wales, northeastern Victoria, and the Australian Capital Territory around the city of Canberra. Infestations in river red gum (E. camaldulensis) forests are generally restricted to southern areas (south of the dotted line in Fig. 1), where the subspecies E. camaldulensis camaldulensis dominates. The northern subspecies, E. camaldulensis obtusa, is not attacked by C. albitextura but supports outbreaks of at least two undescribed species of the spondyliaspidid genus Creiis. These psyllids cause necrosis of the leaves similar to, but not as deeply colored as, those caused by the nymphs of C. albitextura and its close relatives.22
The Nantucket pine tip moth, Rhyacionia frustrana (Comstock), is one of the most common forest insects in the eastern United States. It was first discovered and studied on Nantucket Island, Massachusetts,63 where it was causing severe damage to pines and was described as the “frustrating Retinia” (= Rhyacionia).23 The taxonomic status of R.
frustrana is generally clear except for its relationship with R. bushnelli Miller, thought by some to be a subspecies.59 The primary difference is that R. frustrana overwinters in infested shoots and R. bushnelli overwinters in the duff and soil beneath the trees.
Mountain birch, Betula pubescens Ehrhart ssp. tortuosa (Ledebour) Nyman, forests form the tree line in northwestern Europe and are periodically defoliated by the autumnal moth, Epirrita = Oporinia autumnata (Borkhausen). This chapter analyzes the population dynamics of Epirrita, but many of our conclusions may apply to other defoliators, such as Operophtera brumata (Linnaeus), O. fagata (Scharfenberg), O. bruceata (Hu1st), and Erannis defoliaria (Clerck), which often exhibit synchronous fluctuations in the same or adjacent areas.38,62
The Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), is a common defoliator of fir in the interior forests of western North America. It is one of four western species of Orgyia, but it is the only member of the group that occasionally reaches outbreak numbers while feeding exclusively on conifers.24 Because of the explosive and destructive nature of its outbreaks, the Douglas-fir tussock moth has achieved much deserved notoriety among forest managers. For this reason, considerable effort has been made in recent years to understand the dynamics of tussock moth populations and to develop methods for minimizing their impact.11
The Nun Moth, Lymantria monacha (Linnaeus) (Lepidoptera: Lymantridae), owes its name to its similarity to another moth, the monk (Panthea coenobita), which also has a black and white monk-cloak coloring. It is the classic insect pest of the spruce forests of Europe. Why this is so can be understood by the following description of an outbreak in (then) East Prussia (now Poland—Russia):
On the 27th of July 1853 the forests were invaded by clouds of moths carried by the south winds from Poland. The swarms spread out and it looked as if the forests had been hit by a snowstorm. The outbreak reached its height in 1855 and the larvae then no more discriminated between conifers and decidious trees. They ate everything and of all ages, even in the afforestations, so at last no green leaf was to be seen. The branches of both pine and spruce were so heavy with the weight of larvae that they drooped towards the ground and the falling of excrement sounded like persistent rain. In June and July 1855 great swarms of parasitic flies and wasps began to show up. They stung the Nun Moth larvae which then became sick and fell from the trees. Lying on the forest floor in a layer more than one foot thick they filled the forests with an abominable stench. When the Nun stopped Ips typographus started.
The larch casebearer, Coleophora laricella Hubner (Lepidoptera: Coleophoridae), is a small silver-gray moth whose larvae mine needles of larches, Larix spp. Apparently of European origin, this defoliator was first recorded in North America near Northampton, Massachussetts, in 1886.3 It had spread westward to Minneapolis by 195012 and, in the spring of 1957, was collected just south of St. Manes, Idaho. A survey of larch forests in the intermountain region that year indicated that about 44,000 ha (170 sq mi) were infested.1 The population spread rapidly and uniformly until, in 1970, it occupied virtually all larch stands in the intermountain regions of eastern Washington, Oregon, and northern Idaho (Fig. 1).
The pine beauty moth, Panolis flammea Denis and Schiffermuller (Lepidoptera: Noctuidae), is a pest of lodgepole pine (Pinus contorta) in Scotland. This indigenous species has a widespread distribution throughout the United Kingdom and Europe on its natural host plant, Scots pine (Pinus sylvestris). In the British Isles, very low densities of P. flammea are normally found in Scots pine plantations, the average density being about 0.1 pupae m −2, and densities above 0.3 pupae m −2 being rare.6 However, serious outbreaks have been recorded on Scots pine in central Europe from 1810 onward,20 and it is thought likely that P. flammea was the pest responsible for serious damage in Nurnberg during 1449–1450.9 Pine beauty moth outbreaks have also occurred on Scots pine in Sweden,29 Norway,4 and Finland.35
Two species of insects are well-known pests of the teak tree (Tectona grandis) in India—Hyblaea puera Cramer (Lepidoptera: Hyblaeidae), popularly known as the teak defoliator, and Eutectona machaeralis (Walker) syn. Pyrausta machaeralis Walker (Lepidoptera: Pyraustidae), popularly known as the teak skeletonizer. Larvae of the former feed on the entire leaf, leaving only the major veins, while those of the latter feed only on the green matter, leaving all the veins intact, thus qualifying for the name, skeletonizer. Of the two, H. puera is the more serious because it feeds on young leaves during the early part of the growing season, compared with E. machaeralis, which feeds on old leaves not long before natural leaf fall. First described in 1794,14H. puera, originally included in the family Noctuidae, has been recognized as a pest of teak in India for almost a century. This is not surprising, since the first teak plantation in India was raised as early as 1842, in Nilambur, Kerala State. Preliminary information on the life history of H. puera and the nature of its damage were published from 1898 to 1903.10,11,19.30 The species is fairly widely distributed in the tropics: in the Oriental and Australian regions (India, Burma, Sri Lanka, Java, Papua—New Guinea, Cape York Peninsula of northern Queensland in Australia, and the Solomon Islands); in Central America (West Indies); and in Africa (South Africa and parts of East Africa). 3.9,12,14 Teak is considered the principal host plant, although some other hosts have been recorded.
The pine looper moth, Bupalus piniaria Linnaeus, has been a serious pest of European forestry for more than 200 years, particularly in Germany,15,17,30,32,61 In the Netherlands, where the looper has never attained pest status, the population dynamics and general biology have been intensively studied.10,20,37,38 The pine looper was not known as a pest in Britain until 1953, when larvae totally defoliated 40 ha of Scots pine (Pinus sylvestris) at Cannock Chase, Staffordshire. Subsequent secondary infestations by the bark beetle, Tomicus piniperda Linnaeus, resulted in death of the trees.11 Since then, pupal samples have been taken annually in some 50 different Forestry Commission pine areas. Seven subsequent outbreaks on five different sites have been treated with insecticides. High populations have also been found in plantations of Corsican pine (Pinus nigra) and lodgepole pine (Pinus contorta). This chapter describes the dynamics of populations in Britain, but makes frequent reference to studies in Germany and the Netherlands.
The spruce budworm, Choristoneura fumiferana (Clemens), (Lepidoptera: Tortricidae) was first described from specimens collected in Virginia,17 but this native insect occurs primarily in the northern boreal forest from Newfoundland west to the McKenzie River near 66°N.53 The most extensive and destructive outbreaks have occurred in the maritime provinces (New Brunswick, Nova Scotia, Newfoundland), Quebec, Ontario, Maine, and the Great Lakes states. This defoliator feeds primarily on the new growth of balsam fir (Abies balsamea), red spruce (Picea rubens), white spruce (Picea glauca), and black spruce (Picea mariana). Sometimes it feeds on other conifers, such as eastern larch (Larix lancina), eastern hemlock (Tsuga canadensis), Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), and eastern white pine (Pinus strobus).28,47
The gypsy moth, Lymantria dispar (Linnaeus), is one of the most serious pests of hardwood forests in temperate regions. A cartographical analysis of gypsy moth35 shows it to occur within the latitudes 20°–60°N, where annual rainfall is 25–100 cm and temperature isotherms are 15–27°C for July and —18–12°C for January. The genus probably originated in East Asia,36 which is where L. dispar exhibits its greatest variability39 (Fig. 1). Proceeding westward from East Asia to western Europe, adult and larval coloration patterns become less variable and females progressively lose the ability to fly.36’65 The range of the gypsy moth was extended through a series of founder events westward into Europe and from France to North America.
The pine sawfly, Diprion pini Linné (Hymenoptera, Diprionidae), is widespread from the British Isles to the Soviet Union and from North Africa to Finland. The family Diprionidae includes about 85 species living exclusively in the coniferous forests of the Northern Hemisphere. The species are assumed to be very close to primitive forms derived from panorpoid ancestors in the Permian 70,53 Many of these species belong to the genera Diprion and Neodiprion that differentiated in the subfamily Diprioninae, in the Palaearactic and Nearctic continents, respectively. In the Old World, the subfamily is represented by the genera Diprion, Gilpinia, Microdiprion, Macrodiprion (essentially in Europe), Prionomeion (North Africa), and Nesodiprion (Asia) and by a few species of American origin, such as Neodiprion sertifer Geoffroy.
Woodwasps or horntails (Siricidae) are primitive phytophagous hymenopterans that naturally infest a variety of coniferous and hardwood trees throughout North America, Eurasia, North Africa, and Japan.10,13,27,36,42,43,55,75,78 Although woodwasps have been reported to be responsible for economic degradation of otherwise marketable timber,5,35,55,73,77,85 such infestations are more symptomatic of a prior pathological condition than a primary cause of tree mortality.19 Therefore, in their natural habitat, wood-wasps are secondary to other predisposing agents, which may include defoliation or debilitation of trees by insect and/or fungal attack,6,19 fire or smog damage,15,16 and mechanical injury.46
The major pine species in Japan, Japanese red pine (Pinus densiflora) and Japanese black pine (P. thunbergii), have suffered heavy mortality for several decades. Many beetle species are found under the bark of dead trees, including the Japanese pine sawyer, Monochamus alteratus Hope. On the basis of field observations, entomologists assumed that trees had been diseased before beetle attacks. A research project begun in 1968 proved that the causal agent of the disease was the pine wood nematode, Bursaphelenchus
lignicolus Mamiya et Kiyohara, which was subsequently reclassified as B. xylophilus (Steiner and Buhrer) Nickle. Intensive inspection of the insects associated with dead pine trees demonstrated that the principal vector of the nematode was M. alternatus.12,20
The greater European spruce bark beetle, Dendroctonus micans (Kugelann) (Coleoptera: Scolytidae), is, with the Chinese species Dendroctonus armandi Tsai and Li, the only palaearctic representative of its genus. It appears to have moved to Eurasia in relatively recent times, and its closest relative is the Alaskan D. punctatus LeConte, the two species being doubtfully distinct.79
The Southern pine beetle, Dendroctonus frontalis Zimmerman (Coleoptera: Scolytidae), is the most destructive insect pest of pine forests in the southeastern United States and in parts of Mexico and Central America (Fig. 1). This is a well-worn statement but is nonetheless richly deserved and quite accurate. The beetle epitomizes the definition of its genus, killer of trees. As such, D. frontalis can overcome even vigorous trees when its populations are large. In the United States, the southern pine beetle primarily colonizes loblolly (Pinus taeda) and shortleaf (P. enchinata) pines, both of which are important sources of pulp and timber. These pines are fast-growing species, inhabiting some of the finest timber-growing land on the continent. In addition, most watersheds in the southern pine forest are dominated by these species, and in many recreational areas high-valued old growth pine prevail.
The fir engraver beetle, Scolytus ventralis LeConte (Coleoptera: Scolytidae), was first described from two specimens collected at Vancouver, Washington, but the species has been subsequently recorded throughout the western United States and British Columbia.20,55 Its primary hosts are true firs, Abies; specifically white fir (A. concolor), California red fir (A. magnifica), and grand fir (A. grandis).34 It has also been observed on occasion attacking subalpine fir, Douglas-fir, Engelmann spruce, mountain hemlock, and Western larch.20,55
The striped ambrosia beetle, Trypodendron lineatum (Olivier) (Coleoptera: Scolytidae), is one of nature’s recyclers.10 Along with other ambrosia beetles, its ecological niche is to locate and infest dead and dying timber. It is a pioneer in the degradation process, exploiting this renewed habitat each spring, and leaving it within months to be further degraded by saprophytic fungi and other wood-infesting insects.
... Efforts to prevent or mitigate disturbance impacts have therefore become an integral part of forest management in Europe. The applied measures include, for example, improvement of tree vigor and morphology, modification of stand structure and composition, or reduction of fuel loads and breeding substrate for insects (Berryman, 1988;Gardiner & Quine, 2000;Jactel et al., 2009;Wermelinger, 2004). Research has also highlighted some controversies related to active disturbance management. ...
... In Europe's production forests, management has traditionally strived to control bark beetle populations to prevent or mitigate their impacts (Berryman, 1988;Wermelinger, 2004). These measures either aim to directly control populations of bark beetles or to modify forest structure and composition to create environment that is less conducive to the outbreaks (Wermelinger, 2004). ...
... Previous studies indicated that Norway spruce forests may not be sustained in many regions of Europe because of intensifying outbreaks of bark beetles, genetic maladaptation to future climates, and sensitivity to climatic stress (Frank et al., 2017;Marini et al., 2012;Seidl, Schelhaas, et al., 2014;Zang et al., 2014). The role of active management of forests disturbances, however, has not been included in these investigations although it is an integral aspect of European forest management (Berryman, 1988;Wermelinger, 2004). We showed that contrast in the vulnerability of monospecific forests and forests managed for diversity is considerably amplified by climate change. ...
1. Wind and bark beetle disturbances have increased in recent decades, affecting Europe’s coniferous forests with particular severity. Management fostering forest diversity and resilience is deemed to effectively mitigate disturbance impacts, yet its efficiency and interaction with other disturbance management measures remain unclear.
2. We focused on Central Europe, which has become one of the hotspots of recent disturbance changes. We used the iLand ecosystem model to understand the interplay between species composition of the forest, forest disturbance dynamics affected by climate change and disturbance management. The tested measures included (i) active transformation of tree species composition toward site-matching species; (ii) intensive removal of windfelled trees, which can support the build-up of bark beetle populations; and (ii) reduction of mature and vulnerable trees on the landscape via modified harvesting regimes.
3. We found that management systems aiming to sustain the dominance of Norway spruce in the forest are failing under climate change, and none of the measures applied could mitigate the disturbance impacts. Conversely, management systems fostering forest diversity substantially reduced the level of disturbance. Significant disturbance reduction has been achieved even without salvaging and rotation length reduction, which is beneficial for ecosystem recovery, carbon and biodiversity.
4. Synthesis and applications: We conclude that climate change amplifies the contrast in vulnerability of monospecific and species-diverse forests to wind and bark beetle disturbance. Whereas forests dominated by Norway spruce are not likely to be sustained in Central Europe under aggravating climate change, different management strategies can be applied in species diverse forests to reach the desired control over the disturbance dynamic. Our findings justify some unrealistic expectations about the options to control disturbance dynamics under climate change and highlight the importance of management that fosters forest diversity.
... Other methods, such as experimentally placing logs in rearing conditions, would have been temperatures exceed 18°C (Chapman and Kinghorn 1958;Berryman 1988). Shortly after their dispersion, T. lineatum are highly attracted by ethanol produced by anaerobic metabolism of stressed or dying trees, and in a lesser extent, by low levels of the monoterpene α-pinene (Moeck 1970;Bauer and Vité 1975;Nijholt 1979). ...
... Canadian temperatures such as in the study area. Even if T. lineatum is highly associated with recently dead trees, it has been shown that they rather colonize timber killed at previous fall or winter than those killed the same spring (Dyer and Chapman 1965;Berryman 1988). These trees will have undergone ethanol production for a longer period of time and are more likely to have lower starch content in the sapwood and lower cell viability (Chapman and Dyer 1969). ...
... However, field observations allow to assert that there has been a certain degree of colonization, since several trees had frass (i.e. boring dust and feces cleaned out from the gallery) accumulated on the bark scales and at the base of the bole (Berryman 1988). ...
... Since its introduction from Nova Scotia in 1890 (56), the insect-pathogen complex of beech bark disease (BBD) has dramatically shifted size structure and species composition in northeastern hardwood forests (82). With mortality reaching 80-90% of mature beech stems following widespread BBD infection (9), chronically infested stands experience reduced beech dominance and vigor and dense beech thickets in post-invasion forests. These shifts negatively affect groundlayer plant biodiversity (17,45,111) and nutrient cycling (38,83), including the nitrogen cycle (38,83). ...
Outbreaks of insects and diseases are part of the natural disturbance regime of all forests. However, introduced pathogens have had outsized impacts on many dominant forest tree species over the past century. Mitigating these impacts and restoring these species are dilemmas of the modern era. Here, we review the ecological and economic impact of introduced pathogens, focusing on examples in North America. We then synthesize the successes and challenges of past biotechnological approaches and discuss the integration of genomics and biotechnology to help mitigate the effects of past and future pathogen invasions. These questions are considered in the context of the transgenic American chestnut, which is the most comprehensive example to date of how biotechnological tools have been used to address the impacts of introduced pathogens on naïve forest ecosystems.
... One of the major ecological questions regarding stochastic models is if environment fluctuations can sustain population fluctuations (Mubayi et al., 2019). This topic is connected to the observation of fluctuations in various animal populations with frequencies distinct from those of periodic environmental oscillations (Berryman, 1988;Hudson et al., 1992;Krebs and Myers, 1974;Moss et al., 1996;Watson et al., 1984), comprising plankton (Benincà et al., 2008;Goulden and Hornig, 1980;McCauley and Murdoch, 1987;Pratt, 1943;Rogers et al., 2022). The causes of population fluctuations have long intrigued theoretical ecologists, dating back to the work of Lotka and Volterra (Kendall et al., 1999). ...
Marine ecosystems exist in a noisy and uncertain environment, not governed by deterministic laws. The development of ecological communities is significantly influenced by variability, and the interaction between nonlinearity and stochastic processes can lead to phenomena that deterministic models cannot explain. Plankton, forming the base of the marine food web, are highly affected by stochastic fluctuations due to their short reproductive timescales. Investigating the effects of noise on plankton growth is essential for accurately describing and predicting marine health. We present a realistic biogeochemical model where multiplicative white noise represents environmental stochasticity affecting plankton. The model suggests ergodic properties in the presence of stochastic fluctuations, with temporal and ensemble distributions being coherent. Analytical and numerical analyses reveal that, given sufficiently low noise intensity, dynamics near equilibrium resemble an Ornstein-Uhlenbeck additive process. With higher noise intensities, resonance occurs, particularly when endogenous dynamics are periodic. The results indicate that low noise intensity can positively influence plankton persistence with an higher number of species coexisting, while higher noise intensity can establish a new equilibrium in the system.
... It is theoretically possible to write an equation or system of equations that takes into account all these factors. Systems of ordinary differential equations have been used to design such models since the classic works of A. Lotka and V. Volterra [1,2] to their modern interpretations of the late 20th century [3][4][5][6][7]. Each of those equations described the dynamics of a separate ecosystem component, i.e., a regulatory factor that depends on the density of the modeled insect population. ...
This paper addresses the problem of constructing a mathematical model of population density dynamics and the dynamics of forest areas damaged by spongy moth (Lymantria dispar L.) outbreaks in the United States, Europe, Russia, and Japan. The key variable of the model is either the pest population density or the area of forests damaged by spongy moths during a season. This variable can be considered proportional to the total current pest abundance in the study area. For the purposes of modeling, data from a number of different authors was used (see bibliography), as well as data from surveys conducted at the egg or caterpillar stage. The complexity of modeling the dynamics of L. dispar abundance is largely due to the fact that, when studying the dynamics of spongy moth population density, the values of external factors such as parasites, predators, and the amount of available food are often unknown. A simple model was proposed using only two types of data: population density and monthly weather characteristics. Our analysis demonstrated that, even in the absence of knowledge regarding the characteristics of ecosystem components interacting with the spongy moth population (parasites, predators, and the state of forage trees), it is possible to introduce models that characterize the regulatory processes in the population in terms of (i) the presence of negative and positive feedbacks in the system and (ii) the influence of external weather factors. The system under investigation was described as an autoregressive system, whereby the current state of the population is dependent on its state in previous years. The order of autoregression in the system was estimated using the order of the maximum significant partial autocorrelation function. It was found that the regulation of spongy moth population density was characterized by the presence of two feedback loops: positive feedback between the current population density and the population density in the previous season and negative feedback between the current population density and the population density two years ago. To evaluate the model, its stability margin was calculated and found to be directly proportional to the positive feedback coefficient and inversely proportional to the negative feedback coefficient. The model was demonstrated to explain up to 90% of the observed variance of real data. Although the model coefficients for different local populations (North America, Europe, and Asia) differ, the general form of the equation describing both direct data on population densities and indirect data on pest dynamics characterized by areas of stand damage is consistent. Consequently, the form of the ADL model is general, irrespective of the location of the local population.
... In the stable dispersal phase, the density x 1 of the population is extremely low and its individuals utilize only a small part of the available food objects. The outbreak phase occurs only when the pest population density surpasses a critical value (x r ), eventually reaching the value x 2 , where the entire population consumes all available food objects in the given territory [28][29][30][31][32], and finally returns from state x 2 to state x 1 . ...
Three models of abundance dynamics for forest insects that depict the development of outbreak populations were analyzed. We studied populations of the Siberian silkmoth Dendrolimus sibiricus Tschetv. in Siberia and the Far East of Russia, as well as a population of the pine looper Bupalus piniarius L. in Thuringia, Germany. The first model (autoregression) characterizes the mechanism where current population density is dependent on population densities in previous k years. The second model considers an outbreak as analogous to a first-order phase transition in physical systems and characterizes the outbreak as a transition through a potential barrier from a low-density state to a high-density state. The third model treats an outbreak as an effect of stochastic resonance influenced by a cyclical factor such as solar activity and the “noise” of weather parameters. The discussion focuses on the prediction effectiveness of abundance dynamics and outbreak development for each model.
... As a result, the economic thresholds for insecticide application are much higher in forestry than in agriculture (Letourneau, 2012;Thompson, 2011), and forests are only treated when a risk of total defoliation is anticipated. In temperate regions, a few species of moths (Lepidoptera) and sawflies (Symphyta) show periodic population outbreaks that can pose such a risk (Berryman, 1988), with potentially dire implications for the health of affected trees (Lobinger, 1999;MacLean, 2016). Among them, the spongy moth Lymantria dispar L. (Lepidoptera: Erebidae) is considered the most critical defoliator of temperate hardwood forests, notably in Eastern North America where it has infested millions of acres since its introduction in the late 19th century (McManus & Cs oka, 2007) and considerable resources are expended on slowing its westward expansion (Mayo et al., 2003). ...
Outbreaks of the spongy moth Lymantria dispar can have devastating impacts on forest resources and ecosystems. Lepidoptera‐specific insecticides, such as Bacillus thuringiensis var. kurstaki (BTK) and tebufenozide, are often deployed to prevent heavy defoliation of the forest canopy. While it has been suggested that using BTK poses less risk to non‐target Lepidoptera than leaving an outbreak untreated, in situ testing of this assumption has been impeded by methodological challenges. The trade‐offs between insecticide use and outbreaks have yet to be addressed for tebufenozide, which is believed to have stronger side effects than BTK. We investigated the short‐term trade‐offs between tebufenozide treatments and no‐action strategies for the non‐target herbivore community in forest canopies. Over 3 years, Lepidoptera and Symphyta larvae were sampled by canopy fogging in 48 oak stands in southeast Germany during and after a spongy moth outbreak. Half of the sites were treated with tebufenozide and changes in canopy cover were monitored. We contrasted the impacts of tebufenozide and defoliator outbreaks on the abundance, diversity, and functional structure of chewing herbivore communities. Tebufenozide treatments strongly reduced Lepidoptera up to 6 weeks after spraying. Populations gradually converged back to control levels after 2 years. Shelter‐building species dominated caterpillar assemblages in treated plots in the post‐spray weeks, while flight‐dimorphic species were slow to recover and remained underrepresented in treated stands 2 years post‐treatment. Spongy moth outbreaks had minor effects on leaf chewer communities. Summer Lepidoptera decreased only when severe defoliation occurred, whereas Symphyta declined 1 year after defoliation. Polyphagous species with only partial host plant overlap with the spongy moth were absent from heavily defoliated sites, suggesting greater sensitivity of generalists to defoliation‐induced plant responses. These results demonstrate that both tebufenozide treatments and spongy moth outbreaks alter canopy herbivore communities. Tebufenozide had a stronger and longer lasting impact, but it was restricted to Lepidoptera, whereas the outbreak affected both Lepidoptera and Symphyta. These results are tied to the fact that only half of the outbreak sites experienced severe defoliation. This highlights the limited accuracy of current defoliation forecast methods, which are used as the basis for the decision to spray insecticides.
... Outbreaks collapse as a consequence of one or several of the following factors: destruction of resources, food depletion, host resistance (Benz 1974;Schultz and Baldwin 1982;Schopf 1986;Clancy et al. 1988;Quiring and McKinnon 1999;Mumm and Hilker 2006), natural enemies (Murray and Elkinton 1989;Elkinton et al. 2004;Moreau and Lucarotti 2007;Hilker and McNeil 2008;Möller and Bemmann 2009;Mirchev et al. 2013), or adverse weather (Pernek et al. 2008;Netherer and Schopf 2010;Möller et al. 2017;Hentschel et al. 2018). Population dynamics of important forest pests are discussed in detail in Berryman (1988). ...
The US Department of Agriculture considers insect outbreaks as the most expensive type of natural disturbance. Outbreaks of phyllophagous and xylophagous forest pests have significant ecological and economic impacts. Severe defoliation in combination with specific weather conditions is able to induce widespread forest dieback. Since most insect pests that undergo regular outbreaks are thermophilic, the frequency and magnitude of outbreaks are likely to increase with the predicted climate changes, specifically with rising temperatures. Thus, reliable monitoring and forecast tools as well as containment strategies for insect pests are urgently needed in order to maintain the multi-functionality of our forests in the future.KeywordsBroadleaved forestsClimate changeConiferous forestsHost plantsInsect population dynamicsNatural enemiesPest managementPredispositionTree mortality
... Bark beetles (Coleoptera: Curculionidae: Scolytinae), are the most important pests of coniferous trees [1]. Of those belonging to the genus Ips, Ips typographus is the most destructive species, damaging spruce forests across Eurasia [2], and causing economicallysignificant attacks in spruce forests [3][4][5]. In addition, beetles of the genus Pityogenes can also be of considerable economic importance. ...
The population densities of I. typographus and P. chalcographus inside the Carpathian Mountains increasing mostly because of the non-synchronized and divers management strategies. The growing loss of trees from one year to another indicates assessment to determine the influence of the current management practices (or the absence of such) on bark beetle densities. A comprehensive tree-year assessment were made inside the Apuseni Natural Park, with a surface of 75,784 ha, to assess the population density of bark beetles. High abundance of both species were detected from one year to another, both in managed and unmanaged forests, the latter explained by the presence of scattered wind falling trees which represent favorable places for oviposition. General linear modelling revealed that the effect of environmental variables (forest mean age, forest density, altitude and slope) on I. typographus density were only significant under management systems, and only forest age has significantly negative effect on bark beetles densities. Overall, we conclude that there is little difference in population between non-intervention and intervention areas and even over a relatively short period of time (2011-2013), the population of both species expanded, and new uninfected habitats were infected both in unmanaged and managed forests, therefore a synchronized management system has to be developed. Climate variables as temperature and precipitations has more significant effects on population density than management.
... This indicates that outbreaking species may respond to changes in biological and/or abiotic factors differently from that of non-outbreaking species, and the former may have an intrinsic motivation differing from the latter (Myers, 1993). To date, the physiological responses of outbreak species to some factors have been heavily researched (Berryman, 1988;Veran et al., 2015); however, the molecular basis of these responses is still unclear, which limits our understanding of the intrinsic mechanisms responsible for insect outbreaks. ...
Insect population dynamics are closely related to ‘human’ ecological and economic environments, and a central focus of research is outbreaks. However, the lack of molecular-based investigations restricts our understanding of the intrinsic mechanisms responsible for insect outbreaks. In this context, the moth Dendrolimus punctatus Walker can serve as an ideal model species for insect population dynamics research because it undergoes periodic outbreaks. Here, high-throughput whole-transcriptome sequencing was performed using D. punctatus, sampled during latent and outbreak periods, to systemically explore the molecular basis of insect outbreaks and to identify the involved non-coding RNA (ncRNA) regulators, namely microRNAs, long non-coding RNAs, and circular RNAs. Differentially expressed mRNAs of D. punctatus from different outbreak periods were involved in developmental, reproductive, immune, and chemosensory processes; results that were consistent with the physiological differences in D. punctatus during differing outbreak periods. Targets analysis of the non-coding RNAs indicated that long non-coding RNAs could be the primary ncRNA regulators of D. punctatus outbreaks, while circular RNAs mainly regulated synapses and cell junctions. The target genes of differentially expressed microRNAs mainly regulated the metabolic and reproductive pathways during the D. punctatus outbreaks. Developmental, multi-organismal, and reproductive processes, as well as biological adhesion, characterized the competing endogenous RNA network. Chemosensory and immune genes closely related to the outbreak of D. punctatus were further analyzed in detail: from their ncRNA regulators’ analysis, we deduce that both lncRNA and miRNA may play significant roles. This is the first report to examine the molecular basis of coding and non-coding RNAs’ roles in insect outbreaks. The results provide potential biomarkers for control targets in forest insect management, as well as fresh insights into underlying outbreak-related mechanisms, which could be used for improving insect control strategies in the future.
... Disease can kill trees or predispose them to mechanical failure (Franklin et al., 1987;Berryman, 1988). Tree mortality due to root rot disease (Heterobasidion fig. ...
Abiotic and biotic disturbances in alpine forests can reduce forest cover or change the structure of the forest and consequently reduce the protective effect of forest against natural hazards such as avalanches and rockfalls. In this review article, the effect of the main abiotic (forest fire, windthrow, ice break, snow break, avalanche and rockfall) and biotic (insects and pathogens) disturbances in protection forests are presented along with their potential influence on the protective effect of forest against avalanches and rockfalls. In general, natural disturbances negatively affect the protective effect of forest, especially in the case of large-scale and severe events, which in alpine areas are mostly caused by storms, bark beetle outbreaks, avalanches and forest fires. Climate change induced interactions between disturbances are expected to present challenges in the management of protection forests in the future.
... Outbreaks of forest insects are documented by a vast literature (for example, Morris, 1963;Berryman, 1986Berryman, , 1988. Also there are many attempts at the mathematical modelling of this phenomenon (Isaev et al., 2015). ...
An individual-based model is presented which shows that cyclic insects outbreaks in the forest (here presented as a certain type of the dynamics of total numbers of insects in the forest) can be a result of the joint action of four factors: (1) spatial structure of the system — resources, green tree biomass, used by larval insects are distributed in a two-dimensional space, (2) properties of trees — their limited resistance to feeding by insects, and regeneration ability after some time of relaxation, when they cannot sustain a local insect population, (3) insect properties — the most important of which is the ability of adult individuals to move between spatially distributed resources and to lay eggs on neighbouring trees, and (4) the type of dynamics of local insect population exploiting resources of a tree, which depends on individual variability of insects and their progeny production. Insects disperse from the original tree and occupy successive not infested trees over the forest, omitting the trees with exploited resources that need time for regeneration. The cyclic outbreak dynamics will take place when insects have opportunity to return to the places where there are trees with regenerated resources. In addition to the cyclic outbreak, we will observe permanent outbreaks (small fluctuations of insect, combined with a similar dynamics of tree biomass) or pulse outbreaks (an increase in the number of insects, followed by their extinction and leading to a temporary destruction of tree biomass). The type of the simulation output will depend on the values of the model parameters. Intermediate resistance of trees to insect feeding and their not very short regeneration time will lead to cyclic outbreaks. Additionally great number of dispersing insects will promote cyclic outbreaks. High degree of individual variability, high mortality of adult insects or small progeny production will produce favourable conditions for permanent outbreaks. Pulse outbreaks can easily occur when insect individual variability is small or progeny production is high.
... Food webs in freshwater systems are often highly connected with many omnivorous species [51] and this trophic complexity could mitigate against outbreaks in populations of constituent species. Second, much of the research into population outbreaks has focused on phytophagous terrestrial insects because the impact on their food plants is often conspicuous, and well-studied species typically feed on plants that have economic value, such as forest insects [66][67][68]. If outbreaks in insect populations are peculiar to herbivory on angiosperms, then they are likely to be rare in freshwater systems simply because a minority of aquatic insect species consume macrophytes (Section 3.1). ...
The study of insect populations is dominated by research on terrestrial insects. Are aquatic insect populations different or are they just presumed to be different? We explore the evidence across several topics. (1) Populations of terrestrial herbivorous insects are constrained most often by enemies, whereas aquatic herbivorous insects are constrained more by food supplies, a real difference related to the different plants that dominate in each ecosystem. (2) Population outbreaks are presumed not to occur in aquatic insects. We report three examples of cyclical patterns; there may be more. (3) Aquatic insects, like terrestrial insects, show strong oviposition site selection even though they oviposit on surfaces that are not necessarily food for their larvae. A novel outcome is that density of oviposition habitat can determine larval densities. (4) Aquatic habitats are often largely 1-dimensional shapes and this is presumed to influence dispersal. In rivers, drift by insects is presumed to create downstream dispersal that has to be countered by upstream flight by adults. This idea has persisted for decades but supporting evidence is scarce. Few researchers are currently working on the dynamics of aquatic insect populations; there is scope for many more studies and potentially enlightening contrasts with terrestrial insects.
... Direct control with insecticides is an effective method of control over large areas, whilst pheromone trapping can be used as a means of disrupting mating [6]. Conventional monitoring methods include winter egg counts, larval counts, larval frass estimates, pupal counts, counts of adults resting on tree trunks and defoliation assessments [1][2][3][4][5]7,14,25]. However, these methods are labour-intensive and not good at detecting population increases over short time scales. ...
The studies which were effected by different authors enabled to be published some articles which include scientific results related to the most important defoliator of coniferae-the nun moth Lymantria monacha L., 1758. In this work the researches had an applicative character, with the view to using the results in drawing up a plan for monitoring and control the populations of Lymantria monacha L., 1758, by making use of pheromone bait traps. At the same time, the researches had in view to get new scientific information in order to improve the methods of controlling the pest, existent at the moment and of tracing the focuses of this pest, prejudicial to the forest domain of Sibiu county (Romania). The studies enabled also to be tracked the dynamics of the population of Lymantria monacha L., 1758 and to notice that the male moths can be attracted by using pheromone bait to open areas, 200-250 m distance from the border of the forest. The studies were effected in the spruce and fir arboretum which cover 70 percent of the forest, aged between 50 and 125 years.The researches effected in the last 5 years (2011-2015) aimed at the monitoring of this month, the dynamics of its population, the efficiency of capturing the male moths and the way of installing the pheromone traps in the domain of the state Forest Range Miercurea Sibiului and the private Forest Range Tilișca, totalizing 14,932.37 hectares forest.
... Bark beetles (Ips typographus, L., and Dendroctonus spp.) are important biotic disturbance agents in the coniferous forests of Europe and North America, respectively (Christiansen and Bakke, 1988;Fahse and Heurich, 2011;Raffa et al., 2008;Seidl et al., 2011;Seidl et al., 2014). In the past decades, an increasing number of severe bark beetle outbreaks has led to an extensive economic loss in the forest industry (Goheen and Hansen, 1993;Waring et al., 2009). ...
The European spruce bark beetle Ips typographus, L. (hereafter bark beetle), causes major economic loss to the forest industry in Europe, especially in Norway Spruce (Picea abies). To minimise economic loss and preclude a mass outbreak, early detection of bark beetle infestation (so-called “green attack” stage – a period at which trees are yet to show visual signs of infestation stress) is, therefore, a crucial step in the management of Norway spruce stands. It is expected that a bark beetle infestation at the green attack stage affects a tree's physiological and chemical status. However, the concurrent effect on key foliar biochemical such as foliar nitrogen and chlorophyll as well as spectral responses are not well documented in the literature. Therefore, in this study, the early detection of bark beetle green attacks is investigated by examining foliar biochemical and spectral properties (400–2000 nm). We also assessed whether bark beetle infestation affects the estimation accuracy of foliar biochemicals. An extensive field survey was conducted in the Bavarian Forest National Park (BFNP), Germany, in the early summer of 2015 to collect leaf samples from 120 healthy and green attacked trees. The spectra of the leaf samples were measured using an ASD FieldSpec3 equipped with an integrating sphere. Significant differences (p < 0.05) between healthy and infested needle samples were found in the mean reflectance spectra, with the most pronounced differences being observed in the NIR and SWIR regions between 730 and 1370 nm. Furthermore, significant differences (p < 0.05) were found in the biochemical compositions (chlorophyll and nitrogen concentration) of healthy versus green attacked samples. Our results further demonstrate that the estimation accuracy of foliar chlorophyll and nitrogen concentrations, utilising partial least square regression model, was lower for the infested compared to the healthy trees. We show that early stage of infestation reduces not only foliar biochemical content but also their retrieval accuracy. Our results further indicate that remote sensing measurements can be successfully used for the early detection of the bark beetle infestation. We demonstrated that bark beetle infestation at the green attack stage effects leaf spectral response as well as leaf biochemical properties and their retrievals from hyperspectral measurements.
Forests in Croatia are characterized by higher levels of biodiversity in species composition. Three significant events occurred in Croatian forests over the past ten years, all of which have a common denominator—sanitary felling. The challenge in the sustainable development of forests started with the ice storm of 2014 that amounted to damage and raised costs in forest stands to EUR 231,180,921. The second challenge was in 2017 when the bark beetle outbreak occurred in the Gorski Kotar region. In December 2017, a windstorm in the same area caused damage to approximately 500,000 m3 of wood stock. The third climate extreme was in the summer of 2023 when three storms with strong winds and heavy rain damaged even-aged forests of common beech and pedunculated oak. The damage was substantial: 3,954,181 m3 of timber was mostly broken and destroyed across 21,888.61 ha of area, and the most damage was in the pedunculate oak forests of Slavonia, i.e., Quercus robur subsp. Slavonica, at 1,939,175 m3. For the main meteorological stations in lowland Croatia, data on precipitation amounts (mm) and wind speeds (m/s) were collected for the period 1981–2023, and the results of our analysis for the last decade are presented. Meteorological drought was analyzed using the rain anomaly index RAI. Data regarding open space fires in the Mediterranean karst area of Croatia were collected from the Croatian Firefighting Association, and the calculation of the burned area index (BAI) was determined. Throughout the entire area of Gorski Kotar County, a sample of permanent plots was set and used to assess the extent of forest damage from the ice storm in 2014 and for the establishment of permanent monitoring of the recovery of trees and forests damaged by the ice storm. The monitoring of bark beetles in the Gorski Kotar region started in 1995 and is still in progress. The aftermath of bark beetle outbreaks in two uneven-aged silver fir stands was studied after a bark beetle outbreak and a sanitary felling of 4655.34 m3. In the area of lowland Croatia, a statistically significant and positive correlation was found between sanitary fellings, maximum wind speeds, and rain anomaly indices in even-aged forests. In conclusion, sustainable development will be at risk due to difficult recovery, rising costs, and overall climate change in the years to come.
Wildfire activity in the western U.S. has highlighted the importance of effective management to address this growing threat. The Lookout Mountain Thinning and Fuels Reduction Study (LMS) is an operational-scale, long-term study of the effects of forest restoration and fuel reduction treatments in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and mixed-conifer forests in central Oregon, U.S. The broad objectives of the LMS are to examine the effectiveness and longevity of treatments on wildfire risk and to assess the collateral effects. Treatments include four levels of overstory thinning followed by mastication of the understory vegetation and prescribed burning. Stands were thinned to residual densities of 50, 75, or 100% of the upper management zone (UMZ), which accounts for site differences as reflected by stand density relationships for specific plant communities. A fourth treatment combines the 75 UMZ with small gaps (~0.1 ha) to facilitate regeneration (75 UMZ + Gaps). A fifth treatment comprises an untreated control (UC). We examined the causes and levels of tree mortality that occurred 2–9 years after treatments. A total of 391,292 trees was inventoried, of which 2.3% (9084) died. Higher levels of tree mortality (all causes) occurred on the UC (7.1 ± 1.9%, mean ± SEM) than on the 50 UMZ (0.7 ± 0.1%). Mortality was attributed to several bark beetle species (Coleoptera: Curculionidae) (4002 trees), unknown factors (2682 trees), wind (1958 trees), suppression (327 trees), snow breakage (61 trees), prescribed fire (19 trees), western gall rust (15 trees), cankers (8 trees), mechanical damage (5 trees), dwarf mistletoe (4 trees), and woodborers (3 trees). Among bark beetles, tree mortality was attributed to western pine beetle (Dendroctonus brevicomis LeConte) (1631 trees), fir engraver (Scolytus ventralis LeConte) (1580 trees), mountain pine beetle (Dendroctonus ponderosae Hopkins) (526 trees), engraver beetles (Ips spp.) (169 trees), hemlock engraver (Scolytus tsugae (Swaine)) (77 trees), and Pityogenes spp. (19 trees). Higher levels of bark beetle-caused tree mortality occurred on the UC (2.9 ± 0.7%) than on the 50 UMZ (0.3 ± 0.1%) which, in general, was the relationship observed for individual bark beetle species. Higher levels of tree mortality were attributed to wind on the 100 UMZ (1.0 ± 0.2%) and UC (1.2 ± 1.5%) than on the 50 UMZ (0.2 ± 0.02%) and 75 UMZ (0.4 ± 0.1%). Higher levels of tree mortality were attributed to suppression on the UC (0.5 ± 0.3%) than on the 50 UMZ (0.003 ± 0.002%) and 75 UMZ + Gaps (0.0 ± 0.0%). Significant positive correlations were observed between measures of stand density and levels of tree mortality for most causal agents. Tree size (diameter at 1.37 m) frequently had a significant effect on tree mortality, but relationships varied by causal agent. The forest restoration and fuels reduction treatments implemented on the LMS increased resistance to multiple disturbances. The implications of these and other results to the management of fire-adapted forests are discussed.
The winter mortality of mountain pine beetle (Dendroctonus ponderosae Hopkins) larvae caused by temperatures below survivable thresholds and sudden decreases in temperature is among the most influential factors limiting population growth. Due to the importance of winter mortality in the demise of mountain pine beetle infestations, a widely used winter mortality model was developed at the Canadian Forest Service and the United States Forest Service. It predicts lethal temperatures and survival probabilities given temperature time series over the winter season. We present a rare and possibly the first peer-reviewed validation of this winter mortality model, wherein we independently tested the model at a new region in Canada by comparing model predictions to the observed lower lethal temperature thresholds and cold-associated mortality. Model predictions were biologically reasonable but slightly biased. Bias was exacerbated by the inaccurate translation of air temperature data from weather stations to temperatures under the bark where larvae develop. The spatial prediction of relative mortality observed across the study area in Banff National Park was poor—likely because the mountainous terrain presents a difficult prediction challenge when under-bark temperatures are not directly observed. Our results will help inform users of model constraints and how to optimize the accuracy of model predictions.
Both the eight-spined spruce bark beetle (eight-spined beetle, Ips typographus) and the six-spined spruce bark beetle (six-spined beetle, Pityogenes chalcographus) have major deleterious effects on Norway spruce (i.e., Picea abies, the host tree) in Europe. However, future potential range shifts of the two pests and their range overlap with Norway spruce have not yet been characterized. Through range dynamic models, we characterized their future range expansions, as well as their range overlap with their host tree under current–future change scenarios in 2100. Host availability was the greatest contributor to the range shifts of the two pests, and climatic changes were the main drivers of the range expansion of the host. The potential range, expanded range, and overlapped range were larger for the six-spined beetle than for the eight-spined beetle. The host tree, i.e., Norway spruce, might face increasing threats from the two pests in the future. Future climate change will likely indirectly facilitate range shifts of pests by promoting increases in the area capable of sustaining the host tree. The six-spined beetle might pose a greater threat to Norway spruce than the eight-spined beetle, albeit the latter has previously been considered to have more deleterious effects on Norway spruce.
Citation: Kunz, M.; Esper, J.; Kuhl, E.; Schneider, L.; Büntgen, U.; Hartl, C. Combining Tree-Ring Width and Density to Separate the Effects of Climate Variation and Insect Defoliation. Abstract: Though frequently used in dendroclimatology, European larch (Larix decidua Mill.) is regularly defoliated by mass outbreaks of the larch budmoth (Zeiraphera griseana Hb., LBM). The near-cyclic growth depressions are unrelated to but possibly coincide with cold summers, which challenges signal detection on interannual timescales. LBM defoliation events cause sharp maximum latewood density declines and irregular earlywood/latewood ratios in the outbreak year, followed by one or two anomalously narrow rings. Here, we present a process-based method integrating these diverse response patterns to identify and distinguish LBM-related signals from climate-induced deviations. Application to larch sites along elevational transects in the Swiss Alps reveals the algorithm to perform better than existing extreme event detection methods, though our approach enables additional differentiation between insect-and climate-induced signatures. The new process-based multi-parameter algorithm is a suitable tool to identify different causes of growth disturbances and will therefore help to improve both tree-ring-based climate and insect defoliation reconstructions.
Herbivorous insects are influenced by both ‘bottom-up’ forces mediated through host plants and ‘top-down’ forces from natural enemies. Few studies have tried to evaluate the relative importance of the two forces in determining the abundance of insects. The leaf beetle Phratora vulgatissima Linnaeus sometimes occurs at high densities and severely damages the willow Salix cinerea in forest habitats. For willows growing in open agricultural landscapes (farmland S. cinerea ), the leaf beetle generally occurs at low densities and plants receive little damage. The purpose of the present study was to evaluate the relative importance of host plant quality and natural enemies behind the observed difference in P. vulgatissima abundance. Female egg-laying and larval performance (growth and survival) were studied on caged willow branches in the field to investigate if plant quality differs between S. cinerea trees growing in forest and farmland habitats. The survival of eggs exposed to natural enemies was examined to see if predation could explain the low abundance of leaf beetles on farmland willows. The results indicated no difference in plant quality; female egg laying and larval performance did not differ between the forest and the farmland. However, heteropteran predators (true bugs) were more abundant, and the survival of eggs was lower, on plants in the farmland habitat than in the forest habitat. The data suggest that the low abundance of P. vulgatissima on farmland willows could not be explained by a poor quality of plants, but more likely by high predation from heteropterans.
Balsam woolly adelgid (Hemiptera: Adelges picea Ratzeburg; BWA) is a nonnative, invasive insect that has infested fir trees in the US for over a century, yet robust methods for mapping BWA have remained elusive. We compare three approaches to mapping BWA in the subalpine fir forests of northern Utah, the forefront of BWA spread in the western US: (1) using moderate-resolution, multispectral satellite imagery; (2) using terrain and climate data; and (3) using a combination of imagery, terrain, and climate data. While the spectral data successfully detected forest degradation, they failed to distinguish between causal agents of change (R 2 mean = 0.482; RMSEmean = 0.112). Terrain and climate data identified landscape conditions that promote BWA infestation but lacked the ability to characterize local-scale tree damage (R 2 mean = 0.746; RMSEmean = 0.078). By combining spectral, terrain, and climate data, we present a repeatable approach for accurately mapping infestation severity that captures both regional abiotic drivers and the local damage signals of BWA (R 2 mean = 0.836; RMSEmean = 0.065). Highly infested areas featured increased visible and shortwave infrared reflectance over time in the spectral data. The terrain bore little influence on severity, but climate variables indicated that warmer areas are more prone to severe infestation. This research study presents an analytical framework upon which future BWA monitoring efforts can be built.
The American beech (Fagus grandifolia Ehrh.) has been impacted by the beech bark disease (BBD) complex throughout the northeastern United States for over 100 years, but the disease has been present in the Great Lakes region only for around 20 years, requiring acknowledgement of the evolving context surrounding F. grandifolia. This disease threatens to remove a foundational tree species which is especially important ecologically for wildlife habitat and mast, and as a climax successional species. We review advances in propagation techniques of F. grandifolia with the goal of addressing their use in the rehabilitative restoration of forests affected by BBD. Natural regeneration and artificial methods of propagation are addressed, along with how they may be applied for mitigation. Silvicultural interventions are discussed that may be necessary to protect and release resistant seedlings to promote persistence. An existing framework is used to explore context necessary for decision making in restoration. Nucleated seed orchards of resistant trees may currently be the most effective and practical method for introduction of BBD-resistant F. grandifolia into affected northern hardwood forests.
Sirex noctilio F. is an invasive woodwasp that causes pine mortality in plantations in China. Sirex nitobei M. is a native woodwasp in large areas of China. In this study, the flight capacity of the two woodwasps was studied and compared using a tethered-flight mill system to find individual factors affecting the flight capacity. After flight bioassays, woodwasps were dissected to determine nematode infestation. Post-eclosion-day (PED) age significantly influenced the flight capacity of S. noctilio females and males; as woodwasps become older, their flight capacity decreased. For S. nitobei, PED age did not significantly affect their flight capacity. In general, the flight capacity of S. noctilio was greater than that of S. nitobei. Females flew further and for longer than males for both Sirex species. The Deladenus spp. parasitism status of the two Sirex species did not significantly affect their flight performance parameters. PED age and body mass were key individual factors significantly affecting the flight capacity of the two Sirex species. In this study, detailed and accurate tethered-flight parameters of S. noctilio and S. nitobei were obtained. Although this is different from natural flight, it also provides us substantial laboratory data on their flight capacity, and facilitates risk analysis of the two woodwasp species.
The European Spongy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), is an abundant species found in oak woods in Central and Southern Europe, the Near East, and North Africa and is an important economic pest. It is a voracious eater and can completely defoliate entire trees; repeated severe defoliation can add to other stresses, such as weather extremes or human activities. Lymantria dispar is most destructive in its larval stage (caterpillars), stripping away foliage from a broad variety of trees (>500 species). Caterpillar infestation is an underestimated problem; medical literature reports that established populations of caterpillars may cause health problems to people and animals. Inflammatory reactions may occur in most individuals after exposure to setae, independent of previous exposure. Currently, chemical and mechanical methods, natural predators, and silvicultural practices are included for the control of this species. Various insecticides have been used for its control, often through aerial sprayings, which negatively affect biodiversity, frequently fail, and are inappropriate for urban/recreational areas. However, bioinsecticides based on various microorganisms (e.g., entomopathogenic viruses, bacteria, and fungi) as well as technologies such as mating disruption using sex pheromone traps have replaced insecticides for the management of L. dispar.
The spongy moth (Lymantria dispar) is a forest pest that damages a variety of trees in North America and Eurasia. A spongy moth outbreak occurred in part of South Korea in 2020 and caused severe damage to domestic forests and human society. Since the occurrence of spongy moths is influenced by climatic factors, this study examines the causes of spongy moth outbreaks by analyzing the temporal and spatial differences in climatic factors, influencing spongy moth occurrence using specimens collected during field surveys. Climatic factors were identified using global occurrence coordinates to compare the weather characteristics of spongy moth occurrence in domestic regions, using the kernel density function. Spatial and temporal comparisons were performed for monthly weather factors obtained from field surveys in 2020 and 2021 in areas with high and low spongy moth larvae densities. Spongy moth outbreaks may result from particular combinations of variable seasonality in temperature and precipitation, including high temperatures during cold periods and low precipitation during developmental periods.
Bu çalışmada; iğne yapraklı orman ağaçları tohum ve kozalaklarında zarara yol açan böceklerin listesinin oluşturulması amaçlanmıştır. Gerek tohum ticareti gerekse orman ürünlerinde ülkeler arası ticaretin ivme kazanması birçok zararlının dünya genelinde daha da yayılmasına yol açmaktadır. Ayrıca, iklim değişikliğinin etkisi ile birçok tür yeni yayılış alanları bularak, istila alanlarını ve zarar boyutunu artırabilecektir. Bu nedenle, ağaçların kozalak gibi generatif organlarında olumsuz etki gösteren türlerin bilinmesi kaliteli tohum elde edilebilmesi açısından ayrı bir önem arz etmektedir. Yerli ve yabancı alanyazın çalışmalarından elde edilen sonuçlara göre birçok ağaç türünde tohum ve kozalaklarda zarar yapan türler listelenmiştir. Buna göre; 12’si Türkiye odunsu florasındaki doğal iğne yapraklı orman ağacı türü olmak üzere toplam 82 odunsu taksonda 71 tohum ve kozalak zararlısı listelenmiştir. Bu zararlıların 57’si konofag, 14’ü ise seminifag böcek türü olarak tespit edilmiştir. Bazı zararlı türlerinin birden çok ağaç türünde zarara yol açtığı belirlenmiştir. Ağaç türü çeşitliliği açısından zarar spektrumu en geniş türler sırasıyla; Hemiptera takımından Leptoglossus occidentalis Heidemann (1910) (38 ağaç türü), Lepidoptera takımından Dioryctria abietella’yı (16 ağaç türü), 6’şar tür ile Dioryctria abietivorella, D. mendacella ve D. rubella takip etmektedir. En fazla tohum ve kozalak zararlısı 18 farklı herbivor türü ile Picea abies (L.) Karst. türünde tespit edilmiştir. Bu türü 9 zararlı ile Pseudotsuga menziesii (Mirb.) Franco, 7 türle Picea glauca (Moench) Voss ve Pinus sylvestris L. subsp. hamata (Steven), 6 türle Picea mariana [Mill] B.S.P. ve Pinus strobus L., 5 tür ile Abies alba Mill, Cedrus libani A. Rich ve Pinus pinaster Aiton, 4’er türle Larix laricina (Du Roi) K. Koch, Pinus brutia Ten., Pinus pinea L., Abies lasiocarpa (Hooker) Nuttall, Pinus nigra Arnold ve Cupresus sempervirens L. takip etmiştir. Bu araştırmada ayrıca, ağaç türlerine en fazla zarar yapan türlerin mücadelesi üzerinde de durulmuştur. İklim değişim etkilerinin her geçen gün etkisinin daha şiddetli hissedildiği günümüz koşullarında plantasyon ve gençleştirme başarısı üzerinde dayanıklı klon, genotip ve popülasyonlarının seçim ve kullanımı daha önemli hale gelmiştir. Bu da geleceğin ıslah çalışmalarında resistant ıslahının daha yoğun ve etkin bir araç olarak kullanımını gündeme getirebilecektir.
The southern pine beetle (SPB), Dendroctonus frontalis Zimmermann, is one of the most destructive insects to pine forests in North and Central America. Historical SPB infestations have shown strong cyclical patterns and are attributed to an array of abiotic and biotic factors with climatic conditions being the dominant. Climate change has been projected to increase SPB infestations; however, its impacts on the cyclical patterns of SPB infestations remain unknown. Here, we estimated the statistical relationship between SPB infestations and climatic and other factors using generalized linear regression modeling and historical data, analyzed the cyclical patterns of SPB infestations via periodogram analysis and explored how these patterns would evolve with the projected future climate change in 11 states of the Southern United States. We found that SPB infestations intensified with increases in seasonal average temperatures and minimum winter temperatures and decreases in spring and winter precipitations. Compared to the historical SPB infestation patterns, climate change was estimated to nearly double SPB infestation frequencies although with smaller amplitudes in the region. Our findings advance the understanding of cyclical patterns of SPB infestations, especially climate change impacts on such patterns, aiding in developing and deploying future SPB management practices and strategies.
Forest insect pest phenology and infestation pressure may shift as temperatures continue to warm due to climate change, resulting in greater challenges for sustainable forest management . The Nantucket pine tip moth (NPTM) (Rhyacionia frustrana Comstock) (Lepidoptera: Tortricidae) is a native forest regeneration pest in the southeastern U.S. with multiple generations per year. Changes in NPTM voltinism may result from temperature-induced shifts in NPTM phenology. Degree-day models have been used to develop optimal spray dates (OSDs) for NPTM. The 2000 Spray Timing Model (STM), based on temperature data from 1960 to 2000, provided generation-specific 5-d OSDs to effectively time applications of contact insecticides. An updated degree-day model, the 2019 STM, is based on temperature data from 2000 to 2019 and was used to detect changes in voltinism as well as shifts in phenology and OSDs. Based on the model, increased voltinism occurred at 6 of the 28 study locations (21%). Changes in voltinism occurred in the Piedmont and Coastal Plain of Georgia, U.S., with shifts from three to four or four to five generations a year, depending on location. The OSDs from the 2019 STM were compared to the 2000 STM OSDs. Over half (57%) of the OSDs differed by 5-15 d, with the majority (66%) resulting in earlier spray dates. The 2019 STM will help growers adapt NPTM control tactics to temperature-induced phenology shifts. NPTM serves as an example of temperature-induced changes attributed to climate change in a forest insect pest with important implications to forest management.
Balsam woolly adelgid, Adelges piceae (BWA), is a nonnative insect that has invaded much of the true fir range in North America, reducing host tree growth and causing mortality. Here, we describe a field study to characterize BWA infestation and effects on host trees in Idaho from the onset of infestation within twenty-eight sites with repeated surveys in 2008, 2013, and 2018. Declining tree health was categorized into five BWA damage classes based on the percent of the tree crown–expressing symptoms caused by BWA. Between 2008 and 2018, BWA presence increased across most sites regardless of host species, with an average of 48% (0.1%–100%) host trees per acre being infested. Severe damage or mortality of true fir from BWA occurred across thirteen sampled forest habitat types, including those representing harsh, high elevations. Although a significantly greater proportion of subalpine fir died than grand fir by 2018, BWA caused grand fir mortality. All diameter size classes became infested with BWA, including seedlings, and BWA caused mortality regardless of tree diameter. This assessment provides baseline data for a deeper analysis of insect, host, stand, and environmental interactions that may elucidate factors driving severe stand mortality.
Study Implications
Balsam woolly adelgid (BWA) is a cryptic, nonnative, and chronically lethal insect of true firs that is frequently overlooked until tree health substantially declines. Therefore, it is often not considered a serious damage agent during forest management planning until after severe damage has occurred across a stand. The BWA damage classification, modified from Spiegel et al. (2013), may be applied during stand exams. This simple and effective five-tiered classification system can be used to categorize BWA damage within individual trees or stands based on the collective symptoms caused by the insect. Feeding by BWA can ultimately result in stand-level mortality of both over- and understory fir and may require artificial regeneration to restore forest function. Fir regeneration was abundant at most BWA-damaged sites; however, seedling-sized firs were often heavily gouted from BWA to levels that will prevent them from growing into seed-bearing trees. Reported levels of mortality caused by BWA within 10 years of infestation and forest habitat type associations can be referenced for making management decisions for not-yet or recently infested stands.
Ambrosia beetles bore into the xylem of woody plants, reduce timber quality, and can sometimes cause devastating damage to forest ecosystems. The colonization by different beetle species is dependent on host status, from healthy trees to the early stages of wood decay, although the precise factors influencing their host selection are not well known. Classic studies on plant ecology have determined the niches of different plant species in vegetation succession, based on comparisons of successions in different locations using ordination analyses, although the factors influencing the colonization of each species are largely undetermined. In this study, to characterize the succession of ambrosia beetles after tree felling, two Betulaceae tree species, an alder (Alnus hirsuta), and a white birch (Betula platyphylla var. japonica) were felled as bait logs in central Hokkaido, Japan, in 2016. From 2016 to 2018, the bait logs were dissected late in each flying season, and ambrosia beetles were collected from the logs. During the period of monitoring, the beetle colonization in both tree species was mostly concentrated in the first 2 years. We observed similarities in the beetle faunas colonizing the two plant species, and that individual species appeared in the same sequence in the logs of the two plant species, although the temporal patterns of colonization differed. Consequently, significant differences in beetle community compositions in the two host species were detected in each of the first 2 years of the study, whereas the difference in the overall composition of beetle assemblages (=pooled over 3 years) between the two plant species was smaller than that in either 2016 or 2017. We speculated that the differences in the temporal pattern of colonization could be attributable to differences in the rates at which the wood of the two tree species deteriorated. Treptoplatypus severini and Xylosandrus crassiusculus were considered to be early-successional species that commenced log colonization soon after felling, although T. severini has a wide niche and was collected during all 3 years of the study. Conversely, Xyleborinus attenuatus and Heteroborips seriatus were identified as probable late-successional species that showed a preference for older logs.
The pine looper Bupalus piniaria (L.) is one of the most common pests feeding on the Scots pine Pinus sylvestris L. Pine looper outbreaks show a feature of periodicity and have significant ecological and economic impacts. Climate and weather factors play an important role in pine looper outbreak occurrence. We tried to determine what weather conditions precede B. piniaria outbreaks in the southeast of the West Siberian Plain and what climate oscillations cause them. Due to the insufficient duration and incompleteness of documented observations on outbreaks, we used the history of pine looper outbreaks reconstructed using dendrochronological data. Using logistic regression, we found that the factor influencing an outbreak the most is the weather four years before it. A combination of warm spring, dry summer, and cool autumn triggers population growth. Summer weather two years before an outbreak is also critical: humidity higher than the average annual value in summer is favorable for the pine looper. The logistic regression model predicted six out of seven outbreaks that occurred during the period for which weather data are available. We discovered a link between outbreaks and climatic oscillations (mainly for the North Atlantic oscillation, Pacific/North America index, East Atlantic/Western Russia, West Pacific, and Scandinavian patterns). However, outbreak predictions based on the teleconnection patterns turned out to be unreliable. We believe that the complexity of the interaction between large-scale atmospheric processes makes the direct influence of individual oscillations on weather conditions relatively small. Furthermore, climate changes in recent decades modulated atmospheric processes changing the pattern predicting pine looper outbreaks: Autumn became warmer four years before an outbreak, and summer two years before became drier.
We examined causes and levels of tree mortality one year after thinning and prescribed burning was completed in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests at Pringle Falls Experimental Forest, Oregon, U.S. Four blocks of five experimental units (N = 20) were established. One of each of five treatments was assigned to each experimental unit in each block. Treatments included thinning from below to the upper management zone (UMZ) for the dominant plant association based on stand density index values for ponderosa pine followed by mastication and prescribed burning: (1) 50% UMZ (low density stand), (2) 75% UMZ (medium density stand), (3) 75% UMZ Gap, which involved a regeneration cut, (4) 100% UMZ (high density stand), and (5) an untreated control (high density stand). Experimental units were thinned in 2011 (block 4), 2012 (block 2), and 2013 (blocks 1 and 3); masticated within one year; and prescribed burned two years after thinning (2013–2015). A total of 395,053 trees was inventoried, of which 1.1% (4436) died. Significantly higher levels of tree mortality occurred on 100 UMZ (3.1%) than the untreated control (0.05%). Mortality was attributed to prescribed fire (2706), several species of bark beetles (Coleoptera: Curculionidae) (1592), unknown factors (136), windfall (1 tree), and western gall rust (1 tree). Among bark beetles, tree mortality was attributed to western pine beetle (Dendroctonus brevicomis LeConte) (881 trees), pine engraver (Ips pini (Say)) (385 trees), fir engraver (Scolytus ventralis LeConte) (304 trees), mountain pine beetle (D. ponderosae Hopkins) (20 trees), Ips emarginatus (LeConte) (1 tree), and Pityogenes spp. (1 tree).
Forest health worldwide is impacted by many invasive alien pathogens and pests (IAPPs) that cause significant harm, with severe economic losses and environmental alterations. Destructive tree pathogens and pests have in the past devastated our forests, natural landscapes and cityscapes and still continue to represent a serious threat. The main driver of pathogen and pest invasions is human activities, above all global trade, which allows these invasive species to overstep their natural distribution ranges. While natural transport occurs according to a regular, expected colonization pattern (based on the dispersive capacity of the organism), human-mediated transport takes place on a larger, unpredictable scale. In order for a pathogen or pest species to become invasive in a new territory it must overcome distinct stages (barriers) that strongly affect the outcome of the invasion. Early detection is crucial to enabling successful eradication and containment. Although sophisticated diagnostic techniques are now available for disease and pest surveillance and monitoring, few control and mitigation options are usable in forestry; of these, biological control is one of the most frequently adopted. Since invasion by pathogens and pests is an economic and ecological problem of supranational relevance, governments should endorse all necessary preventive and corrective actions. To this end, establishing and harmonizing measures among countries is essential, both for preventing new introductions and for diminishing the eventual range expansion of IAPPs present at a local scale. Research is fundamental for: (i) developing effective and rapid diagnostic tools; (ii) investigating the epidemiology and ecology of IAPPs in newly introduced areas; and (iii) supporting policymakers in the implementation of quarantine regulations.
The potential for adaptive evolution to enable species persistence under a changing climate is one of the most important questions for understanding impacts of future climate change. Climate adaptation may be particularly likely for short-lived ectotherms, including many pest, pathogen, and vector species. For these taxa, estimating climate adaptive potential is critical for accurate predictive modeling and public health preparedness. Here, we demonstrate how a simple theoretical framework used in conservation biology—evolutionary rescue models—can be used to investigate the potential for climate adaptation in these taxa, using mosquito thermal adaptation as a focal case. Synthesizing current evidence, we find that short mosquito generation times, high population growth rates, and strong temperature-imposed selection favor thermal adaptation. However, knowledge gaps about the extent of phenotypic and genotypic variation in thermal tolerance within mosquito populations, the environmental sensitivity of selection, and the role of phenotypic plasticity constrain our ability to make more precise estimates. We describe how common garden and selection experiments can be used to fill these data gaps. Lastly, we investigate the consequences of mosquito climate adaptation on disease transmission using Aedes aegypti -transmitted dengue virus in Northern Brazil as a case study. The approach outlined here can be applied to any disease vector or pest species and type of environmental change.
The pine looper Bupalus piniaria is one of the most widespread phyllophagous insect species across Northern Eurasia, defoliating Scots pine forests over vast territories. Since there are not enough long-term documented observations on a series of outbreaks, there is a need for methods allowing them to be reconstructed to study their dynamics patterns. Previously, dendrochronological methods were successfully used to solve such issues. However, the most common approach is not applicable for the Western Siberian forest-steppe since it requires comparison with a non-damaged tree species close to pine in terms of longevity and resistance to rot. In the pine forests of the steppe and forest-steppe zones of Western Siberia, there are no species that are not damaged by the pine looper that meets these requirements. Methods allowing not using control species are also not free from disadvantages (e.g., weak specificity). Therefore, we have developed a new method based on the analysis, not of the tree-ring width but the early- and latewood width to reconstruct past defoliation events. The past defoliation by the pine looper is indicated by the presence of a negative pointer year for latewood, followed by a negative pointer year for earlywood in a subsequent year among the majority of individuals. Linear modeling showed a difference between the climate impact on radial growth and the defoliation one. The obtained reconstruction was compared with the results of other methods (mowing window, OUTBREAK, independent component analysis), literature, and Forest Service data. The developed new method (pointer year method; PYM) showed high efficiency confirmed by results of the tree-ring series analysis (11 revealed outbreaks in the past). Compared with other reconstruction techniques under the given conditions (a favorable combination of heat and humidity; probably low-intense and short defoliation), the proposed method provided more precise results than those proposed earlier. Due to high accuracy, the PYM can be useful for detecting late-summer and autumn past defoliations of tree species with clear difference between early- and latewood even though the damage was weak.
Die Frage nach der Stabilität gehört zu den großen, zentralen Fragen in der Ökologie. Über den Begriff der Stabilität herrscht eine derartige Verwirrung, dass er vermieden werden sollte. Es wird die Verwendung des Begriffes Stabilitätseigenschaften vorgeschlagen. Es kann zwischen natürlichen und anthropogenen Stabilitäts‐ und Instabilitätseigenschaften unterschieden werden. Aufgrund des dynamischen Verhaltens von ökologischen Kenngrößen und des Vorkommens oder Fehlens von Störfaktoren können die Stabilitätseigenschaften in die folgenden Typen eingeteilt werden: Konstanz, Zyklizität, Resistenz und Resilienz (Elastizität). Eine weitere, besondere Stabilitätseigenschaft ist die Persistenz: Fortbestehen eines ökologischen Systems als identifizierbare Einheit. Analog können auch die Instabilitätseigenschaften in sechs Typen eingeteilt werden. Zu allen Typen werden Beispiele aus der Feldökologie gegeben. Alle Typen von Stabilitäts‐ wie Instabilitätseigenschaften können vom Menschen je nach Standpunkt positiv oder negativ bewertet werden. Als Hilfsmittel für die Beschreibung der Stabilitätseigenschaften wird eine Checkliste mit 10 Punkten gegeben. Sie betreffen u. a. den raumzeitlichen Rahmen, die Referenzdynamik, die quantitativen Maße und statistische Verfahren zur Beurteilung von Systemveränderungen. Auf die letztgenannten Aspekte wird speziell eingegangen. An zwei Fallbeispielen wird das Dargelegte weiter erläutert. Möglichkeiten und Grenzen der Beurteilung von Stabilitätseigenschaften werden aufgezeigt.
Ips hauseri Reitter is the most important bark beetle on Picea schrenkiana in southeast Kazakhstan, but its biology, ecology, and outbreak dynamics are poorly known. We dendrochronologically reconstructed a 200-year history of disturbances in the Kazakh Tien Shan P. schrenkiana forests. Only localized, low-severity bark beetle events occurred during the reconstructed period, indicating that extensive high-severity bark beetle outbreaks have not occurred historically in the Tien Shan spruce forest, unlike bark beetle outbreaks in spruce forests in North America, Europe, and Russia. Disturbance frequency doubled after about 1965, probably due to warming climate. Results, combined with the failure of an outbreak to fully develop after blowdown events associated with hurricane-force windstorms in 2011, indicate that prolonged drought may be necessary to sustain I. hauseri outbreaks, or that year-to-year variation in the Tien Shan weather prevents outbreak development. I. hauseri is probably less aggressive than I. typographus, at least on their natural hosts within their natural ranges.
During drought, the tree subpopulations (such as size or vigour classes) that suffer disproportionate mortality can be conceptually arrayed along a continuum defined by the actions of biotic agents, particularly insects. At one extreme, stress dominates: insects are absent or simply kill the most physiologically stressed trees. At the opposite extreme, host selection dominates: outbreaking insects kill trees independently of their stress, instead selecting trees based on size or other traits. Intermediate responses are also possible. Yet for mixed‐species forests, we lack a broad understanding of the relative importance of insects in determining exactly which subpopulations of trees suffer disproportionate mortality during drought, and whether these subpopulations differ among co‐occurring tree species.
During an extreme drought, we documented the roles of native bark beetles in the mortality of five tree species in California’s Sierra Nevada. We analysed the patterns and agents of tree mortality in 12 permanent plots and the patterns of mortality in 89 temporary plots.
Most tree mortality was associated with bark beetles. However, the growth rates (an indicator of chronic stress) and sizes of trees that suffered greatest bark beetle‐related mortality differed sharply among tree taxa, variously conforming with domination by stress (Abies concolor), domination by host selection (Pinus lambertiana and P. ponderosa) or a mix of the two (Calocedrus decurrens). Quercus kelloggii mortality remained relatively low. Thus, even during extreme drought substantial proportions of stressed trees survived because they were of sizes that mostly avoided fatal insect attack. Conversely, substantial proportions of comparatively unstressed trees died because they were of sizes that were selectively killed by outbreaking insects.
Synthesis. Native bark beetles were primarily responsible for determining which subpopulations of trees suffered greatest mortality during drought. However, idiosyncratic host‐tree selection by the different bark beetle taxa meant that the tree subpopulations suffering greatest mortality differed strikingly among tree taxa—for example, high mortality of small trees of one species, but of large trees of another. If idiosyncratic host‐tree selection by biotic mortality agents proves to be a generally common phenomenon, it could help explain weak broadscale correlations between tree traits and tree mortality during drought.
Research Highlights: We found that the initial attack location together with the aggregation pheromones played an important role in mediating the aggressive behavior of T. brevipilosus on P. kesiya. Background and Objectives: T. brevipilosus was identified as an aggressive species, which possesses the ability to kill live, healthy P. kesiya. In this scenario, we study the top-down attack pattern of T. brevipilosus on P. kesiya during the entirety of the reproductive period. Materials and Methods: We investigated the phenology of trunk attack on P. kesiya over a period of three years in Pu’er City, China. The hindguts extracts of the females and males T. brevipilosus were analyzed by coupled gas chromatography-mass spectrometry (GC-MS). The candidate aggregation pheromone compounds of T. brevipilosus were determined through electrophysiology experiments (electroantennographic detection, EAD and electroantennography, EAG), laboratory olfactometer bioassays, and field trapping. Results: we found that the pioneer beetles preferentially infested the crown of P. kesiya at the early stage of attack following spring flight with the later arriving beetles selectively attacking the lower area of the trunk to avoid intraspecific competition and better utilize limited resources, which exhibits a top-down attack pattern. During gallery initiation, the beetles release aggregation pheromones to attract conspecifics to conduct a mass attack. The chemical analyses indicated that the hindgut extracts of gallery-initiating beetles contained a larger amount of myrtenol, cis-verbenol, trans-verbenol, and verbenone. Myrtenol and trans-verbenol were identified as candidate aggregation pheromone compounds. In addition, a blend of these two components with S-(−)-α-pinene and S-(−)-β-pinene attracted more T. brevipilosus individuals in a field bioassay. Conclusions: We concluded that the preference for the initial attack location together with the aggregation pheromones played an important role in mediating the top-down attack pattern of T. brevipilosus on P. kesiya.
Forest soils are major sinks of terrestrial carbon, but this function may be threatened by mass outbreak events of forest pests. Here, we measured soil CO2-C and N2O-N fluxes from a Scots pine (Pinus sylvestris L.) forest that was heavily infested by the nun moth (Lymantria monacha L.) and an adjacent noninfested (control) forest site during one year. In the infested forest, net emissions of CO2-C were higher during main defoliation, summer and autumn, while indications of increased N2O-N emissions were found at one sampling date. On basis of this, a microcosm incubation experiment with different organic matter treatments was conducted. Soil treatments with needle litter, insect feces plus needle litter, and insect feces showed 3.7-, 10.6-, and 13.5-fold higher CO2-C emissions while N2O-N of the insect feces plus needle litter, and insect feces treatment was 8.9-, and 10.4-fold higher compared with soil treatments without added organic matter (control). Hence, the defoliation in combination with high inputs of organic matter during insect outbreaks distinctly accelerate decomposition processes in pine forest soils, which in turn alters forests nutrient cycling and the functioning of forests as carbon sinks.
Trypodendron laeve Eggers, 1939 is a species of ambrosia beetle much less known than the other three Trypodendron species occurring in Europe. Its status (native or alien) in Central Europe has been a subject of debate over the past two decades. In Romania, the species was discovered in 2008 and the aim of the research presented in this paper was to investigate its distribution in the Carpathians, mainly at high altitudes (>800 m), in tree stands with Norway spruce (Picea abies [L.] H. Karst). Panel intercept traps baited with synthetic pheromone for Trypodendron lineatum (Olivier, 1795) were used in the spring of 2015, at 31 locations. Adults of T. laeve were caught in 20 of them. Additional observations were made within some studies using similar baits and T. laeve specimens were caught in eight locations. T. laeve was always trapped together with T. lineatum, and at some locations also together with T. domesticum (Linnaeus, 1758) and T. signatum (Fabricius, 1787). In all traps, fewer specimens of T. laeve were caught compared to T. lineatum. The species has a widespread distribution in the mountain regions, within forests composed of native tree species and generally located far away from commercial routes. There, it occurs together with other native species of the same taxonomic genus. It seems to be more abundant at high altitudes, but overall its populations are less abundant than those of T. lineatum.
In recent years, next generation sequencing (NGS) technologies have helped to improve our understanding of the bacterial communities associated with insects, shedding light on their wide taxonomic and functional diversity. To date, little is known about the microbiota of lepidopterans, which includes some of the most damaging agricultural and forest pests worldwide. Studying their microbiota could help us better understand their ecology and offer insights into developing new pest control strategies. In this paper, we review the literature pertaining to the microbiota of lepidopterans with a focus on pests, and highlight potential recurrent patterns regarding microbiota structure and composition.
The Bliss of Ignorance What Are the Implications? Implications: Weeds and Beyond Uncertainties and Limitations Future Direction A Word in Your Ear References
Introduction Crop Losses and Weeds: An Overview Weed Competition and Crop Losses with Climate Change Pests and Disease: Gimme Shelter Summary References
Wildfires play a significant role in many different elements of Mediterranean forest
ecosystems. In recent years, prescribed fires have started being used more often as a fuel reduction
tool, and also as silvicultural treatment to help the regeneration and health improvement of stands.
Apart from the fact that fire may alter microsite conditions, very little is known about the impact of
prescribed burning on natural regeneration or plant species renewal in Mediterranean pine forests.
Likewise, knowledge about the influence of seedling predators on post-fire regeneration is still
scarce. In this study, we aimed to compare the effects of seedling predation on recruitment in earlier
stages after prescribed burnings in three pine stands in Central Spain: a pure stand of Pinus nigra;
a mixed stand of Pinus halepensis and Pinus pinaster and a mixed stand P. nigra with P. pinaster. In
situ we superficially sowed seeds from two different species. In the sowing experiment, we tested
two different seed provenances (drier and more humid spanish regions) for each species. In all,
60 plots (30 burned, 30 unburned) per site, with 10 seeding units per plot and more than 20,000
seeds, were used in the whole study. Seedling predation was evaluated by replicating the seeding
units inside and outside a wire cage as protection for rodents and birds. Our results showed that
prescribed fires alter initial seedling predation intensity: predation was significantly higher in the
seedlings grown in the plots affected by prescribed fire. The individuals sown before the fire passed
showed slightly more predation than those sown after fire passage. Provenances did not appear as an
important predation drive. Understanding the role of the predation associated with these treatments
can help improve Mediterranean pine forest management.
The Panel on Plant Health performed a pest categorisation of the great spruce bark beetle, Dendroctonus micans (Kugelann), (Coleoptera: Curculionidae, Scolytinae), for the EU. D. micans is a well-defined and distinguishable species, recognised mainly as a pest of spruce (Picea spp.) and pine (Pinus spp.) in Eurasia. Attacks on other conifers (Abies spp., Larix decidua, Pseudotsuga menziesii) are also reported. Supposedly originating from north-eastern Eurasia, D. micans has spread westward and is now distributed throughout the EU (22 Member States). It is a quarantine pest listed in Annex IIB of Council Directive 2000/29/EC for Greece, Ireland and the United Kingdom (Northern Ireland, Isle of Man and Jersey) as protected zones. Wood, wood products, bark and wood packaging material of the conifers genera listed as hosts are considered as the main pathways for the pest, which is also able to disperse several kilometres by flight. The sib-mating habits of the species allow each single female to start a new colony on her own. The pest's wide current geographic range suggests that it is able to establish anywhere in the EU where its hosts are present. The beetles attack living trees and usually complete their life cycle without killing their host, except under epidemic conditions at the limits of their distribution range, where hundreds of thousands of trees can be killed. Sitka spruce (Picea sitchensis) is particularly susceptible. Biological control using the very specific predatory beetle, Rhizophagus grandis, is a widespread and efficient option that has been implemented in all areas suffering from outbreaks. It is complemented by sanitary thinning or clear-felling. All criteria assessed by EFSA for consideration as potential protected zone quarantine pest were met. The criteria for considering D. micans as a potential regulated non-quarantine pest are not met since plants for planting are not the main pathway.
Bark beetle outbreaks and tree mortality patterns should be better understood to control outbreak impacts. We investigated landscape-level patterns of Norway spruce mortality caused by Ips typographus outbreaks across three periods from 1999–2012 in Tatra National Park (Poland) using high-resolution aerial orthophotos and satellite imagery. Shifts in tree mortality related to elevation, slope, and solar equinox radiation were analyzed with ANOVAs (Tukey’s HSD tests). Boosted regression trees were employed to assess the forecasting effectiveness of these variables related to mortality period. Spruce mortality severity increased significantly across time in both managed and unmanaged forests. Management activities did not effectively reduce spruce mortality severity. Mortality severity increased significantly at higher elevations over time, while slope and radiation trends varied. Elevation and radiation were the best forecasters of mortality period, exhibiting moderate predictive ability. Beetle-induced spruce mortality increased significantly in Tatra National Park from 1999–2012, particularly at high elevations. Management strategies aimed at minimizing spruce mortality have been ineffective.
With the increasing volume of international trade in forest products around the world, hidden organisms in cargos were brought into the destination countries. These alien organisms, including insects, plants, and microorganisms, were introduced to new ecosystems, spread and threaten local biodiversity (also known as biological invasions). Nowadays, vulnerable forests in China are being threatened by large numbers of invasive species. In this chapter, we introduce current situation of invasive species in forest ecosystems in China, propose novel theoretical researches on biological invasions in forest ecosystems and several invasive species, as well as discuss main strategies and policies for management of forest pest invasions.
ResearchGate has not been able to resolve any references for this publication.