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Variations in the attack pattern of Dendroctonus micans and the colonization rate of Rhizophagus grandis in Picea orientalis stands
Abstract
The great spruce bark beetle, Dendroctonus micans, is an invasive pest that has spread to almost all of the Picea orientalis forests in Turkey, affecting many trees and causing active damage. The species-specific predator Rhizophagus grandis plays an important role in suppressing populations of this pest because it is only found in D. micans galleries. In this study, the attack pattern of D. micans and the colonization rate of R. grandis were investigated according to some stand characteristics, such as aspect, developmental stage, crown closure, and stand type. It was determined that 20.5% of the 2025 sample trees evaluated in 83 sample plots were attacked by the beetle and that active damage from the beetle was currently continuing in 5.8% of the trees. There was no difference in the attack pattern of D. micans between shady and sunny aspects. However, trees showed significant differences in terms of susceptibility to beetle attacks based on developmental stage, crown closure, and stand type. The damage rates of the beetle were 19.8% and 29.6% for the mature and overmature stages, respectively; 28.5%, 18.8%, and 16.4% for low, medium, and full coverage stands, respectively; and 10.5–32.3% for different stand types. The colonization rate of R. grandis was 18.2%. This rate was not affected by the aspect, developmental stage, crown closure, or stand type. However, the rate was higher in the stands heavily infested by D. micans. In addition, there was a moderate correlation between the total number of D. micans individuals in active galleries and the total number of R. grandis individuals in these galleries.
... However, forests with lower density (29%) were more susceptible to attack than were dense stands (16%). Conversely, mature (20%) and over-mature forests (30%) were more susceptible to attack by this bark beetle than young forests were [49]. Additionally, the physical characteristics of trees, particularly their spacing, health, maturity, social position, and diameter, influence bark beetle population dynamics, as demonstrated by research on Pinus contorta Douglas and Dendroctonus ponderosae Hopkins: trees in dense populations have thinner phloem than trees growing in more open environments. ...
The spatial distribution of Dendroctonus frontalis Zimmermann, 1868, and Dendroctonus mexicanus Hopkins, 1905, was determined from 2020 to 2021 in the Tixtlancingo ejido. The information came from two surveys because, despite the abundant forested areas in this geographical area of the state of Guerrero, Mexico, economic resources for pest biomonitoring are limited. However, it was possible to identify the presence of 76 outbreaks affecting 1117.697 hectares and 95,078 trees, totaling 14,223.8 m3 of standing timber volume. In 2020, 28 outbreaks were reported, with the eastern spatial distribution showing the most damage from bark beetles, particularly in outbreaks 7 and 14 of the surveyed area. The most affected conifers were Pinus maximinoi H. E. Moore (44.71%), Pinus oocarpa Schiede ex Schltdl. (39.93%), and Pinus pseudostrobus Lindl. (15.36%). The affected timber volume was observed in diameter categories of 30 cm for the three pine species, with infestation of 90,549 trees (13,497.6 m3 t.t.v. (total tree volume)) across 1057.64 hectares. In 2021, 48 outbreaks were recorded, with the northeastern and southern parts of the surveyed area showing the most damage from the bark beetle. The trees most affected by the bark beetle were P. oocarpa (59.17%), P. maximinoi (33.94%), and P. pseudostrobus (6.89%). It was observed that the affected volume occurred in trees with diameter categories of 50 cm for the three pine species, affecting 4529 trees (726.214 m3 t.t.v.) distributed over 60.06 hectares. The contribution of this work lies in establishing a baseline for monitoring damage caused by this beetle, which affects forest resources and diminishes the possibility of maintaining carbon capture areas in the medium and long term, thus impacting the Sustainable Development Goals (SDGs) of the 2030 agenda, specifically Goals 11, 13, and 15.
... Invasion pest Dendroctonus micans (Kugelann,1974) (Coleoptera: Curculionidae), sometimes known as the great spruce bark beetle, has expanded throughout practically all of Türkiye Picea orientalis (L.) Link. forests, where it aggressively damages numerous trees [6]. ...
In this study, to determine an effective fungal agent against Dendroctonus micans (Kugelann, 1794) (Coleoptera: Curculionidae), which causes significant economic losses in forested areas, Picea orientalis (L.) Link in Artvin between 2021-2022. Dendroctonus micans larvae and adults were collected from the trees, and 18 fungi were isolated from larvae and adult insects. Morphological (infection type, colony morphology, spore form) and molecular (ITS1-5.8S ITS2 gene region) characterization determined that the isolates were Metarhizium anisopliae (Metschn.) Sorokin, 1883 (Hypocreales: Clavicipitaceae), M. robertsii, M. pinghaense and Clonostachys rosea Samuels & Rossman, 1999 (Hypocreales: Bionectriaceae). Isolates M. robertsii (OZM4) and M. pinhaense (OZM9) have been isolated from this pest for the first time. As a result of insecticidal activity tests performed on D. micans larvae and adults of 1x10 7 spore/ml spore suspension, the larvae, M. anisopliae (OZM2), showed a mortality rate of 92% within 7 days and adults mortality was determined 100% at the end of the experiment, and mycosis rates were found to be consistent with mortality rates. These results show that isolates with high virulence are promising in microbial and integrated control applications against important forest pests.
Ormanların sürdürülebilirliği için silvikültürel müdahaleler önemli bir araç olmasına rağmen üretim faaliyetleri aşamasında kalan meşcerede zarar oluşturabilmektedir. Meydana gelecek bu zararlar ormanların stabilitesini azaltacak, kabuk böceği zararlarına duyarlı ve bunun sonucunda da ekonomik kayıplara neden olacaktır. Bu çalışmada, üretim faaliyetlerinin kalan meşcereye verdiği zararın ortaya konulması ve kalan meşceredeki kabuk böceği duyarlılığının tespiti amaçlanmıştır. Çalışma alanındaki ağaçların %27,4’ünün yaralı, %5,5’inin kabuk böceği zararına uğramış ağaçlar olduğu tespit edilmiştir. Kabuk böceği zararının bulunduğu ağaç sayısı ile hem yaralı hem de böcek zararının bulunduğu ağaç sayısı arasında pozitif yönde orta düzeyde bir ilişki tespit edilmiştir. Üretim sonrasında kabuk böceği ve kalan meşcere zararının en fazla orta ağaçlık çağındaki ağaçlarda meydana geldiği belirlenmiştir. Üretim faaliyetleri aşamasında kalan meşecereye verilecek zararın minimuma indirecek gerekli tedbirler alınması ekonomik kayıp açısından önemlidir.
Dendroctonus micans (Kugelann, 1794), which was first discovered in 1966 in Turkey, has established almost in all oriental spruce forests in the Eastern Black Sea region until the late 2000s. In its expanding front it is responsible for killing spruce trees representing millions of cubic meters of wood. In recent years, oriental spruce forests have endemic population of this pest. But extreme climatic conditions that cause extreme weather circumstances may trigger suitable environment that favors D. micans outbreaks. In this study, we aimed to examine tree vitality of naturally infested and uninfested trees in the forest. Field studies were performed at a pure spruce stand in Taşlıca Forest Sub-District, Artvin Directorate of Forestry in 2016. Both infested and uninfested trees were selected in the stand closure. One core per tree was extracted from 30 naturally infested and 30 uninfested oriental spruce trees at the same stand. Core samples were taken at the second week of September. Phloem thickness, recent tree growth rates, diameter of breast height and the average number of xylem cells in a radial file formed until the sampling date were studied. Phloem thickness, recent tree growth rates and number of xylem cells were higher in infested trees. Host selection of D. micans was discussed in relation to characteristics of infested and uninfested trees.
Climate change is one of the major threats to biodiversity, but its impact varies among the species. Bark beetles ( Ips spp.), as well as other wood-boring pests of European forests, show escalating numbers in response to the changes driven by climate change and seriously affect the survival of the forests through the massive killing of trees. Many methods were developed to control these wood-boring beetles, however, their implementation can be detrimental for other forest specialists. Ants are widely used for biological pest-control, so in our study, we aimed to test the effect of Formica polyctena on the control of the wood-boring beetles. The results show that the proportion of infested trees is significantly reduced by the increase of the number of F. polyctena nests, with a strong effect on those infested by Ips species. We also show that the boring beetle community is shaped by different biotic and abiotic factors, including the presence of F. polyctena nests. However, the boring beetle infestation was not related to the latitude, altitude and age of the forests. Based on our results, we assert the effectiveness of the red wood ants as biological pest control and the importance of their conservation to keep the health of the forests.
The aim of this study was to determine the progeny production of predator beetle Rhizophagus grandis (Gyllenhal) (Coleoptera: Monotomidae) under laboratory conditions. Different numbers of male and female predators introduced into breeding logs and the numbers of new progenies and their sex ratios were determined in the early and late spring periods. A total of 8776, 13,402, 5742 and 7864 R. grandis individuals were reared in 60, 109, 128 and 56 breeding logs in four consecutive years, respectively. Of the prepupae that have dropped from breeding logs to enter the sand in experimental basins, 81.4 % of them have emerged as adults at the end of the experimental periods. The average number of R. grandis per log was 146.2, 123, 44.9 and 140.4 according to experimental years, and 181.7 and 93.2, 123, 62.4 and 32.9, 163.8 and 101.5 according to the early and late spring periods in the experimental years, respectively. In the second year of the experiments, only early spring rearings have been performed that have yielded 123 R. grandis per log on average. Progeny production of a female R. grandis was 18.3, 18.7, 5.8 and 17.6 on average, 2004, 2005, 2006 and 2007 respectively. Different numbers of predator females and males were used in early and late spring experiments in the study. Progeny production was higher in early spring when the experiments were performed with 6 females and 2 males. Of the 35,784 R. grandis individuals that were obtained from the experiment, 16.4 %, 28.3 % and 55.3 % were collected from the first, second and third part of the sand environment where the breeding logs kept during experiment.
Abstract Fifty bacterial cultures were isolated from 156 soil samples. In order to identify six bacteria in both systems, a fatty acid methyl ester (FAMEs) analysis was conducted, and carbon utilization profiles were assessed, using microbial identification, Biolog Microplac Systems, and the VITEK bacterial identification systems (bioMerieux, Prod. No. 21341 and 21342). Results showed that four species of Bacillus ssp., isolated from soil, were safe and efficient biological control agent for plant pests in Ordu, Turkey. These bacteria were Bacillus mycoides, B. cereus, B. thuringiensis, Paenibacillus validus, B. atrophaeus, and Arthrobacter globiformis. Laboratory tests were conducted to assess the potential of the isolates against the great spruce bark beetle, Dendroctonus micans (Kugelann) (Coleoptera: Curculionidae, Scolytinae) (Curculionidae, Scolytinae). Mortality rates of larvae and adults were 60 and 50%, 40 and 30%, and 80 and 70% when using B. mycoides, B. cereus, and B. thuringiensis, respectively. P. validus, B. atrophaeus, and A. globiformis showed insufficient rates of mortality, 30 and 20% on the larvae and adults of D. micans, respectively. Also, these isolates had no antimicrobial effect on pathogen microorganisms. They have, however, a lethal effect on some insect groups that are agriculture and forest pests. The results indicated that the Bacillus isolates in question can be used as one of the biological control agent.
Due to recent outbreaks of native bark beetles, forest ecosystems have experienced substantial changes in landscape structure and function, which also affect nearby human populations. As a result, land managers have been tasked with sustaining ecosystem services in impacted areas by considering the best available science, public perceptions, and monitoring data to develop strategies to suppress bark beetle epidemics, and in some cases to restore affected lands and ecosystem services. The effects of bark beetle outbreaks are often detrimental to the provision of ecosystem services, including degraded landscape aesthetics and diminished air and water quality. However, there have been instances where bark beetle outbreaks have benefited communities by, for example, improving habitat for grazing animals and enhancing real-estate values. As a consequence of the interaction of a warming climate and susceptible forest stand conditions, the frequency, severity, and extent of bark beetle outbreaks are expected to increase and therefore will continue to challenge many social–ecological systems. We synthesize experiences from recent outbreaks to encourage knowledge transfer from previously impacted communities to potentially vulnerable locations that may be at risk from future bark beetle epidemics.
Forests in Europe and North America are being affected by large and severe outbreaks of bark beetles, which have caused widespread concern about forest health and have led to proposals for tree removal in affected or susceptible forests. Any such intervention, as well as broader decisions of whether any active interventions are appropriate, should be based on the best scientific data. This is true for all forests, including those whose purposes include timber production, watershed protection, biogeochemical function and recreation, and especially protected and conservation areas as the latter often provide particularly unique and important cultural, social, scientific and other ecosystem services. Here, I summarize peer-reviewed literature on the effects of bark beetle outbreaks and on silvicultural treatments aimed at mitigating beetle-induced tree mortality. From an objective scientific perspective, beetle outbreaks do not destroy forests. Instead, in many cases they play an important role in promoting wildlife, biodiversity and other ecological services. The best available data indicate that logging in conservation areas is unlikely to stop ongoing bark beetle outbreaks and instead may be more ecologically detrimental to the forests than the outbreaks themselves. If the purpose of a forest is timber production, then logging is desirable and can be planned based on appropriate analyses of timber yield and economic profit. However, in areas in which conservation is the determined goal, it is recommended that cutting trees be limited to removing hazards, such as trees that might fall in areas of high human activity in order to limit property damage and personal injury. Based on extensive research in Europe and North America, logging beetle-affected forests is inconsistent with most conservation goals.
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
Bark beetles infest several pine tree species, often creating major economic losses. Biotic interactions between Scolytinae populations inhabiting Pinus sylvestris were analyzed using a new sampling method involving a two dimensional division of tree space resources into units and sections. The goal was to evaluate the effects of the type of available reproduction material on insect infestation. The P. sylvestris stands in this study included an analysis of bark beetles colonizing dead trees and uninfested living trees (trap trees). Analyzed trees were harvested and their stems divided into ten equal units; each unit was halved into two sections (half of the stem circumference). The colonization of dead trees by insects was evaluated immediately after cutting for infested trees and 2 months after cutting for trap trees. The type of breeding material significantly affected the species composition of bark beetles infesting P. sylvestris. The dead trees were colonized mostly by Trypodendron lineatum and Tomicus minor, and to a lesser extent by Tomicus piniperda, which dominated in trap trees. Tomicus piniperda and T. lineatum preferred thicker stems; however, T. minor, Hylurgops palliatus and Pityogenes bidentatus preferred thinner ones. The application of the new sampling method helped to increase the accuracy of niche segregation among insect species. The results of niche segregation indicate bark beetles exhibited spatial specialization in the use of resources, mainly related to the moisture content of breeding material and the availability of food resources which is the main factor determining the coexistence of bark beetles in the same environment.
The bark beetle Dendroctonus mesoamericanus sp. nov. is described from a population in
Parque Nacional Lagunas de Montebello, La Trinitaria, Chiapas, Mexico. This species belongs to the
D. frontalis complex, which includes D. adjunctus Blandford 1897, D. approximatus Dietz 1890, D. brevicomis
LeConte 1876, D. frontalis Zimmermann 1868, D. mexicanus Hopkins 1905, and D. vitei Wood
1975. The new species can be distinguished from closely related species D. frontalis, D. mexicanus, and
D. vitei by four diagnostic morphological characters: the presence of striations on the preepisternal area
of the prothorax (anterolateral pronotum) in both sexes, seminal rod with an approximately linear posterior
margin of the dorsal process (in lateral view), irregularly sized ornamentations on the distal edge of
squamiform plates present on the eighth abdominal tergite in females, and an inconspicuous pronotal
callus in females. Furthermore, the karyotype of D. mesoamericanus sp. nov. (5AAþXyp / XX) differs
from that of its sister species D. frontalis (7AAþ Xyp / XX). Dendroctonus mesoamericanus sp. nov. is distributed in Belize, Guatemala, El Salvador, Honduras, Nicaragua, and in the Michoaca´n, Oaxaca, and
Chiapas states in Mexico. In these countries, this species has been collected at elevations above from 311
to 2600mon six pine species, and it commonly occurs in syntopy with D. frontalis.
While phylogeographic patterns of organisms are often interpreted through past environmental disturbances, mediated by climate changes, and geographic barriers, they may also be strongly influenced by species-specific traits. To investigate the impact of such traits, we focused on two Eurasian spruce bark beetles that share a similar geographical distribution, but differ in their ecology and reproduction. Ips typographus is an aggressive tree-killing species characterized by strong dispersal, whereas Dendroctonus micans is a discrete inbreeding species (sib-mating is the rule), parasite of living trees and a poor disperser. We compared genetic variation between the two species over both beetles' entire range in Eurasia with five independent gene fragments, to evaluate whether their intrinsic differences could have an influence over their phylogeographic patterns. We highlighted widely divergent patterns of genetic variation for the two species, and argue that the difference is indeed largely compatible with their contrasting dispersal strategies and modes of reproduction. In addition, genetic structure in I. typographus divides European populations in a northern and a southern group, as was previously observed for its host plant, and suggests past allopatric divergence. A long divergence time was estimated between East Asian and other populations of both species, indicating their long-standing presence in Eurasia, prior to the last glacial maximum. Finally, the strong population structure observed in D. micans for the mitochondrial locus provides insights into the recent colonization history of this species, from its native European range to regions where it was recently introduced. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Scolytine beetles show enormous diversity in their mating behaviors, host plant associations, chemical and acoustic signaling, symbiotic relationships, and other critical aspects of their life histories. They can be monogamous or polygamous, solitary or gregarious, and employ levels of parental care that range from gallery maintenance in many tribes to eusociality in some ambrosia beetles. Within this complexity, however, scolytines display some generalities that arise from reproducing within plants, such as sophisticated host location systems, morphological adaptations that facilitate tunneling, advanced communication systems that provide very specific information about plants, and close associations with microbial symbionts. Bark beetles produce pheromones that both attract mates and serve additional functions that vary with the beetles' host-plant relationships. Some species use aggregation pheromones to coordinate cooperative resource procurement, a behavior needed to overcome the sophisticated defenses of live trees. A broad array of microbial symbionts is associated with bark beetles, and these fungi and bacteria vary in their degrees of association, impacts, mechanisms, and functional substitutabilities. Some symbionts contribute to acquisition, utilization, and defense of the host plant resource, and some provide a direct food base. A wide array of predators, competitors, and parasites exploit bark beetles. Many of these natural enemies utilize chemical signals emanating from the beetles or their symbionts in host location, depending on the stage they attack. The habitat in which bark beetles reside poses significant challenges to predators and parasites, so their effects on population dynamics are often limited. Some behavioral, reproductive, and landscape patterns emerge when bark beetle species are functionally categorized by the physiological condition of host plants they colonize. Bark beetles play important and varied roles in ecosystem processes, contributing to biodiversity, nutrient cycling, and heterogeneity. They also pose challenges to resource management in both native and commercial ecosystems. The scale at which beetles exert impacts varies markedly among functional groups, with most species having very localized effects. A few species exert landscape-scale effects, and these ecosystem engineers are among the most pronounced disturbance agents of the biomes they help shape. Their population dynamics are characterized by cross-scale interactions, density-dependent feedbacks, plasticity in host selection decisions, critical thresholds at multiple levels of interaction, and multi-equilibria. A variety of anthropogenic inputs, specifically transport into new regions, habitat manipulations that homogenize forest structure or impede predators, and climatic changes such as elevated temperature and increased drought, increase the socioeconomic losses caused by both eruptive and historically noneruptive species.
The population level and flight periods of Ips sexdentatus (Boerner) (Coleoptera: Curculionidae) was determined according to certain stand dynamics, altitude steps and temperatures based on the capture amounts in pheromone traps hung on some spruce stands in the oriental spruce, Picea orientalis (L.) Link. Forests of Turkey in 2006 to 2009. Average number of I. sexdentatus was statistically different between years and average annual highest number of captured beetles showed differences according to regions. The averages of the numbers of beetles caught in two different altitudes in two separate years are statistically different. In higher altitudes, average number of beetles caught per trap was higher. Provided data showed that I. sexdentatus has at least 2 generations in the forests of the region. First adult flight ranged from end of April to mid-June in both altitude steps, while second flight started in mid-June and continued until the mid-September. It was concluded that the beetles that were caught during fourth week of August and first week of September were the adults that would start a third generation. The predator species Thanasimus formicarius (L.) (Coleoptera: Cleridae) was caught in the pheromone traps as well as I. sexdentatus. In each trap, an average of 43.92 I. sexdentatus adults was captured per 1 T. formicarius adult. A total of 18 I. typographus (L.) (Coleoptera: Curculionidae) adults were captured by 5 traps containing Tryphreon Ipstyp aggregation pheromones. The trapping works in the research region have once again detected the existence of this species, which has densities that cannot be detected by other methods, and which is very dangerous for spruce stands since the first detection 75 years ago.
e Eurasian spruce bark beetle Dendroctonus micans is a major pest of spruce, which is expanding its range mainly in Turkey, Georgia, England
and France. Pathogens and predators are the main tool for biological control program of this pest. Now there is good evidence that predator
Rhizophagus grandis is established in Turkey and other countries and is important in regulating of D. micans abundance. ere are several ways
to use entomopathogenic algae Helicosporidium sp. as biological control agents, but it is necessary to explain the possibility of transmission
between R. grandis and D. micans.
The study showed some site and stand factors affecting host colonization, quantitative and qualitative losses in wood of oriental spruce as a source of raw material during the outbreak of Dendroctonus micans (Kug.). A total of 22.8 million m3 standing trees were damaged. In 11.43 million m 3 standing trees infestations were observed and 6.96 million m 3 of trees were cut which occupied 120,000 ha of D. micans infestation areas. In pure spruce stands, 26.5% of the trees were infested. There was no statistically significant difference among the volume of crowns, crown base height and ages in infested and healthy trees. There was a positive correlation between stand density and number of D. micans, and number of attacks inversely correlated with altitude.
The spatial pattern of Dendroctonus micans (Kug.) attacks on individual spruce stands was analysed at the regional scale in Britain using data collected between 1982 and 1984 by the British Forestry Commission. These survey data reflect at least 10 years of D. micans spread, in the absence of natural enemies and of pest management control measures. A large-scale spatial gradient in the attack density at the stand level was identified and modelled. The large-scale spatial trend model explained 31.3% of the variability, and divided the study area in three separate areas: a zone where the insect was well established and where attack density presented low variations, a transition zone where attack density sharply decreased, and a zone not yet colonized. Attack density was related to site and stand factors, and to landscape neighbourhood in a linear spatial regression model. The factors correlated to attack density and the spatial autocorrelation structure of remaining variability were found to vary according to the zones, reflecting the predominance of different ecological processes occurring in colonized and uncolonized areas. The shape and orientation of the large-scale spatial model was shown to be mostly influenced by the spatial distribution of early attacks.
Summary The predator,Rhizophagus grandis, is linked to its specific prey,Dendroctonus micans, by semiochemical signals regulating oviposition and long range orientation. A mixture of simple oxygenated monoterpenes [(-)—fenchone, (-)—pinocamphone, rac. camphor, terpinene-4-ol, borneol, fenchol and verbenone], identified from the frass ofD. micans has been found to be extremely active in a flight windtunnel as a long—range attractant for the predator. The mixture elicited 84 % of the response to larval frass of the prey. Excluding pinocamphone from the mixture did not influence its activity. Also, changing the absolute configurations of some of the components (fenchol, terpinene-4-ol and borneol) did not influence the predators' response. However, the addition of (-)—a-terpineol increased the attractivity of the synthetic blend to almost that of larval frass of the prey. Ecological implications of the identified semiochemicals and their use in pest management are discussed.
Climatic changes are predicted to significantly affect the frequency and severity of disturbances that shape forest ecosystems. We provide a synthesis of climate change effects on native bark beetles, important mortality agents of conifers in western North America. Because of differences in temperature-dependent life-history strategies, including cold-induced mortality and developmental timing, responses to warming will differ among and within bark beetle species. The success of bark beetle populations will also be influenced indirectly by the effects of climate on community associates and host-tree vigor, although little information is available to quantify these relationships. We used available population models and climate forecasts to explore the responses of two eruptive bark beetle species. Based on projected warming, increases in thermal regimes conducive to population success are predicted for Dendroctonus rufipennis (Kirby) and Dendroctonus ponderosae Hopkins, although there is considerable spatial and temporal variability. These predictions from population models suggest a movement of temperature suitability to higher latitudes and elevations and identify regions with a high potential for bark beetle outbreaks and associated tree mortality in the coming century.
Scolytinae (Coleoptera: Curculionidae) species and their host plants of coniferous forests of the Mediterranean region of Western Turkey were determined between 2006 and 2008. A total of 27 species of Scolytinae were collected from 59 different sites in Afyonkarahisar, Antalya, Burdur, Denizli, Isparta, and Muğla provinces. Hylastes angustatus (Herbst), H. linearis Erichson, Tomicus destruens (Wollaston), Hylurgus ligniperda (Fabricius), Pityogenes calcaratus (Eichhoff), P. pennidens Reitter, Orthotomicus robustus (Knotek), and O. suturalis (Gyllenhal) were recorded as new species for the Scolytinae fauna of the Mediterranean region of Western Turkey. Orthotomicus robustus (Knotek) was recorded for the first time from Turkey. Türkiye faunası için yeni bir kayıtla birlikte Batı Akdeniz Bölgesi iğne yapraklı ormanlarının kabuk böcekleri (Coleoptera: Scolytinae) faunası Özet: Batı Akdeniz Bölgesi iğne yapraklı ormanlarında Scolytinae (Coleoptera: Curculionidae) alt familyasına ait tür ve bu türlerin konukçu bitkileri 2006-2008 yıllarında tespit edilmiştir. Antalya, Afyonkarahisar, Burdur, Denizli, Isparta ve Muğla yörelerinde 59 farklı alandan toplanan örnekler değerlendirilmiş, Hylastes angustatus (Herbst), H. linearis Erichson, Tomicus destruens (Wollaston), Hylurgus ligniperda (Fabricius), Pityogenes calcaratus (Eichhoff), P. pennidens Reitter, Orthotomicus robustus (Knotek) ve O. suturalis (Gyllenhal) türleri Batı Akdeniz Bölgesi için yeni kayıt olarak belirlenmiştir. Bu türlerden O. robustus (Knotek) aynı zamanda Türkiye faunası için yeni kayıttır.
While most bark beetles attack only dead or weakened trees, many species in the genus Dendroctonus have the ability to kill healthy conifers through mass attack of the host tree, and can exhibit devastating outbreaks. Other species in this group are able to successfully colonize trees in small numbers without killing the host. We reconstruct the evolution of these ecological and life history traits, first classifying the extant Dendroctonus species by attack type (mass or few), outbreaks (yes or no), host genus (Pinus and others), location of attacks on the tree (bole, base, etc.), whether the host is killed (yes or no), and if the larvae are gregarious or have individual galleries (yes or no). We then estimated a molecular phylogeny for a data set of cytochrome oxidase I sequences sampled from nearly all Dendroctonus species, and used this phylogeny to reconstruct the ancestral state at various nodes on the tree, employing maximum parsimony, maximum likelihood, and Bayesian methods. Our reconstructions suggest that extant Dendroctonus species likely evolved from an ancestor that killed host pines through mass attack of the bole, had individual larvae, and exhibited outbreaks. The ability to colonize a host tree in small numbers (as well as gregarious larvae and attacks at the tree base) apparently evolved later, possibly as two separate events in different clades. It is likely that tree mortality and outbreaks have been continuing features of the interaction between conifers and Dendroctonus bark beetles.
Food webs in nature have multiple, reticulate connections between a diversity of consumers and resources. Such complexity affect web dynamics: it first spreads the direct effects of consumption and productivity throughout the web rather than focusing them at particular 'trophic levels'. Second, consumer densities are often donor controlled with food from across the trophic spectrum, the herbivore and detrital channels, other habitats, life-history omnivory, and even trophic mutualism. Although consumers usually do not affect these resources, increased numbers often allow consumers to depress other resources to levels lower than if donor-controlled resources were absent. We propose that such donor-controlled and "multi-channel" omnivory is a general feature of consumer control and central to fooweb dynamics. This observation is contrary to the normal practice of inferring dynamics by simplifying webs into few linear "trophic levels" as per "green world" theories. Such theories do not accomodate common and dynamically important features of real webs such as the ubiquity of donor control and the importance and dynamics of detritus, omnivory, resources crossing habitats, life history, nutrients(as opposed to energy), pathogens, resources defenses, and trophic symbioses. We conclude that trophic cascades and top-down community regulation as envisioned by trophic-level theories are relatively uncommon in nature.
Although drought affects directly tree physiology and growth, the impact of secondary factors (insect pests, pathogens and fire) is often greater than the impact of the original stress and can lead to important tree mortality. In 2003, Western and Central Europe experienced a drought and heat waves that led to extensive forest damage. This paper reports on the impacts of drought and high temperatures on forest insect populations in the context of this exceptional event. Observations of changes in population levels of the main European forest insect pests during and after the drought are presented and discussed in the light of current knowledge and theories of interactions between drought and insects. We investigated the direct effects of drought on life history traits and indirect effects through physiological changes experienced by host trees. Forest pest insects were separated in 4 feeding guilds: woodborers, leaf-chewers, leaf-miners and leaf-suckers. The impact of water stress varied according to feeding guilds. Woodborers were positively influenced by prolonged water stress and the decline of host resistance. In contrast, defoliators profited better from the increased nitrogen in plant tissues linked to moderate or intermittent water stress. Field observations showed the importance of the soil water status in tree resistance against pest attacks. Thus, the 2003 drought confirmed observations from earlier droughts that, is case of bad choice of tree species in some plantations, site matching becomes a prominent and primary cause of the development of pest outbreaks. This exceptional drought may give us some indication of the impacts of extreme climatic events. However, observations of the performance at the individual level were not sufficient for predicting long-term insect population dynamics, which depends on complex interactions between biotic and abiotic factors.
Biome-scaledisturbancesbyeruptiveherbivoresprovidevaluableinsightsintospeciesinteractions,ecosystemfunction,andimpactsof globalchange. We present a conceptual framework using one system as a model, emphasizing interactions across levels of biological hierarchy and spatiotemporal scales. Bark beetles are major natural disturbance agents in western North American forests. However, recent bark beetle population eruptions have exceeded the frequencies, impacts, and ranges documented during the previous 125 years. Extensive host abundance and susceptibility, concentrated beetle density, favorable weather, optimal symbiotic associations, and escape from natural enemies must occur jointly for beetles to surpass a series of thresholds and exert widespread disturbance. Opposing feedbacks determine qualitatively distinct outcomes at junctures at the biochemical through landscape levels. Eruptions occur when key thresholds are surpassed, prior constraints cease to exert influence, and positive feedbacks amplify across scales. These dynamics are bidirectional, as landscape features influence how lower-scale processes are amplified or buffered. Climate change and reduced habitat heterogeneity increase the likelihood that key thresholds will be exceeded, and may cause fundamental regime shifts. Systems in which endogenous feedbacks can dominate after external forces foster the initial breach of thresholds appear particularly sensitive to anthropogenic perturbations.
Ecological disturbances of forests by insects have a complex array of associated human dimensions presenting complications for natural resource decision making and relationships between stakeholders and managers. This article discusses the human context of forest disturbances by insects by reviewing four cases of bark beetle forest disturbance from British Columbia in Canada, Bavarian Forest National Park in Germany, the Kenai Peninsula in Alaska, and the north central region of Colorado. Findings and lessons learned from these studies are outlined along with their implications for managing forest disturbances by insects in general. Conclusions focus on the need to assess the broad array of impacts and risks perceived by local residents and the capacity for local action and involvement in managing forest disturbances. Communication and interaction between resource managers and local stakeholders can facilitate the identification of management priorities and potentially reduce some of the risks associated with forest disturbances by insects.
Climate is an important driver of the establishment and impact of invasive alien species. Species transported to new regions can only invade those with a climate that meets their thermal requirements, but climate change is likely to alter the invasibility of recipient environments. Likewise, species are unlikely to reach pest status where climatic conditions are suboptimal. Here our objectives were to determine the relationship between climatic conditions and flight activity of two alien pine bark beetles (Hylastes ater and Hylurgus ligniperda) and to anticipate how climate change may affect the future distribution of these species. We used elevational gradients and slope aspect (north versus south-facing slopes), which are known to affect microclimates, to assess the effects on beetle flight across 18 locations in pine forests in the South Island, New Zealand. Using panel traps baited with alpha-pinene and ethanol we caught a total of 45,363 H. ligniperda and 6676 H. ater. Catches of both species decreased significantly and substantially with increasing elevation. Significantly more beetles were caught at north-facing than at south-facing sites towards the end of the flight season in autumn, leading to an extended flight period at northerly aspects. These results are important for pest management and the identification of ‘areas of low pest prevalence’ as a measure to reduce post-harvest infestations of logs destined for export. For example, during risk periods, logs could be harvested preferentially from stands with reduced flight activity (i.e., southerly aspects and higher elevations). Furthermore, such sites could be chosen to reduce post-harvest infestation risks during periods of temporary log storage at skid sites in the forest. Our findings are also important because climate change can be an important factor contributing to population expansion of bark beetles, and warmer temperatures could lead to increased flight activity and abundance, as well as enhanced suitability of sites that are currently less favourable.
This report updates the literature review and synthesis of economic valuation studies on the impacts of forest insect pests by Rosenberger and Smith (1997). A conceptual framework is presented to establish context for the studies. This report also discusses the concept of ecosystem services; identifies key elements of each study; examines areas of future research; and includes appendices that further explain nonmarket valuation methods, a narrative of each study, and tables that summarize each study. The primary services affected by insects are restricted in the literature to include recreation, aesthetic or scenic beauty of landscapes, and property values. Monetary metrics across studies include willingness to pay estimates per acre, per person or household, per tree, and/or for various levels of damages. While this literature is limited and heterogeneous, individual studies may prove useful in assessing current and future policies associated with forest insect pests in the United States.
Bark beetles are powerful agents of change in dynamic forest ecosystems. Most assessments of the effects of bark beetle outbreaks have been based on negative impacts on timber production. The positive effects of bark beetle activities are much less well understood. Bark beetles perform vital functions at all levels of scale in forest ecosystems. At the landscape level they influence forest regeneration, and at the stand level they kill mature trees thus creating gaps and forest openings that are beneficial to wildlife. They also cause overall increases in forest and stand resiliency by promoting variability in sizes and ages of trees and in species compositions. The effects of bark beetles on forest ecosystems differ with beetle species, geographical location, host species, stand density and tree age. Whereas ecological consequences are normally beneficial to forest ecosystems, socioeconomic perceptions range from positive to negative. We provide several examples from western regions that illustrate ecological, economic, or social effects of bark beetle outbreaks. These examples include information on management of bark beetle outbreaks and identify research needs for the future.
Large bark beetle outbreaks are regarded as major forest disturbances, ranking first in the USA before hurricanes, tornadoes, and fire, with a 20,400,000 ha average annual impact area and annual average costs (shared with pathogens) above US$2 billion per year. In Europe, over the period 1950–2000, insect damage (which equates mostly to bark beetles) ranked third, with 8% of the total damage due to forest disturbances. The damage amounted to 2.88 million m3 per year between 1958 and 2001. The major direct economic consequences of these outbreaks have been widely analyzed, various mitigation methods have been designed and implemented, and diverse political, industrial, and commercial initiatives have been developed to salvage the remains of the devastated forests. However, the many other environmental and sociological consequences of these disturbances are still largely unexplored. Significant progress has been made in analyzing the multi-scale positive influence of bark beetle activity, from the landscape to the stand level, as well as the various socioeconomic changes brought by bark beetle outbreaks. Silvicultural, environmental, and social consequences of bark beetle outbreaks are described and discussed, as well as the different issues related to the salvage of damaged forests. The wider context of management policies, including risk management and exotic species management, is discussed. Five case studies are presented to illustrate how biological features of specific systems lead to particular sociopolitical issues: Ips typographus in Europe; secondary ambrosia beetles attacking living beech in Europe; Dendroctonus rufipennis in Alaska; Dendroctonus ponderosae in British Columbia; and Ips pini in North America.
Dendroctonus Erichson is a relatively small genus, but one with a disproportionately large impact on coniferous forests. Its name is particularly suitable (Dendro- tree, -tonus destroyer) for a group that contains most of the major conifer-killing bark beetles in the world. The ability of several members of the genus to develop outbreaks and the strong response of several species to anthropogenic change makes these insects of significant economic and ecological importance. The group is also interesting from an evolutionary perspective because of the varied life history strategies and symbiotic associations of its members. This chapter synthesizes a vast and broad literature on Dendroctonus and examines how new approaches are rapidly adding to our understanding of this important group.
There is an evolutionary trade-off between the resources that a species invests in dispersal versus those invested in reproduction. For many insects, reproductive success in patchily-distributed species can be improved by sibling-mating. In many cases, such strategies correspond to sexual dimorphism, with males-whose reproductive activities can take place without dispersal-investing less energy in development of dispersive resources such as large body size and wings. This dimorphism is particularly likely when males have little or no chance of mating outside their place of birth, such as when sperm competition precludes successful fertilisation in females that have already mated. The economically important bark beetle pest species Dendroctonus micans (Coleoptera: Curculionidae, Scolytinae) has been considered to be exclusively sibling-mating, with 90% of females having already mated with their brothers by emergence. The species does not, however, show strong sexual dimorphism; males closely resemble females, and have been observed flying through forests. We hypothesised that this lack of sexual dimorphism indicates that male D. micans are able to mate with unrelated females, and to sire some or all of their offspring, permitting extrafamilial reproduction. Using novel microsatellite markers, we carried out cross-breeding laboratory experiments and conducted paternity analyses of resulting offspring. Our results demonstrate that a second mating with a less-related male can indeed lead to some offspring being sired by the latecomer, but that most are sired by the first, sibling male. We discuss these findings in the context of sperm competition versus possible outbreeding depression.Heredity advance online publication, 16 April 2014; doi:10.1038/hdy.2014.34.
Great spruce bark beetle, Dendroctonus micans, first discovered in the UK in 1982, has been the subject of an integrated pest management (IPM) programme developed by the Forestry Commission. The programme is based on acombination of forest management practice, including sanitation felling and restriction of transport of infested spruce, and biological control through introduction, rearing and release of the exotic predatory beetle, Rhizophagus grandis. Five phases in the development of the IPM programme are recognised and described, although all are interrelated: (i) initial survey and sanitation felling reduced numbers below critical levels; (ii) initial forest management strategy was to introduce a scheduled area restricting movement of infested spruce to approved mills; (iii) introduction and release of R. grandis through an inoculativer release strategy; (iv) refinements to forest management to reduce further accidental spread and to monitor natural spread of Dendroctonus micans; (v) assessment of the impact of R. grandis using a range of criteria. Populations of Dendroctonus micans are now at low levels and there is strong evidence that R. grandis has established well, is spreading and is an important factor in regulating the bark beetle populations.
Trunk wounds that injure both xylem and phloem can structurally weaken trees, reduce translocation of sap, and provide entry for insects or inoculation sites for disease organisms. Rapid wound closure is beneficial. Illinois data in- dicate that wound closure is directly related to tree vigor, that large wounds close more in 1 year than small wounds, that wounds less than 12 mm wide are likely to close in 1 year, that annually inflicted wounds less than 25 mm in diameter are not likely to slow tree growth, and that wounds on slow-growing trees close more per unit of radial trunk growth than wounds on fast-growing trees. Resume. Les blessures au tronc qui endommagent le xyleme et le phloeme peuvent affaiblir la structure de I'arbre, reduire le transport de la seve et procurer des entrees aux insectes ou des sites d'inoculation aux pathogenes. line fermeture rapide des blessures est ben^fique. Des donnees recueillies en Illinois indiquent que la Vitesse de fermeture des blessures est directement reliee a la vigueur de I'arbre, que les grosses blessures se ferment plus au cours d'une ann6e que les petites, que les blessures de moins de 12 mm de diametre se ferment habituellement en moins d'un an, que les blessures de moins de 25 mm de diametre infligees annuellement ne causent pas de diminution de la croissance de I'arbre et que les blessures sur les arbres a croissance lente se ferment plus par unite de croissance radiale du tronc que les blessures sur les arbres a croissance rapide.
It is widely believed that population outbreaks of the southern pine beetle (Dendroctonus frontalis Zimm.) are caused by vagaries of climate, such as periods of severe drought. According to this view, D. frontalis population dynamics are dominated by density-independent processes. We have statistically analyzed a 30-yr record of D. frontalis activity in east Texas and have assessed the relative roles of density-independent and density-dependent factors in beetle population fluctuations. Regressions of the rate of population change on three climatic variables were not significant. By contrast, both time-series and regression analyses provided strong and consistent evidence for delayed density regulation of D. frontalis populations. Thus, in contrast to previous analyses, we conclude that D. frontalis outbreaks are driven not by stochastic fluctuations of weather, but by some unknown population process acting in a delayed density-dependent manner. This result provides a starting point for a current study that will experimentally test various hypotheses concerning the role of natural enemies in D. frontalis cycles.
The predatory beetle, Rhizophagus grandis Gyll. is the most important specific insect enemy of the great European spruce bark beetle Dendroctonus micans. R. grandis was introduced into Britain in 1983 and has subsequently been artificially mass reared and released into spruce forest attacked by D. micans . The introduction of R. grandis appears to have been successful, and the predator has established as a breeding species. The absence of prior research gave little scope for optimising densities and distribution of the predator.
Two experiments (one using marked insects) showed that R. grandis dispersed effectively, ranging in excess of 200 m from the release point and rapidly locating its prey. The predator was most attracted to mature larval D. micans broods. Releases of 1000+ predators per hectare (ha) compared favourably with low level introductions of 50–100 predators per ha used throughout the main release programme. Levels of colonisation by the predator four weeks after release at high numbers were equal to those resulting from low density introductions two years after release. Other observations on the dispersal of R. grandis show that this species will pioneer new D. micans populations, with flight ranges up to 4 km being recorded.
Zusammenfassung
Untersuchungen zum Dispersionsflug und zur Wirtsfindung bei Rhizophagus grandis Gyll. (Col., Rhizophagidae )
Der räuberisch lebende Käfer Rhizophagus grandis gehört zu den wichtigsten spezifischen Feinden des Riesenbastkäfers, Dendroctonus micans . 1983 wurde R. grandis in Großbritannien eingeführt und wurde anschließend in Massenzucht genommen und in Fichtenbeständen ausgesetzt, die Schäden durch D. micans aufwiesen. Die Einführung von R. grandis scheint gelungen zu sein, und der Käfer tritt in Großbritannien inzwischen als sich hier fortpflanzende Art auf. Mangels früherer Forschungsergebnisse war wenig über die Optimierung von Dichte und Verteilung dieser Käferart bekannt.
In zwei Versuchen — einer davon mit markierten Käfern — konnte gezeigt werden, daß sich R. grandis effektiv verbreitet. Vom Freisetzungspunkt aus wurde R. grandis im Umkreis von 200 m nachgewiesen, und der Käfer konnte seine Beute schnell lokalisieren. Am attraktivsten für R. grandis waren D.‐micans ‐Brutbilder mit Altlarven. Bei einem Vergleich von hohen Freilassungsraten (1000 Käfer/ha) mit Freilassungsraten von 50–100 Käfern/ha zeigte sich, daß die Koloniebildung hier vier Wochen nach der Freilassung unabhängig von der Freilassungsrate die gleiche Stärke erreichte.
Weiterhin konnte festgestellt werden, daß R. grandis neue D.‐micans ‐Populationen auffinden kann, die über 4 km entfernt sind.
This study investigated the effects of aspect (north and south) and slope position (top slope: 1100 -1700 m and bottom slope: 1700 -2200 m) on Ips typographus (L.) and its major predator Thanasimus formicarius (L.) populations and body length and weight of the pest I. typographus (L.) in oriental spruce [Picea orientalis (L.) Link.], dominated stands in Artvin-Hatila Valley National Park, Turkey for two years (2006-2007). A total of 120 pheromone traps were used to assess the population levels of both insect species. The results of the study were as follows: 1.) I. typographus (L.) population on each aspect was significantly higher at the top slope stands than the other sites whereas T. formicarius (L.) population was higher at the bottom slope stands on the north-facing site. 2.) There was no correlation between the number of T. formicarius (L.) and I. typographus (L.) caught by pheromone traps. 3.) Body length and weight of I. typographus (L.) were significantly higher on south aspect and at the top slope on each aspect.
The Eurasian spruce bark beetle Dendroctonus micans is a major pest of spruce which is expanding its range in France, Turkey, England and Wales. Its monospecific predator Rhizophagus grandis has followed its prey naturally into most areas and since the 1960s has also been mass‐produced and released within newly infested locations. Assessing bark‐beetle presence at previously uninfested sites, or predator establishment after release or natural spread, currently depends on direct observation of D. micans brood chambers. This is a slow and unreliable process because bark‐beetle attacks are solitary, cryptic and occur on living trees. An effective trapping method would thus be most useful.
A synthetic lure for R. grandis was first field‐tested in release–recapture experiments. Release points were surrounded by one or two concentric rings of traps baited with either D. micans larval frass or with a blend of synthetic chemicals. Kairomone‐trapping using the synthetic lure was then tested in the field, monitoring R. grandis in 58 spruce stands in Belgium and France.
In the release–recapture experiments, up to 65% of the released predators were caught within 48 h. Catches with the synthetic lure and with prey frass were not significantly different.
Field‐trapping assays showed R. grandis establishment in 30 stands, including areas where the predator had been introduced artificially. Trapping was unsuccessful at the southern and western limits of D. micans ’ range. Combined visual and trapping approaches identified 32 stands containing the predators, with two false negatives with the trapping method, compared to 19 for the visual surveys.
Unexpectedly, male and female D. micans adults were trapped in some cases. The combined approach identified 43 attacked stands, among which there were four false negatives with the trapping method and 11 with the visual surveys.
Synthesis and applications. To our knowledge, this is one of the first cases of using kairomone traps to monitor a predator after releases for biocontrol. Furthermore, because this predator is strictly prey‐specific, this technique also identifies stands colonized by D. micans bark beetles. Following inoculative predator releases, kairomone trapping could be used to survey for D. micans in areas under colonization or in European Union ‘Protected Zones’.
This paper, based on a literature review, presents a quantitative overview of the role of natural disturbances in European forests from 1850 to 2000. Such an overview provides a basis for modelling the possible impacts of climate change and enables one to assess trends in disturbance regimes in different countries and/or periods. Over the period 1950–2000, an annual average of 35 million m3 wood was damaged by disturbances; there was much variation between years. Storms were responsible for 53% of the total damage, fire for 16%, snow for 3% and other abiotic causes for 5%. Biotic factors caused 16% of the damage, and half of this was caused by bark beetles. For 7% of the damage, no cause was given or there was a combination of causes. The 35 million m3 of damage is about 8.1% of the total fellings in Europe and about 0.15% of the total volume of growing stock. Over the period 1961–2000, the average annual area of forest fires was 213 000 ha, which is 0.15% of the total forest area in Europe. Most types of damage seem to be increasing. This is partly an artefact of the improved availability of information. The most likely explanations for an increase in damage from disturbances are changes in forest management and resulting changes in the condition of the forest. Forest area, average volume of growing stock and average stand age have increased considerably, making the forest more vulnerable and increasing the resources that can be damaged. Since forest resources are expected to continue to increase, it is likely that damage from disturbances will also increase in future.
1. A spatio-temporal study of host selection and local spread of a solitary bark beetle attacking live spruce Dendroctonus micans (Kugelann) was carried out using a combination of standard statistical methods, geostatistical analyses, and modelling. The study was based on data from three plots (150–300 trees, 0.3–1 ha) from 1978 to 1993. All trees were mapped and successful and abortive bark-beetle attacks on each tree were counted annually. Because the attacked trees usually survived, temporal attack patterns as well as spatial patterns could be analysed.
2. The distribution of successful insect attacks on the trees was slightly aggregative, indicating some degree of choice rather than totally random establishment.
3. The level of yearly individual attacks per tree was very stable, suggesting that D. micans usually leave the host in which they develop.
4. The attacked trees were distributed randomly in the plots; at the study's spatial scale, the insects dispersed freely throughout the plot (no spatial dependence).
5. On the other hand, time dependence was strong; some trees were attacked repeatedly while others were left untouched.
6. Among a choice of scenarios (random attack, fixed variability in individual host susceptibility, induced host susceptibility following random attack), the best fit was obtained with the model involving induced individual host susceptibility. This type of relation to the host tree contrasts strongly with patterns generally described in host–plant relationships (including gregarious, tree-killing bark beetles), where local herbivore damage results in induced resistance.
7. These results suggest that the first attacks in a new stand are made at random, that all or most of the beetles emerging from a tree disperse and resample the stand, and that they settle preferentially on trees that were colonised successfully by previous generations.
1. Aggregation in bark beetles (Coleoptera: Scolytidae) aids in mate attraction and resource procurement when colonising well‐defended plants; however, some species colonise primarily poorly defended plants, and intraspecific competition increases mortality. The hypothesis that decreased risk of predation was a potential benefit to aggregation in such circumstances was tested, using the pine engraver, Ips pini (Say) and its two major predators Thanasimus dubius (F.) (Coleoptera: Cleridae) and Platysoma cylindrica (Paykull) (Coleoptera: Histeridae). Both single‐ and multiple‐predator effects, across a range of prey densities, were tested.
2. Both male and female colonisation events increased with herbivore density, in an asymptotic fashion.
3. Predators decreased the number of colonisers in a density‐dependent manner, consistent with a type II functional response.
4. The proportional impact of predators decreased with increased herbivore colonisation densities. These findings indicate that predator dilution may be a viable benefit to aggregation.
5. Total emergence of the herbivore also increased with density, although the net replacement rate during one generation was independent of initial arrival density. This was likely due to larval predation, which negates potential relationships between per capita reproductive success and establishment density.
6. Each predator species decreased I. pini 's net replacement rate by approximately 42%, and their combined effect was approximately 70%.
7. Overall, these predators modified their prey's establishment and adult mortality relationships in additive manners. This is somewhat surprising, given the potential for emergent effects due to interactions between multiple predators foraging within a common habitat. The persistence of additivity, rather than risk reduction or enhancement to the prey, may increase the predator‐swamping benefit to aggregation for this herbivore.
8. The effects of these predators are substitutable, and likely exert equivalent selective pressures to mask signals at the whole‐plant level.
Bark beetle populations may undergo dramatic fluctuations and are often important pests in coniferous forests. Their dynamics
are thought to be primarily driven by factors affecting the resistance of the host tree to attack, i.e., bottom-up forces,
while natural enemies are usually assigned a minor role in these systems. I present behavioral experiments that suggest that
the clerid beetle Thanasimus dubius may be an important source of mortality for the bark beetle Dendroctonus frontalis during attack of the host tree, and determine the nature of the functional response of T. dubius under conditions close to natural. I also examine the numerical response of T. dubius to large-scale fluctuations in D. frontalis density, and the relationship between bark beetle population trends and predator density, and find that beetle populations
tend to decline when predator densities are high. Combined with the effects of clerid larvae on bark beetle broods, these
results suggest that top-down forces generated by natural enemies could also be an important component of bark beetle dynamics.
The implications of these results for bark beetle dynamics are discussed in relation to the prolonged life-cycle of clerid
beetles.
Bark beetle infestations are often scattered throughout the forest landscape and therefore difficult to accurately and rapidly assess. We tested a roadside sampling technique in a pure maritime pine forest (Pinus pinaster) of ca. 1300 ha where bark beetle outbreak foci were observed following a windstorm. The sampling method relied on the count along stand edges of all dying or dead trees sighted within a fixed distance from the road. About 2300 trees attacked by Ips sexdentatus were recorded and located using colour-infrared aerial photography. Accuracy of the infestation map was verified by ground sampling. Piles of cut logs stored along the edge significantly increased the percentage of attacked trees in the neighbouring stand. However, the percentage of attacked trees within the stand edges did not differ with the percentage within the stand interior. It allowed us to use stand edges as sampling units to estimate the mean percentage of attacked trees per stand. At the stand scale, the use of a fixed 10 m wide strip along stand edges maximized the detection of attacked trees and minimized the bias of estimated percent of attacked trees. Based on GIS data, various stratified roadside sampling plans with increasing numbers of edges per stand and increasing numbers of stands per forest were simulated by bootstrap resampling. In a forest without any storage of cut logs, systematic roadside surveys underestimated the level of damage. The sampling accuracy increased with the kilometers of edges surveyed. In a forest with piles of cut logs on which bark beetles can breed, the best option was an adaptive sampling plan where at least two additional consecutive edges were observed in stands close to the pile. As compared to systematic sampling plans, adaptive plans were three times less expensive in terms of sampling effort for the same accuracy. Overall, adaptive sampling plans were also more robust as they provided less biased estimates as the proportion of stands with nearby piles increased in simulated forests.
The outbreaks of Ips typographus (L.) in Central Europe after severe storms in the 1990s triggered extensive research. Molecular techniques were used to analyze the relations and origins of European Ips species. The biological characteristics of I. typographus such as the influence of temperature on life history parameters and flight behavior have been analyzed in detail. The spruce bark beetle was found to disperse well beyond 500 m. However, new attacks mostly occurred in the vicinity of old ones.Many studies refer to invertebrate natural enemies of I. typographus such as predatory beetles and flies as well as various parasitoids. While the species assemblages of antagonists have been extensively investigated their dynamics and impact on I. typographus populations are controversial.The susceptibility and defense mechanisms of host trees are crucial for a successful attack by bark beetles. Newly attacked trees respond with preformed resin, local wound reactions and eventually with systemic changes in their physiology. Risk assessments have been performed at both tree and stand level. Risk of attack seems to be mainly related to the exposition, age, and nutrient and water supply of the trees. The dynamics of outbreaks largely depends on insect abundance, tree susceptibility, weather conditions, and human measures. This renders predictions difficult. Various control techniques are reviewed and the need for more sophisticated risk assessment tools is stressed.
Pest status of Dendroctonus micans (Kugelann) (Coleoptera: Scolytidae) and the effect of Rhizophagus grandis (Gyllenhal) (Coleoptera: Rhizophagidae) on the population of Dendroctonus micans in the oriental spruce forests of Turkey
- G E Özcan
- M Eroğlu
- Alkan Akıncı
Özcan GE, Eroğlu M, Alkan Akıncı H (2006) Pest status of Dendroctonus micans (Kugelann) (Coleoptera: Scolytidae) and the effect
of Rhizophagus grandis (Gyllenhal) (Coleoptera: Rhizophagidae) on the population of Dendroctonus micans in the oriental
spruce forests of Turkey. Turk J Entomol 30(1):11-22