Influence of global warming on forest coleopteran communities with special reference to ambrosia and bark beetles

Forest insect pests are one of the major disturbance factors in forest ecosystems and their outbreaks are expected to be more severe under the influence of global warming. Coleopterans are dominant among forest insects and their ecological functions include general detritivores, dead wood feeders, fungivores, herbivores, live wood feeders and predators. Ambrosia and bark beetles contribute to ecological succession of forests and, therefore, ecological functions of forests can be changed in response to their outbreaks. Mountain pine beetle (MPB) outbreaks are the most dramatic example of changes in the ecological functions of forest due to the outbreak of a forest insect pest altered by global warming. Composition of coleopteran species varies with latitude. However, composition of functional groups is consistent with latitude which indicates that resources available to beetles are consistent. In coleopteran communities, ambrosia and bark beetles can become dominant due to increases of dead or stressed trees due to the warming climate. This can also induce changes in the ecological functions of coleopterans, i.e. selective force to displace trees that have lower ecological fitness due to temperature increase. Therefore, recent increases in the density ambrosia and bark beetles offer a chance to study ecological processes in forests under the influence of global warming.     

Time structure and dynamics of the insect communities in bush vegetation restoration areas of Zhifanggou watershed in Loess hilly region

The insects were investigated in Zhifanggou watershed, Ansai County, Shaanxi Province, China. The results showed that the insect species varied spatially in the following order: the natural bush forests, the mixed forests and the simple forests. The individual number of insects in Caragana korshinskii was the highest, followed by mixed forests and Hippaphae rhamnoides, and the change range of the insect individuals in the natural bush forests was the smallest. The species number of insects with seasonal changes and the individual number of insects in various types of vegetation can be described by the Univariate cubic equation. The order of the diversity index of the insect communities in various types of vegetation from May to September was the natural bush forests, the mixed forests and the simple forests. The change ranges of the evenness values of the simple forests and the mixed forests were higher, and that of the natural bush forests was smaller. The reverse trend was assumed between the dominance values and the evenness values in the time course. Moreover, the main factors and temporal patterns of the insect communities in the natural bush forests were more complicated, fluctuative and obvious than those in the mixed forests and the simple forests by using the principal component analysis.     

Habitat heterogeneity affects predation of European pine sawfly cocoons

Habitat heterogeneity is thought to affect top‐down control of herbivorous insects and contribute to population stability by providing a more attractive microhabitat for natural enemies, potentially leading to reduced population fluctuations. Identifying the parameters that contribute to habitat heterogeneity promoting top‐down control of herbivorous insects by natural enemies could facilitate appropriate management decisions, resulting in a decreased risk of pest insect outbreaks because of a higher level of predation. In our study, we measured the top‐down pressure exerted by small mammals on the cocoons of a notorious pest insect in pine forests, the European pine sawfly (Neodiprion sertifer), which is known to be regulated by small mammal predation. The forest stands used differed in heterogeneity measured in terms of differences in tree diversity and density, understory vegetation height, presence/absence, and density of dead wood. We found higher predation in more dense spots within forest stands. Further, the effect of dead wood on sawfly cocoon predation depended on the pine proportion in forest stands. The addition of dead wood in a manipulation experiment had a slight positive effect on cocoon predation, while dead wood removal caused a clear decrease in predation rate, and the decrease was more pronounced when the proportion of pine increased. Our results show that habitat heterogeneity affects predation by generalist predators on herbivorous insects. This knowledge could be applied to reduce the risk of insect outbreaks by applying management methods that increase heterogeneity in perennial systems such as forests and orchards, thus decreasing the levels of insect damage.     

Epidemiological landscape models reproduce cyclic insect outbreaks

Forest insect outbreaks can have large impacts on ecosystems and understanding the underlying ecological processes is critical for their management. Current process-based modeling approaches of insect outbreaks are often based on population processes operating at small spatial scales (i.e. within individual forest stands). As such, they are difficult to parameterize and offer limited applicability when modeling and predicting outbreaks at the landscape level where management actions take place. In this paper, we propose a new process-based landscape model of forest insect outbreaks that is based on stand defoliation, the Forest-Infected-Recovering-Forest (FIRF) model. We explore both spatially-implicit (mean field equations with global dispersal) and spatially-explicit (cellular automata with limited dispersal between neighboring stands) versions of this model to assess the role of dispersal in the landscape dynamics of outbreaks. We show that density-dependent dispersal is necessary to generate cyclic outbreaks in the spatially-implicit version of the model. The spatially-explicit FIRF model with local and stochastic dispersal displays cyclic outbreaks at the landscape scale and patchy outbreaks in space, even without density-dependence. Our simple, process-based FIRF model reproduces large scale outbreaks and can provide an innovative approach to model and manage forest pests at the landscape scale.     

纸坊沟流域植被恢复区灌木林昆虫群落时间结构及动态

通过对纸房沟流域不同植被恢复区昆虫进行调查,结果表明:昆虫种类数以天然灌木林最高,混交林次之,单纯林分较低,个体数量以柠条林昆虫数量最高,其次为混交林和沙棘林,天然灌木林变化幅度最小。各植被昆虫种类和数量季节变化符合y=ax3 bx2 cx d函数变化规律。从特征指数来分析:昆虫群落多样性指数5～9月份大小次序均为天然灌木林>混交林>单纯林分,均匀度以单纯林和混交林的昆虫群落变化幅度较大,天然灌木林变化幅度最小。群落的优势度与均匀度值的变化呈相反趋势。主分量分析表明:植物类型不同的昆虫群落,其主导因素和时间格局不同,且结构越复杂,主导因素和时间格局越明显;相反,则主导因素和时间格局分化不明显;通过排序植食性昆虫、捕食性昆虫、寄生性昆虫在各植被昆虫群落变化的不同时期占主导因素。     

Is insect defoliation in eucalypt forests greater than that in other temperate forests?

Claims have been made in the past that insect defoliation in eucalypt forests of Australia is both chronically high and greater than defoliation levels in northern temperate forests. Recent published data, however, indicate that some eucalypt forests may sustain low level defoliation. Careful reexamination of the literature on defoliation in eucalypt forests indicates that there are not enough data available to quantify defoliation on an Australian-wide basis. Therefore it cannot be claimed that insect defoliation in eucalypt forests is greater than that in other temperate forests. There are also insufficient data to claim that insects are a major factor responsible for the growth differential between indigenous and overseas plantation-grown eucalypts. The ecological impact of herbivorous insects in eucalypt and northern temperate forests is also discussed.     

Insect‐induced tree mortality of boreal forests in eastern Canada under a changing climate

Forest insects are major disturbances that induce tree mortality in eastern coniferous (or fir-spruce) forests in eastern North America. The spruce budworm (SBW) (Choristoneura fumiferana [Clemens]) is the most devastating insect causing tree mortality. However, the relative importance of insect-caused mortality versus tree mortality caused by other agents and how this relationship will change with climate change is not known. Based on permanent sample plots across eastern Canada, we combined a logistic model with a negative model to estimate tree mortality. The results showed that tree mortality increased mainly due to forest insects. The mean difference in annual tree mortality between plots disturbed by insects and those without insect disturbance was 0.0680 per year (P < 0.0001, T-test), and the carbon sink loss was about 2.87t C ha⁻¹ year⁻¹ larger than in natural forests. We also found that annual tree mortality increased significantly with the annual climate moisture index (CMI) and decreased significantly with annual minimum temperature (T_min), annual mean temperature (T_mean) and the number of degree days below 0°C (DD0), which was inconsistent with previous studies (Adams et al. 2009; van Mantgem et al. 2009; Allen et al. 2010). Furthermore, the results for the trends in the magnitude of forest insect outbreaks were consistent with those of climate factors for annual tree mortality. Our results demonstrate that forest insects are the dominant cause of the tree mortality in eastern Canada but that tree mortality induced by insect outbreaks will decrease in eastern Canada under warming climate.     

Selection of floral resources to optimise conservation of agriculturally-functional insect groups

Non-crop vegetation in agricultural landscapes can provide a means of conserving insects in farmed landscapes and optimising on-farm ecosystem services as a result. Inclusion of floral resources may be particularly useful in conserving many beneficial insects, where groups including pollinators and pest natural enemies often rely on nectar and pollen during (at least part of) their life-cycle. As not all flowers are equally suited to all beneficial insects, selection of appropriate flowering plants is key to ensuring that conservation targets are met and benefits to ecosystems services realised as a result. This short paper describes an experiment conducted to assess the ‘total temporal attractiveness’ of a range of British wildflowers to selected functional insect groups. The results obtained demonstrate that flowering period alone is a poor indicator of plant suitability to insects, where no relationship existed between this and attraction to insects overall. Data also suggest that, based on attraction over a season, certain flowering plants are more likely to be of general insect conservation value and/or benefit to functional insect groups than others. Attraction to pest insects was also considered, with relatively high catches of thrips and pollen beetles observed in flowering stands of some plants.     

Food limitation and insect outbreaks: complex dynamics in plant-herbivore models

1. The population dynamics of many herbivorous insects are characterized by rapid outbreaks, during which the insects severely defoliate their host plants. These outbreaks are separated by periods of low insect density and little defoliation. In many cases, the underlying cause of these outbreaks is unknown. 2. Mechanistic models are an important tool for understanding population outbreaks, but existing consumer-resource models predict that severe defoliation should happen much more often than is seen in nature. 3. We develop new models to describe the population dynamics of plants and insect herbivores. Our models show that outbreaking insects may be resource-limited without inflicting unrealistic levels of defoliation. 4. We tested our models against two different types of field data. The models successfully predict many major features of natural outbreaks. Our results demonstrate that insect outbreaks can be explained by a combination of food limitation in the herbivore and defoliation and intraspecific competition in the host plant.     

Spatial synchrony of the two-year cycle budworm outbreaks in central British Columbia, Canada

Outbreaks of forest defoliating insects are usually synchronized over a large spatial scale. Observed records of past outbreaks are usually short and incomplete, therefore long proxy data are useful for better understanding of the spatial synchrony. In this study, we developed tree-ring proxy records of two-year cycle spruce budworm ( Choristoneura biennis Freeman) outbreaks in central British Columbia, Canada, and examined the spatial patterns of past outbreaks. This budworm is a major defoliating insect of the interior spruce ( Picea engelmannii Parry× P. glauca Moench) and subalpine fir ( Abies lasiocarpa [Hook.] Nutt.) forests in the Prince George Region of British Columbia. Four outbreaks occurred in relatively close synchrony over the entire region in the period 1880–1999, however, the initiation year, the intensity and extent of outbreaks varied spatially and from one outbreak to another. In some instances, the occurrence of outbreaks was restricted to only one area. The general synchrony of outbreaks suggested that a large-scale extrinsic factor, such as weather, was at play. However, the imperfect synchrony of outbreaks suggested that local stand characteristics, such as canopy structure, composition of tree species and host plant quality, probably played a major role in preconditioning outbreaks. Dispersal might play a role in synchronizing outbreaks, but the extent to which it contributed to the synchrony was limited in this mountainous region.     

Host-pathogen interactions, insect outbreaks, and natural selection for disease resistance

The theory of insect population dynamics has shown that heterogeneity in natural-enemy attack rates is strongly stabilizing. We tested the usefulness of this theory for outbreaking insects, many of which are attacked by infectious pathogens. We measured heterogeneity among gypsy moth larvae in their risk of infection with a nucleopolyhedrovirus, which is effectively heterogeneity in the pathogen's attack rate. Our data show that heterogeneity in infection risk in this insect is so high that it leads to a stable equilibrium in the models, which is inconsistent with the outbreaks seen in North American gypsy moth populations. Our data further suggest that infection risk declines after epidemics, in turn suggesting that the model assumption of constant infection risk is incorrect. We therefore constructed an alternative model in which natural selection drives fluctuations in infection risk, leading to reductions after epidemics because of selection for resistance and increases after epidemics because of a cost of resistance. This model shows cycles even for high heterogeneity, and experiments confirm that infection risk is indeed heritable. The model is very general, and so we argue that natural selection for disease resistance may play a role in many insect outbreaks.     

Lianas as a food resource for herbivorous insects: a comparison with trees

Woody climbers or, ‘lianas’, are one of the features that characterise rainforests. They contribute substantially to plant diversity and leaf biomass which makes them a potentially important food source for herbivores. Here, we focus on insect herbivores, folivores in particular, to show how disparities in the quantitative and qualitative availability of leaves between lianas and trees may differentially influence insect folivory and the herbivore communities themselves. We develop a conceptual model and show that lianas in general have lower structural and chemical defences, a greater nutritional profile and a preferable phenology in comparison with trees, which, contrary to our expectations, has led to assemblages of more‐specialised insects. The impacts this has on higher trophic levels and broader ecological networks, however, are poorly known. We show through a study of four tropical floras from different biogeographic realms that lianas are likely to be a target for a wide range of insect herbivore taxa as they are a phylogenetically diverse group and increase diversity of higher taxa at local scales. This, in combination with their highly palatable leaves, may also make them a suitable temporary food source for insects during times when preferred host plants are scarce. This phenomenon has been observed in mammalian herbivores but awaits investigation in insects as does the effects this may have on survival and fitness. Apparent recent increases in liana abundances in some forests, likely due to climate change, makes understanding their role in supporting and maintaining biodiversity an increasingly important and necessary challenge. Since trees or saplings have usually been the subject of studies on insect herbivory, major knowledge gaps remain about the ways in which lianas contribute to, support and maintain the ecosystems in which they exist. We use our conceptual model to guide future research directions and express the necessity for caution when extrapolating explanations of herbivory derived from data on trees to growth forms with fundamentally different ecologies.     

Insect herbivory and vertebrate grazing impact food limitation and grasshopper populations during a severe outbreak

1. Competition between herbivores often plays an important role in population ecology and appears strongest when densities are high or plant production is low. Phytophagous insects are often highly abundant, but relatively few experiments have examined competition between vertebrates and phytophagous insects. 2. In grassland systems worldwide, grasshoppers are often the dominant phytophagous insect, and livestock grazing is a dominant land use. For this study, a novel experiment was conducted examining competition between vertebrates and invertebrates, where both grasshopper densities and sheep grazing were manipulated inside 10‐m² caged mesocosms during a grasshopper outbreak. We examined how grasshopper densities and the timing of vertebrate herbivory affected grasshopper densities, if the effects of vertebrates on survival and reproduction changed with grasshopper density, and how a naturally occurring grasshopper outbreak affected grasshopper populations in the following year. 3. Densities of grasshoppers at the site peaked at 130 m^–2. Food‐limited competition was stronger in treatments with higher grasshopper densities and repeated or late livestock herbivory, leading to reduced survival, femur length, and functional ovarioles, a measure of future reproduction. Strong food‐limited density‐dependent reproduction and survival led to reduced hatching densities in 2001. 4. As competition was typically stronger with high grasshopper densities than with livestock grazing, competition from vertebrates could be relatively less important for phytophagous insect population dynamics during outbreaks. The experiment provides insights into how competition between insect and vertebrate herbivores influences insect population dynamics, and indicates that severe outbreaks can rapidly subside with strong competition from vertebrate and insect herbivores.     

Infestation of Chocolate-based Products: Insects Responsible and Origins of Contamination

In response to on-going consumer complaints regarding insect infestation of chocolate-based products manufactured at a factory in southern Australia, research was undertaken to determine the insects responsible for infestation and locate the points along the manufacture/distribution network where insect pests were most likely to be entering the produce. Phycitine moths were responsible for almost all cases of product infestation, with most infestation occurring after goods had been packaged. Methods of identifying storage environments suspected of unknowingly harbouring phycitine populations or of regularly handling infested goods are discussed. the detrimental consequences for the manufacturer, and for the processed food industry in general, of the presence of stored product insects in wholesale and retail outlets are also considered.     

A guide to the use of the exuding-stylet technique in phloem physiology

The use of exuding stylets holds considerable promise for the investigation of sieve-tube physiology. However, largely because of difficulties in cutting insect stylets, the technique has been applied to only a few plant species. Based on our experience, a comparison is made of the available means of obtaining sieve-tube exudate from the exuding stylets of phloem-feeding insects, including aphids, scale and mealybugs. Forty-one plant species and approx. 35 insect species were tested for their ability to provide stylet exudate. Stylets on all but a few of the plant species tested yielded at least some exudate, but the success rate and duration of exudation on many species were unsatisfactory for detailed investigations of phloem transport. Plant species appears to be the most important factor for obtaining reliably exuding stylets, although the size of the insect species used and the physiological condition of the plant are also important variables. Armored scale provide a simple and reliable source of exuding stylets, but are impractical for most experimental purposes. Radio-frequency microcautery of aphid stylets was substantially the most effective means of cutting stylets. Instructions are provided for constructing a microcautery unit at minimal expense, using a citizen's band radio as the radio-frequency source.Abbreviations CB citizen's band - R.F. radio frequency     

虫害叶损失造成的树木非结构性碳减少与树木生长、死亡的关系研究进展

大规模虫害爆发可造成区域森林死亡, 近年的气候变化进一步增加了虫害的频度和危害程度。森林和林地植物死亡会导致植被生产力降低, 改变生态系统结构和功能, 使森林由一个净的碳汇转变为一个碳源。因此, 加深虫害对树木危害机制的认识有重要意义。虫害造成的叶损失(虫害叶损失)降低树木光合作用能力, 增加非结构性碳(NSC)消耗, 使得树木体内碳储备降低, NSC降低到一定程度会导致树木因碳饥饿而死亡。外部环境和树木自身的补偿性机制也会对这个过程产生正或负的影响。在近年气候变化背景下, 树木死亡在全球尺度上增多, 重新激起了人们对碳饥饿的重视, 碳饥饿被视为解释树木死亡的主要生理机制之一。该文介绍了碳饥饿的定义, 综述了虫害叶损失减少树木NSC储备与树木生长、死亡的关系, 以及树木虫害和叶损失与气候变化之间的关系, 并对今后的研究进行了展望。     

The relationship between the reduction of nonstructural carbohydrate induced by defoliator and the growth and mortality of trees

Large scale herbivorous insect outbreaks can cause death of regional forests, and the events are expected to be exacerbated with climate change. Mortality of forest and woodland plants would cause a series of serious consequences, such as decrease in vegetation production, shifts in ecosystem structure and function, and transformation of forest function from a net carbon sink into a net carbon source. There is thus a need to better understand the impact of insects on trees. Defoliation by insect pests mainly reduces photosynthesis (source decrease) and increases carbon consumption (sink increase), and hence causes reduction of nonstructural carbohydrate (NSC). When the reduction in NSC reaches to a certain level, trees would die of carbon starvation. External environment and internal compensatory mechanisms can also positively or negatively influence the process of tree death. At present, the research of carbon starvation is a hotspot because the increase of tree mortality globally with climate change, and carbon starvation is considered as one of the dominating physiological mechanisms for explaining tree death. In this study, we reviewed the definition of carbon starvation, and the relationships between the reduction of NSC induced by defoliation and the growth and death of trees, and the relationships among insect outbreaks, leaf loss and climate change. We also presented the potential directions of future studies on insect-caused defoliation and tree mortality.     

The impact of resource limitation and the phenology of parasitoid attack on the duration of insect herbivore outbreaks

Fluctuations in resource quality and quantity, and changes in mortality due to predators and parasites are thought to be of prime importance in the regular fluctuations of forest insects. We examine how food limitation and parasitoids with different phenologies of attack regulate the population cycles of insect hosts. Our analysis of the limit cycle of a model with a biologically realistic form of density dependence in the host yields two novel predictions. First, outbreaks will typically last for only 2 generations after parasitoids begin to reduce the host population below the maximum density. Second, host growth rate is important in determining cycle length only when parasitoids attack before the impacts of resource limitation affect the host. The robustness of these predictions are tested using a more general form of density dependence in the host, revealing that our predictions are valid as long as density dependence in the host is not too overcompensatory.     

唾液成分在刺吸式昆虫与植物关系中的作用

近年来,人们对刺吸式昆虫唾液成分的研究,揭示出其在刺吸式昆虫与植物关系中的重要作用。对多数刺吸式昆虫而言,他们取食时会分泌胶状和水状两种唾液,其中胶状唾液会在取食早期分泌形成唾液鞘来围绕并保护口针,通过直接和间接的作用来帮助取食;而水状唾液中则包含了果胶酶、纤维素酶、多酚氧化酶、过氧化物酶、碱性磷酸酯酶、蔗糖酶等组分,来帮助刺吸式昆虫对植物穿刺、消化食物、解毒次生物质并破坏植物的防御反应。有趣的是,唾液成分同时还可以诱导植物的防御反应,包括诱导植物的伤信号引起直接防御反应和诱导植物产生挥发物吸引植食者的天敌引起间接防御反应。并且,许多刺吸式昆虫取 食能够特异性地引发植物的病理反应,有研究推测刺吸式昆虫唾液中多聚半乳糖醛酸酶、碱性磷酸酯酶、蔗糖酶、多酚氧化酶等成分可能是某些植物特定病理反应的激发子,但是目前还没有定论,同时许多刺吸式昆虫唾液中的氨基酸和蛋白酶还是引起植物虫瘿的原因之一。 迄今的研究表明,刺吸式昆虫会根据不同的寄主植物和不同的生理需要,通过唾液组分的改变,来达到取食和发育的目的。对刺吸式昆虫唾液成分和作用机理的研究,可以为揭示刺吸式昆虫致害机理特别是传毒机理、指导害虫有效治理、阐明其与植物的协同进化等提供一定的思路。     

973项目“重大农业害虫猖獗危害的机制及可持续控制的基础研究”简介

2006年9月,国家重点基础研究发展计划(973)农业领域2006年度项目“重大农业害虫猖獗危害的机制及可持续控制的基础研究”经科技部批准正式立项启动。该项目以全系统管理思想为指导,在基因、个体、种群、生态系统等不同层次,阐明我国重大农业害虫种群分化与暴发的分子基础,解析害虫与寄主作物及天敌间的相互作用机制,建立害虫监测与预警系统,提出重大农业害虫可持续控制的新途径和新方法,为我国农业减灾、经济的可持续发展奠定科学基础。项目的主要研究内容包括:害虫生长发育与生殖调控的分子机制;害虫对环境胁迫的适应机制;杀虫药剂诱导害虫再猖獗的机制;害虫与寄主植物的协同进化;天敌与害虫的互作及控害机制;作物-害虫-天敌食物网关系及其调控机理;重大害虫区域性暴发监测与预警。项目的总体目标为:阐明害虫生长发育、种群分化的分子基础,揭示害虫种群调节的内在机制;解析作物、害虫及天敌间的互作机制,丰富和发展植物-害虫-天敌协同进化理论;阐明主要害虫区域性灾变机理,发展害虫预警新技术;发展与环境相容的、增强自然控害功能的新技术,提出重大农业害虫可持续控制的新途径和新方法;凝炼一支害虫控制基础研究的创新团队,丰富和发展我国害虫管理的科学理论与实践,提升我国有害生物防控的原始创新和集成创新能力,扩大国际影响。