昆虫病原微生物对其寄主行为的调控作用研究进展

昆虫病原微生物是调控昆虫种群数量动态的重要因子,其作为生物防治害虫的重要手段被广泛应用。昆虫病原物往往通过调控其寄主行为来提高自身的适应性,而有些寄主行为的改变却是其应对病原物侵染的免疫反应。发烧行为被证明可抑制病原增殖并延长寄主死亡;取食行为变化影响病原物或寄主的适应性;繁殖行为主要表现在产卵力、交配行为和性信息素等方面的变化;社会性行为改变对整个社会群体的适应性或病原物传播有影响;病原物所引起的寄主防卫和群集能力下降被认为对病原传播不利;病虫趋光和趋地行为、顶峰行为和活体寄主传病行为等被认为是病原物操纵的有利于病原微生物扩散和传播的行为。明确昆虫病原物调控其寄主行为的策略和机制对于寻找到新的害虫防治方法有指导意义。     

昆虫天然免疫反应分子机制研究进展

昆虫体内缺乏高等脊椎动物所具有的获得性免疫系统, 只能依赖发达的天然免疫系统抵抗细菌、 真菌、 病毒等外源病原物的侵染。本文概括了昆虫天然免疫反应发生和作用的分子机制相关进展, 重点阐述了重要免疫相关因子在昆虫天然免疫反应中的功能和作用机制。昆虫天然免疫反应分为体液免疫和细胞免疫两种, 二者共同作用完成对病原物的吞噬 (phagocytosis)、 集结 (nodulation)、 包囊 (encapsulation)、 凝结 (coagulation)和黑化（melanization）等。当昆虫受到外界病原物的侵染时, 首先通过体内的模式识别蛋白（pattern recognition proteins/receptor, PRPs）识别并结合病原物表面特有的模式分子（pathogen-associated molecular pattern, PAMPs）, 继而一系列包括丝氨酸蛋白酶和丝氨酸蛋白酶抑制剂在内的级联激活反应被激活和调控, 产生抗菌肽、 黑色素等免疫效应分子, 清除或杀灭外源物。抗菌肽是一类小分子量的阳离子肽, 具有广谱抗菌活性, 针对不同类型的病原物, 抗菌肽的产生机制也不尽相同。昆虫体内存在着两种信号转导途径调节抗菌肽的产生： 一是由真菌和大部分革兰氏阳性菌激活的Toll途径; 二是由革兰氏阴性菌激活的Imd途径（immune deficiency pathway）。这两个途径通过激活不同转录因子调控不同抗菌肽基因的表达参与昆虫体内的天然免疫反应。     

植物病原茵产生的降解酶及其作用

综述了植物病原微生物产生的降解酶的种类、作用方式、在致病中的地位及研究进展,阐明了细胞壁降解酶的双重作用即作为病原物侵染的致病因子及作为植物防卫反应的激发子,为寄主一病原物分子互作提供一定的参考.     

植物病原菌产生的降解酶及其作用*

综述了植物病原微生物产生的降解酶的种类、作用方式、在致病中的地位及研究进展,阐明了细胞壁降解酶的双重作用:即作为病原物侵染的致病因子及作为植物防卫反应的激发子,为寄主一病原物分子互作提供一定的参考。     

植物病原菌产生的降解酶及其作用

综述了植物病原微生物产生的降解酶的种类、作用方式、在致病中的地位及研究进展,阐明了细胞壁降解酶的双重作用：即作为病原物侵染的致病因子及作为植物防卫反应的激发子,为寄主一病原物分子互作提供一定的参考。     

昆虫病原线虫感染寄主行为研究进展

昆虫病原线虫斯氏属Steinernema和异小杆属Heterorhabditids线虫是新型的生物杀虫剂。其感染期幼虫是惟一能够侵染寄主昆虫的虫态。这类线虫感染寄主的行为分为寻找寄主、识别寄主和侵染寄主。文章综述昆虫病原线虫感染寄主昆虫的行为以及在感染寄主过程中的影响因素。     

《昆虫的寄生性天敌和病原微生物》

全书分二卷。第一卷：寄生性天敌;第二卷：病原微生物。论述了昆虫与寄生性天敌和病原微生物的相互作用和影响。从基础生物学、生物化学和分子生物学的角度进行研究。第一卷：寄生性天敌（V．1Parasites）。共14章,364页。分1．昆虫寄生性天敌发育的模式;2寄生性天敌的作用：在寄生性天敌和寄主相互关系中蛋白质和肽所起的作用;3．昆虫内寄生性天敌和寄主相互关系中激素的作用;4．昆虫寄生性天敌和病原微生物引起的繁殖干扰;5．昆虫寄生性天敌和病原微生物对寄主行为的影响;6．寄生新陈代谢的变化对奇生性天敌营养的影响;7．畸形细…     

白蚁抗病原微生物侵染机制研究进展

白蚁作为古老的社会性昆虫,在其生活史内易受到多种病原物的潜在威胁。本文主要根据白蚁的生理免疫及其社会性行为,如白蚁的细胞免疫和体液免疫以及相互清理等利他性行为,对其抵抗病原物侵染和扩散的个体生理免疫和群体行为防御策略进行了综述,以期为白蚁免疫策略的研究提供必要的信息。目前已从白蚁额腺和胸腺中分离到具抗菌活性的分泌物,且已明确白蚁能产生termicin、spinigerin等抗菌肽和转铁蛋白、溶菌酶等抗菌蛋白,抗菌肽的理化性质已得到初步研究。此外,白蚁的社会性行为( 如相互清理、交哺等) 能有效降低白蚁被病原物侵染的几率。运用RNA干扰等分子生物学方法证明利用病原微生物防治白蚁具有广阔的前景,但需要我们对白蚁抗菌肽的进化、各种抗菌肽和抗菌蛋白之间的相互作用以及各种生理免疫策略与群体内的社会性行为之间的联系进行更深入的研究。     

昆虫病原线虫与环境生物、非生物因素关系的研究进展

昆虫病原线虫(Entomopathogenic nematodes)是业已商业化的昆虫寄生性天敌,对农林和卫生等重要害虫具有安全和有效的控制作用.这类线虫与环境生物和非生物因素存在密切的联系.影响昆虫病原线虫的环境生物因素包括同类线虫、共生细菌、寄主昆虫、寄生真菌以及其它昆虫病原物等;影响昆虫病原线虫的环境非生物因素主要有土壤类型、温湿度、盐度、紫外线等.本文从昆虫病原线虫与环境生物、非生物因素的关系综述这类线虫的研究进展,为昆虫病原线虫的研发和应用提供参考.     

昆虫免疫识别与病原物免疫逃避机理研究进展

昆虫在长期进化过程中形成复杂的天然免疫系统,病原识别是启动下游免疫反应的第一步,这一过程主要是由不同的模式识别蛋白来完成的。目前发现并鉴定的昆虫模式识别蛋白主要包括肽聚糖识别蛋白、类免疫球蛋白、β-1,3-葡聚糖结合蛋白、C型凝集素及具多功能的载脂蛋白等,不同的蛋白种类具有不同的结构、功能及识别对象。与昆虫免疫识别相对应的是,不同昆虫病原物在进化过程中发展出不同策略的免疫逃避能力,以战胜宿主免疫而致病或最终杀死昆虫。本文就昆虫免疫过程中不同模式识别蛋白的结合对象、结构与功能,以及逐渐兴起的病原物通过分子伪装等进行免疫逃避的研究进展进行了综述。并在此基础上,作者就昆虫免疫与昆虫病理研究的发展方向进行了展望,认为只有当两方面研究相结合时,才能更好地揭示昆虫宿主与病原物之间免疫与抗免疫的动态相互作用过程。     

Dissecting the immune response to the entomopathogen Photorhabdus

Bacterial pathogens either hide from or modulate the host's immune response to ensure their survival. Photorhabdus is a potent insect pathogenic bacterium that uses entomopathogenic nematodes as vectors in a system that represents a useful tool for probing the molecular basis of immunity. During the course of infection, Photorhabdus multiplies rapidly within the insect, producing a range of toxins that inhibit phagocytosis of the invading bacteria and eventually kill the insect host. Photorhabdus bacteria have recently been established as a tool for investigating immune recognition and defense mechanisms in model hosts such as Manduca and Drosophila. Such studies pave the way for investigations of gene interactions between pathogen virulence factors and host immune genes, which ultimately could lead to an understanding of how some Photorhabdus species have made the leap to becoming human pathogens.     

Patterns of virulence and benevolence in insect‐borne pathogens of plants

Direct and indirect interactions between insect‐borne pathogens and their host plants are reviewed in the context of theoretical analyses of the evolution of virulence. Unlike earlier theories, which maintained that parasites should evolve to be harmless or even beneficial to their hosts, recent models predict that coevolution between pathogen and host may lead to virulence or avirulence, depending on the pathogen transmission system. The studies reviewed here support the hypothesis that virulence can be advantageous for insect‐borne pathogens of plants. Virulent pathogens may be transmitted more readily by vector insects and are likely to induce stronger disease symptoms, thereby potentially making the plant more attractive to vectors. In contrast, the transmission advantage of virulence for seed‐transmitted pathogens is lower and the costs of virulence are high. Pathogens may sometimes benefit plants via indirect interactions that arise through relationships with other organisms. Evidence for the effects of insect‐borne pathogens on plant competition, herbivory, and parasitism also is reviewed, but few studies have measured the outcome of both direct and indirect interactions. Benefits of pathogen infection that accrue to plants from indirect interactions may sometimes outweigh the direct detrimental effects of virulence.     

How the insect pathogen bacteria Bacillus thuringiensis and Xenorhabdus/Photorhabdus occupy their hosts

Insects are the largest group of animals on earth. Like mammals, virus, fungi, bacteria and parasites infect them. Several tissue barriers and defense mechanisms are common for vertebrates and invertebrates. Therefore some insects, notably the fly Drosophila and the caterpillar Galleria mellonella, have been used as models to study host-pathogen interactions for several insect and mammal pathogens. They are excellent tools to identify pathogen determinants and host tissue cell responses. We focus here on the comparison of effectors used by two different groups of bacterial insect pathogens to accomplish the infection process in their lepidopteran larval host: Bacillus thuringiensis and the nematode-associated bacteria, Photorhabdus and Xenorhabdus. The comparison reveals similarities in function and expression profiles for some genes, which suggest that such factors are conserved during evolution in order to attack the tissue encountered during the infection process.     

Infection dynamics of endemic malaria in a wild bird population: parasite species-dependent drivers of spatial and temporal variation in transmission rates

1.?Investigating the ecological context in which host-parasite interactions occur and the roles of biotic and abiotic factors in forcing infection dynamics is essential to understanding disease transmission, spread and maintenance. 2.?Despite their prominence as model host-pathogen systems, the relative influence of environmental heterogeneity and host characteristics in influencing the infection dynamics of avian blood parasites has rarely been assessed in the wild, particularly at a within-population scale. 3.?We used a novel multievent modelling framework (an extension of multistate mark-recapture modelling) that allows for uncertainty in disease state, to estimate transmission parameters and assess variation in the infection dynamics of avian malaria in a large, longitudinally sampled data set of breeding blue tits infected with two divergent species of Plasmodium parasites. 4.?We found striking temporal and spatial heterogeneity in the disease incidence rate and the likelihood of recovery within this single population and demonstrate marked differences in the relative influence of environmental and host factors in forcing the infection dynamics of the two Plasmodium species. 5.?Proximity to a permanent water source greatly influenced the transmission rates of P.?circumflexum, but not of P.?relictum, suggesting that these parasites are transmitted by different vectors. 6.?Host characteristics (age/sex) were found to influence infection rates but not recovery rates, and their influence on infection rates was also dependent on parasite species: P.?relictum infection rates varied with host age, whilst P.?circumflexum infection rates varied with host sex. 7.?Our analyses reveal that transmission of endemic avian malaria is a result of complex interactions between biotic and abiotic components that can operate on small spatial scales and demonstrate that knowledge of the drivers of spatial and temporal heterogeneity in disease transmission will be crucial for developing accurate epidemiological models and a thorough understanding of the evolutionary implications of pathogens.     

Entomopathogenic fungi and insect behaviour: from unsuspecting hosts to targeted vectors

The behavioural response of an insect to a fungal pathogen will have a direct effect on the efficacy of the fungus as a biological control agent. In this paper we describe two processes that have a significant effect on the interactions between insects and entomopathogenic fungi: (a) the ability of target insects to detect and avoid fungal pathogens and (b) the transmission of fungal pathogens between host insects. The behavioural interactions between insects and entomopathogenic fungi are described for a variety of fungal pathogens ranging from commercially available bio-pesticides to non-formulated naturally occurring pathogens. The artificial manipulation of insect behaviour using dissemination devices to contaminate insects with entomopathogenic fungi is then described. The implications of insect behaviour on the use of fungal pathogens as biological control agents are discussed.     

Population dynamic models of the spread of Wolbachia

Wolbachia are endosymbionts that are found in many insect species and can spread rapidly when introduced into a naive host population. Most Wolbachia spread when their infection frequency exceeds a threshold normally calculated using purely population genetic models. However, spread may also depend on the population dynamics of the insect host. We develop models to explore interactions between host population dynamics and Wolbachia infection frequency for an age-structured insect population regulated by larval density dependence. We first derive a new expression for the threshold frequency that extends existing theory to incorporate important details of the insect's life history. In the presence of immigration and emigration, the threshold also depends on the form of density-dependent regulation. We show how the type of immigration (constant or pulsed) and the temporal dynamics of the host population can strongly affect the spread of Wolbachia. The results help understand the natural dynamics of Wolbachia infections and aid the design of programs to introduce Wolbachia to control insects that are disease vectors or pests.     

Masters of conquest and pillage: Xenorhabdus nematophila global regulators control transitions from virulence to nutrient acquisition

Invertebrate animal models are experimentally tractable and have immunity and disease symptoms that mirror those of vertebrates. Therefore they are of particular utility in understanding fundamental aspects of pathogenesis. Indeed, artificial models using human pathogens and invertebrate hosts have revealed conserved and novel molecular mechanisms of bacterial infection and host immune responses. Additional insights may be gained from investigating interactions between invertebrates and pathogens they encounter in their natural environments. For example, enteric bacteria in the genera Photorhabdus and Xenorhabdus are pathogens of insects that also mutualistically associate with nematodes in the genera Heterorhabditis and Steinernema respectively. These bacteria serve as models to understand naturally occurring symbiotic associations that result in disease in or benefit for animals. Xenorhabdus nematophila is the best-studied species of its genus with regard to the molecular mechanisms of its symbiotic associations. In this review, we summarize recent advances in understanding X. nematophila –host interactions. We emphasize regulatory cascades involved in coordinating transitions between various stages of the X. nematophila life cycle: infection, reproduction and transmission.     

Host thermal biology: the key to understanding host–pathogen interactions and microbial pest control?

1 The role of pathogens in insect population dynamics remains poorly understood and their performance in biological control is erratic. Here we identify that temperature and host thermal behaviour, both the active interaction with environmental temperature and solar radiation via thermoregulation and the passive interception of these factors by thermal generalists, are central to understanding host–pathogen interactions. 2 We demonstrate that pathogenicity, the latent period of infection and host recovery rate can all vary dramatically across and between seasons due to thermal biology of the host and changes in environmental temperature. 3 Such effects have not been thoroughly explored in any previous investigations but may have major implications for disease dynamics in insects and possibly in ectotherms in general, and for development of effective biopesticides.     

Insect immune responses to nematode parasites

Host innate immunity plays a central role in detecting and eliminating microbial pathogenic infections in both vertebrate and invertebrate animals. Entomopathogenic or insect pathogenic nematodes are of particular importance for the control of insect pests and vectors of pathogens, while insect-borne nematodes cause serious diseases in humans. Recent work has begun to use the power of insect models to investigate host-nematode interactions and uncover host antiparasitic immune reactions. This review describes recent findings on innate immune evasion strategies of parasitic nematodes and host cellular and humoral responses to the infection. Such information can be used to model diseases caused by human parasitic nematodes and provide clues indicating directions for research into the interplay between vector insects and their invading tropical parasites.     

The interaction between plant competition and disease

It is well documented that pathogens can affect the survival, reproduction, and growth of individual plants. Drawing together insights from diverse studies in ecology and agriculture, we evaluate the evidence for pathogens affecting competitive interactions between plants of both the same and different species. Our objective is to explore the potential ecological and evolutionary consequences of such interactions. First, we address how disease interacts with intraspecific competition and present a simple graphical model suggesting that diverse outcomes should be expected. We conclude that the presence of pathogens may have either large or minimal effects on population dynamics depending on many factors including the density-dependent compensatory ability of healthy plants and spatial patterns of infection. Second, we consider how disease can alter competitive abilities of genotypes, and thus may affect the genetic composition of populations. These genetic processes feed back on population dynamics given trade-offs between disease resistance and other fitness components. Third, we examine how the effect of disease on interspecific plant interactions may have potentially far-reaching effects on community composition. A host-specific pathogen, for example, may alter a competitive hierarchy that exists between host and non-host species. Generalist pathogens can also induce indirect competitive interactions between host species. We conclude by highlighting lacunae in our current understanding and suggest that future studies should (1) examine a broader taxonomic range of pathogens since work to date has largely focused on fungal pathogens; (2) increase the use of field competition studies; (3) follow interactions for multiple generations; (4) characterize density-dependent processes; and (5) quantify pathogen, as well as plant, population and community dynamics.