昆虫趋光性及其机理的研究进展

依据目前已有资料 ,从行为学、生理学及田间应用调查等方面概述了近几十年昆虫趋光性的国内外研究进展。其中 ,行为学与生理学研究较多 ,且两者结果基本一致 ,相互补充 ,为趋光性机制的假说提供了可靠的依据。关于昆虫趋光性机制的假说较多 ,其中报道较多的是光干扰假说、光定向行为假说和生物天线假说 3种 ,现在较为普遍接受的是前两者。光干扰假说是指刺眼作用干扰昆虫的正常活动导致趋光 ,而光定向行为假说则指昆虫趋光是由于光定向行为所致     

桃蚜对不同单色光趋性反应的测定

为了探讨蚜虫对不同色光选择反应的定量指标, 采用滤光片技术测定了有翅和无翅桃蚜Myzus persicae对不同波长单色光的趋性反应。结果表明: 有翅蚜对490~550 nm范围内的单色光表现出明显趋性, 其中对538.9和549.9 nm的绿偏黄色光趋性最强, 平均位移分别达25.29和22.97 cm, 其次为491.5 nm的蓝绿色光, 而对于波长576.0 nm的黄色光并没有表现出明显趋性。无翅蚜对不同单色光的趋性反应则没有明显的峰值, 最高相对平均位移仅1.41。行为测定结果与前人电生理测定的结果基本一致, 说明以位移作为小体昆虫趋光性强弱的指标是可靠的。     

昆虫复眼结构及视觉导航研究进展

复眼是昆虫主要的视觉器官,具有感受物体的大小、形状和颜色等功能。研究复眼结构是了解昆虫感光机制的基础,进而明确视觉信号在昆虫行为中的作用。昆虫的复眼包括了重叠像眼和并列像眼两种类型,重叠像眼具有聚光作用,可以感受到低强度的光,但是分辨率较低;并列像眼没有聚光作用,分辨率较高。大多数白天活动的昆虫具有并列像眼,夜晚活动的昆虫具有重叠像眼。分子生物学、视网膜电位和行为学研究结果均表明昆虫对紫外、蓝和绿光最敏感。昆虫利用天体和地面目标物信号定向和导航,依靠天体发出的偏振光和地面目标物与背景颜色的对比度进行视觉判断,对于任何一种昆虫,这两种信号都可能同时应用。视觉信号在昆虫定位植物寄主、寻找配偶和产卵过程中起着至关重要的作用,不能低估昆虫视觉能力的作用。利用昆虫对不同波长光波的趋性,研制专一性强的诱捕装置,可为害虫的无公害防治提供理论基础。     

昆虫的生物光电效应与虫害治理应用

农业虫害的治理需要依据为害昆虫的特性提出与环境适宜、生态兼容的技术体系和关键技术。为害昆虫表现了对敏感光源具有个体差异性和群体一贯性的趋光性行为特征,并通过视觉神经信号响应和生理光子能量需求的方式呈现出生物光电效应的作用本质。利用昆虫的这种趋性行为诱导增益特性,一些光电诱导杀虫灯技术以及害虫诱导捕集技术广泛地应用于农业虫害的防治,具有良好的应用前景。     

植食性昆虫与其植物性食物间的相互关系

昆虫是地球上种类和数量最多的动物群体之一 ,而大多数昆虫又是以植物为食的。因此研究昆虫和植物间的相互关系 ,对于植物繁衍后代 ,对于消灭有害昆虫、保护有益昆虫意义重大。1　昆虫摄食植物的一般机理首先 ,昆虫依靠视觉或嗅觉对植物产生行为的定向和趋性。例如蝗虫对垂直线条 ,苹果实蝇对绿色、黄色和橙色球形物有趋性 ,它们依靠嗅觉和触觉对植物的理化刺激作出反应 ;之后 ,依靠味觉作用决定对某种植物大量摄食还是放弃取食。昆虫对植物是否取食 ,是植物中的化学成分与昆虫食性间既互相依存、又处于主动与被动的关系。2　植物与植食性昆…     

连续温度梯度下昆虫趋温性的研究现状与展望

昆虫作为一种能够自由活动的生物,可以通过运动主动选择对其有利的环境温度。大多数研究中昆虫被迫接受人为设定的恒温或变温,并未体现出昆虫本身对适宜温度的主动选择性。连续温度梯度是在某一介质的两端产生由高到低连续变化的温度范围。在一定温度梯度中昆虫趋温行为的研究揭示了其主动选择的适宜温度,这对了解昆虫的空间动态、提高测报准确性和开发防治新方法有重要意义。总结了产生连续温度梯度的各种装置,致冷、加热和温度测量方法以及昆虫趋温行为的观察装置和方法,包括在植物体上(内)及空气、下垫面、粮食和土壤等介质中产生温度梯度的方法及装置。各装置以水浴或电器设备制冷或加热,肉眼观察手工记录或以摄像机、声音信号采集系统等方法记录昆虫的行为。综述了多种昆虫生长发育、栖息、产卵或取食的偏好温度,总结了性别、发育阶段和生态型等生理因素及光照、湿度和预适应温度等环境因子对昆虫偏好温度变化的影响。昆虫的趋温性因种而异,同种昆虫不同发育阶段或不同生命活动所趋温度不同。多数种类昆虫雄性成虫的偏好温度比雌性略高。某些昆虫的多型现象可能导致其种内不同生态型的偏好温度存在差异。光照和湿度的变化会影响某些昆虫对温度的反应。有些昆虫经预适应温度训练后,其偏好温度发生改变。某些昆虫对温度的偏好呈现出一定的日变化和季节变化规律。饥饿条件下昆虫的偏好温度降低。温度梯度的有无及其方向、温度的高低、温差的大小等因素都会影响昆虫的活动性。最后分析了本类研究中存在的问题和不足,并展望了未来的研究方向,指出开展对重要农林作物害虫和天敌趋温行为及其生理学机制,外界环境因素影响昆虫趋温性等方面的探索将是未来该领域研究的重点内容。     

我国夜蛾趋光行为的研究及其应用

影响昆虫行为的环境因素很多,一般按自然特征分为气候因素与生物因素两大类,前者如温度、光照、降水等,后者如食料、无教等。气候因素对行为的作用为综合性的,但所起的作用和对生命活动的意义各有特点,其中光对昆虫活动有特殊意义。从间接关系说,光是昆虫不可缺少的条件,但不同昆虫对光的需求各异。昆虫的趋光行为是昆虫行为中最为重要和普遍的行为。许多学者对昆虫的行为影响进行了细致的研宪,特别对夜蛾的趋光行为特点的研究较为深入。了解其趋光行为,对昆虫预测预报及制定防治策略和方法,可提供重要依据。现将夜蛾趋光行为特点…     

昆虫趋光行为的光胁迫假说

趋光性是昆虫的固有行为特征之一,被广泛的应用在害虫物理防治中。本文综述了几种主流的昆虫趋光性假说,着重介绍了昆虫在趋光过程中的行为反应、受光胁迫后生理应激和补偿效应,提出了昆虫趋光行为的光胁迫假说,以期为昆虫趋光性理论研究提供新的思路。     

不同光源和暗适应时间对棉铃虫蛾趋光行为的影响

1　引　　言诱虫灯是监测昆虫迁飞、扩散、发生期和发生量的重要工具 ,也是害虫综合治理的重要措施之一 .一般认为 ,昆虫飞向光源是一种趋光行为 ,但国内外很多学者认为这种行为是光源对昆虫正常活动的干扰 ,并非是昆虫的趋性[4 ].昆虫对不同波长的光源反应不同 .丁岩钦[6 ]对棉铃虫蛾 (Helicover paarmigera)进行了 1 3种单色光的行为选择实验 ,最高峰在333nm ;侯无危等[9]对桃小食心虫 (Carposinaniponensis)的趋光性研究发现 ,其对 333nm以上的单色光均有趋光反应 .魏国树等[12～ 14 ]在 340～ 6 0 5nm波谱范围内测定了棉铃虫蛾的行为反…     

昆虫色素研究进展

昆虫体表具有丰富的色彩,这一优势有助于其更有效地实现性别识别、伪装警戒、趋敌避害等功能。相对于微纳米结构对昆虫体表色彩效应影响的研究,昆虫色素的研究相对较弱,而且一些已知的色素在成色机制中的作用也不是特别清楚。本文对昆虫色素的种类、存在部位、理化性质、部分目(11目300多种昆虫)中的色素、生物合成途径等进行了概述;对目前昆虫色素研究中存在的问题提出了可能的解决办法,并对昆虫色素的应用现状、研究意义及可能的仿生应用进行了总结和展望。     

Extreme Divergence of Wolbachia Tropism for the Stem-Cell-Niche in the Drosophila Testis

Microbial tropism, the infection of specific cells and tissues by a microorganism, is a fundamental aspect of host-microbe interactions. The intracellular bacteria Wolbachia have a peculiar tropism for the stem cell niches in the Drosophila ovary, the microenvironments that support the cells producing the eggs. The molecular underpinnings of Wolbachia stem cell niche tropism are unknown. We have previously shown that the patterns of tropism in the ovary show a high degree of conservation across the Wolbachia lineage, with closely related Wolbachia strains usually displaying the same pattern of stem cell niche tropism. It has also been shown that tropism to these structures in the ovary facilitates both vertical and horizontal transmission, providing a strong selective pressure towards evolutionary conservation of tropism. Here we show great disparity in the evolutionary conservation and underlying mechanisms of stem cell niche tropism between male and female gonads. In contrast to females, niche tropism in the male testis is not pervasive, present in only 45% of niches analyzed. The patterns of niche tropism in the testis are not evolutionarily maintained across the Wolbachia lineage, unlike what was shown in the females. Furthermore, hub tropism does not correlate with cytoplasmic incompatibility, a Wolbachia-driven phenotype imprinted during spermatogenesis. Towards identifying the molecular mechanism of hub tropism, we performed hybrid analyses of Wolbachia strains in non-native hosts. These results indicate that both Wolbachia and host derived factors play a role in the targeting of the stem cell niche in the testis. Surprisingly, even closely related Wolbachia strains in Drosophila melanogaster, derived from a single ancestor only 8,000 years ago, have significantly different tropisms to the hub, highlighting that stem cell niche tropism is rapidly diverging in males. These findings provide a powerful system to investigate the mechanisms and evolution of microbial tissue tropism.     

A Novel Effect in Phycomyces Phototropism : Positive Bending and Compensation Spectrum in Far UV

A novel effect—positive phototropic bending under far UV irradiation (between 260 and 305 nanometers) at low intensities—is reported. Natural compensation points (intensities which cause no bending under unilateral irradiation) have been determined for different wavelengths. The curve connecting these points, the compensation spectrum, divides the intensity-wavelength plane into areas of negative and positive tropism. It is further shown that a highly asymmetrical pattern of light stimulus within the sporangiophore underlies the symmetrical growth response at each compensation point. This suggests that some unknown additional factor is involved in perceiving a UV stimulus at the level of the photoreceptor. It is also demonstrated here that positive tropism in the UV range is due to a lens effect. We conclude that the hypothesis of optical attenuation of the stimulus (considered until now as the most plausible explanation of negative tropism in the UV spectral range) must be dismissed. The results presented here represent the first application of our quantitative theoretical consideration of spatial factors in phototropism heretofore neglected by others.     

Specific tropism caused by ultraviolet C radiation in Phycomyces

The giant sporangiophores of Phycomyces blakesleeanus turn towards blue and away from ultraviolet C sources (wavelength under 310 nm). We have isolated fifteen mutants with normal blue tropism but defective ultraviolet tropism. Wild-type sporangiophores described a double turn when exposed successively to blue and ultraviolet beams coming from the same side; under certain conditions, the mutants turned only to the blue. The new uvi mutations modified the behaviour in heterokaryosis and were lethal in homokaryosis, i.e., they affected essential cellular components. The responses of the wild type and one of the mutants were registered and evaluated with a computer-aided device. The mutant behaved normally under blue light, but took longer than the wild type to turn away from the ultraviolet source. With very weak ultraviolet stimuli (10(-8) and l0(-9) W m-2), the wild type turned towards the source, but the mutant did not respond. Calculations of absorbed-energy distributions in the sporangiophore showed that Phycomyces responds differently to similar spatial distributions of blue and ultraviolet radiations. Wild-type and mutant sporangiophores had the same high ultraviolet absorption due to gallic acid. We conclude that ultraviolet tropism is not just a modification of blue phototropism due to the high ultraviolet absorption of the sporangiophores. Phycomyces has a separate sensory system responsive to ultraviolet radiation, but not to blue light.     

The role of cell signaling in poxvirus tropism: the case of the M-T5 host range protein of myxoma virus

Poxviruses demonstrate strict species specificity in vivo that range from narrow to broad, however the fundamental factors that mediate the basis of poxvirus tropism remain poorly understood. It is generally believed that most, if not all, poxviruses can efficiently bind and enter a wide range of mammalian cells and all of the known host anti-viral pathways that block viral replication in nonpremissive cells operate downstream of virus entry. A productive poxvirus infection is heavily dependent upon the production of a vast array of host modulatory products that specifically target and manipulate both extracellular immune response pathways of the host, as well as intracellular signal transduction pathways of the individually infected cells. The unique pathogenesis and host tropism of specific poxviruses can be attributed to the broad diversity of host modulatory proteins they express. Myxoma virus (MV) is a rabbit-specific poxviruses that encodes multiple host range factors, including an ankyrin-repeat protein M-T5, which functions to regulate tropism of MV for rabbit lymphocytes and some human cancer cells. At the molecular level, M-T5 binds and alters at least two distinct cellular proteins: Akt and cullin-1. The direct interaction between M-T5 and Akt was shown to be a key restriction determinant for MV tropism in a spectrum of human cancer cells making MV an excellent oncolytic candidate. Thus, the intricate relationship between viral encoded proteins and components of the host cell signaling networks can have profound impact on poxvirus tropism. The lessons we continue to learn from poxvirus host range factors like M-T5 will provide further insights into the factors that regulate poxvirus tropism and the mechanisms by which poxviruses micromanipulate the signaling pathways of the infected cell.     

Regulation of Stomatal Tropism and Infection by Light in Cercospora zeae-maydis: Evidence for Coordinated Host/Pathogen Responses to Photoperiod?

Cercospora zeae-maydis causes gray leaf spot of maize, which has become one of the most widespread and destructive diseases of maize in the world. C. zeae-maydis infects leaves through stomata, which is predicated on the ability of the pathogen to perceive stomata and reorient growth accordingly. In this study, the discovery that light was required for C. zeae-maydis to perceive stomata and infect leaves led to the identification of CRP1, a gene encoding a putative blue-light photoreceptor homologous to White Collar-1 (WC-1) of Neurospora crassa. Disrupting CRP1 via homologous recombination revealed roles in multiple aspects of pathogenesis, including tropism of hyphae to stomata, the formation of appressoria, conidiation, and the biosynthesis of cercosporin. CRP1 was also required for photoreactivation after lethal doses of UV exposure. Intriguingly, putative orthologs of CRP1 are central regulators of circadian clocks in other filamentous fungi, raising the possibility that C. zeae-maydis uses light as a key environmental input to coordinate pathogenesis with maize photoperiodic responses. This study identified a novel molecular mechanism underlying stomatal tropism in a foliar fungal pathogen, provides specific insight into how light regulates pathogenesis in C. zeae-maydis, and establishes a genetic framework for the molecular dissection of infection via stomata and the integration of host and pathogen responses to photoperiod.     

The region of the envelope gene of human immunodeficiency virus type 1 responsible for determination of cell tropism.

Different isolates of human immunodeficiency virus type 1 (HIV-1) vary in the cell tropisms they display, i.e., the range of cell types in which they are able to establish a productive infection. Here, we report on the phenotypes of recombinants between two molecularly cloned strains of HIV-1. Our results prove that the envelope glycoprotein gp120 is solely responsible for the difference in cell tropism between the two parental isolates and that no other genes or sequences are involved in determining the cell tropism of these strains. The region of the envelope involved in the determination of cell tropism includes sequences which encode the V3 loop of gp120. Control of cell tropism by this region of the virus env gene is a general phenomenon which applies to many different HIV-1 isolates.     

Host cell invasion by Trypanosoma cruzi: a unique strategy that promotes persistence

The intracellular protozoan parasite Trypanosoma cruzi is the causative agent of Chagas' disease, a serious disorder that affects millions of people in Latin America. Despite the development of lifelong immunity following infections, the immune system fails to completely clear the parasites, which persist for decades within host tissues. Cardiomyopathy is one of the most serious clinical manifestations of the disease, and a major cause of sudden death in endemic areas. Despite decades of study, there is still debate about the apparent preferential tropism of the parasites for cardiac muscle, and its role in the pathology of the disease. In this review, we discuss these issues in light of recent observations, which indicate that T. cruzi invades host cells by subverting a highly conserved cellular pathway for the repair of plasma membrane lesions. Plasma membrane injury and repair is particularly prevalent in muscle cells, suggesting that the mechanism used by the parasites for cell invasion may be a primary determinant of tissue tropism, intracellular persistence, and Chagas' disease pathology.     

Role of Naturally Occurring Basic Amino Acid Substitutions in the Human Immunodeficiency Virus Type 1 Subtype E Envelope V3 Loop on Viral Coreceptor Usage and Cell Tropism

To assess the role of naturally occurring basic amino acid substitutions in the V3 loop of human immunodeficiency virus type 1 (HIV-1) subtype E on viral coreceptor usage and cell tropism, we have constructed a panel of chimeric viruses with mutant V3 loops of HIV-1 subtype E in the genetic background of HIV-1LAI. The arginine substitutions naturally occurring at positions 8, 11, and 18 of the V3 loop in an HIV-1 subtype E X4 strain were systematically introduced into that of an R5 strain to generate a series of V3 loop mutant chimera. These chimeric viruses were employed in virus infectivity assays using HOS-CD4 cells expressing either CCR5 or CXCR4, peripheral blood mononuclear cells, T-cell lines, or macrophages. The arginine substitution at position 11 of the V3 loop uniformly caused the loss of infectivity in HOS-CD4-CCR5 cells, indicating that position 11 is critical for utilization of CCR5. CXCR4 usage was conferred by a minimum of two arginine substitutions, regardless of combination, whereas arginine substitutions at position 8 and 11 were required for T-cell line tropism. Nonetheless, macrophage tropism was not conferred by the V3 loop of subtype E R5 strain per se. We found that the specific combinations of amino acid changes in HIV-1 subtype E env V3 loop are critical for determining viral coreceptor usage and cell tropism. However, the ability to infect HOS-CD4 cells through either CXCR4 or CCR5 is not necessarily correlated with T-cell or macrophage tropism, suggesting that cellular tropism is not dictated solely by viral coreceptor utilization.     

Charge cluster-to-alanine scanning of UL128 for fine tuning of the endothelial cell tropism of human cytomegalovirus

The viral genes UL128, UL130, and UL131A have been identified as major determinants of endothelial cell (EC) tropism of human cytomegalovirus (HCMV), with deletion of either gene causing a null phenotype. We hypothesized that a functional scanning of these genes by minor genetic modifications would allow for the generation of mutants with an intermediate phenotype. By combining charge cluster-to-alanine (CCTA) mutagenesis with markerless mutagenesis of a bacterial artificial chromosome-cloned endotheliotropic HCMV strain, we analyzed UL128 in order to identify functional sites and hence enable targeted modulation of the EC tropism of HCMV. A total of nine mutations in eight charge clusters were tested. Three of the CCTA mutations severely reduced EC tropism, three were irrelevant, two had a weak effect on cell tropism, and one mutation in the most C-terminal cluster caused an intermediate phenotype. All of the highly effective mutations were located in a core region (amino acids 72 to 106) which appears to be particularly crucial for EC tropism. The intermediate effect of mutations in the C-terminal cluster could be modulated by varying the number of amino acids replaced with alanine. This study provides a rational approach for targeted modulation of HCMV cell tropism, which may aid in the development of HCMV strains with a desired degree of attenuation.     

Predicting host tropism of influenza A virus proteins using random forest

Background

Majority of influenza A viruses reside and circulate among animal populations, seldom infecting humans due to host range restriction. Yet when some avian strains do acquire the ability to overcome species barrier, they might become adapted to humans, replicating efficiently and causing diseases, leading to potential pandemic. With the huge influenza A virus reservoir in wild birds, it is a cause for concern when a new influenza strain emerges with the ability to cross host species barrier, as shown in light of the recent H7N9 outbreak in China. Several influenza proteins have been shown to be major determinants in host tropism. Further understanding and determining host tropism would be important in identifying zoonotic influenza virus strains capable of crossing species barrier and infecting humans.

Results

In this study, computational models for 11 influenza proteins have been constructed using the machine learning algorithm random forest for prediction of host tropism. The prediction models were trained on influenza protein sequences isolated from both avian and human samples, which were transformed into amino acid physicochemical properties feature vectors. The results were highly accurate prediction models (ACC>96.57; AUC>0.980; MCC>0.916) capable of determining host tropism of individual influenza proteins. In addition, features from all 11 proteins were used to construct a combined model to predict host tropism of influenza virus strains. This would help assess a novel influenza strain's host range capability.

Conclusions

From the prediction models constructed, all achieved high prediction performance, indicating clear distinctions in both avian and human proteins. When used together as a host tropism prediction system, zoonotic strains could potentially be identified based on different protein prediction results. Understanding and predicting host tropism of influenza proteins lay an important foundation for future work in constructing computation models capable of directly predicting interspecies transmission of influenza viruses. The models are available for prediction at http://fluleap.bic.nus.edu.sg.