Reactions of adult female parasitoids, particularly Aphidius rhopalosiphi, to volatile chemical cues from the host plants of their aphid prey

Abstract. In Y-tube olfactometer tests, Aphidius ervi Hal., Trioxys sp., Praon sp., Aphelinus flavus (Nees), Lysiphlebus fabarum (Marsh.) and Aphidius rophalosiphi De Stef. responded positively to the odour of the plant on which aphid mummies containing them had been collected. The response to host plant odour was greater than the response to the odour of host aphids, their honeydew or a combination of the two. The strongest response was to a combination of plant and host aphids. A. rhopalosiphi showed a strong positive response to three wheat volatiles (cis-3-hexenyl acetate, cis-3-hexen-1-ol and trans-2-hexenal) as well as to indole-3-acetaldehyde (a breakdown product of tryptophan in aphid honeydew). In both olfactometer tests with odours and choice trials with whole plants, newly emerged A. rhopalosiphi distinguished and preferred the variety of wheat on which their development had occurred to other wheat varieties.     

Contributions of Robert (Bob) J. O’Neil to the field of predaceous Heteroptera

Predaceous Heteroptera are important components of natural and managed habitats. The extent of predatory habits among taxa ranges from those that are totally (or nearly totally) predaceous to those that are nearly totally phytophagous, but occasionally feed on arthropod prey. Because of that variability in predatory habit, the contributions of heteropteran taxa to management of pest species will vary greatly. The late Robert (Bob) J. O’Neil (1955–2008) added significantly to understanding the roles of and benefits from facultatively predaceous Heteroptera. His focus on behavioral and physiological attributes that permitted facultatively predaceous species to persist in agricultural habitats demonstrated that facultative predators could help prevent pest outbreaks, but were less effective at reducing numbers of species already considered above economic thresholds.     

A decade of progress in understanding vitamin E synthesis in plants

The chloroplasts of higher plants contain and elaborate many unique biochemical pathways that produce an astonishing array of compounds that are vital for plastid function and are also important from agricultural and nutritional perspectives. One such group of compounds is the tocochromanols (more commonly known as Vitamin E), which is a class of four tocopherols and four toctorienols, lipid-soluble antioxidants that are only synthesized by plants and other oxygenic, photosynthetic organisms. Though the essential nature of tocopherols in mammalian diets was recognized over 80 years ago and the biosynthetic pathway in plants and algae elucidated in the late 1970s and early 80s, it has only been in the past decade that the genes and proteins for tocopherol synthesis have finally been isolated and characterized. The use of model plant and cyanobacterial systems has driven this gene discovery to the point that manipulation of tocopherol levels and types in various plant tissues and crops is becoming a reality. This article reviews progress since 1996 in the molecular and genetic understanding of tocopherol synthesis in the model photosynthetic organisms Arabidopsis thaliana and Synechocystis PCC6803 as a primer for current and future efforts to manipulate the levels of this essential nutrient in food crops by breeding and transgenic approaches.     

The effects of mullein plants (Verbascum thapsus) on the population dynamics of Dicyphus hesperus (Heteroptera: Miridae) in tomato greenhouses

The response of Dicyphus hesperus Knight (Heteroptera: Miridae) to whitefly populations in tomato greenhouses was measured in the presence and absence of mullein (Verbascum thapsus L.) as an alternative host plant. The dynamics of the D. hesperus population on tomato (Lycopersicon esculentum Mill.) and on mullein plants were followed through an entire growing season. In houses with mullein plants, more predators occurred on mullein when whitefly density was low on tomato. A mark-release-recapture experiment where rabbit IgG was used as an external marker showed that D. hesperus adults moved from mullein plants to tomato plants. D. hesperus was always more abundant in houses with mullein than in the houses with tomato plants alone. Movements between tomato and mullein plants are discussed as a strategy to optimize predator foraging. The use of mullein as an alternative host plant may contribute to the establishment of D. hesperus and help to preserve the predator population when prey on tomato crops is scarce.     

Generalism Versus Specialism: Responses of Diadegma mollipla (Holmgren) and Diadegma semiclausum (Hellen), to the Host Shift of the Diamondback Moth (Plutella xylostella L.) to Peas

A population of the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) (DBM) was recently found to infest sugar snap- and snowpeas in the Rift Valley in Kenya, causing heavy damage. The influence of this host shift on host location preferences of two parasitoids was investigated: The indigenous Diadegma mollipla (Holmgren) regarded as a relative generalist, and Diadegma semiclausum(Hellen), regarded as highly specific to DBM. The attractiveness of different odour sources was compared for the two parasitoid species using a Y-tube olfactometer using naïve females. D. mollipla was not significantly attracted to any cabbage related odours but showed a significant preference for the DBM infested pea plant when tested against clean air. D. semiclausum was highly attracted to the undamaged cabbage plant and odours related to cabbage. On the other hand, peas infested with DBM, showed no attractiveness to this parasitoid. The results showed that specialisation of D. semiclausum is mediated by host plant signals, associated with crucifers, which are not encountered in DBM feeding on peas. For D. mollipla,although a frequent parasitoid on DBM in crucifers, volatiles emitted by these plants might not be used as primary cues for host location. This species may respond largely to chemicals yet unknown and associated with a variety of plant-herbivore interactions.     

Microarray data quality analysis: lessons from the AFGC project

Genome-wide expression profiling with DNA microarrays has and will provide a great deal of data to the plant scientific community. However, reliability concerns have required the development data quality tests for common systematic biases. Fortunately, most large-scale systematic biases are detectable and some are correctable by normalization. Technical replication experiments and statistical surveys indicate that these biases vary widely in severity and appearance. As a result, no single normalization or correction method currently available is able to address all the issues. However, careful sequence selection, array design, experimental design and experimental annotation can substantially improve the quality and biological of microarray data. In this review, we discuss these issues with reference to examples from the Arabidopsis Functional Genomics Consortium (AFGC) microarray project.     

Plant ion channels: from molecular structures to physiological functions

Progress in identification of plant ion channels and development of electrophysiological analyses in heterologous expression systems and in planta, in combination with reverse genetic approaches, are providing the possibility of associating molecular entities with physiological functions. Recently, the first attempts to determine in vivo functions using knockout mutants demonstrated the roles of root ion channels. The search for proteins interacting with such channels leads to an even more complex view of the concerted action in protein networks.     

Nitrogen and water affect direct and indirect plant systemic induced defense in cotton

Plants have direct and indirect constitutively produced and inducible defenses against herbivores and pathogens, which can substantially aid in their ability to defend themselves. However, very little is known about the influence of agronomic factors on such defenses. Here, we tested the effects of nitrogen levels and water availability on the ability of cotton plants to deter feeding by Spodoptera exigua through induction of anti-feedants, and to attract Microplitis croceipes through systemic induction of volatile emission. Cotton plants were grown with various nitrogen levels and were either exposed to water stress or normal water before being exposed to S. exigua for 48 h for induction of defenses. Dual choices of various nitrogen and water treatments were provided to M. croceipes in flight tunnel bioassays. Dual choices of leaf tissue from the various nitrogen and water treatments were provided to S. exigua larvae. Both water stress and nitrogen levels under and over the recommended levels increased leaf tissue consumption and decreased attraction of M. croceipes to the plants. Analyses of induced volatiles released from herbivore damaged plants indicate that their concentrations differ among the nitrogen levels tested with plants receiving no nitrogen or twice the recommended dose having amounts much lower than plants receiving the recommended dose. Because both direct and indirect plant defense mechanisms are negatively affected by improper nitrogen and insufficient water, we argue that these factors should be considered for a better natural control of pests in cotton and most probably in other crops.     

An ecological cost of plant defence: attractiveness of bitter cucumber plants to natural enemies of herbivores

Plants produce defences that act directly on herbivores and indirectly via the attraction of natural enemies of herbivores. We examined the pleiotropic effects of direct chemical defence production on indirect defence employing near‐isogenic varieties of cucumber plants (Cucumis sativus) that differ qualitatively in the production of terpenoid cucurbitacins, the most bitter compounds known. In release–recapture experiments conducted in greenhouse common gardens, blind predatory mites were attracted to plants infested by herbivorous mites. Infested sweet plants (lacking cucurbitacins), however, attracted 37% more predatory mites than infested bitter plants (that produce constitutive and inducible cucurbitacins). Analysis of the headspace of plants revealed that production of cucurbitacins was genetically correlated with large increases in the qualitative and quantitative spectrum of volatile compounds produced by plants, including induced production of (E )‐β‐ocimene (3E )‐4,8‐dimethyl‐1,3,7‐nonatriene, (E,E)‐α‐farnesene, and methyl salicylate, all known to be attractants of predators. Nevertheless, plants that produced cucurbitacins were less attractive to predatory mites than plants that lacked cucurbitacins and predators were also half as fecund on these bitter plants. Thus, we provide novel evidence for an ecological trade‐off between direct and indirect plant defence. This cost of defence is mediated by the effects of cucurbitacins on predator fecundity and potentially by the production of volatile compounds that may be repellent to predators.     

海南典型有害植物的入侵扩散机理研究进展

有害植物成灾会对农林业生态系统、经济和环境造成巨大影响。本文对海南典型入侵植物薇甘菊、假臭草及土著灾变植物金钟藤的成灾扩散机理研究做一综述,以期为海南有害植物的研究和管理提供依据。自然及人为干扰造成的薇甘菊匍匐茎克隆片段有较高的再生能力,其再生能力和生长与储存在节间和叶子中的资源呈正相关。假臭草随土壤养分条件的改善比本地种获利更多,说明农田施肥等干扰因素可能促进假臭草相对于本地种的种群优势。金钟藤已扩散至海南五指山有旅游活动的自然林;调查和移栽试验发现,其可能是先在受干扰严重的林缘和旅游小径边定植,之后通过匍匐和攀爬生长扩散至附近的自然林。这些结果强调了人类活动、高养分条件及物种自身性状等在有害植物成灾中的作用。未来仍需系统、深入地研究有害植物成灾扩散的机理及其控制对策,为减弱有害植物的扩散和危害提供参考,并为海南国际旅游岛的建设提供安全保证。     

海洋奇古菌门认知的拓展：从新类群到新功能

奇古菌门是全球海洋中的重要微生物类群,在海洋原核浮游生物中的比例可达20%–40%。作为一类化能无机自养微生物,奇古菌门成员可通过氧化氨获得能量,实现不依赖光照的无机碳固定,在碳、氮等元素的地球化学循环中起关键作用。奇古菌门是海洋中氨氧化反应的主要执行者,其化能合成的有机质是海洋特别是深海环境中微生物的重要能量来源。随着研究的逐步深入,有关该类群生理代谢特性的认知不断被拓展,包括奇古菌门异养代谢的揭示、不具氨氧化能力类群在深海中的发现,以及最新报道的奇古菌门在厌氧条件下介导氧气、氧化亚氮和氮气的产生等。这些研究揭示了奇古菌门参与海洋生物地球化学循环和气候变化调节的新机制,为围绕该类群的深入探究和培养提供了新的思路和方向。本文从群落组成、环境适应、生态功能、进化历史和培养现状等方面综述了近年来有关海洋奇古菌门的新发现和新认识,以期增进对该类群的了解。     

模式植物短柄草研究新进展

短柄草(Brachypodium distachyon)株型矮小,易于种植栽培,生长周期短,自花授粉,容易繁殖。另外,短柄草基因组比较小,易于转化,与小麦具有比较近的亲缘关系,是理想的草类特别是禾本科模式植物。近年来,短柄草的研究工作在细胞遗传学、基因组学、比较基因组学、植物-病原菌相互作用、功能基因组学等研究领域取得了许多进展,包括完成了Bd-21全基因组的测序工作、构建了T-DNA插入突变体库、用遗传学的方法首次研究短柄草基因的生物学功能等。本文综述了近年来特别是2009年以来短柄草的研究进展,并对未来的研究工作做了展望。     

比较基因组学分析不同来源罗伊氏乳杆菌基因多样性及生境适应性

【目的】研究34株不同来源罗伊氏乳杆菌(Lactobacillus reuteri)基因多样性及生境适应性机制,了解该菌株在肠外生境及肠内生境中适应性的异同,为L. reuteri优良菌株的开发提供理论基础。【方法】基于二代测序平台对11株源于发酵食品(酸马奶、酸粥)的L. reuteri进行测序,并应用比较基因组学将其与发酵食品、酸面团、食草动物L. reuteri分离株基因组进行比较分析。【结果】分离自酸马奶、酸粥L. reuteri基因组大小平均为2.14 Mb,GC含量平均为38.77%,且同种来源分离株系统发育关系距离较近。泛-核心基因集分别包含7242个、969个基因家族,其中酸马奶分离株特异性基因最多为459个。功能注释结果显示不同来源菌株碳水化合物、氨基酸相关基因数量及种类差异较大,仅在发酵食品和食草动物株中发现抗生素耐药性基因。注释到的碳水化合物活性酶中仅出现在发酵食品与食草动物分离株的为GH3 (β-葡萄糖苷酶等)和GH43 (β-木糖苷酶等),特有的分别为AA3 (纤维二糖脱氢酶等)和GH66 (葡萄糖转移酶等)。【结论】不同来源L. reuteri具有广泛的基因...     

两种Eupristina属小蜂对宿主榕果挥发物和合成信息素的行为反应

高榕,雌雄同株,与其共生的形态高度相似的传粉小蜂Eupristina altissima与非传粉小蜂Eupristina sp.均为果内产卵。利用Y型嗅觉仪生物测定法研究E.altissima和Eupristina sp.对不同发育期高榕榕果挥发物以及合成信息素混合物的行为反应差异。结果表明:E.altissima和Eupristina sp.对高榕雌花期榕果挥发物具极显著趋向行为,对高榕雄花期榕果挥发物具极显著驱避行为,表明E.altissima与Eupristina sp.雌蜂能够敏锐辨别高榕雌花期和雄花期榕果的挥发物,快速远离雄花期榕果,并实现对宿主雌花期榕果的定位。但是,E.altissima与Eupristina sp.对其它发育时期榕果挥发物的行为反应具有差异性,前者对雌前期榕果和传粉或产卵后榕果释放的挥发物存在显著的趋避反应,而后者无明显的行为偏向性,表明E.altissima能够识别雌前期榕果和传粉或产卵后榕果,可避免误入其中而无法繁殖后代,Eupristina sp.则不具备这种识别能力。E.altissima和Eupristina sp.小蜂对合成信息素的行为反应也高度相似,表现为芳樟醇、苯乙烯,以及苯乙烯和金合欢醇的交互作用对两种小蜂选择行为影响显著,组合A_1B_2C_2(0.5%Linalool+1%Benzyl ethylene+1%Farnesol)的混合信息素对两种小蜂具有极显著的驱避作用,而组合A_2B_1C_1(1%Linalool+0.5%Benzyl ethylene+0.5%Farnesol),A_2B_1C_2(1%Linalool+0.5%Benzyl ethylene+1%Farnesol),A2B2C1(1%Linalool+1%Benzyl ethylene+0.5%Farnesol)的混合信息素对其具有极显著的吸引作用,但两种小蜂对组合A_1B_1C_1(0.5%Linalool+0.5%Benzyl ethylene+0.5%Farnesol)的行为反应存在差异。两种小蜂对榕果挥发物和合成信息素的反应异同,可能与其触角结构的差异密切相关。研究结果为探究榕-蜂共生体系的化学信号传导机制提供科学依据。     

一株羽毛针禾内生细菌的鉴定、功能及促生特性

【背景】羽毛针禾是沙漠群落演替中的“先锋”草本植物,可在荒漠贫瘠地带繁殖,其生命力顽强、繁殖速度快、种子量大、扩散广。【目的】探究羽毛针禾具有促生效应的内生细菌资源。【方法】从种子中分离出内源性细菌Z1,并对其进行了生物化学、发酵和促生等方面的研究。【结果】Z1菌落呈黄色球形,不透明,中央有小突起,边缘褶皱而湿润,镜检成直杆状,表面有细鞭毛,大小范围为(0.5-1.0)μm×(1.0-3.0)μm。经革兰氏染色试验、靛基质、甲基红、氧化酶、淀粉生产水解试验、V-P试验、明胶液化学试验测定后均呈阳性,甲基红试验、尿素分解实验测定均呈现阴性,是泛生菌属(Pantoea)的细菌。Z1具有产吲哚乙酸的能力,单位产量为3.14 mg/L;而且具有溶磷、解钾、分泌铁载体的能力。Z1菌株最佳发酵培养基条件是:氮源为蛋白胨,碳源是溶性淀粉,无机盐为碳酸钙,pH 9.0。Z1接种小麦10 d后促生效果明显,叶宽、株高、根长等指标分别增长了60.0%、13.5%和8.0%;小麦幼苗的叶片含水量、总叶绿素含量、氮含量、可溶性蛋白等指标均有显著提升(P<0.05)。【结论】Z1是一株具有促生潜力的功能菌...     

Beyond promiscuity: From sexuality to apomixis in flowering plants

Summary Little is known about the genetic basis and molecular mechanisms regulating female gametogenesis in flowering plants. In many species sexuality is replaced by apomixis, a method of asexual reproduction that circumvents female meiosis and fertilization, and culminates in the formation of clonal seeds. Using a new generation of transposon based insertional mutagenesis strategies and their resulting molecular tools, we are investigating how female meiotically derived cells (megaspores) acquire their identity. We are also determining their function and interactions, and attempting the induction of apomixis initiation in the ovule of Arabidopsis. This basic knowledge will contribute to establish the transfer of apomixis into sexual crops, a major challenge faced by plant biotechnology. The introduction of apomixis as a reproductive alternative could represent a unique opportunity to simplify breeding schemes and genetically perpetuate any desired heterozygous genotype, including hybrids.     

Structural damage to oak leaves alters natural enemy attack on a leafminer

A field experiment was conducted to test the role of structural changes in oak leaves caused by folivory on natural enemy attack of leafmining larvae and pupae of Cameraria sp. nov., while controlling for induced chemical responses. Damaged and intact leaves of Quercus emoryi were sealed with a fluorocarbon telomer in 1988–1989 to prevent release of long-range or contact chemical cues that might be perceived by searching parasitoids and predators. These leaves were attached to Q. emoryi leaves harboring first instars of Cameraria, but otherwise were undamaged. Rates of attack by natural enemies of leafminers in leaves with sealed, damaged leaves attached were significantly greater than those in control leaves, indicating that structural damage alone influences attack by natural enemies. Survival of leafminers in leaves with attached damaged leaves was significantly less than that of controls, suggesting that structural changes in leaves due to folivore feeding affect population dynamics of Cameraria via increased attack by the third trophic level.

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Résumé Des expériences ont été faites dans la nature pour évaluer l'influence des modifications structurales provoquées par la défoliation sur les attaques des ennemis naturels des chenilles mineuses et des chrysalides de Cameraria sp. nov. En 1988–89 des feuilles saines et endommagées de Quercus emoryi ont été enduites de télomère de fluorocarbone pour empêcher l'émission d'indicateurs chimiques à distance ou de contact pouvant être utilisés par les parasitoïdes et les prédateurs lors de leur prospection. Ces feuilles ont été attachées à des feuilles apparemment intactes de Q. emoryi mais hébergeant des Cameraria du premier stade. Les attaques par les ennemis naturels des mineuses étaient plus importantes sur feuilles associées à des feuilles endommagées mais enduites de fluorocarbone que sur feuilles témoins, ce qui montre que les dégâts structuraux seuls influent sur les attaques par les ennemis naturels. La survie des mineuses dans les feuilles associées à des feuilles endommagées était plus faible que chez les témoins, ce qui suggère des changements structuraux dans les feuilles provoqués par les phytophages affectant la dynamique de population de Cameraria via une attaque accrue par le troisième niveau trophique.