遮阴对柠檬香茅中萜类化合物及其合成酶基因影响研究

为获取柠檬香茅(Cymbopogon citratus)中萜类化合物及其合成酶基因信息,以正常生长及遮阴下的柠檬香茅嫩叶为材料,进行代谢组学和转录组学结合q RT-PCR验证分析。代谢组分析结果表明,柠檬香茅所含萜类共23种,包括单萜4种、倍半萜4种、二萜8种、三萜3种和四萜4种。在遮阴下,柠檬香茅的二萜类银杏内酯C和四萜类虾青素相对含量更高。转录组测序结果表明,单萜生物合成涉及4类合成酶的24个基因,二萜生物合成涉及11类合成酶的49个基因,倍半萜和三萜生物合成涉及12类合成酶的58个基因,其中6类合成酶的8个基因在遮阴下的相对表达量显著提高,而前萘二烯加氧酶(c64786.0)基因正好相反。q RT-PCR分析表明,遮阴下4个FPKM值差异明显的萜类合成酶基因表达的变化趋势与转录组测序结果一致,但不同合成酶基因的差异表达量存在差异。因此,柠檬香茅所含4类共23种萜类化合物由27类合成酶共131个基因编码而来,不同光照强度影响9个合成酶基因的表达和2种萜类化合物含量。     

Interactions between white mealybugs and red spider mites sequentially colonizing coffee plants

Plants under herbivore attack often respond defensively by mounting chemical and physical defences. However, some herbivores can manipulate plant defences to their own benefit by suppressing the expression of induced defences. These herbivore‐induced changes specific to the attacking herbivore can either facilitate or impede the colonization and establishment of a second herbivore. Although recent studies have focused on the effect of multiple herbivory on plant induced response and the third trophic level, few have examined the ecological relevance of multiple herbivores sharing the host. Here, we investigated whether herbivory by the white mealybug Planococcus minor (Maskell) (Hemiptera: Pseudococcidae) or the red spider mite Olygonychus ilicis (McGregor) (Acari: Tetranychidae), two herbivores that peak in coffee plantations during the dry season, may facilitate the colonization and establishment of the other species in coffee plants. Dual‐choice arena tests showed that white mealybugs preferred mite‐infested over uninfested coffee plants as hosts. Fifteen days after the release of 50 first‐instar P. minor nymphs, greater numbers of nymphs and adults were found on mite‐infested than uninfested plants, indicating superior performance on mite‐infested plants. On the other hand, female red spider mites did not show clear preference between uninfested and mealybug‐infested plants and deposited similar numbers of eggs on both treatments. In a no‐choice test, red spider mites performed poorly on mealybug‐infested plants with a smaller number of eggs, nymphs, females and males found in mealybug‐infested plants relative to uninfested plants. Thus, our results indicate that coffee plants are more likely to be infested by the red spider mite before white mealybug, rather than the inverse sequence (i.e. mealybug infestation followed by red spider mites). Our findings are discussed in the context of plant manipulation reported for pseudococcid mealybugs and spider mites.     

Vector and virus induce plant responses that benefit a non-vector herbivore

The negative cross-talk between induced plant defences against pathogens and arthropod herbivores is exploited by vectors of plant pathogens: a plant challenged by pathogens reduces investment in defences that would otherwise be elicited by herbivores. This negative cross-talk may also be exploited by non-vector herbivores which elicit similar anti-herbivore defences in the plant. We studied how damage by the thrips Frankliniella occidentalis and/or infection with Tomato spotted wilt virus (TSWV) affect the performance of a non-vector arthropod: the two-spotted spider mite Tetranychus urticae, a parenchym feeder just like F. occidentalis. Juvenile survival of spider mites on plants inoculated with TSWV by thrips was higher than on control and on thrips-damaged plants. However, thrips damage did not reduce spider-mite survival as compared to the control, suggesting that the positive effect of TSWV on spider-mite survival is independent of anti-thrips defence. Developmental and oviposition rates were enhanced on plants inoculated with TSWV by thrips and on plants with thrips damage. Therefore, spider mites benefit from TSWV-infection of pepper plants, but also from the response of plants to thrips damage. We suggest that the positive effects of TSWV on this non-vector species cannot be explained exclusively by cross-talk between anti-herbivore and anti-pathogen plant defences.     

Pesticide-induced mite outbreaks: pyrethroids and spider mites

Factors inducing outbreaks of spider mites (Acari: Tetranychidae) following use of pyrethroid insecticides are reviewed. Differentials in direct toxicity between spider mites and phytoseiid (Acari: Phytoseiidae) predators provide one explanation. Wide variation exists between pyrethroids in their direct toxicity toTetranychus urticae. The acaricidal action of pyrethroids is largely controlled by the amount of irritancy or repellency induced by the respective chemicals. Laboratory assays for repellency reflect field results. Repellent activity induces spider-mite dispersal to either recolonise plants free of residues or leave the treated habitat. Pyrethroids may also affect reproduction and development rates. Residual activity is likely to vary, so limiting any general theory of spider-mite responses to pyrethroids. Variable responses to pyrethroids, strain variation and development of behavioural resistance also add complications to understanding outbreaks. Future research needs are identified.     

Spider-Mite Problems and Control in Taiwan

Problems with spider mites first appeared in Taiwan in 1958, eight years after the importation of synthetic pesticides, and the mites evolved into major pests on many crops during the 1980s. Of the 74 spider mite species recorded from Taiwan 10 are major pests, with Tetranychus kanzawai most important, followed by T. urticae, Panonychus citri, T. cinnabarinus, T. truncatus and Oligonychus litchii. Most crops suffer from more than one species. Spider mites reproduce year-round in Taiwan. Diapause occurs only in high-elevation areas. Precipitation is the most important abiotic factor restricting spider-mite populations. Control is usually accomplished by applying chemicals. Fifty acaricides are currently registered for the control of spider mites. Acaricide resistance is a serious problem, with regional variation in resistance levels. Several phytoseiid mites and a chrysopid predator have been studied for control of spider mites with good effect. Efforts to market these predators should be intensified so that biological control can be a real choice for farmers.     

Resurgences of spider mites (Acari: Tetranychidae) induced by synthetic pyrethroids

Causes of spider mite (Acari: Tetranychidae) population resurgences consequent upon exposure to synthetic pyrethroid (SP) treatments are reviewed. Resurgences may be seen as soon as 1 week, or even as late as a whole season, post-treatment. Synthetic pyrethroids vary in their adverse effects on spider mites, and also differ in their ability to invoke resurgences of different spidermite species on diverse plants. These pesticides are lethal as well as repellent to phytoseiids and other predators that prey on spider mites, may inhibit fungi which attack the latter, and affect phytophagous competitors. Spider mites are likewise repelled by SPs, thus becoming more evenlydistributed and less web-restricted, with a resultant increase in fecundity. Spider-mite development is shortened due to SPs and the sex ratio becomes more female-biased; onset of winter diapause also seems to be delayed. Synthetic pyrethroids appear to sensitize to spider-mite infestation plants which have not hitherto been attacked. Some SP effects (whether on spider mites, natural enemies or competitors) appear to be direct, whereas others may be mediated through the host plants. The effect of SPs on the other Acari is variable within the Prostigmata and Astigmata. Most Mesostigmata and Metastigmata (ticks) are very sensitive, whilst the Cryptostigmata (Oribatei) appear to be insensitive. Synthetic pyrethroids-induced resurgences of Homoptera are comparatively reviewed, with the conclusion that some of the phenomena may be similar to those observed in spider mites. Various resurgence models are discussed, as well as the three main causes of variation (SPs, spider-mite species, host plants) in the observed phenomena. The need for more rigorous and carefully controlled experimentation is emphasized.     

Combined transcript and metabolite analysis reveals genes involved in spider mite induced volatile formation in cucumber plants

Many plants have an indirect defense against herbivores by emitting volatiles that attract carnivorous enemies of the herbivores. In cucumber (Cucumis sativus) the production of carnivore attractants can be induced by herbivory or jasmonic acid spraying. From the leaves of cucumber plants with and without spider mite infestation, two subtractive cDNA libraries were made that were enriched in cDNA fragments up- or down-regulated by spider mite infestation. A total of 713 randomly selected clones from these libraries were used to make a cDNA microarray. Subsequently, cucumber plants were sprayed with jasmonic acid, mechanically damaged, infested with spider mites, or left untreated (control). Leaf samples were taken at a range of different time points, and induced volatile compounds and mRNA (from the same leaves) were collected. cDNAs prepared from the mRNA were hybridized to the clones on the microarray. The resulting gene expression profiles were analyzed in combination with volatile production data in order to gain insight in the possible involvement of the studied genes in the synthesis of those volatiles. The clones on the microarray and the induced cucumber volatiles could be grouped into a number of clusters in which specific biosynthetic genes clustered with the product of that pathway. For example, lipoxygenase cDNA clones clustered with the volatile (Z)-3-hexenyl acetate and the volatile sesquiterpene (E,E)- alpha-farnesene clustered with an up-regulated sesquiterpene synthase fragment. This fragment was used to screen a cDNA library which resulted in the cloning of the cucumber (E,E)-alpha-farnesene and (E)-beta-caryophyllene synthases. The use of combined global gene expression analysis and metabolite analysis for the discovery of genes involved in specific biosynthetic processes is discussed.     

Diapause incidence in the two-spotted spider mite increases due to predator presence, not due to selective predation

We recently reported evidence for increased diapause incidence in the spider mite Tetranychus urticae in presence of the predatory mite Typhlodromus pyri. This effect may arise from (1) selective predation on non-diapause spider mites, (2) predator-induced diapause in spider mites, or (3) both. Using a different strain of T. urticae, we first recovered increased diapause incidence in association with predators. Then, we tested for selective feeding in two-choice experiments with equal numbers of non-diapause and diapause spider mites. We found that the predatory mite had a significant preference for the latter. This indicates that increased diapause incidence in association with predatory mites is not due to selective predation. Therefore, predator-mediated physiological induction of diapause seems a more likely explanation. The cues leading to induction appear to relate to the predators, not their effects, since predation simulated by spider-mite removal or puncturing did not significantly affect diapause incidence. Why spider mites benefit from this response, remains an open question.This revised version was published online in May 2005 with a corrected cover date.     

Volatile spider-mite pheromone and host-plant kairomone, involved in spaced-out gregariousness in the spider mite Tetranychus urticae

ABSTRACT. From the host plant-spider mite complex Phaseolus lunatus—Tetranychus urticae Koch a volatile chemical is emitted that acts as a kairomone for the predatory mite Phytoseiulus persimilis Athias-Henriot (Sabelis et al. , 1984a). This kairomone is apparently a byproduct of a vital physiological process and/or it has a function in the biology of the spider mite as well.
The spider mite—host plant complex also emits a volatile spider-mite dispersing pheromone. This is shown in the present study where spider mites were introduced into an odour patch on a horizontal screen in a vertical airflow olfactometer. When spider-mite infested leaves of Lima bean are offered, the spider mites walk mainly straight and soon reach the edge of the screen. On the other hand, when clean Lima bean leaves are offered, the mites walk tortuously most of the time and reach the edge of the screen much later. Artificially damaged plants elicit the same response as undamaged plants. Differences in spider-mite behaviour are observed in the vertical airflow olfactometer when odour of either clean or spider-mite infested leaves is offered. A comparison of the behaviour in these two situations with that when no odour was offered suggests that Lima bean leaves emit a volatile kairomone that activates T. urticae and makes them return after losing the stimulus. A Y-tube olfactometer experiment confirms the existence of this kairomone.
At a low ratio of dispersing pheromone to plant kairomone, the spider mites behave as if only kairomone is present, walking mainly tortuously. At a high ratio they disperse. No aggregation-pheromonal effect is observed.
The possibility that the spider-mite dispersing pheromone acts as a kairomone for P. persimilis is discussed.     

Changes in Eucalyptus camaldulensis essential oil composition as response to drought preconditioning

Abstract

Water deficit, a common constraint in forestry, is the main cause of plant stress during plantation. The survival and growth of seedlings is also compromised by herbivory during establishment. The potential of nursery preconditioning to enhance survival chances of future trees by reducing palatability or attracting beneficial insects as a result of changes in chemical defences may be an answer to overcome this situation. Changes in essential oil production and composition were evaluated by GC and GC-MS in Eucalytus camaldulensis seedlings submitted to drought during four weeks at the last stage of nursery period (20 weeks). Significant changes in essential oil relative composition were found. Seedlings (young leaves) submitted to drought developed a terpenoid blend, which has been previously associated to mature leaves and related to their higher resistance towards herbivory. Total amount of non-oxygenated terpenes decreased by 44%, whereas some oxygenated sesquiterpenes (globulol, epiglobulol and ledol) were doubled, and 1,8-cineole content was enhanced by 28.3%.     

Spider mite infestations reduce Bacillus thuringiensis toxin concentration in corn leaves and predators avoid spider mites that have fed on Bacillus thuringiensis corn

Perceived benefits of insecticidal transgenic crops include reduced usage of broad‐based insecticides, and therefore lower risk to non‐target organisms. Numerous studies have documented low or no direct toxicity of Bacillus thuringiensis (Bt)‐derived toxins against non‐target organisms, but there has been less research on (a) effects of secondary pest infestations on Bt expressing in crops and (b) behavioural responses by predators feeding on host arthropods from Bt crops – both topics are investigated in this study. We quantified predation by the obligate spider mite predator Phytoseiulus persimilis of carmine spider mites (Tetranychus cinnabarinus), reared on Bt or non‐Bt corn (Zea mays). Both no‐choice and two‐choice studies were conducted. In addition, we quantified toxin levels in corn leaves with/without spider mite infestation. Under no‐choice conditions, P. persimilis consumed non‐Bt spider mites at a faster rate than Bt spider mites. Under two‐choice conditions, P. persimilis spent more time in the vicinity of non‐Bt spider mites than near Bt spider mites. Corn infested with spider mites exhibited lower toxin levels than non‐infested plants. These results suggest potentially complex interactions among non‐target herbivores, their natural enemies and Bt crops.     

Positive association between thrips and spider mites in seedling cotton

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Odour-mediated responses of phytophagous mites to conspecific and heterospecific competitors

Plants under herbivore attack produce volatiles, thus attracting natural enemies of the herbivores. However, in doing so, the plant becomes more conspicuous to other herbivores. Herbivores may use the odours as a cue to refrain from visiting plants that are already infested, thereby avoiding competition for food, or, alternatively, to visit plants with defences weakened by earlier attacks. We investigated the response of one species of herbivore (the spider mite Tetranychus urticae) to odours emanating from cucumber plants infested by conspecific or heterospecific (the western flower thrips, Frankliniella occidentalis) herbivores. Olfactometer experiments in the laboratory showed that spider mites have a slight, but significant, preference for plants infested with conspecifics, but strongly avoid plants with thrips. These results were substantiated with greenhouse experiments. We released spider mites on the soil in the centre of a circle of six plants, half of which were infested with either conspecifics or heterospecifics (thrips), whereas the other half were uninfested. It was found that 60–70% of the mites were recaptured on the plants within 5 h after release. Results of these experiments were in agreement with results of the olfactometer experiments: (1) significantly fewer spider mites were found on plants infested with thrips than on uninfested plants and (2) more mites were found on plants with conspecifics than on clean plants (although this difference was not significant). From a functional point of view it makes sense that spider mites prefer clean plants over thrips-infested plants, since thrips are not only competitors, but are also known as intraguild predators of spider mites. Possible reasons for the slight attraction of spider mites to plants infested with conspecifics are discussed. Received: 22 June 1996 / Accepted: 29 September 1996     

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.     

Influence of leaf herbivory,root herbivory,and pollination on plant performance in Cucurbita moschata

Abstract 1. Plants experience herbivory on many different tissues that can affect reproduction directly by damaging tissues and decreasing resource availability, or indirectly via interactions with other species such as pollinators. 2. This study investigated the combined effects of leaf herbivory, root herbivory, and pollination on subsequent damage, pollinator preference, and plant performance in a field experiment using butternut squash (Cucurbita moschata). Leaf and root herbivory were manipulated using adult and larval striped cucumber beetles (Acalymma vittatum F.), a cucurbit specialist. 3. Leaf herbivory reduced subsequent pistillate floral damage and powdery mildew (Sphaerotheca fuliginea) infection. In spite of these induced defences, the overall effect of leaf herbivory on plant reproduction was negative. Leaf herbivory reduced staminate flower production, fruit number, and seed weight. In contrast, root herbivory had a minimal impact on plant reproduction. 4. Neither leaf nor root herbivory altered pollinator visitation or floral traits, suggesting that reductions in plant performance from herbivory were as a result of direct rather than indirect effects. In addition, no measured aspect of reproduction was pollen limited. 5. Our study reveals that although leaf herbivory by the striped cucumber beetle can protect against subsequent damage, this protection was not enough to prevent the negative impacts on plant performance.     

Influence of dispersal from almonds on the population dynamics and acaricide resistance frequencies of spider mites infesting neighboring cotton

Neighboring almond and cotton fields were sampled for spider mites in four locations in the San Joaquin Valley of California. The dominant species in the almonds wasTetranychus pacificus McGregor. In three cotton sites.T. pacificus was present in significantly higher densities near the almonds on at least one sampling date. In contrast.T. urticae Koch andT. turkestani Ugarov & Nikolski were equally abundant across the cotton fields. Almonds appeared to act as a continuous early-season source ofT. pacificus for cotton, with peaks in aerial dispersal from almonds occurring due to overcrowding, plant water stress, and applications of repellent acaricides. Cotton, which experienced little water stress, supported very high densities of spider mites and so acted primarily as a sink for spider-mite dispersal from almonds and other field crops throughout the growth-season. The frequencies of resistance expressed byT. pacificus andT. urticae were similar between neighboring crops, even if the acaricide had been registered for use only in almonds (cyhexatin) or cotton (dicofol). Thus, longterm acaricide selection and movement of spider mites between the two crops resulted in similar proportions of resistant individuals. In these study sites, large-scale dispersal ofT. pacificus from almonds rarely directly affected acaricide efficacy in cotton, because resistance frequencies were similar for spider mites from the two crops and because acaricide applications were usually made in cotton after dispersal from almonds was completed. In two cotton sites, field selection with dicofol was reversed by subsequent immigration of spider mites from neighboring field crops.