Polyphagy and primary host plants: oviposition preference versus larval performance in the lepidopteran pest Helicoverpa armigera

Oviposition preference and several measures of offspring performance of Helicoverpa armigera (Hübner) were investigated on a subset of its host plants that were selected for their reputed importance in the field in Australia. They included cotton, pigeon pea, sweet corn, mungbean, bean and common sowthistle. Plants were at their flowering stage when presented to gravid female moths. Flowering pigeon pea evoked far more oviposition than did the other plant species and was the most preferred plant for neonate larval feeding. It also supported development of the most robust larvae and pupae, and these produced the most fecund moths. Common sowthistle and cotton were equally suitable to pigeon pea for larval development, but these two species received far fewer H. armigera eggs than did pigeon pea. Mungbean also received relatively few eggs, but it did support intermediate measures of larval growth and survival. Fewest eggs were laid on bean and it was also the least beneficial in terms of larval growth. Among the host plant species tested, only flowering pigeon pea supported a good relationship between oviposition preference of H. armigera and its subsequent offspring performance. Australian H. armigera moths are thus consistent with Indian H. armigera moths in their ovipositional behaviour and larval performance relative to pigeon pea. The results suggest that the host recognition and acceptance behaviour of this species is fixed across its geographical distribution and they support the theory that pigeon pea might be one of the primary host plants of this insect. These insights, together with published results on the sensory responses of the females to volatiles derived from the different host plant species tested here, help to explain why some plant species are primary targets for the ovipositing moths whereas others are only secondary targets of this polyphagous pest, which has a notoriously broad host range. Handling Editor: Joseph Dickens     

Connecting plant–microbial interactions above and belowground: a fungal endophyte affects decomposition

Mutualisms can strongly affect the structure of communities, but their influence on ecosystem processes is not well resolved. Here we show that a plant–microbial mutualism affects the rate of leaf litter decomposition using the widespread interaction between tall fescue grass (Lolium arundinaceum) and the fungal endophyte Neotyphodium coenophialum. In grasses, fungal endophytes live symbiotically in the aboveground tissues, where the fungi gain protection and nutrients from their host and often protect host plants from biotic and abiotic stress. In a field experiment, decomposition rate depended on a complex interaction between the litter source (collected from endophyte-infected or endophyte-free plots), the decomposition microenvironment (endophyte-infected or endophyte-free plots), and the presence of mesoinvertebrates (manipulated by the mesh size of litter bags). Over all treatments, decomposition was slower for endophyte-infected fescue litter than for endophyte-free litter. When mesoinvertebrates were excluded using fine mesh and litter was placed in a microenvironment with the endophyte, the difference between endophyte-infected and endophyte-free litter was strongest. In the presence of mesoinvertebrates, endophyte-infected litter decomposed faster in microenvironments with the endophyte than in microenvironments lacking the endophyte, suggesting that plots differ in the detritivore assemblage. Indeed, the presence of the endophyte in plots shifted the composition of Collembola, with more Hypogastruridae in the presence of the endophyte and more Isotomidae in endophyte-free plots. In a separate outdoor pot experiment, we did not find strong effects of the litter source or the soil microbial/microinvertebrate community on decomposition, which may reflect differences between pot and field conditions or other differences in methodology. Our work is among the first to demonstrate an effect of plant–endophyte mutualisms on ecosystem processes under field conditions.     

棉铃虫成虫对两种关键花香气味的联系性学习

为了明确棉铃虫对苯乙醛和乙酸苯甲酯两种关键花香气味的联系性学习行为,在室内分别测定了不同学习训练的棉铃虫雌雄成虫对两种关键花香气味的选择偏好性反应和雄成虫的触角电位反应。偏好性测定结果表明,无花香气味接触经历的棉铃虫对苯乙醛和乙酸苯甲酯的选择频次均无显著差异,且单纯的花香气味接触经历也不能诱导棉铃虫气味偏好性的显著改变,唯有花香气味接触经历伴随蔗糖溶液进行强化训练时,才能诱导气味偏好性的显著性改变。从对两种花香气味的联系性学习看,棉铃虫更容易将苯乙醛与蔗糖溶液进行联系性学习,而不容易将乙酸苯甲酯与蔗糖溶液进行联系性学习。从性别差异看,雌虫比雄虫具有更强的将花香气味与蔗糖溶液进行联系性学习的能力。触角电位测定结果表明,不同学习训练的棉铃虫雄成虫对两种花香气味和绿叶气味顺-3-己烯-1-醇的EAG反应值之间不存在显著性差异。总之,花香气味伴随食物资源的联系性学习经历,能够明显提高棉铃虫成虫对花香气味的选择偏好,可以此为基础进一步优化花香引诱剂的配方设计和应用技术。     

Fungal endophyte negative effects on herbivory are enhanced on intact plants and maintained in a subsequent generation

1. Fungal endophytes are ubiquitous associates of virtually all plant species. Although many studies have focused on the role of these microorganisms as mediators of plant–herbivore interactions, these studies have usually been conducted using short‐term experiments. 2. Truly effective defences against herbivores may require normal functioning of the plant, as excised leaves may be less resistant as compared with those still attached to the plant. Yet, most studies investigating possible effects of endophytes in conferring host resistance to herbivores have been conducted with plant parts rather than intact plants. 3. Using the root endophytic fungus (Acremonium strictum)—broad bean (Vicia faba)—generalist herbivore (Helicoverpa armigera) model, we conducted experiments to examine whether endophyte effects on herbivory would depend on the experimental setting used in the investigation and whether they would translate into a subsequent generation of the herbivore. 4. Acremonium strictum negative effects on the fitness of H. armigera first generation were more evident when the larvae foraged freely on inoculated intact whole plants than when offered leaf discs of inoculated plants. Furthermore, these effects were carried over into H. armigera second generation reared on an artificial diet. 5. Acremonium strictum could not be re‐isolated from V. faba leaves; hence direct contact between the endophyte and the insect could be excluded. Alternatively, loss of volatiles or inhibitory effects of compounds that were stronger in situ might have caused changes in larval feeding and performance on leaf discs as compared with intact plants, regardless of infection status. 6. We suggest that the reduction in fitness parameters of H. armigera across two generations is caused indirectly via an endophyte‐triggered reduction in plant quality.     

Indirect interaction between an unspecialized endophytic fungus and a polyphagous moth

Despite their ubiquitous occurrence in natural and managed ecosystems, the role of unspecialized fungal endophytes in mediating insect-plant interactions have been largely ignored compared to clavicipitaceous fungal endophytes of grasses. We conducted laboratory and glasshouse experiments to test the hypothesis that an unspecialized fungal endophyte (Acremonium strictum) restricted to the root system of the host plant is able to mediate the interaction between a polyphagous herbivorous insect (Helicoverpa armigera) and its host plant (tomatoes, Lycopersicum esculentum). Our studies indicated a significant variation in the ability of inoculated and control plants to support the life history stages of the insect. Larvae reared on inoculated plants suffer significant reduction in growth rate, prolonged development times, suppressed moulting, and produced smaller pupae that were more likely to die, and emerged adults were less fecund compared to larvae reared on control plants. In glasshouse bioassays were larvae were allowed to graze freely, on inoculated plants only 20% survived to the final stadium compared to 54.5% on control plants. No significant differences in the amount of foliage consumed were found between inoculated and control plants, suggesting that A. strictum does not act as a feeding deterrent for H. armigera larvae. Larvae fed inoculated plants showed a significant increase in the relative consumption rate, although the approximate digestibility of ingested food, and efficiency with which both ingested food and digested food was converted to insect biomass decreased during the same period. In addition to reduced efficiency of food utilization, surviving larvae on inoculated plants displayed a significant reduction in relative growth rate. We hypothesized that alterations in phytosterol composition mediated by infection of the fungal endophyte, may explain the reduced larval performance on inoculated plants.Obwohl unspezialisierte endophytische Pilze in allen Ökosystemen weit verbreitet und häufig sind, blieb ihre Rolle bei Interaktionen zwischen Pflanzen und herbivoren Insekten bisher weitgehend unberücksichtigt. In Labor- und Gewächshausexperimenten haben wir die Hypothese untersucht, dass ein unspezialisierter Wurzelendophyt (Acremonium strictum) die Wechselwirkungen zwischen einem polyphagen Insekt (Helicoverpa armigera) und Tomatenpflanzen (Lycopersicum esculentum) beeinflussen kann. Die Entwicklung der Insekten weist deutliche Unterschiede zwischen inokulierten und Kontrollpflanzen auf. Larven, die auf inokulierten Pflanzen gehalten wurden, zeigten gegenüber solchen von Kontrollpflanzen jeweils signifikant verringerte Wachstumsraten, verlängerte Entwicklungszeiten, verzögerte Häutungen, und bildeten kleinere Puppen aus, welche eine höhere Mortalität aufwiesen. Die geschlüpften Weibchen hatten zudem eine verringerte Fekundität. In Frassversuchen im Gewächshaus überlebten an inokulierten Pflanzen nur 20% der Larven während an Kontrollpflanzen 54,5% überlebten. Da die gefressene Biomasse in beiden Varianten gleich war, ist eine deterrente Wirkung des Pilzes auszuschließen. Vielmehr deuten signifikante Veränderungen der Fraß- und Verwertungsindices sowie die niedrigeren relativen Wachstumsraten darauf hin, das sich die Nahrungsqualität auf inokulierten Pflanzen verschlechtert hatte. Wir diskutieren die Hypothese, dass der Phytosterolgehalt, welcher durch eine Inokulation der Pflanzen verändert wird, zu den verschlechterten Entwicklungsbedingungen der Larven geführt hat.     

Photosynthetic pigments and photosynthetic products of endophyte-infected and endophyte-free Lolium perenne L. under drought stress conditions

Endophyte-infected (EI) seeds of Lolium perenne L. were used to attain endophyte-free (EF) population by heating the seeds at 43°C for 15 min and then 57°C for 25 min. Relative water content (RWC), chlorophyll, soluble sugar and starch content of EI and EF populations under normal and drought stress conditions were compared to investigate the effect of endophyte infection on the host plant. Under severe stress, RWC of EI leaf was significantly higher than that of EF leaf, i.e. EI plants took more advantages over EF plants in water-holding ability. Under mild stress, endophyte could enhance soluble sugars in host plants to improve their osmotic ability. With stress intensification, the improvement of endophyte no longer existed, and more photosynthetic products (such as starch) accumulated in EI plants to survive through the undesirable conditions. In the next spring, EI populations will recover more rapidly than EF populations. The biomass of a population is closely related to its photosynthesis. Under severe stress, EI population significantly accumulated more biomass than EF population. As far as photosynthetic pigments were concerned, contents of Chla, Chlb and Car of EI plants were close to those of EF plants, which suggested that endophyte infection didn’t alleviate photosynthetic pigments from being destroyed by drought stress, and endophyte might improve photosynthesis ability of its host plant in other ways. __________ Translated from Acta Ecologica Sinica, 2005, 25 (2) [译自: 生态学报, 2005, 25(2)]     

Kairomones ofheliothis armigera andcorcyra cephalonica and their influence on the parasitic potential oftrichogramma chilonis (Trichogrammatidae: hymenoptera)

Kairomones from moth scales tend to influence the parasitic potential byTrichogramma chilonis Ishii. Hexatriacontane, pentacosane, heptadecane, docosane and 2, 6, l0-dodecatrienal-3, 7, 11-trimethyl were identified from the active moth scale extract ofHeliothis armigera Hubner (its natural host) andCorcyra cephalonica Stainton (a laboratory host). The significance of an array of compounds from moth scales with kairomonal activity for manipulating entomophagous insects in biological control programmes is discussed.     

Host plant selection by a monophagous herbivore is not mediated by quantitative changes in unique plant chemistry: Agonopterix alstroemeriana and Conium maculatum

Host plant selection by ovipositing females is a key process determining the success of phytophagous insects. In oligophagous lepidopterans, host-specific plant secondary chemicals are expected to be dominant factors governing oviposition behavior; distinctive compounds can serve as high-contrast signals that clearly differentiate confamilial hosts from non-hosts increasing the accuracy of host quality evaluation. Agonopterix alstroemeriana (Clerk) (Lepidoptera: Oecophoridae) and Conium maculatum L. (Apiaceae) form an extremely specialized plant-herbivore system, with A. alstroemeriana monophagous on C. maculatum, a plant with few other insect herbivores at least in part due to its virtually unique capacity among plants to produce piperidine alkaloids. Here we have studied the response of A. alstroemeriana oviposition to unique host plant secondary metabolites, piperidine alkaloids, and widespread compounds, mono- and sesquiterpenes, in a concentration-dependent fashion. Rates of oviposition were negatively correlated with Z-ocimene concentrations. To confirm the deterrent properties of this monoterpene for A. alstroemeriana oviposition, we conducted a choice experiment using artificially damaged C. maculatum plants, with higher emission of volatiles, and undamaged control plants. Damaged plants were less preferred as oviposition sites compared to the controls. The lack of association between oviposition and piperidine alkaloids, defenses unique to Conium species, suggests that quantitative changes of these species-specific chemicals do not play a predominant role in host selection by the monophagous A. alstroemeriana.     

甘肃马先蒿不同寄生密度对紫花针茅内生真菌共生体生理特性的影响

【目的】根寄生植物持续掠夺禾草体内营养物质成为禾草生长过程中的生物逆境,禾草内生真菌提高冷季型禾草对生物和非生物逆境耐受能力。然而,有关禾草内生真菌对根寄生逆境下禾草生理过程调控作用的研究鲜有报道。【方法】开展温室盆栽试验,以带菌(E+)和不带菌(E-)紫花针茅为研究对象,研究甘肃马先蒿不同寄生密度对紫花针茅抗氧化酶活性、渗透调节物质和根系活力影响的动态变化规律。【结果】甘肃马先蒿寄生显著增加紫花针茅抗氧化酶活性、丙二醛和脯氨酸含量,而根系活力却快速降低;高密度寄生紫花针茅植株生理特性指标显著高于低密度寄生或自然生长植株;同时,E+紫花针茅抗氧化酶活性、脯氨酸含量和根系活力显著高于E-植株,而E-植株丙二醛含量显著高于E+植株。【结论】禾草内生真菌通过增强抗氧化酶活性、调节细胞膜透性和增强根系生长能力的途径提高紫花针茅对根寄生逆境的耐受能力,利用植物替代方法带菌紫花针茅可以作为一种生物防治手段用于防控根寄生杂草。     

The inhibitory effects of rose powdery mildew infection on the oviposition behaviour and performance of beet armyworms

In this study, we investigated whether the oviposition behaviour and performance of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), on the rose cultivar Rosa chinensis Jacq. (Rosaceae) were affected when the plants were infected by rose powdery mildew, Podosphaera pannosa (Wallr.: Fr.) de Bary (Erysiphales). The bioassays revealed that the moths significantly avoided ovipositing on mildew‐infected rose leaves when compared to healthy leaves. Pupal weights, emergence rates, and fecundity decreased when the caterpillars were fed mildewed rose leaves. Further laboratory bioassays aimed to elucidate the effects of two volatile headspace extracts (separately collected from healthy and mildewed rose plants) on the oviposition behaviour and performance of the moths. The moths clearly preferred to oviposit on healthy rose leaves that were not sprayed with additional volatiles rather than on healthy leaves sprayed with the volatile extracts from mildewed plants. The mean number of eggs laid on the former leaves was more than six times higher than that laid on the latter leaves. Olfactory bioassays demonstrated that ovipositing moths were significantly more attracted to volatiles emitted by healthy rose leaves than to those emitted by mildew‐infected leaves. Similar results were obtained when comparisons were made between the volatile extracts collected from healthy and mildewed rose plants. Thus, volatiles from mildew‐infected roses have a strong inhibitory effect against the moths. These results indicated that rose volatiles play a role in the oviposition behaviour of the moths, and that the volatiles induced by powdery mildew might be used for insect control.     

Oviposition site selection in Cactoblastis cactorum (Lepidoptera): constraints and compromises

Summary Oviposition by Cactoblastis cactorum on Opuntia ficus-indica and O. aurantiaca was assessed from the positioning of egg sticks on plants in the field. The number of egg sticks laid on O. ficus-indica plants was affected by: (1) plant size; (2) moth emergence near the plant; (3) cladode condition; and (4) plant conspicuousness. These factors contributed towards the clumping of egg sticks on plants. There was no apparent oviposition preference for one of the two host plant species despite the fact that egg predation was higher and fecundity lower on O. aurantiaca. The selection of a site for oviposition on the host plants was influenced by: (1) cladode condition; (2) height above ground; and (3) shelter from wind during oviposition. Succulent cladodes were the favoured sites for oviposition. The evidence suggests that in C. cactorum, oviposition site selection is largely the net result of a compromise between oviposition behaviour selected for increasing the probability of juvenile survival and oviposition behaviour selected for increasing the probability of laying the full complement of eggs. In addition, environmental and physiological factors such as wind and wing-loading, are thought to place constraints on the range of sites available for oviposition.     

Volatiles that encode host-plant quality in the grapevine moth

Plant volatiles are signals used by herbivorous insects to locate host plants and select oviposition sites. Whether such volatiles are used as indicators of plant quality by adult insects in search of host plants has been rarely tested. We tested whether volatiles indicate plant quality by studying the oviposition of the grapevine moth Lobesia botrana on the grapevine plant Vitis vinifera. Host plants were infected with a variety of microorganisms, and larval fitness was correlated to the infected state of the substrate. Our results show an oviposition preference for volatiles that is significantly correlated with the fitness of the substrate. The chemical profiles of the bouquets from each V. vinifera–microorganism system are clearly differentiated in a PCA analysis. Both the volatile signal and the quality of the plant as larval food were affected by the introduction of microorganisms. Our study represents a broad approach to the study of plant–insect interactions by considering not only the direct effect of the plant but also the effect of plant–microorganism interactions on insect population dynamics.     

Volatiles released from bean plants in response to agromyzid flies

Liriomyza sativae Blanchard and Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) are two invasive flies in China that have caused economical damage on vegetables and ornamental plants. In this article, we report the profiles of emitted volatiles from healthy, mechanically damaged, and leafminer-damaged bean, Phaseolus vulgaris L., plants. Among 25 emitted volatiles identified, (E)-2-hexen-1-al, (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, (syn)- and (anti)-2-methylpropanal oxime, (syn)-2-methylbutanal oxime, linalool, and (E,E)-α-farnesene were consistently released from damaged bean plants. Combined amounts of these nine compounds made up more than 70% of the total volatiles emitted from each treatment. No qualitative differences in volatile emission were found between bean plants damaged by the two fly species; however, amounts of several major compounds induced by L. huidobrensis damage were significantly higher than those from plants damaged by L. sativae. The mechanically damaged plants released a higher proportion of green leaf volatiles than plants in the other treatments, whereas leafminer-damaged plants produced more terpenoids and oximes. Furthermore, the volatile profiles emitted from plants, damaged by adult leafminers, by second instar larvae, and even the plants with empty mines left by leafminer larvae (the pupal stage) were significantly different. The identification of volatile oximes released from damaged plants was confirmed and is discussed in a behavioral and biological control context.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

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.     

The role of two plant-derived volatiles in the foraging movement of 1st instar Helicoverpa armigera (Hübner): time to stop and smell the flowers

Positive phototaxis and negative geotaxis are behaviours that 1st instar Helicoverpa armigera use to direct their foraging movement upward towards nutritious new plant growth and reproductive structures. Odours emitted by fruits or seeds can attract larvae directly via chemotaxis. In this study we clarify the effect of leaf and flower odours on foraging 1st instar H. armigera. Using a Y-tube olfactometer we tested for chemotaxis towards two plant volatiles and found larvae were not attracted. Bioassays for phototaxis towards UV, blue, green and white light showed that a green leaf volatile ((Z)-3-hexenyl acetate) and a flower volatile (phenylacetaldehyde) reduced larval phototaxis towards blue light. Feeding on a host plant reduced phototaxis towards blue and green light. We concluded that the upward movement of 1st instars on plants is largely due to phototaxis towards the blue wavelengths of skylight. Plant attributes such as volatile chemicals affect the expression of phototaxis and therefore, indirectly influence larval movement to locate food resources. Handling Editor: Anna-Karin Borg-Karlson     

Migratory moths as dispersal vectors of an introduced plant-pathogenic fungus in Japan

The plant-pathogenic fungus Claviceps paspali infects florets of the dallisgrass Paspalum dilatatum and induces the plant to produce honeydew (containing massive amounts of conidia), which in turn attracts insects for dispersal of the fungal spores. In Japan, the association between C. paspali and its host plant is common, although both P. dilatatum and C. paspali are introduced species. To determine the dispersal agents of the introduced C. paspali, we examined which insects sapped the P. dilatatum honeydew produced by C. paspali. The study was conducted from September to October 2003 in central Japan. Adults of 48 moth species and two lacewing species visited infected spikelets of P. dilatatum and sapped the honeydew at night. The dominant moths, which carried C. paspali conidia on their proboscises, migrate long distances every year. Therefore, migratory moths may transmit C. paspali spores from diseased to healthy host plants and may have spread C. paspali to other areas in Japan where C. paspali did not previously exist.     

Oviposition and reproductive performance of a generalist parasitoid (Trichogramma pretiosum) exposed to host species that differ in their physical characteristics

The response of generalist egg parasitoids to alternative natural hosts that are present simultaneously is not well known. We investigated the behavior of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in relation to two field hosts Helicoverpa armigera Hübner and Spodoptera litura Fabricius, in choice and no choice tests. We quantified the effects of natal host species and post-emergence adult age on the oviposition preference of the parasitoids. H. armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs (average of 17 ± 2.7 vs. 13 ± 3.0, H. armigera to S. litura). The adult lifespan and lifetime fecundity of T. pretiosum were variable but were affected by natal host species and/or host species to which they were exposed. Mean lifespan and fecundity of parasitoids that had developed in H. armigera eggs and were exposed to H. armigera eggs for oviposition were 13.9 ± 1.8 days and 98.7 ± 11.0 adult offspring. By contrast, those that developed in S. litura eggs and were exposed to S. litura eggs for oviposition lived for 7 ± 0.9 days and produced 53.8 ± 8.0 adult offspring. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better than S. litura eggs. These results are used to predict parasitoid behavior in the field when both hosts are available.     

Are endophyte-mediated effects on herbivores conditional on soil nutrients?

Neotyphodium endophytes are assumed to have mutualistic relationship with their grass hosts, mainly resulting from mycotoxin production increasing plant resistance to herbivores by the fungus that subsists on the plant. To study importance of often ignored environmental effects on these associations, we performed a greenhouse experiment to examine the significance of endophyte infection and nutrient availability for bird-cherry aphid (Rhopalosiphum padi) performance on meadow fescue (Lolium pratense). Naturally endophyte-infected (E+), uninfected (E–), or manipulatively endophyte-free (ME–) half-sib families of meadow fescue were grown on two soil nutrient levels. Endophyte infection reduced aphid performance in general. However, to our knowledge, this is the first study to demonstrate experimentally that herbivore performance decreases on E+ host plants with increasing availability of nutrients in soils. Potential improvement in herbivore performance in high nutrient soils and decreased plant performance in low nutrient soils in ME– plants, compared to E– and E+ plants, suggests that loss of endophyte infection after long coevolutionary relationship may be critical to plant fitness.     

感染内生真菌的羽茅对大针茅的化感作用

以羽茅(Achnatherum sibiricum)为材料,采用室内生物测定法研究感染不同内生真菌的羽茅浸提液对大针茅(Stipa grandis)种子萌发和幼苗生长的化感作用,并采用气相色谱-质谱(GC-MS)联用技术对羽茅浸提液中的化学成分进行分析。结果表明:(1)内生真菌感染可缓解宿主羽茅对群落优势种大针茅的化感作用;(2)内生真菌感染对宿主羽茅化感作用的影响与内生真菌种类有关,具体表现为相比于未染菌羽茅,感染Epichloё gansuensis可显著缓解宿主羽茅对大针茅的抑制作用,而感染Neotyphodium sibiricum、Neotyphodium gansuensis有缓解羽茅对大针茅化感作用的趋势,但未达到显著影响;(3)羽茅浸提液中含有2,4-二叔丁基苯酚、邻苯二甲酸、邻苯二甲酸二丁酯和硬脂酸甲酯等潜在化感物质,这4种物质相对含量的差异可能是不同内生真菌感染状态的羽茅产生不同化感效应的主要原因;(4)对羽茅浸提液中4种潜在化感物质的化感作用进行验证实验,结果表明,2,4-二叔丁基苯酚对大针茅的化感作用基本表现为低浓度无影响,高浓度抑制,邻苯二甲酸二丁酯的化感作用表现为"低促高抑"的效应趋势,而邻苯二甲酸和硬脂酸甲酯对大针茅均表现出"剂量效应"的化感作用趋势,即4种潜在化感物质在高浓度时均可显著抑制大针茅的种子萌发和幼苗生长。     

甘肃马先蒿寄生对禾草内生真菌共生体光合特性的影响

[目的]甘肃马先蒿与感染内生真菌的禾草(紫花针茅和麦宾草)建立根寄生关系,有关内生真菌对根寄生危害禾草光合作用调控方面的研究较少。[方法]本研究以紫花针茅和麦宾草带菌(E+)、不带菌(E-)植株为研究对象,研究甘肃马先蒿寄生和未寄生处理对紫花针茅和麦宾草E+、E-植株不同生长阶段光合特性影响的动态变化。[结果]甘肃马先蒿寄生显著降低紫花针茅和麦宾草的净光合速率、蒸腾速率和气孔导度,而胞间二氧化碳浓度和水分利用率却显著增加,这与禾草是否感染内生真菌无关。甘肃马先蒿寄生后E+紫花针茅的净光合速率、气孔导度和蒸腾速率高于E-植株,而麦宾草E+植株的净光合速率、气孔导度和蒸腾速率却低于E-植株;同时,根寄生条件下E+紫花针茅的胞间二氧化碳浓度和水分利用率低于E-植株;而E-麦宾草植株的胞间二氧化碳浓度和水分利用率却低于E+植株。[结论]内生真菌侵染影响甘肃马先蒿根寄生危害禾草的光合作用;甘肃马先蒿和内生真菌同时成为禾草营养消耗库时,内生真菌与禾草的共生关系处于一种互惠共生和相互拮抗的动态变化。