昆虫取食诱导的植物防御反应

植物被昆虫取食后可产生直接防御或间接防御。直接防御通过增加有毒的次生代谢产物或防御蛋白对昆虫生理代谢产生不利的影响,但对植物的消耗较大。间接防御通过释放挥发性化合物吸引天敌昆虫,并以此控制植食性昆虫。特异性的昆虫激发子(insect specific elicitors)能够诱导挥发性化合物的释放。多种信号途径参与昆虫取食诱导的植物防御反应,它们之间的相互作用协同或拮抗。了解昆虫取食诱导的植物防御反应,对于害虫综合治理策略的完善具有重要的意义。     

The effects of herbivore-induced plant volatiles on interactions between plants and flower-visiting insects

Plants are faced with a trade-off between on the one hand growth, development and reproduction and on the other hand defence against environmental stresses. Yet, research on insect-plant interactions has addressed plant-pollinator interactions and plant-attacker interactions separately. Plants have evolved a high diversity of constitutive and induced responses to attack, including the systemic emission of herbivore-induced plant volatiles (HIPVs). The effect of HIPVs on the behaviour of carnivorous insects has received ample attention for leaf-feeding (folivorous) species and their parasitoids and predators. Here, we review whether and to what extent HIPVs affect the interaction of plants in the flowering stage with mutualistic and antagonistic insects. Whereas the role of flower volatiles in the interactions between plants and insect pollinators has received increased attention over the last decade, studies addressing both HIPVs and pollinator behaviour are rare, despite the fact that in a number of plant species herbivory is known to affect flower traits, including size, nectar secretion and composition. In addition, folivory and florivory can also result in significant changes in flower volatile emission and in most systems investigated, pollinator visitation decreased, although exceptions have been found. Negative effects of HIPVs on pollinator visitation rates likely exert negative selection pressure on HIPV emission. The systemic nature of herbivore-induced plant responses and the behavioural responses of antagonistic and mutualistic insects, requires the study of volatile emission of entire plants in the flowering stage. We conclude that approaches to integrate the study of plant defences and pollination are essential to advance plant biology, in particular in the context of the trade-off between defence and growth/reproduction.     

Hyperparasitoids Use Herbivore-Induced Plant Volatiles to Locate Their Parasitoid Host

Plants respond to herbivory with the emission of induced plant volatiles. These volatiles may attract parasitic wasps (parasitoids) that attack the herbivores. Although in this sense the emission of volatiles has been hypothesized to be beneficial to the plant, it is still debated whether this is also the case under natural conditions because other organisms such as herbivores also respond to the emitted volatiles. One important group of organisms, the enemies of parasitoids, hyperparasitoids, has not been included in this debate because little is known about their foraging behaviour. Here, we address whether hyperparasitoids use herbivore-induced plant volatiles to locate their host. We show that hyperparasitoids find their victims through herbivore-induced plant volatiles emitted in response to attack by caterpillars that in turn had been parasitized by primary parasitoids. Moreover, only one of two species of parasitoids affected herbivore-induced plant volatiles resulting in the attraction of more hyperparasitoids than volatiles from plants damaged by healthy caterpillars. This resulted in higher levels of hyperparasitism of the parasitoid that indirectly gave away its presence through its effect on plant odours induced by its caterpillar host. Here, we provide evidence for a role of compounds in the oral secretion of parasitized caterpillars that induce these changes in plant volatile emission. Our results demonstrate that the effects of herbivore-induced plant volatiles should be placed in a community-wide perspective that includes species in the fourth trophic level to improve our understanding of the ecological functions of volatile release by plants. Furthermore, these findings suggest that the impact of species in the fourth trophic level should also be considered when developing Integrated Pest Management strategies aimed at optimizing the control of insect pests using parasitoids.     

Herbivore induced plant volatiles: Their role in plant defense for pest management

Plants respond to herbivory through different defensive mechanisms. The induction of volatile emission is one of the important and immediate response of plants to herbivory. Herbivore-induced plant volatiles (HIPVs) are involved in plant communication with natural enemies of the insect herbivores, neighboring plants, and different parts of the damaged plant. Release of a wide variety of HIPVs in response to herbivore damage and their role in plant-plant, plant-carnivore and intraplant communications represents a new facet of the complex interactions among different trophic levels. HIPVs are released from leaves, flowers, and fruits into the atmosphere or into the soil from roots in response to herbivore attack. Moreover, HIPVs act as feeding and/or oviposition deterrents to insect pests. HIPVs also mediate the interactions between the plants and the microorganisms. This review presents an overview of HIPVs emitted by plants, their role in plant defense against herbivores and their implications for pest management.     

Eco-evolutionary dynamics in herbivorous insect communities mediated by induced plant responses

It is increasingly recognized that the ecology of communities and evolution of species within communities are interdependent, and researchers have been paying attention to this rapidly emerging field of research, i.e., through studies on eco-evolutionary dynamics. Most of the studies on eco-evolutionary dynamics have been concerned with direct trophic interactions. However, community ecologists have shown that trait-mediated indirect effects play an important role in shaping the structure of natural communities. In particular, in terrestrial plant–insect systems, indirect effects mediated through herbivore-induced plant responses are common and have a great impact on the structure of herbivore communities. This review describes eco-evolutionary dynamics in herbivorous insect communities, and specifically focuses on the key role of herbivore-induced plant responses in eco-evolutionary dynamics. First, I review studies on the evolution of herbivore traits relevant to plant induction and discuss evolution in a community context mediated by induced plant responses. Second, I highlight how intraspecific genetic variation or evolution in herbivore traits can influence herbivore community structure. Finally, I propose the hypothetical model that induced plant responses supports eco-evolutionary feedback in herbivore communities. In this review, I argue that the application of the indirect interaction web approaches into studies on eco-evolutionary will provide profound insights into understanding of mechanisms of the generation and maintenance of biodiversity.     

植物抗虫“防御警备”: 概念、机理与应用

植物抗虫“防御警备”是指受到某些生物或者非生物因子刺激警备后,植物会提前做好抗虫防御准备,之后当再次受到害虫袭击时,植物会产生更加快速和强烈的抗虫防御反应,从而使自身抗虫性显著提高.这是近年来新发现的植物防御害虫的一种策略,是一种特殊的诱导抗虫机制.植食性昆虫的取食、分泌物、产卵、为害诱导的植物挥发物(HIPVs)以及某些有益微生物、植物营养元素、重金属和一些化学物质均可以引起植物产生抗虫防御警备.防御警备具有抗性高效、持久、环境友好,甚至可以遗传到子代等优点.本文综述了近年来有关植物抗虫防御警备的研究,主要概括了植物抗虫防御警备的一般特征、刺激警备因子和形成机制,并对其在生产实践中的应用前景进行了简要分析,提出了这一领域尚未解决的问题和亟待深入的研究方向.通过合适的方法使植物产生抗虫防御警备可以大大减少杀虫剂的使用,成为害虫综合防治的重要手段.     

Are herbivore-induced plant volatiles reliable indicators of herbivore identity to foraging carnivorous arthropods?

Plants that are damaged by herbivorous arthropods provide carnivorous enemies of the herbivores with important information. They emit an induced volatile blend that is highly detectable to the carnivores from a distance. Such detectable signals that indicate herbivore presence are important for the carnivores because herbivores themselves are under strong selection not to expose themselves. In addition, carnivores would benefit from a specificity of the induced plant volatiles. Whether herbivore-induced plant volatiles are reliable indicators of herbivore identity, however, has not been resolved unambiguously. Some studies support the reliability of herbivore-induced plant volatiles, while others do not. Different approaches have been used such as chemical analysis, behavioural analysis or a combination of the two. Based on the total of chemical studies one might conclude that in most cases herbivore-induced plant volatiles are not very specific for the herbivore that damages the plant. However, arthropod chemosensors are much more sensitive than the detectors of analytical instruments. Therefore, chemical analyses are not suitable to demonstrate whether or not herbivore-induced plant volatiles are reliable indicators of herbivore identity to carnivores. Behavioural studies should provide this information. In analysing carnivore behaviour it should be realised, however, that arthropod behaviour can be highly variable. Arthropod foraging decisions are affected by external and internal factors such as (a) abiotic environmental factors, (b) presence of competitors or enemies, (c) deprivation of food or oviposition sites, (d) specific deprivation of certain nutrients or (e) learning. In this paper their effect on discrimination of carnivores between volatile blends emitted by plants infested by different herbivores is reviewed. This provides testable hypotheses of why discrimination was not found in some studies. The ability of carnivores to discriminate is likely to be more common than is clear to date, which should invoke functional studies of the conditions that influence the occurrence of this discrimination.     

Herbivore-specific plant volatiles prime neighboring plants for nonspecific defense responses

Plants produce species-specific herbivore-induced plant volatiles (HIPVs) after damage. We tested the hypothesis that herbivore-specific HIPVs prime neighboring plants to induce defenses specific to the priming herbivore. Since Manduca sexta (specialist) and Heliothis virescens (generalist) herbivory induced unique HIPV profiles in Nicotiana benthamiana, we used these HIPVs to prime receiver plants for defense responses to simulated herbivory (mechanical wounding and herbivore regurgitant application). Jasmonic acid (JA) accumulations and emitted volatile profiles were monitored as representative defense responses since JA is the major plant hormone involved in wound and defense signaling and HIPVs have been implicated as signals in tritrophic interactions. Herbivore species-specific HIPVs primed neighboring plants, which produced 2 to 4 times more volatiles and JA after simulated herbivory when compared to similarly treated constitutive volatile-exposed plants. However, HIPV-exposed plants accumulated similar amounts of volatiles and JA independent of the combination of priming or challenging herbivore. Furthermore, volatile profiles emitted by primed plants depended only on the challenging herbivore species but not on the species-specific HIPV profile of damaged emitter plants. This suggests that feeding by either herbivore species primed neighboring plants for increased HIPV emissions specific to the subsequently attacking herbivore and is probably controlled by JA.     

Facilitation and inhibition: changes in plant nitrogen and secondary metabolites mediate interactions between above-ground and below-ground herbivores

To date, it remains unclear how herbivore-induced changes in plant primary and secondary metabolites impact above-ground and below-ground herbivore interactions. Here, we report effects of above-ground (adult) and below-ground (larval) feeding by Bikasha collaris on nitrogen and secondary chemicals in shoots and roots of Triadica sebifera to explain reciprocal above-ground and below-ground insect interactions. Plants increased root tannins with below-ground herbivory, but above-ground herbivory prevented this increase and larval survival doubled. Above-ground herbivory elevated root nitrogen, probably contributing to increased larval survival. However, plants increased foliar tannins with above-ground herbivory and below-ground herbivory amplified this increase, and adult survival decreased. As either foliar or root tannins increased, foliar flavonoids decreased, suggesting a trade-off between these chemicals. Together, these results show that plant chemicals mediate contrasting effects of conspecific larval and adult insects, whereas insects may take advantage of plant responses to facilitate their offspring performance, which may influence population dynamics.     

Start making scents: the challenge of integrating chemistry into pollination ecology

Although research on plant volatiles and pollination ecology has grown explosively over the past 15 years, there remains little dialogue between these fields. Here I examine the historical and cultural reasons for this impasse, focusing on the ways that questions in each field are addressed, and the potential for productive cross-talk. The specialization–generalization debate in pollination has cast doubt on the importance of sensory biology in mediating plant–pollinator interactions on the community scale. However, chemical 'filters' of volatile or nectar-borne repellents are likely to explain the absence of specific interactions in plant–pollinator webs. In addition, the omission of plant volatiles from path analyses measuring the relative impacts of herbivores and pollinators on plant fitness may be one reason for large unexplained variance terms in such models. Floral scent functions in concert with visual and gustatory cues by attracting pollinators from a distance, increasing approaches and landings, and mediating outcrossing rates through changes in visitation frequency and duration. All dimensions of floral chemistry, including ontogenetic and diel variation in scent emissions, have the potential to respond to balancing selection between herbivores and pollinators. The available data reveal that chemical aspects of floral phenotypes are important across the specialization–generalization spectrum, and thus are widely applicable to mainstream pollination ecology.     

Oviposition by a moth suppresses constitutive and herbivore-induced plant volatiles in maize

Plant volatiles function as important signals for herbivores, parasitoids, predators, and neighboring plants. Herbivore attack can dramatically increase plant volatile emissions in many species. However, plants do not only react to herbivore-inflicted damage, but also already start adjusting their metabolism upon egg deposition by insects. Several studies have found evidence that egg deposition itself can induce the release of volatiles, but little is known about the effects of oviposition on the volatiles released in response to subsequent herbivory. To study this we measured the effect of oviposition by Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) moths on constitutive and herbivore-induced volatiles in maize (Zea mays L.). Results demonstrate that egg deposition reduces the constitutive emission of volatiles and suppresses the typical burst of inducible volatiles following mechanical damage and application of caterpillar regurgitant, a treatment that mimics herbivory. We discuss the possible mechanisms responsible for reducing the plant’s signaling capacity triggered by S. frugiperda oviposition and how suppression of volatile organic compounds can influence the interaction between the plant, the herbivore, and other organisms in its environment. Future studies should consider oviposition as a potential modulator of plant responses to insect herbivores.     

Plant—Phytoseiid Interactions Mediated by Herbivore-Induced Plant Volatiles: Variation in Production of Cues and in Responses of Predatory Mites

Phytoseiid mites use herbivore-induced plant volatiles in long-range prey-habitat location and are arrested by these volatiles in a prey patch. The responses of predatory mites to these volatiles are considered to be an important factor in the local extermination of prey populations by phytoseiids such as Phytoseiulus persimilis. Prey-induced plant volatiles are highly detectable and can be reliable indicators of prey presence and prey identity. The composition of herbivore-induced plant volatiles depends on plant species and plant cultivar. Moreover, the composition may also vary with the herbivore species that infests a plant. The responses of phytoseiids to prey-induced plant volatiles from a specific plant-herbivore combination are highly variable. Causal factors include starvation, specific hunger, experience, pathogen infestation and the presence of competitors. Investigating variation in the phytoseiid's behavioural response in relation to these factors is important for understanding how and why behavioural strategies maximize phytoseiid fitness.     

Fall Armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), Female Moths Respond to Herbivore-Induced Corn Volatiles

In response to herbivore attack, plants release herbivore-induced plant volatiles (HIPVs) that represent important chemical cues for herbivore natural enemies. Additionally, HIPVs have been shown to mediate other ecological interactions with herbivores. Differently from natural enemies that are generally attracted to HIPVs, herbivores can be either attracted or repelled depending on several biological and ecological parameters. Our study aimed to assess the olfactory response of fall armyworm-mated female moths toward odors released by mechanically and herbivore-induced corn at different time intervals. Results showed that female moths strongly respond to corn volatiles, although fresh damaged corn odors (0?C1?h) are not recognized by moths. Moreover, females preferred volatiles released by undamaged plant over herbivore-induced plants at 5?C6?h. This preference for undamaged plants may reflect an adaptive strategy of moths to avoid competitors and natural enemies for their offspring. We discussed our results based on knowledge about corn volatile release pattern and raise possible explanations for fall armyworm moth behavior.     

Plant volatiles as method of communication

Plants emit volatile compounds that can act as a communication method to insects, neighboring plants and pathogens. Plants respond to leaf and root damage by herbivores and pathogens by emitting these compounds. The volatile compounds can deter the herbivores or pathogens directly or indirectly by attracting their natural enemies to kill them. The simultaneous damage of plants by herbivores and pathogens can influence plant defense. The induced plant volatiles can also make neighboring plants ready for defense or induce defense in parts distant from the damaged area of the same plant. Belowground root herbivory can alter the defense response to aboveground leaf herbivory. In addition, most plants normally emit volatile compounds from their flowers that directly attract foraging mutualistic insects for nectar, which in turn perform the very important function of pollination for subsequent reproduction. The volatile compounds emitted from the floral and vegetative parts of plants belong to three main classes of compounds: terpenoids, phenylpropanoids/benzenoids, and C6-aldehydes (green-leaf volatiles). The volatile phytohormones methyl salicylate and methyl jasmonate serve as important signaling molecules for communication purposes, and interact with each other to optimize the plant defense response. Here we discuss and integrate the current knowledge on all types of communication between plants and insects, neighboring plants and pathogens that are mediated through plant volatiles.     

Herbivore-induced indirect interaction webs on terrestrial plants: the importance of non-trophic, indirect, and facilitative interactions

One of the most important issues in ecology is understanding the causal mechanisms that shape the structure of ecological communities through trophic interactions. The focus on direct, trophic interactions in much of the research to date means that the potential significance of non-trophic, indirect, and facilitative interactions has been largely ignored in traditional food webs. There is a growing appreciation of the community consequences of such non-trophic effects, and the need to start including them in food web research. This review highlights how non-trophic, indirect, and facilitative interactions play an important role in organizing the structure of plant-centered arthropod communities. I argue that herbivore-induced plant responses, insect ecosystem engineers, and mutualisms involving ant–honeydew-producing insects all generate interaction linkages among insect herbivores, thereby producing complex indirect interaction webs on terrestrial plants. These interactions are all very common and widespread on terrestrial plants, in fact they are almost ubiquitous, but these interactions have rarely been included in traditional food webs. Finally, I will emphasize that because the important community consequences of these non-trophic and indirect interactions have been largely unexplored, it is critical that indirect interaction webs should be the focus of future research.     

Tiadinil, a plant activator of systemic acquired resistance, boosts the production of herbivore-induced plant volatiles that attract the predatory mite Neoseiulus womersleyi in the tea plant Camellia sinensis

Plants respond with various defense mechanisms to pathogenic or herbivorous attack. Some chemicals called plant activators that induce the plant defense response against pathogens have been commercially used to protect plants. Here we studied the effects of tiadinil (TDL) on defense mechanisms against herbivores. TDL suppresses pathogenic fungi on tea leaves by inducing defense mechanisms. We used one of the major trophic systems in tea consisting of the herbivorous mite, Tetranychus kanzawai, and the predatory mite, Neoseiulus womersleyi. TDL enhanced the production of herbivore-induced plant volatiles that attract predatory mites. The predatory mites preferred the T. kanzawai-induced volatiles from TDL-treated plants to those produced by untreated plants. These results suggest that TDL activates the plant defense response via an indirect process mediated by plant volatiles that attract natural enemies of the herbivores. In contrast, the oviposition rate, adult maturation rate, and sex ratio of T. kanzawai were not affected by TDL treatment. These results suggest that TDL did not activate any direct defense against the herbivorous mite.     

虫害诱导的植物挥发物:植物与植食性昆虫及其天敌相互作用的进化产物

综述了植物、植食性昆虫及其天敌相互作用的进化过程。虫害诱导的植物挥发物的特征和功能是植物-植食性昆虫-天敌之间长期进化的结果。在植物、植食性昆虫与天敌相互作用的进化过程中,3个不同营养级,包括植物、植食性昆虫和天敌有着各自的调节和利用虫害诱导的植物挥发物的策略。但有一些问题,如通过实验研究得出的诱导防御在田间是否真正能起到保护作用等需进一步研究、阐明。     

What makes a volatile organic compound a reliable indicator of insect herbivory?

Plants that are subject to insect herbivory emit a blend of so‐called herbivore‐induced plant volatiles (HIPVs), of which only a few serve as cues for the carnivorous enemies to locate their host. We lack understanding which HIPVs are reliable indicators of insect herbivory. Here, we take a modelling approach to elucidate which physicochemical and physiological properties contribute to the information value of a HIPV. A leaf‐level HIPV synthesis and emission model is developed and parameterized to poplar. Next, HIPV concentrations within the canopy are inferred as a function of dispersion, transport and chemical degradation of the compounds. We show that the ability of HIPVs to reveal herbivory varies from almost perfect to no better than chance and interacts with canopy conditions. Model predictions matched well with leaf‐emission measurements and field and laboratory assays. The chemical class a compound belongs to predicted the signalling ability of a compound only to a minor extent, whereas compound characteristics such as its reaction rate with atmospheric oxidants, biosynthesis rate upon herbivory and volatility were much more important predictors. This study shows the power of merging fields of plant–insect interactions and atmospheric chemistry research to increase our understanding of the ecological significance of HIPVs.     

Does selective defoliation mediate competitive interactions in a semiarid savanna? A demographic evaluation

Abstract. Three patterns of target-neighbor plant defoliation were imposed on a late-seral, perennial, C₄-grass, Bouteloua curtipendula, in three long-term grazing regimes to determine the influence of selective defoliation on competitive interactions and species replacement in a semiarid savanna on the Edwards Plateau, Texas, USA. Short-term (3-yr) target plant defoliation did not significantly affect either tiller or plant responses in any of the three grazing regimes. Neighbor plant defoliation, either alone or in combination with target plants, produced a significant defoliation interaction with time for tiller number and basal area per plant, but not for tiller recruitment or mortality. The minimal effect of selective defoliation on the intensity of competitive interactions in this semiarid community indicates that selective grazing has a less definitive role in mediating herbivore-induced species replacement than it does in mesic grasslands and savannas. This interpretation is discussed within the context of long-term (45-yr) change in herbaceous vegetation associated with grazing in this community. Cumulative tiller recruitment in the intensively grazed regime was only 44% of that in the ungrazed regime because of greater plant mortality and fewer surviving plants that recruited tillers. Target plant mortality (50%) only occurred in the intensively grazed regime and the proportion of target plants that initiated tillers decreased by 70, 48 and 32% in the ungrazed, moderately and intensively grazed regimes, respectively, during the final two years of the investigation. The decrease in cumulative tiller recruitment in all grazing regimes was probably mediated by a drought-induced increase in median tiller age the second year of the study. However, tiller per tiller recruitment rate among plants that recruited at least one tiller remained relatively constant among grazing regimes and years. Intensive, long-term grazing has modified the population structure of this late-seral perennial grass to the extent that population responses to both herbivory and periodic drought have been altered in comparison with those of ungrazed and moderately grazed populations. Ecological consequences of a herbivore-induced transition in population structure may be to minimize the effect of selective herbivory on competitive interactions and to function as an avoidance mechanism to reduce the probability of localized population extinction in response to intensive long-term herbivory.     

Seasonal variation of responses to herbivory and volatile communication in sagebrush (<Emphasis Type="Italic">Artemisia tridentata</Emphasis>) (Asteraceae)

Plants can respond to insect herbivory in various ways to avoid reductions in fitness. However, the effect of herbivory on plant performance can vary depending on the seasonal timing of herbivory. We investigated the effects of the seasonal timing of herbivory on the performance of sagebrush (Artemisia tridentata). Sagebrush is known to induce systemic resistance by receiving volatiles emitted from clipped leaves of the same or neighboring plants, which is called volatile communication. Resistance to leaf herbivory is known to be induced most effectively after volatile communication in spring. We experimentally clipped 25 % of leaves of sagebrush in May when leaves were expanding, or in July when inflorescences were forming. We measured the growth and flower production of clipped plants and neighboring plants which were exposed to volatiles emitted from clipped plants. The treatment conducted in spring reduced the growth of clipped plants. This suggests that early season leaf herbivory is detrimental because it reduces the opportunities for resource acquisition after herbivory, resulting in strong induction of resistance in leaves. On the other hand, the late season treatment increased flower production in plants exposed to volatiles, which was caused mainly by the increase in the number of inflorescences. Because the late season treatment occurred when sagebrush produces inflorescences, sagebrush may respond to late herbivory by increasing compensation ability and/or resistance in inflorescences rather than in leaves. Our results suggest that sagebrush can change responses to herbivory and subsequent volatile communication seasonally and that the seasonal variation in responses may reduce the cost of induced resistance.