No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Simplified Perspective of Complex Insect–Plant Interactions
Abstract
Scientific literature pertaining to the investigations on insect–plant interactions spans more than a century. This is a challenging frontier area today as it was for the pioneers, and it would continue to be so for researchers in their pursuit to help elucidate the complex relationship between the insects and plants. Despite the ready availability of exhaustive literature on this subject, the mechanisms of insect–plant interactions are still not completely understood. Insect–plant interaction is an extremely rich subject that transcends several disciplines of science and has far-reaching implications, especially in the management of ecosystem and crop protection. The interaction between pests and plants starts at the interface of plasma membrane and in response to perception of a pest and release of herbivore-associated molecular patterns (HAMPs); plants respond quickly by setting up the electrical signalling followed by depolarization of membrane, leading to increase in Ca²⁺ ion concentration and activation of calcium-sensing proteins. Further, this interaction is primarily governed by various signalling mechanisms, such as mitogen-activated kinase (MAP-kinase), jasmonic acid (JA), salicylic acid (SA) and ethylene (ET)-based pathways that regulate changes in gene and protein expression leading to synthesis of defensive compounds. Plants defend themselves not only by direct means but also by indirect means, wherein plants emit volatiles to attract natural enemies of the herbivores. Herein, we summarize the molecular and ecological aspects of complex insect–plant interactions to enable researchers to direct their course of action towards addressing them for making a meaningful contribution in this field, which will have far reaching implications in the success of insect pest management programs.
Pesticides are important tools to increase agriculture productivity and to deal with domestic pests. Once they were elevated to the category of relevant items brought by modernity. However, when Rachel Carson published her famous work “Silent Spring” humans worldwide were awakened to the problems caused by excessive and inappropriate use of these compounds, in that particular case due to biomagnification. Nowadays, pesticides are still regarded as important tools to improve human lifestyle, but now pesticides are less persistent, less toxic (especially toward mammals), and special emphasis is put on reducing the toxic effects of new pesticides once they are released into the market. These new rules and regulations have greatly reduced the adverse effects of pesticides on the environment. Unfortunately, there are many commercial formulations and active ingredients that are still greatly toxic to nontarget organisms of which we know a few details on fate and toxicology. This chapter would try to fill up some of the blanks that exist in this information and give a general perspective on the topic. At the end of the chapter, we would recommend future prospective works and research that might enlighten what we already know about the fate and adverse effects of pesticides.
There is tremendous diversity of interactions between plants and other species. These relationships range from antagonism to mutualism. Interactions of plants with members of their ecological community can lead to a profound metabolic reconfiguration of the plants' physiology. This reconfiguration can favour beneficial organisms and deter antagonists like pathogens or herbivores. Determining the cellular and molecular dialogue between plants, microbes, and insects, and its ecological and evolutionary implications is important for understanding the options for each partner to adopt an adaptive response to its biotic environment. Moving forward , understanding how such ecological interactions are shaped by environmental change and how we potentially mitigate deleterious effects will be increasingly important. The development of integrative multidisciplinary approaches may provide new solutions to the major ecological and societal issues ahead of us. The rapid evolution of technology provides valuable tools and opens up novel ways to test hypotheses that were previously unanswerable, but requires that scientists master these tools, understand potential ethical problems flowing from their implementation , and train new generations of biologists with diverse technical skills. Here, we provide brief perspectives and discuss future promise and challenges for research on insect-plant interactions building on the 16th International Symposium on Insect-Plant interactions (SIP) meeting that was held in Tours, France (2-6 July 2017). Talks, posters, and discussions are distilled into key
Plants and insects are highly diverse groups due to their ability to exploit a wide range of niches, from the desert to the arctic zone and also almost all the plant species growing on the planet. Plants and insects make up together approximately half of all known species of multicellular organisms. Each plant interacts with insects in a different manner; insects may act as protection, dispersers, or fertilizers for plants while plants may be a food/energy resource or nest location for insects. Starting with herbivory, plant-insect interactions date back to the Devonian period, about 420 million years ago, when plants first began their conquest of the land. But it was most probably in the Upper Carboniferous, about 320 million years ago, that these interactions became more intense, characterized also by the appearance of entomophily (i.e., insect pollination) about 252 million years ago, before the appearance of flowering plants (angiosperms).
The effects of intercropping aromatic plants (AP) on behavior and population development of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) were investigated in the field (adults) and in the greenhouse (nymphs). The responses of adults to the volatiles of tomato, Solanum lycopersicum L. (Solanaceae), plants plus AP [T + coriander (Co), rue (R), marigold (M), Greek basil (B), or citronella (Ci)] vs. humidified air or tomato volatiles only were assessed in laboratory Y-tube olfactometer assays. We found higher responses of adult B. tabaci to the humidified air than to the T + Co, T + B, and T + Ci treatments. The responses to T + R and T + M were similar to those to the humidified air. Responses to tomato volatiles were also greater than to T + Co, T + B, and T + Ci. In field assays, populations of adult insects were evaluated in tomato alone, in tomato intercropped with coriander or Greek basil, and in tomato mulched with citronella grass for 6 weeks. Adult whiteflies were generally found in greater numbers in the tomato-alone treatment compared to tomato intercropped with coriander or basil and tomato with citronella grass mulch. Reduction in adult whitefly populations compared to the population found in tomato alone was 84, 79, and 69% in intercrops of T + Co and T + B, and the tomato with citronella mulch treatment, respectively. Infestations of B. tabaci nymphs in plots of tomato plants cultivated alone or intercropped with reseeded coriander plants were also determined in a greenhouse. Nymph counts in the greenhouse assay were generally lower in tomato intercropped with coriander than in tomato alone for all six assessments. The mean reduction in nymphs in tomato intercropped with coriander was 37.7% compared with tomato alone. These results indicate that intercropping aromatic plants reduces infestations of B. tabaci.
In nature, most plants are resistant to most potential insect attackers. The world is green, right? The same is true of domesticated crops, although we are sensitive to any insect damage that reduces yield, quality and profits to the farmer. And indeed, certain insects can indeed devastate their crop host leaving nothing to harvest. The ancestors of modern day crop plants coevolved with insects and through natural selection accumulated many physical and chemical traits that formed a core defense against attackers. Plant domestication and breeding involving selection for improved yield and quality has generally made crops more susceptible to pest damage. The pre-adapted traits providing protection from insect pests still exist in the plant genome and finding and exploiting these traits forms the basis of host plant resistance. The mechanisms of host plant resistance traits can be broadly grouped as non-preference or antixenosis, antibiosis, and tolerance. The physiological basis for these traits is often not understood, and this is one reason host plant resistance is not pursued as a pest control tactic in many crops. Also, pesticides have been an inexpensive replacement for the natural plant defenses that have been lost. For certain crops where pesticides are not practical or cost effective such as cereals and grains host plant resistance is the primary tactic for pest control.
This article introduces the 11 papers in this special issue of Entomologia Experimentalis et Applicata. The articles explore various aspects of plant insect interactions and current methods and technology for improving crop resistance, and reflect the current state of the art.
Flowers are a remarkable component of every-day life. Their diversity of shape, colour and fragrance witnesses the importance of the joint evolutionary processes resulting from the interactions between plants and their insect pollinators. Indeed, pollination mutualisms with insects are key factors that have allowed the evolutionary success and diversification of flowering plants (McKey & Hossaert-McKey, 2008). This diversification of plants has led to an even more impressive diversification of insects. This chapter retraces the main steps of the past history of diversification of pollination interactions with the emergence of some major pollinator groups of insects, and proposes some insights into the selective processes acting on the evolution of the entomophilous pollination.
Cost efficient foraging is of especial importance for animals like hawkmoths or hummingbirds that are feeding 'on the wing', making their foraging energetically demanding. The economic decisions made by these animals have a strong influence on the plants they pollinate and floral volatiles are often guiding these decisions. Here we show that the hawkmoth Manduca sexta exhibits an innate preference for volatiles of those Nicotiana flowers, which match the length of the moth's proboscis. This preference becomes apparent already at the initial inflight encounter, with the odour plume. Free-flight respiration analyses combined with nectar calorimetry revealed a significant caloric gain per invested flight energy only for preferred-matching-flowers. Our data therefore support Darwin's initial hypothesis on the coevolution of flower length and moth proboscis. We demonstrate that this interaction is mediated by an adaptive and hardwired olfactory preference of the moth for flowers offering the highest net-energy reward.
Pest management is a critical component of agricultural and forestry production systems. In the past, chemical pesticides were the standard control measures. Today, other approaches, such as biological control, are becoming viable options to chemicals. Biological control agents are living organisms (or parts of living organisms) that interfere with the productivity of other living organisms. In terms of biotechnology, biological control agents are used by human beings for the protection of resources that they want. Biological control agents encompass a wide range of organisms from insects, mites, fungi, bacteria, to viruses. Biological control programs have been successfully used to control noxious weeds, plant pathogens, and invertebrate and vertebrate pests. Production, deployment, and establishment of biological control agents are important parameters in determining the success of these agents for pest management. Also, recent advances in genetic engineering have incorporated some biological control agents into the genomes of crops. Biological control agents are part of a complex natural ecosystem and can be regarded as biotechnology practiced at the level of simple anthropogenic ecosystems.
In this review, we argue for a research initiative on wheat's responses to biotic stress. One goal is to begin a conversation between the disparate communities of plant pathology and entomology. Another is to understand how responses to a variety of agents of biotic stress are integrated in an important crop. We propose gene-for-gene interactions as the focus of the research initiative. On the parasite's side is an Avirulence (Avr) gene that encodes one of the many effector proteins the parasite applies to the plant to assist with colonization. On the plant's side is a Resistance (R) gene that mediates a surveillance system that detects the Avr protein directly or indirectly and triggers effector-triggered plant immunity. Even though arthropods are responsible for a significant proportion of plant biotic stress, they have not been integrated into important models of plant immunity that come from plant pathology. A roadblock has been the absence of molecular evidence for arthropod Avr effectors. Thirty years after this evidence was discovered in a plant pathogen, there is now evidence for arthropods with the cloning of the Hessian fly's vH13 Avr gene. After reviewing the two models of plant immunity, we discuss how arthropods could be incorporated. We end by showing features that make wheat an interesting system for plant immunity, including 479 resistance genes known from agriculture that target viruses, bacteria, fungi, nematodes, insects, and mites. It is not likely that humans will be subsisting on Arabidopsis in the year 2050. It is time to start understanding how agricultural plants integrate responses to biotic stress.
© The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.
The tea aphid, Toxoptera aurantii Boyer (Hemiptera: Aphididae), is a major pest of the tea plant, Camellia sinensis (L.) O. Kuntze (Theaceae). The attraction of the aphids to different colors and volatile compounds from tea shoots was investigated. Fourteen compounds were identified using gas chromatography‐mass spectrometry from headspace samples of intact tea shoot volatiles (ITSV). Electrophysiological and behavioral responses of winged tea aphids to ITSV as well as to the full blend of 14 synthetic compounds, to a partial mixture of green leaf volatiles (GLV) included in the 14 compounds, and to individual synthetic compounds were studied by using electroantennography (EAG) and a Y‐tube olfactometer. The various tea volatiles and blends were strongly active, with ITSV being the strongest. In the greenhouse and in tea plantations, sticky boards of six different colors strongly attracted tea aphids in flight, with ‘rape‐flower yellow’ and ‘Chinese olive‐yellow‐green’ being the most attractive. Furthermore, these two boards in combination with ITSV attracted winged tea aphids more strongly than their corresponding colored sticky boards alone. In the greenhouse, plastic models of tea seedlings baited with (Z)‐3‐hexen‐1‐ol or the GLV mixture significantly attracted winged tea aphids in flight. This study demonstrates that green leaf volatiles from tea shoots are attractive to the tea aphid. The combination of these volatiles with the color light yellow or green, and the shape of tender tea shoots result in orientation flight and landing of winged tea aphids on host tea shoots.
This short review points out some of the major physical problems faced by insects feeding on plants, and some of the kinds of morphological adaptations that have been noted to date. Major emphasis is given to two factors: the nature of the plant surface, and the difficulty of dealing with hard or tough food. The surface provides a great variety of terrains that require specialization for maximizing tenacity and agility, especially for small insects. It is suggested that natural enemies may provide significant selection for the relevant morphologies. The difficulty of feeding upon certain plant tissues is shown to be overcome in different ways by different herbivore groups. In the case of tough leaves for example, grasshopper mandible adaptations appear to have evolved to maximize efficiency of processing. On the other hand, in the case of caterpillars, mandible adaptations for tough food appear to be minimizing handling time with a concomitant reduction in risk of predation. Convergent evolution is shown in both grasshoppers and caterpillars for dealing with leaves of similar design and an example is given of rapid evolution of mouthpart morphology in response to differences in host characteristics. These examples are used to indicate the risks of using such characters in establishing phylogenetic relationships. Finally, it is pointed out that plant chemical qualities and plant ecological factors can influence insect morphological features.
The ca. 275,000 species of flowering plants are the result of a recent adaptive radiation driven largely by the coevolution between plants and their animal pollinators. Identification of genes and mutations responsible for floral trait variation underlying pollinator specificity is crucial to understanding how pollinator shifts occur between closely related species. Petunia, Mimulus, and Antirrhinum have provided a high standard of experimental evidence to establish causal links from genes to floral traits to pollinator responses. In all three systems, MYB transcription factors seem to play a prominent role in the diversification of pollinator-associated floral traits.
Eggs deposited on plants by herbivorous insects represent a threat as they develop into feeding larvae. Plants are not a passive substrate and have evolved sophisticated mechanisms to detect eggs and induce direct and indirect defenses. Recent years have seen exciting development in molecular aspects of egg-induced responses. Some egg-associated elicitors have been identified, and signaling pathways and egg-induced expression profiles are being uncovered. Depending on the mode of oviposition, both the jasmonic acid and salicylic acid pathways seem to play a role in the induction of defense responses. An emerging concept is that eggs are recognized like microbial pathogens and innate immune responses are triggered. In addition, some eggs contain elicitors that induce highly specific defenses in plants. Examples of egg-induced suppression of defense or, on the contrary, egg-induced resistance highlight the complexity of plant-egg interactions in an on-going arms race between herbivores and their hosts. A major challenge is to identify plant receptors for egg-associated elicitors, to assess the specificity of these elicitors and to identify molecular components that underlie various responses to oviposition.
Herbivorous insects recognize and locate their hosts by detecting characteristic blends of volatile compounds these plants emit. The possibility that insects may use the same compounds in a different context as nonhost cues has received relatively little attention. Volatiles normally emitted by the host but encountered without other host volatiles could theoretically function as nonhost cues. We hypothesized that insects might show a positive response to host volatile compounds when encountered together in a blend but avoid the same volatiles when encountered individually. To test this we examined the behavioural responses of the black bean aphid, Aphis fabae, to physiologically relevant doses of volatile compounds emitted by its host, Vicia faba, which had been previously implicated in host recognition. Of 15 volatiles tested for behavioural activity, 10 caused aphids to respond negatively, suggesting they were repellent. We then made a blend comprising each of these compounds at the concentration at which they elicited the most negative behavioural response. The resultant blend elicited a positive response, suggesting it was attractive/arrestant. This demonstrated that the same volatile compounds can function as both host and nonhost cues, depending upon the context in which they are perceived. Thus, background odour context needs to be considered for successful use of behaviourally active volatile compounds in integrated pest management strategies. Furthermore, the finding that odorants are perceived differently when combined suggests that there is an emergent property of odour perception whereby discrimination of odour quality can occur according to blend properties
Plant Anti-Insect Armaments
Because individual plants are unable to relocate, they are subject to extreme selection by the insects feeding upon them. One means by which plants suppress herbivory is to produce toxic compounds to deter feeding (see the Perspective by Hare ). Agrawal et al. (p. 113 ) compared pesticide–treated or untreated evening primroses. Over 5 years of pesticide treatment, the production of defensive chemicals in the fruit reduced and flowering times shifted, and the primrose's competitive ability against dandelions improved. Züst et al. (p. 116 ) examined large-scale geographic patterns in a polymorphic chemical defense locus in the model plant Arabidopsis thaliana and found that it is matched by changes in the relative abundance of two specialist aphids. Thus, herbivory has strong and immediate effects on the local genotypic composition of plants and traits associated with herbivore resistance.
Insect herbivores are hypothesized to be major factors affecting the ecology and evolution of plants. We tested this prediction
by suppressing insects in replicated field populations of a native plant, Oenothera biennis, which reduced seed predation, altered interspecific competitive dynamics, and resulted in rapid evolutionary divergence.
Comparative genotyping and phenotyping of nearly 12,000 O. biennis individuals revealed that in plots protected from insects, resistance to herbivores declined through time owing to changes
in flowering time and lower defensive ellagitannins in fruits, whereas plant competitive ability increased. This independent
real-time evolution of plant resistance and competitive ability in the field resulted from the relaxation of direct selective
effects of insects on plant defense and through indirect effects due to reduced herbivory on plant competitors.
Covering: up to April 2012In plants, successful defense relies on fast and specific response to biotic attack. In plant-microbial and plant-plant interactions several elicitors, effectors and modulators are recognized by specific and unspecific receptors that trigger signal cascades eventually leading to gene expression and plant responses. Here we review the chemical nature and signaling pathways of natural products released by microorganisms, herbivores, and plants during pathogenic infections, herbivory, symbioses and allelopathic interactions.
The roles of signaling pathways in the production of trypsin proteinase inhibitors (TrypPIs) in rice infested by the leaf
folder (LF) Cnaphalocrocis medinalis were studied. Infestation by LF increased TrypPI levels in the leaves of rice plants at the tillering, booting and flowering
stages but decreased TrypPI levels at the ripening stage; TrypPI levels in rice stems did not increase at any developmental
stage. Infestation by LF at the tillering stage systemically increased TrypPI levels in leaves but not in stems; it also enhanced
salicylic acid (SA) levels in leaves and stems, and the ethylene level released from plants. However, LF infestation did not
increase JA concentrations. Exogenous application of SA or ethylene enhanced TrypPI levels in the leaves and stems of plants
at the tillering stage, whereas treatment with both SA and ethylene induced lower levels of TrypPIs than treatment with SA
or ethylene alone, suggesting an antagonistic effect of SA and ethylene on TrypPIs induction. The results suggest that both
SA and ethylene signaling pathways are involved in the production of TrypPIs in rice induced by LF; moreover, the antagonistic
effect of SA and ethylene may explain the changes in TrypPI levels seen at different plant developmental stages and in different
organs.
Keywordsrice–
Cnaphalocrocis medinalis
–jasmonic acid–salicylic acid–ethylene–trypsin proteinase inhibitor–herbivore-induced defense response
Within modern gymnosperms, conifers and Ginkgo are exclusively wind pollinated whereas many gnetaleans and cycads are insect pollinated. For cycads, thrips are specialized pollinators. We report such a specialized pollination mode from Early Cretaceous amber of Spain, wherein four female thrips representing a genus and two species in the family Melanthripidae were covered by abundant Cycadopites pollen grains. These females bear unique ring setae interpreted as specialized structures for pollen grain collection, functionally equivalent to the hook-tipped sensilla and plumose setae on the bodies of bees. The most parsimonious explanation for this structure is parental food provisioning for larvae, indicating subsociality. This association provides direct evidence of specialized collection and transportation of pollen grains and likely gymnosperm pollination by 110-105 million years ago, possibly considerably earlier.
Plant hormones have pivotal roles in the regulation of plant growth, development, and reproduction. Additionally, they emerged as cellular signal molecules with key functions in the regulation of immune responses to microbial pathogens, insect herbivores, and beneficial microbes. Their signaling pathways are interconnected in a complex network, which provides plants with an enormous regulatory potential to rapidly adapt to their biotic environment and to utilize their limited resources for growth and survival in a cost-efficient manner. Plants activate their immune system to counteract attack by pathogens or herbivorous insects. Intriguingly, successful plant enemies evolved ingenious mechanisms to rewire the plant's hormone signaling circuitry to suppress or evade host immunity. Evidence is emerging that beneficial root-inhabiting microbes also hijack the hormone-regulated immune signaling network to establish a prolonged mutualistic association, highlighting the central role of plant hormones in the regulation of plant growth and survival.
Diverse molecular processes regulate the interactions between plants and insect herbivores. Here, we review genes and proteins that are involved in plant–herbivore interactions and discuss how their discovery has structured the current standard model of plant–herbivore interactions. Plants perceive damage-associated and, possibly, herbivore-associated molecular patterns via receptors that activate early signaling components such as Ca2+, reactive oxygen species, and MAP kinases. Specific defense reprogramming proceeds via signaling networks that include phytohormones, secondary metabolites, and transcription factors. Local and systemic regulation of toxins, defense proteins, physical barriers, and tolerance traits protect plants against herbivores. Herbivores counteract plant defenses through biochemical defense deactivation, effector-mediated suppression of defense signaling, and chemically controlled behavioral changes. The molecular basis of plant–herbivore interactions is now well established for select model systems. Expanding molecular approaches to unexplored dimensions of plant–insect interactions should be a future priority. Expected final online publication date for the Annual Review of Plant Biology Volume 70 is April 29, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
More than 87% of flowering plant species are animal-pollinated [1] and produce floral scents and other signals to attract pollinators. These floral cues may however also attract antagonistic visitors, including herbivores [2]. The dilemma is exacerbated when adult insects pollinate the same plant that their larvae consume. It remains largely unclear how plants maximize their fitness under these circumstances. Here we show that in the night-flowering wild tobacco Nicotiana attenuata, the emission of a sesquiterpene, (E)-α-bergamotene, in flowers increases adult Manduca sexta moth-mediated pollination success, while the same compound in leaves is known to mediate indirect defense against M. sexta larvae [3, 4]. Forward and reverse genetic analyses demonstrated that both herbivory-induced and floral (E)-α-bergamotene are regulated by the expression of a monoterpene-synthase-derived sesquiterpene synthase (NaTPS38). The expression pattern of NaTPS38 also accounts for variation in (E)-α-bergamotene emission among natural accessions. These results highlight that differential expression of a single gene that results in tissue-specific emission of one compound contributes to resolving the dilemma for plants when their pollinators are also herbivores. Furthermore, this study provides genetic evidence that pollinators and herbivores interactively shape the evolution of floral signals and plant defense.
In this study, we review recent works in the phylogenetic investigations of plant–insect interactions. Thanks to the development of novel methodological approaches and the ever-increasing availability of informative molecular markers, it is indeed now possible to test more and more complex evolutionary scenarios. Here, we are limiting our review to studies on herbivorous insects (excluding work on the evolution of pollinating insects), and we provide an overview of the variety of approaches employed to answer fundamental questions in plant/insect evolution. More specifically, our review addresses studies that have focused on the following: (1) reconstructing the evolutionary history of the associations with plants; (2) inferring the diversification dynamics of herbivorous insects and (3) studying the biogeographic history of herbivorous insects. Finally, we attempt to decipher whether general trends in the evolution of plant–insect interactions have emerged from these studies and highlight the most promising perspectives in this field.
Phytophagous insects have developed mechanisms of various complexity levels to utilize plants in spite of the barriers that plants have built to resist aggressions. Plant exploitation, the simplest level, is the use of plant defence chemicals for the benefit of insects. It is illustrated by the use of plant toxins for defence against predators. The energetic cost of that defence strategy is discussed according to the toxicity of the chemicals and the necessity of protecting the herbivore, and the modes of action on predators are presented. Furthermore, manipulation of the plant can reorient the plant metabolism to satisfy insect needs. Drastic remodelling of the host plant can occur, from ultrastructure to anatomy levels, with alteration of both its nutritional quality and secondary metabolism. The mechanisms involved are being investigated. Outcomes concern optimization of the nutritional value of the host plant and protection from adverse abiotic and biotic (natural enemies, competition) conditions. Cooperation with conspecifics or microorganisms often interferes. At the highest level of complexity, mutualism is the result of a compromise between insect and plant where each partner benefits from the association. Pollination is a typical example. Pollinators vary from generalists to specialists and belong to a community of insect linked to a community of plants. In the fig–fig wasp mutualism, the various mechanisms involved in situations of monoecy and dioecy are discussed, as well as the existence of coadaptations and cospeciations. The chapter ends with a presentation of research perspectives for improving crop productivity.
In this investigation of orchids, first published in 1862, Darwin expands on a point made in On the Origin of Species that he felt required further explanation, namely that he believes it to be 'a universal law of nature that organic beings require an occasional cross with another individual'. Darwin explains the method by which orchids are fertilised by insects, and argues that the intricate structure of their flowers evolved to favour cross pollination because of its advantages to the species. The book is written in Darwin's usual precise and elegant style, accessible despite its intricate detail. It includes a brief explanation of botanical terms and is illustrated with 34 woodcuts.
In an environment with changing availability and quality of host plants, phytophagous insects are under selection pressure to find quality hosts. They need to maximize their fitness by locating suitable plants and avoiding unsuitable ones. Thus, they have evolved a finely tuned sensory system, for detection of host cues, and a nervous system, capable of integrating inputs from sensory neurons with a high level of spatio-temporal resolution. Insect responses to cues are not fixed but depend on the context in which they are perceived, the physiological state of the insect, and prior learning experiences. However, there are examples of insects making 'mistakes' and being attracted to poor quality hosts. While insects have evolved ways of finding hosts, plants have been under selection pressure to do precisely the opposite and evade detection or defend themselves when attacked. Once on the plant, insect-associated molecules may trigger or suppress defence depending on whether the plant or the insect is ahead in evolutionary terms. Plant volatile emission is influenced by defence responses induced by insect feeding or oviposition which can attract natural enemies but repel herbivores. Conversely, plant reproductive fitness is increased by attraction of pollinators. Interactions can be altered by other organisms associated with the plant such as other insects, plant pathogens, or mycorrhizal fungi. Plant phenotype is plastic and can be changed by epigenetic factors in adaptation to periods of biotic stress. Space and time play crucial roles in influencing the outcome of interactions between insects and plants.
The digestion of prey by carnivorous plants is determined in part by suites of enzymes that are associated with morphologically and anatomically diverse trapping mechanisms. Chitinases represent a group of enzymes known to be integral to effective plant carnivory. In non-carnivorous plants, chitinases commonly act as pathogenesis-related proteins, which are either induced in response to insect herbivory and fungal elicitors, or constitutively expressed in tissues vulnerable to attack. In the Caryophyllales carnivorous plant lineage, multiple classes of chitinases are likely involved in both pathogenic response and digestion of prey items. We review what is currently known about trap morphologies, provide an examination of the diversity, roles, and evolution of chitinases, and examine how herbivore and pathogen defense mechanisms may have been coopted for plant carnivory in the Caryophyllales.
Fossil plant-insect associations (PIAs) such as herbivory and pollination have become increasingly relevant to paleobiology and biology. Researchers studying fossil PIAs now employ procedures for assuring unbiased representation of field specimens, use of varied analytical quantitative techniques, and address ecological and evolutionarily important issues. For herbivory, the major developments are: Late Silurian-Middle Devonian (ca. 420-385Ma(a)) origin of herbivory; Late Pennsylvanian (318-299Ma) expansion of herbivory; Permian (299-252Ma) herbivore colonization of new habitats; consequences of the end-Permian (252Ma) global crisis; early Mesozoic (ca. 235-215Ma) rediversification of plants and herbivores; end-Cretaceous (66.5Ma) effects on extinction; and biological effects of the Paleocene-Eocene Thermal Maximum (PETM) (55.8Ma). For pollination, salient issues include: Permian pollination evidence; the plant hosts of mid-Mesozoic (ca. 160-110Ma) long-proboscid pollinators; and effect of the angiosperm revolution (ca. 125-90Ma) on earlier pollinator relationships. Multispecies interaction studies, such as contrasting damage types with insect diversity and establishing robust food webs, expand the compass and relevance of past PIAs.
The major diversification of flowering plants (angiosperms) in the Early
Cretaceous, between about 130 and 90 million years ago, initiated
fundamental changes in terrestrial ecosystems and set in motion
processes that generated most of the extant plant diversity. New
palaeobotanical discoveries, combined with recent phylogenetic analyses
of morphological and molecular data, have clarified the initial phases
of this radiation and changed our perspective on early angiosperm
evolution, though important issues remain unresolved.
Searching behavior is an active movement by which insects seek resources such as food, mates, oviposition and nesting sites, and refugia. Efficient searching mechanisms and accurate assessment mechanisms are crucial for an individual's chances of survival and reproduction. Searching behavior incurs costs in addition to the energy used for locomotion, eg the risks of predation while engaged in searching, and the time taken away from other activities such as holding territory or protecting nests. Natural selection would be expected to favor searching mechanisms that maximize the difference between searching costs and benefits and that reduce various types of risks incurred while searching. Searching behavior represents the confluence of: 1) the biological characteristics and abilities of an insect including locomotory patterns and perception of sensory information; 2) external environmental factors determining the resources available and the risks inherent in their quest; and 3) internal factors, such as deprivation or sexual receptivity, determining what an individual needs at a particular time. Mechanisms for locating and remaining in profitable resource patches can be reduced to relatively simple neural responses. Patch times are regulated by locomotory shifts from restricted to straight walking after resource utilization, satiation and habituation to patch cues. -from Author
The most common biological interaction among species on Earth is that between plants and the insects that feed on them ( 1 ). Insect herbivores are thought to impose natural selection, which favors resistant plant genotypes and drives the evolutionary diversification of plant species. Two reports in this issue—by Zust et al. on page 116 ( 2 ) and Agrawal et al. on page 113 ( 3 )—independently provide strong empirical evidence for the rapid evolution of plant traits that confer resistance to herbivores when herbivores are present but for the evolution of traits that confer increased competitive ability when herbivores are absent.
The effect of visual and olfactory stimuli from leaves of two maize cultivars, Basilocal (susceptible) and Kisan (resistant), in eliciting orientational responses by first instar Chilo partellus (Swinhoe) larvae was investigated in the laboratory. The polar and non-polar chemical constituents of these cultivars were extracted in methanol and hexane, respectively. Orientational preference of the larvae for the leaf whorls and hexane extracts of Basilocal leaves was significantly greater than that for Kisan. The methanol extracts of the two cultivars were, however, equally effective in eliciting larval attraction. These observations imply that the non-polar fraction of maize leaves is more effective than the polar fraction in eliciting larval orientation in C. partellus. Moreover, certain chemicals of Kisan leaves, extractable in hexane, elicited larval repulsion whereas those of Basilocal leaves elicited larval attraction. Identification of the chemicals eliciting attraction or repulsion would be valuable in a management programme for this economically important insect pest of gramineous crops.
1. Herbivores consume a large portion of the biomass produced by plants in virtually all ecosystems, which has dramatic effects on both the ecology and evolution of plants. In response to this threat, plants have evolved a diverse arsenal of direct and indirect defences to reduce herbivory and the impacts of damage on plant performance.
2. This special feature is a broad synthesis of the evolution and ecology of plant defences. The first objective of this special feature is to provide a review of what we have learned about plant defences against herbivores. The second objective is to stimulate debate and sow fresh ideas for the future research.
3. The 11 articles in this issue address three fundamental questions: (i) How do plants defend themselves against a diverse array of enemies? (ii) Why do plant species vary in defence? And (iii) What are the ecological and ecosystem-level consequences of plant defence? In addressing these questions the articles cover the interdisciplinary nature of plant–herbivore evolutionary ecology, from genes to global patterns.
4. The articles contained in the special feature question existing paradigms and provide new analyses of data. In some cases, influential hypotheses are firmly supported with new analyses (e.g. the Resource Availability Hypothesis), whereas in other instances conventional wisdom is called into question (e.g. the importance of secondary metabolites in the microevolution of resistance) and popular hypotheses are rejected (e.g. the Apparency Hypothesis, the Latitudinal Biotic Interaction Hypothesis).
5. This is an exciting time for research on the evolutionary ecology of plant defences. The articles in this special feature provide a guide to how we can move forward in resolving existing problems and tackling new questions.
1. Herbivores exert significant selection on plants, and plants have evolved a variety of constitutive and inducible defences to resist and tolerate herbivory. Assessing the genetic mechanisms that influence defences against herbivores will deepen our understanding of the evolution of essential phenotypic traits.
2. Ecogenomics is a powerful interdisciplinary approach that can address fundamental questions about the ecology and evolutionary biology of species, such as: which evolutionary forces maintain variation within a population? and What is the genetic architecture of adaptation? This field seeks to identify gene regions that influence ecologically important traits, assess the fitness consequences under natural conditions of alleles at key quantitative trait loci (QTLs), and test how the abiotic and biotic environment affects gene expression.
3. Here, we review ecogenomics techniques and emphasize how this framework can address long-standing and emerging questions relating to anti-herbivore defences in plants. For example, ecogenomics tools can be used to investigate: inducible vs. constitutive defences; tradeoffs between resistance and tolerance; adaptation to the local herbivore community; selection on alleles that confer resistance and tolerance in natural populations; and whether different genes are activated in response to specialist vs. generalist herbivores and to different types of damage.
4. Ecogenomic studies can be conducted with model species, such as Arabidopsis, or their relatives, in which case myriad molecular tools are already available. Burgeoning sequence data will also facilitate ecogenomic studies of non-model species. Throughout this paper, we highlight approaches that are particularly suitable for ecological studies of non-model organisms, discuss the benefits and disadvantages of specific techniques and review bioinformatic tools for analysing data.
5. We focus on established and promising techniques, such as QTL mapping with pedigreed populations, genome wide association studies, transcription profiling strategies, population genomics and transgenic methodologies. Many of these techniques are complementary and can be used jointly to investigate the genetic architecture of defence traits and selection on alleles in nature.
Crop yields are reduced and destabilized by pests which also affect the quality of harvested produce. To keep pace with growing
demand, global food production needs to increase by an estimated 70% by 2050. Thus, the losses caused by pests need to be
tackled. Synthetic pesticides have provided cost-effective control of pests over the last few decades but have several disadvantages.
They may adversely affect natural enemies of insect pests, which would otherwise provide a degree of control and pests may
evolve resistance to the pesticide. The discovery rate of novel bioactive compounds is low and their exploitation increasingly
inhibited by stringent regulatory requirements. Use of resistant crop cultivars is another solution but when based on single
genes it also suffers from the evolution of biotypes of pests that can overcome the resistance conferred by the gene. Biocontrol
with natural enemies can contribute to pest management but biocontrol agents are often hard to maintain at sufficiently high
levels in open field environments. New solutions could include novel resistant cultivars with multiple resistance genes, suitable
epigenetic imprints and improved defence responses that are induced by attack. Plant activator agrochemicals could be used
to switch on natural plant defence. Habitat manipulations such as push-pull can improve pest management and yields in less
intensive systems. Genomic and transcriptomic information will facilitate development of new resistant crop cultivars once
annotation and availability of data on multiple cultivars is improved. Knowledge of the chemical ecology of pest-plant interactions
will be better exploited once the genes for biosynthesis of key plant metabolites are discovered. Genetic modification of
crops has the potential for speeding the development of crops with novel resistance.
KeywordsCrop pest–Food security–Induced defence–IPM–Resistant cultivar
In this experiment, the aphid–wheat interaction system was chosen to study the changes in activity levels of key enzymes [lipoxygenase (LOX), polyphenoloxidase (PPO), phenylalanine ammonialyse (PAL) and β-1,3-glucanase] and in transcript level of key defense genes [encoding farnesyl pyrophosphate synthetase (fps), encoding allene oxide synthase (aos), and encoding phenylalanine ammonialyse (pal)] under pressure of aphid-feeding, aphid-induced volatiles, as well as specific volatiles using enzymes assay, RT-PCR and real-time quantitative PCR techniques. At the same time, the induction of enzymatic and transcript levels of defense genes with artificial wounding, wounding-induced volatiles and inductive chemical agents (jasmonic acid and methyl salicylate) were also studied. Our results showed that the activities of key enzymes which belong to both jasmonic acid (JA) and salicylic acid (SA)-signaling pathways increased significantly with aphid-feeding. The relative transcript levels of key defense genes in the signaling pathways were also enhanced. So we propose that aphid-feeding could activate both jasmonic acid (JA) and salicylic acid (SA)-signaling transduction pathways. Mechanical wounding and aphid-feeding are not equivalent. Sitobion avenae-induced volatiles elicit the transcript of all three defense genes in neighboring plants, suggesting that the volatiles emitted from aphid-infested plants might induce the activity of LOX followed by activating the JA-signaling pathway and the transcript level of multiple defense genes that JA mediates. 6-Methyl-5-hepten-2-one, 2-tridecanone and (E)-2-hexen-1-ol in S. avenae-induced volatiles not only activated the transcript level of defense genes, but also inhibited aphid-feeding behavior and population growth.
Recapitulation des determinants ecologiques, genetiques et comportementaux du comportement d'oviposition chez diverses mouches. Evaluation de l'influence de ce comportement sur l'evolution du choix de l'hote