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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Plant-mediated insect interactions on a perennial plant : consequences for community dynamics
    Stam, J.M. - \ 2016
    Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Erik Poelman. - Wageningen : Wageningen University - ISBN 9789462578647 - 254
    016-3976 - perennials - brassica oleracea - defence mechanisms - glucosinolates - insect pests - herbivory - plutella xylostella - mamestra brassicae - pieris rapae - herbivore induced plant volatiles - animal communities - population dynamics - overblijvende planten - brassica oleracea - verdedigingsmechanismen - glucosinolaten - insectenplagen - herbivorie - plutella xylostella - mamestra brassicae - pieris rapae - herbivoor-geinduceerde plantengeuren - diergemeenschappen - populatiedynamica

    Plants interact with many organisms around them, and one of the most important groups that a plant has to deal with, are the herbivores. Insects represent the most diverse group of herbivores and have many different ways of using the plant as a food source. Plants can, however, defend themselves against those herbivores, either by constitutive defences, or by traits that are induced upon herbivory. These traits, such as the formation of more trichomes or the production of secondary metabolites, can deter an insect herbivore in its decision to eat from the plant, can be toxic, or otherwise hamper the insect to feed, grow or reproduce. The way a plant responds to herbivory is very specific, depending on the feeding mode or the species of the attacking insect. Furthermore, plant responses to dual herbivory differ from the sum of responses to each herbivore alone. Also the time and order at which multiple insects arrive on a plant, influence the plant’s response. Finally, plant species or populations can show different responses to herbivory. Altogether these factors result in a plant phenotype that the attacking herbivore has to deal with. In addition to the attacker, also subsequently arriving insects will be affected by a change in plant phenotype. Because plants and insects can respond to each other in a continuous chain of interactions, an herbivore early in the season can indirectly affect the later-season community composition through the induced plant response. However, we know only little about the consequences of a dual-herbivore induced plant phenotype for subsequent feeders, and ultimately, the effects on the assembly and dynamics of an insect community as a whole.

    The aim of this thesis project was to study the consequences of feeding by multiple insects from the same plant, not only to a subsequent herbivore, but also to the dynamics of a whole insect community over the course of a growing season, and beyond. Furthermore, I studied how the order of herbivore arrival and timing of arrival affected both a next herbivore’s choice and performance in a greenhouse setting, as well as the development of the whole insect community in the field. In addition, I studied how plant populations vary in induced responses, have specific plant-mediated interactions among insect herbivores, and how long these induced responses influence the insect community and plant fitness. Finally, I identified non-additive effects of the history of insect attacks and plant ontogeny to the future insect community.

    In the first chapter of this thesis, I introduce the study system. For this project I used several populations of the wild cabbage plant, Brassica oleracea. This is an herbaceous perennial plant that flowers from the second growing season onwards, and supports a large and diverse above-ground arthropod community of more than thirty different species. The plant belongs to the family of Brassicaceae, which is known for the biosynthesis of a group of secondary metabolites, the glucosinolates. These metabolites may deter insects, although some insect species use it as a feeding cue. Two specialist insect herbivores from different feeding guilds, the caterpillar of the diamondback moth Plutella xylostella and the cabbage aphid Brevicoryne brassicae, were used to study their effect as early-season inducer of plant responses either alone or in combination. The caterpillar of the generalist cabbage moth, Mamestra brassicae, was used in bioassays to assess the effects of the induced plant phenotype by single or dual herbivory. Furthermore, in three chapters (Chapters 4, 6 and 7) I have closely studied the composition of the naturally occurring insect community throughout the season for one or two years in a common-garden field setting. In the last of these three chapters, I used the caterpillars of the specialist cabbage white, Pieris rapae, to induce plants at different moments of their ontogeny, while excluding the insect community for varying periods of time by a net or exposing plants to their natural insect community.

    In an elaborate literature review, I and my collaborators concluded in chapter 2 that plant responses to dual herbivory evoke different plant responses than the sum of each herbivore alone. This has consequences at all levels from arthropod community assembly to the choice and performance of individual insects. The mechanisms of plant responses to dual herbivory are found in gene expression, hormone production and other molecular processes within the plant. All these aspects of interactions between insects and plants occur and are connected at different time scales.

    To follow up on the question how timing plays a role in dual herbivory, we varied the time between, as well as the order of arrival of aphids and/or caterpillars on a plant. We observed that both affected the preference and performance of a subsequently feeding caterpillar (Chapter 3). Mamestra brassicae performed better on plants with a longer time interval between the first and second feeder. Also in a field setting (Chapter 4), the order of herbivore arrival early in the season affected the insect community composition later in the season in two different years, likely through a chain of indirect insect interactions. In this field study, the plant population influenced the outcome of early-season herbivory to later community dynamics. In chapter 5 we found that three plant populations in response to simultaneous aphid and caterpillar attack differed in the expression of two genes that are important for the regulation of herbivore-induced responses. Also, the production of one of two important plant hormones, salicylic acid, responded differently to single or dual herbivory in a unique pattern for each of the plant populations. These different plant responses subsequently negatively affected a next caterpillar on the same plant; M. brassicae growth was impaired on plants which had been fed upon by both aphids and caterpillars, in comparison to control plants. These field and greenhouse studies thus show the implications of dual herbivory beyond effects in the plant; it affects subsequent herbivory, and through a chain of plant-mediated insect interactions, the dynamics of a whole insect community.

    In the sixth chapter we show that variation in insect community dynamics can last beyond the moment that the insects were present, even across years. In this field study, the naturally occurring carnivore community influenced the carnivore community composition a year later. Importantly, the herbivore community affected plant fitness across years (but not within years). We propose that such legacy effects are mediated by plant traits, which vary upon insect induction in the first year, and affect the insect community in the next year.

    Finally, the history of all insect attacks to a plant up until that moment shape the future insect community by influencing the colonisation of insect species on the plant. Moreover, also plant ontogeny plays a role in shaping the insect community; plant-mediated responses to herbivory at different plant ages resulted in different insect colonisation rates. The most important conclusion from this last data chapter (Chapter 7) is that the two processes, insect community history and plant ontogeny, are non-additive and affect the colonisation of insect species in the same (synergistic) or opposite (antagonistic) direction.

    By framing my study results in a time line from minutes to months to years, I show in the general discussion (Chapter 8) that the consequences of dual herbivory for subsequently arriving insects are connected at different time scales. Plant responses to herbivory can occur within hours to days, which affect herbivore choices and performance in the following days and weeks. In their turn, variation of a few days in arrival time of insects may change how plants respond and prioritize their responses to insects throughout the rest of the season. The insects that subsequently arrive on a dual-herbivore induced plant may change the plant phenotype even further and through a chain of insect-plant interactions, the effects on the insects and the plant can last throughout the season, and even across seasons. Furthermore, various factors such as the species of the attacking insect and its feeding guild, the timing after previous attack and the plant age at which herbivory occurs, as well as the genotypic background of the plant, all affect the outcomes of dynamic insect-plant interactions.

    The results presented in this thesis thus contribute to the knowledge and interpretation of plant interactions with multiple herbivores. As plants are seldom attacked by a single herbivore, this implies that we have to take into account that multiple herbivory is not the same as the additive effects of single herbivores, and that this has long-lasting consequences for the insect community and the plant. To further understand how plants and insects have adapted to such a dynamic environment, I suggest future research to focus even more on the kinetics of plant physiological responses to dual attack, and to aim at answering the question of how predictable insect communities on a plant really are.

    Plant responses to multiple herbivory : phenotypic changes and their ecological consequences
    Li, Yehua - \ 2016
    Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Rieta Gols. - Wageningen : Wageningen University - ISBN 9789462578043 - 165
    brassica oleracea - brevicoryne brassicae - aphidoidea - caterpillars - insect pests - pest resistance - defence mechanisms - phenotypes - insect plant relations - parasitoids - natural enemies - herbivore induced plant volatiles - plant-herbivore interactions - genetic variation - brassica oleracea - brevicoryne brassicae - aphidoidea - rupsen - insectenplagen - plaagresistentie - verdedigingsmechanismen - fenotypen - insect-plant relaties - parasitoïden - natuurlijke vijanden - herbivoor-geinduceerde plantengeuren - plant-herbivoor relaties - genetische variatie

    This thesis explores whether aphid-infestation interferes with the plant response to chewing herbivores and whether this impacts performance and behaviour of individual chewing insect herbivores and their natural enemies, as well as the entire insect community. I investigated this using three wild cabbage populations (Brassica oleracea) that are known to differ in inducible secondary chemistry, to reveal whether patterns were consistent.

    A literature review on recent developments in the field of plant interactions with multiple herbivores (Chapter 2) addressed how plant traits mediate interactions with various species of the associated insect community and their dynamics. In addition, the mechanisms underlying phenotypic changes in response to different herbivores were discussed from the expression of defence-related genes, phytohormones and secondary metabolites in plants to their effects on the performance and behaviour of individual insects as well as the entire insect community. In Chapter 3, I investigated the effects of early-season infestation by the aphid Brevicoryne brassicae on the composition and dynamics of the entire insect community throughout the season in a garden experiment replicated in two consecutive years. Aphid infestation in the early season only affected a subset of the community, i.e. the natural enemies of aphids, but not the chewing herbivores and their natural enemies. Moreover, the effects were only significant in the first half (June & July), but waned in the second half of the season (August & September). The effect of aphid infestation on the community of natural enemies also varied among the cabbage populations. Chapter 4 investigated the effects of aphid infestation on plant direct defences against chewing herbivores in laboratory experiments by comparing the performance of chewing herbivores and their parasitoids on aphid-infested and aphid-free plants. The performance of the specialist herbivore Plutella xylostella and its parasitoid Diadegma semiclausum was better on plants infested with aphids than on aphid-free plants, whereas the performance of the generalist herbivore Mamestra brassicae and its parasitoid Microplitis mediator was not affected by aphid infestation. These results suggest that aphid induced changes in plant traits may differentially affect the performance of leaf-chewing herbivore species attacking the same host plant, and also varied among the cabbage populations. Chapter 5 examined the effects of B. brassicae aphid infestation on plant indirect defences against chewing herbivores. In a two-choice olfactometer bioassay, preference behaviour for volatiles emitted by plants infested with hosts alone and those emitted by plants infested with aphids and hosts was compared for D. semiclausum and M mediator, larval endoparasitoids of caterpillars of P. xylostella and M. brassicae, respectively. In addition, the headspace volatiles emitted by host-infested and dually-infested plants were collected and analyzed. Co-infestation with aphids differentially affected volatile-mediated foraging behaviour of the two parasitoid species in an infestation period-dependent manner. Diadegma semiclausum preferred dually infested plants over host-infested plants when aphids infested the plants for a short time period, i.e. 7 days, but the volatile preference of D. semiclausum was reversed when aphid infestation was extended to 14 days. In contrast, M. mediator consistently preferred volatiles emitted by the dually-infested plants over those emitted by host-infested plants. The patterns of preference behaviour of the two wasp species were consistent across the three cabbage populations. Interestingly, the emission rate of most volatile compounds was reduced in plants dually-infested with caterpillars and aphids compared to singly-infested with caterpillars. This study showed that aphid infestation increased plant indirect defences against caterpillars, but depended on the aphid infestation period and specific caterpillar-parasitoid association. We hypothesized a negative interference of aphid infestation on plant defences against chewing herbivores based on previously reported SA-JA antagonism. In Chapter 6, we assessed the activation of SA and JA signaling pathways in plants infested by both aphids (B. brassicae) and various caterpillar species (P. xylostella, M. brassicae and Pieris brassicae) in different time sequences by quantifying transcription levels of the SA- and JA-responsive marker genes, PR-1 and LOX respectively. The results did not provide support for SA-JA antagonism. Compared to single infestation with each of the herbivore species, dual infestation with aphid and caterpillars had no interactive effects on the transcription levels of the SA- and JA-responsive maker genes, regardless of the temporal sequence of aphid and caterpillar attack, or the identity of the attacking caterpillar species.

    The findings of this thesis contribute to our understanding of plant responses to herbivory by insect species belonging to different feeding guilds and their ecological effects on other associated community members. Aphid infestation may interfere with plant direct and indirect defences against leaf-chewing herbivores at the individual species level, but the effects are species-specific and also depend on the infestation period of aphids. Early-season aphid infestation may further affect the composition of the insect community, but the effect is smaller influencing only a subset of the community compared to early infestation by chewing herbivores. The molecular mechanism underlying plant responses to both phloem-feeding and leaf-chewing herbivores are complex and require the investigation of a range of genes involved in JA- and SA-mediated defence signal transduction. Plant interact with multiple herbivores at different levels of biological organization ranging from the subcellular level to the individual and the community level, and an integrated multidisciplinary approach is required to investigate plant-insect interactions.

    Plants under dual attack : consequences for plant chemistry and parasitoid behavior
    Ponzio, C.A.M. - \ 2016
    Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Rieta Gols. - Wageningen : Wageningen University - ISBN 9789462577718 - 191
    016-3954 - brassica nigra - insect pests - pieris brassicae - parasitoids - parasitoid wasps - cotesia glomerata - defence mechanisms - phytochemistry - herbivore induced plant volatiles - insect plant relations - animal behaviour - multitrophic interactions - plant pathogenic bacteria - xanthomonas campestris - brassica nigra - insectenplagen - pieris brassicae - parasitoïden - sluipwespen - cotesia glomerata - verdedigingsmechanismen - fytochemie - herbivoor-geinduceerde plantengeuren - insect-plant relaties - diergedrag - multitrofe interacties - plantenziekteverwekkende bacteriën - xanthomonas campestris

    Though immobile, plants are members of complex environments, and are under constant threat from a wide range of attackers, which includes organisms such as insect herbivores or plant pathogens. Plants have developed sophisticated defenses against these attackers, and include chemical responses such as the production of and emission of volatile compounds, which can be used by natural enemies of the herbivores to locate herbivore-infested plants. While the production and use of induced volatiles by foraging natural enemies has been well studied in a single attacker/natural enemy combination, in natural situations it is common for a plant to be challenged by multiple attackers. However there is little knowledge about what happens during multiple attack, especially when one of the secondary attackers is a plant pathogen.

    The aim of this thesis was to explore how dual attack modifies plant chemistry, and how changes in the emitted volatile blends then affect the behavior of foraging parasitoid, with a strong focus on the effects of non-host herbivore density and plant pathogen challenge. This study focused on the system consisting of black mustard plants (Brassica nigra), the large cabbage white butterfly, Pieris brassicae, and its larval parasitoid, Cotesia glomerata. Butterfly eggs, Brevicoryne brassicae aphids and the plant pathogen Xanthomonas campestris were used as secondary attackers. The results presented in the thesis showed that C. glomerata wasps are attracted to host-infested plants, irrespective of the presence and identity of the non-host attacker. However, when the responses of several parasitoid species to volatiles of plants infested with Pieris and/or aphids were compared, the wasp species were not equally affected and aphid infestation altered, in a density-dependent manner, the foraging behavior of all three species. In terms of volatiles, while differences in induced blends could be seen between individual attackers, these effects disappeared when plants were subjected to dual attack with caterpillars, and in the case of infestation with different aphid densities, non-linear volatile responses were revealed. Furthermore, the effects of dual attack by aphids and caterpillars were present at the level of leaf chemistry. Single and dual herbivory, as well as aphid density, led to metabolome-wide effects, driven mainly by changes in glucosinolates, sugars and antioxidant-related metabolites. The effect of pathogen challenge was further assessed by comparing the effects of virulent and avirulent pathovars, and results showed that both virulence and disease severity strongly affected the induced plant volatile blend. Remarkably, C.glomerata wasps were strongly attracted to volatiles of all the pathogen-challenged treatments, even in the absence of hosts.

    The data presented in this thesis contribute to our understanding of how dual attack affects the chemistry of B. nigra plants, and modifies plant interactions with the natural enemies of attacking herbivores. This work reveals that plant pathogen challenge can affect volatile-mediated tritrophic interactions, and shows that focusing only on general species-specific effects of dual attack is too simplistic of an approach. The outcomes of this thesis contribute to our understanding of how plants modulate their defense responses against multiple attackers.

    Regulation of cucumber (Cucumis sativus) induced defence against the two-spotted spider mite (Tetranychus urticae
    He, J. - \ 2016
    Wageningen University. Promotor(en): Harro Bouwmeester; Marcel Dicke, co-promotor(en): Iris Kappers. - Wageningen : Wageningen University - ISBN 9789462576810 - 211
    cucumis sativus - cucumbers - induced resistance - plant pests - tetranychus urticae - mites - defence mechanisms - herbivore induced plant volatiles - herbivory - metabolomics - terpenoids - genomics - cucumis sativus - komkommers - geïnduceerde resistentie - plantenplagen - tetranychus urticae - mijten - verdedigingsmechanismen - herbivoor-geinduceerde plantengeuren - herbivorie - metabolomica - terpenen - genomica

    Plants have evolved mechanisms to combat herbivory. These mechanisms can be classified as direct defences which have a negative influence on the herbivores and indirect defence that attracts natural enemies of the attacking herbivores. Both direct and indirect defences can be constantly present or induced upon attack. This study, using cucumber (Cucumis sativus) and the two-spotted spider mite (Tetranychus urticae) as model, aimed to reveal the molecular mechanisms underlying the induced defence during herbivory, with emphasis on transcriptional changes and the involved TFs, the enzymatic function of the genes associated with volatile biosynthesis, and their promoters which regulate their expression.

    Host location by hyperparasitoids: an ecogenomic approach
    Zhu, F. - \ 2015
    Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Erik Poelman. - Wageningen : Wageningen University - ISBN 9789462574441 - 191
    insect-plant relaties - insectenplagen - herbivorie - parasitoïden - planten - verdedigingsmechanismen - symbionten - plant-herbivoor relaties - herbivoor-geinduceerde plantengeuren - hyperparasitoïden - insect plant relations - insect pests - herbivory - parasitoids - plants - defence mechanisms - symbionts - plant-herbivore interactions - herbivore induced plant volatiles - hyperparasitoids

    It is fascinating that our ecological systems are structured by both direct and indirect species interactions. In terrestrial ecosystems, plants interact with many species of insects that include both harmful herbivores and beneficial natural enemies of herbivores. During the last 30 years, substantial progress has been made in different plant-insect systems regarding plant trait-mediated species interactions in a tritrophic context. However, plant-based food webs generally consist of more than three trophic levels. For example, hyperparasitoids are parasitic wasps at the fourth trophic level within the plant-associated insect community. They parasitize larvae or pupae of primary parasitoids that are broadly used in biological pest control programmes. Surprisingly, the cues that hyperparasitoids use for host location have remained largely unknown.

    The studies presented in this thesis aimed to investigate the cues that are used by hyperparasitoids in host location using an ecogenomic approach that combines metabolomic, transcriptomic and proteomic tools with behavioural studies and field experiments. In addition, we addressed the role of herbivore-associated organisms in plant-mediated indirect species interactions. A naturally existing study system of the Brassica oleracea plant-based food web, including four trophic levels was used. In this system, the two herbivorous insect species, Pieris brassicae and P. rapae, are specialists on Brassica plants. The plants emit herbivore-induced plant volatiles (HIPVs) in response to Pieris caterpillar feeding damage which results in attraction of natural enemies of the herbivores, i.e. Cotesia wasps. These parasitic wasps, in turn, are attacked by hyperparasitoids, such as Lysiba nana. The results presented in this thesis show that hyperparasitoids also use HIPVs for host searching. Interestingly, they are especially attracted by plant odours induced by parasitized caterpillars. Moreover, hyperparasitoids can also use caterpillar body odours to find their hosts at close distance. These findings indicate that infochemicals are the major cues that mediate host searching behaviour of hyperparastioids. Similar to other herbivore-associated organisms, parasitoid larvae feeding inside a herbivore host can induce both behavioral and physiological changes in the host. To further investigate how parasitoid larvae indirectly affect plant responses to herbivory and plant volatile-mediated multitrophic interactions, the role of caterpillar labial salivary glands in plant-hyperparasitoid interactions were investigated. The secretions of labial saliva were eliminated by using an ablation technique. Remarkably, the results show that when the labial salivary glands of the caterpillars were completely removed, plants induced by either unparasitized or Cotesia glomerata-parasitized caterpillars were equally attractive to the hyperparasitoid. Moreover, plants became less attractive to the hyperparasitoid when damaged by ablated caterpillars compared to plants damaged by mock-treated caterpillars and the hyperparasitoids were not able to distinguish between volatiles emitted by herbivore-damaged plants and undamaged control plants when caterpillar salivary glands had been removed. These results suggest that parasitism alters the composition of labial saliva of parasitized caterpillar, which thereby alters the plant phenotype and subsequently plant-hyperparasitoid interactions. The outcomes of this thesis contribute to our understanding of the role of infochemicals in foraging decisions of hyperparasitoids.

    Getting prepared for future attack : induction of plant defences by herbivore egg deposition and consequences for the insect community
    Pashalidou, F.G. - \ 2015
    Wageningen University. Promotor(en): Marcel Dicke; Joop van Loon, co-promotor(en): Nina Fatouros. - Wageningen : Wageningen University - ISBN 9789462574120 - 168
    insect-plant relaties - planten - insectenplagen - herbivorie - verdedigingsmechanismen - geïnduceerde resistentie - herbivoor-geinduceerde plantengeuren - ovipositie - natuurlijke vijanden - brassica - pieris brassicae - trofische graden - sluipwespen - hyperparasitoïden - insectengemeenschappen - insect plant relations - plants - insect pests - herbivory - defence mechanisms - induced resistance - herbivore induced plant volatiles - oviposition - natural enemies - brassica - pieris brassicae - trophic levels - parasitoid wasps - hyperparasitoids - insect communities

    Plants have evolved intriguing defences against insect herbivores. Compared to constitutive Plants have evolved intriguing defences against insect herbivores. Compared to constitutive defences that are always present, plants can respond with inducible defences when they are attacked. Insect herbivores can induce phenotypic changes in plants and consequently these changes may differentially affect subsequent attackers and their associated insect communities. Many studies consider herbivore-feeding damage as the first interaction between plants and insects. The originality of this study was to start with the first phase of herbivore attack, egg deposition, to understand the consequences of plant responses to eggs on subsequently feeding caterpillars and their natural enemies. The main plant species used for most of the experiments was Brassica nigra (black mustard), which occurs naturally in The Netherlands. The main herbivore used was the lepidopteran Pieris brassicae, which lays eggs in clusters and feeds on plants belonging to the Brassicaceae family. This study investigated plant-mediated responses to oviposition and their effects on different developmental stages of the herbivore, such as larvae and pupae. Furthermore, the effects of oviposition were extended to four more plant species of the same family, and to higher trophic levels including parasitoids and hyperparasitoids. The experiments were conducted under laboratory, semi-field and field conditions. This study shows that B. nigra plants recognize the eggs of P. brassicae and initiate resistance against subsequent developmental stages of the herbivore. Interestingly, plant responses to oviposition were found to be species specific. Plants did not respond to egg deposition by another herbivore species, the generalist moth Mamestra brassicae. Moreover, most of the Brassicaceae species tested were found to respond to P. brassicae eggs, which indicates that plant responses against oviposition are more common among the family of Brassicaceae. To assess effects on other members of the food chain, the effects of oviposition on plant volatile emission and the attraction of parasitic wasps, such as the larval parasitoid Cotesia glomerata, were tested. It was shown that the wasps were able to use the blend of plant volatiles, altered by their hosts’ oviposition, to locate young caterpillars just after hatching from eggs. The observed behaviour of the wasps was associated with higher parasitism success and higher fitness in young hosts. Similar results were obtained in a field experiment, where plants infested with eggs and caterpillars attracted more larval parasitoids and hyperparasitoids and eventually produced more seeds compared to plants infested with caterpillars only. This study shows that an annual weed like B. nigra uses egg deposition as reliable information for upcoming herbivory and responds accordingly with induced defences. Egg deposition could influence plant-associated community members at different levels in the food chain and benefit seed production. As the importance of oviposition on plant-herbivore interactions is only recently discovered, more research is needed to elucidate the mechanisms that underlie such plant responses and how these interactions affect the structure of insect communities in nature.

    Tales on insect-flowering plant interactions : the ecological significance of plant responses to herbivores and pollinators
    Lucas Gomes Marques Barbosa, D. - \ 2015
    Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462572119 - 207
    bloeiende planten - insecten - insect-plant relaties - plant-herbivoor relaties - herbivoren - bestuivers (dieren) - trofische graden - parasitoïden - herbivoor-geinduceerde plantengeuren - flowering plants - insects - insect plant relations - plant-herbivore interactions - herbivores - pollinators - trophic levels - parasitoids - herbivore induced plant volatiles - cum laude
    cum laude graduation
    Induction of indirect plant defense in the context of multiple herbivory : gene transcription, volatile emission, and predator behavior
    Menzel, T.R. - \ 2014
    Wageningen University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462571297 - 146
    planten - plaagresistentie - geïnduceerde resistentie - verdedigingsmechanismen - multitrofe interacties - phaseolus lunatus - mijten - tetranychus urticae - roofmijten - phytoseiulus persimilis - voedingsgedrag - genen - transcriptie - genexpressie - herbivoor-geinduceerde plantengeuren - plants - pest resistance - induced resistance - defence mechanisms - multitrophic interactions - phaseolus lunatus - mites - tetranychus urticae - predatory mites - phytoseiulus persimilis - feeding behaviour - genes - transcription - gene expression - herbivore induced plant volatiles

    Abstract

    Plants live in complex environments and are under constant threat of being attacked by herbivorous arthropods. Consequently plants possess an arsenal of sophisticated mechanisms in order to defend themselves against their ubiquitous attackers. Induced indirect defenses involve the attraction of natural enemies of herbivores, such as predators and parasitoids. Predators and parasitoids use odors emitted by damaged plants that serve as a “cry for help” to find their respective prey or host herbivore. The aim of this thesis was to use a multidisciplinary approach, with focus on molecular and chemical methods, combined with behavioral investigations, to elucidate the mechanisms of plant responses to multiple herbivory that affect a tritrophic system consisting of a plant, an herbivore and a natural enemy.

    Induced plant defenses are regulated by a network of defense signaling pathways in which phytohormones act as signaling molecules. Accordingly, simulation of herbivory by exogenous application of phytohormones and actual herbivory by the two-spotted spider mite Tetranychus urticae affected transcript levels of a defense gene involved in indirect defense in Lima bean. However, two other genes involved in defense were not affected at the time point investigated. Moreover, application of a low dose of JA followed by minor herbivory by T. urticae spider mites affected gene transcript levels and emissions of plant volatiles commonly associated with herbivory. Only endogenous phytohormone levels of jasmonic acid (JA), but not salicylic acid (SA), were affected by treatments. Nevertheless, the low-dose JA application resulted in a synergistic effect on gene transcription and an increased emission of a volatile compound involved in indirect defense after herbivore infestation.

    Caterpillar feeding as well as application of caterpillar oral secretion on mechanically inflicted wounds are frequently used to induce plant defense against biting-chewing insects, which is JA-related. Feeding damage by two caterpillar species caused mostly identical induction of gene transcription, but combination of mechanical damage and oral secretions of caterpillars caused differential induction of the transcription of defense genes. Nevertheless, gene transcript levels for plants that subsequently experienced an infestation by T. urticae were only different for a gene potentially involved in direct defense of plants that experienced a single event of herbivory by T. urticae. Indirect defense was not affected. Also sequential induction of plant defense by caterpillar oral secretion and an infestation by T. urticae spider mites did not interfere with attraction of the specialist predatory mite P. persimilis in olfactometer assays. The predator did distinguish between plants induced by spider mites and plants induced by the combination of mechanical damage and caterpillar oral secretion but not between plants with single spider mite infestation and plants induced by caterpillar oral secretion prior to spider mite infestation. The composition of the volatile blends emitted by plants induced by spider mites only or by the sequential induction treatment of caterpillar oral secretion followed by spider mite infestation were similar. Consequently, the induction of plant indirect defense as applied in these experiments was not affected by previous treatment with oral secretion of caterpillars. Moreover, herbivory by conspecific T. urticae mites did not affect gene transcript levels or emission of volatiles of plants that experienced two bouts of herbivore attack by conspecific spider mites compared to plants that experienced only one bout of spider mite attack. This suggests that Lima bean plants do no increase defense in response to sequential herbivory by T. urticae.

    In conclusion, using a multidisciplinary approach new insights were obtained in the mechanisms of induction of indirect plant defense and tritrophic interactions in a multiple herbivore context, providing helpful leads for future research on plant responses to multiple stresses.

    Temporal dynamics of induced responses in Brassica juncea
    Mathur, V. - \ 2012
    Wageningen University. Promotor(en): Louise Vet; N.M. van Dam, co-promotor(en): A.S. Reddy. - S.l. : s.n. - ISBN 9789461733085 - 219
    brassica juncea - insectenplagen - insect-plant relaties - gastheer parasiet relaties - herbivoren - brassicaceae - entomologie - ecologie - herbivoor-geinduceerde plantengeuren - brassica juncea - insect pests - insect plant relations - host parasite relationships - herbivores - brassicaceae - entomology - ecology - herbivore induced plant volatiles

    Plants induce a suite of direct and indirect responses after herbivore attack. For utilizing these plant attributes in agriculture, it is important to compare the relative importance of these two defence types in the same plant species. Precise timing of these responses is vital for their effect on the herbivores feeding on the plant.
    In my thesis, I present an analysis of the temporal dynamics of various direct and indirect responses in Indian/ Brown mustard, Brassica juncea due to herbivory by a generalist Spodoptera spp, a specialist Plutella xylostella or both of these herbivores together. Morphological (leaf size and trichome densities) and chemical (volatiles, glucosinolates, amino acids, sugars) responses were analysed over temporal range of 24 hours to 20 days. The effect of direct systemic responses was assessed using a specialist (Plutella xylostella) and a generalist (Spodoptera litura) herbivore. In addition, to investigate indirect responses, orientation experiments were conducted on the generalist (Cotesia marginiventris) and specialist (C. plutellae) parasitoids. Results were validated with analysis of genes involved in signalling and biosynthetic pathways that govern the expression of these responses.
    For the first time, the presence of extrafloral nectar (EFN) in Brassicaceae is being reported. Their sugar and amino acid contents were measured in five different varieties of B. juncea. The indirect function of these EFN droplets was assessed by testing their inducibility and attraction and survival of parasitoids on them.
    These studies thus show that although morphological responses are slower than chemical responses, they also contribute to induced plant resistance in a relatively short time span. Moreover, before considering induced responses as resistance factors, their effect should be assessed at different points in time with both generalist and specialist herbivores.

    Herbivore-induced indirect defense of Arabidopsis : ecogenomic approach to the role of infochemicals in parasitoid attraction
    Snoeren, T.A.L. - \ 2009
    Wageningen University. Promotor(en): Marcel Dicke. - [S.l. : S.n. - ISBN 9789085853596 - 169
    arabidopsis - pieris rapae - verdedigingsmechanismen - herbivoren - jasmonzuur - herbivoor-geinduceerde plantengeuren - insect-plant relaties - transcriptomics - arabidopsis - pieris rapae - defence mechanisms - herbivores - jasmonic acid - herbivore induced plant volatiles - insect plant relations - transcriptomics
    Plants defend themselves against herbivorous insects with the induced production of volatiles that attract the enemies of the herbivores. In this thesis I used an ecogenomic approach to study the role of signal-transduction pathways that regulate the induction of herbivore-induced plant volatiles (HIPV) and the effects of HIPVs on parasitoid host-finding behavior. To this end, I have combined transcriptomics, metabolite analyses and insect behavioral analyses.

    Nine Arabidopsis thaliana accessions were screened for the emission of HIPVs. The accessions varied in the emission rate of Pieris rapae–induced volatiles after folivory or treatment with the herbivory-mimicking plant hormone jasmonic acid (JA). The relevance of this observed variation in the emission of JA-induced volatiles for host location was tested with Diadegma semiclausum parasitoids. Furthermore, the accessions also varied in transcript levels of genes that are (putatively) involved in the production of some of the recorded HIPV-compounds.
    The oxylipin JA is the key plant hormone involved in the induction of the HIPV-blend emitted in response to caterpillar folivory. Mutant plants affected in the oxylipin signal-transduction pathway were studied to assess the effects of JA and its oxylipin intermediates 12-oxo-phytodienoate (OPDA) and dinor-OPDA (dnOPDA) on HIPV emission and attraction of the parasitoid D. semiclausum. In contrast to the effect of JA on the induced production of HIPVs, dnOPDA and OPDA were found to have no and little effect, respectively. The HIPV-compound methyl salicylate was shown to be JA-regulated and its abundance in the headspace varied among accessions. The contribution of methyl salicylate to parasitoid attraction was investigated. Bioassays with P. rapae-infested transgenic plants, lacking MeSA production, showed that MeSA negatively influenced D. semiclausum host-finding behavior.
    Mutant plants were also studied to assess whether JA and its intermediates affected the induction of genes potentially involved in defense. The different oxylipins were shown to have distinct roles in induced defense signaling. Jasmonic acid had the strongest effect on transcript levels of defense-related genes from the oxylipin- and shikimate signal-transduction pathway. Minor roles were observed for OPDA and dnOPDA in the induction of one of these genes.

    Utilizing an ecogenomic approach has provided new insight into the mechanisms underlying insect-plant interactions and holds promising opportunities.


    Linking variation in plant defence to biodiversity at higher trophic levels: a multidisciplinary approach
    Poelman, E.H. - \ 2008
    Wageningen University. Promotor(en): Marcel Dicke; Louise Vet, co-promotor(en): Joop van Loon; N.M. van Dam. - [S.l.] : s.n. - ISBN 9789085049623 - 163
    brassica oleracea - cotesia - parasitoïden - verdedigingsmechanismen - hyperparasieten - trofische graden - gastheer parasiet relaties - pieris brassicae - insectenplagen - plant-herbivoor relaties - herbivoor-geinduceerde plantengeuren - brassica oleracea - cotesia - parasitoids - defence mechanisms - hyperparasites - trophic levels - host parasite relationships - pieris brassicae - insect pests - plant-herbivore interactions - herbivore induced plant volatiles - cum laude
    cum laude graduation (with distinction)
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