Staff Publications

Staff Publications

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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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Mothers in the woods: multitrophic interactions and oviposition preference in the bronze big Thaumastocoris pergrinus, a pest of Eucalyptus
Martínez, Gonzalo - \ 2017
University. Promotor(en): Marcel Dicke. - Wageningen : Wageningen University - ISBN 9789463436786 - 172
eucalyptus - forest plantations - forest pests - multitrophic interactions - biological control - hemiptera - oviposition - host plants - uruguay - insect plant relations - bosplantages - bosplagen - multitrofe interacties - biologische bestrijding - ovipositie - waardplanten - insect-plant relaties

The bronze bug is an important pest of Eucalyptus trees. Originally restricted to Australia, it has become an important pest of Eucalyptus plantations, colonizing in 15 years the major production areas worldwide. The aim of this thesis was to investigate the factors affecting the oviposition behavior of the bronze bug within a multitrophic system comprised of its host plant (Eucalyptus spp.), a common co-occurring sap-feeder (Glycaspis brimblecombei) and a specialist egg parasitoid (Cleruchoides noackae). I assessed the life parameters of this species in a newly developed rearing. Based on the preference-performance hypothesis, I tested the effects of host-plant quality, conspecifics, or the infestation by a potential competitor on preference-performance correlations of the bronze bug. The egg parasitoid (C. noackae) was introduced, reared, and released. Finally, I assessed host-selection behavior of the parasitoid, testing its responses towards different contact cues. The findings of this investigation provided new insights on the oviposition behavior by true bugs, and towards the development of management strategies for T. peregrinus.

Host-plant resistance to western flower thrips in Arabidopsis
Thoen, Manus P.M. - \ 2016
University. Promotor(en): Marcel Dicke; Harro Bouwmeester, co-promotor(en): Maarten Jongsma. - Wageningen : Wageningen University - ISBN 9789462578807 - 191
arabidopsis thaliana - host plants - insect pests - frankliniella occidentalis - defence mechanisms - pest resistance - genomics - genome analysis - host-seeking behaviour - optical tracking - data analysis - insect plant relations - waardplanten - insectenplagen - verdedigingsmechanismen - plaagresistentie - genomica - genoomanalyse - gedrag bij zoeken van een gastheer - optisch sporen - gegevensanalyse - insect-plant relaties

Western flower thrips is a pest on a large variety of vegetable, fruit and ornamental crops. The damage these minute slender insects cause in agriculture through feeding and the transmission of tospoviruses requires a sustainable solution. Host-plant resistance is a cornerstone of Integrated Pest Management (IPM). Plants have many natural defense compounds and morphological features that aid in the protection against herbivorous insects. However, the molecular and physiological aspects that control host-plant resistance to thrips are largely unknown.

A novel and powerful tool to study host-plant resistance to insects in natural populations is genome-wide association (GWA) mapping. GWA mapping provides a comprehensive untargeted approach to explore the whole array of plant defense mechanisms. The development of high-throughput phenotyping (HTP) systems is a necessity when large plant panels need to be screened for host-plant resistance to insects. An automated video-tracking platform that could screen large plant panels for host-plant resistance to thrips, and dissect host-plant resistance to thrips in component traits related to thrips behavior, was developed. This phenotyping platform allows the screening for host-plant resistance against thrips in a parallel two-choice setup using EthoVision tracking software. The platform was used to establish host-plant preference of thrips with a large plant population of 345 wild Arabidopsis accessions (the Arabidopsis HapMap population) and the method was optimized with two extreme accessions from this population that differed in resistance to thrips. This method can be a reliable and effective high throughput phenotyping tool to assess host-plant resistance to thrips in large plant populations. EthoAnalysis, a novel software package was developed to improve the analyses of insect behavior. There were several benefits from using EthoAnalysis to analyze EthoVision data. The detailed event statistics that could be extracted from EthoAnalysis allows researchers to distinguish detailed differences in moving and feeding behavior of thrips. The potential of this additional information is discussed in the light of quantitative genetic studies.

Stress resistance was studied in the HapMap population on a total of 15 different biotic and abiotic stresses ranging from biotic stresses like insects and nematodes, to abiotic stresses like drought and salt. A multi-trait GWA study to unravel the genetic architecture underlying plant responses to the different stresses was performed. A genetic network in this study revealed little correlation between the plant responses to the different insect herbivores studied (aphids, whiteflies, thrips and caterpillars). For thrips resistance a weak positive correlation with resistance to drought stress and Botrytis, and a negative correlation with resistance to parasitic plants were observed. One of the surprising outcomes of this study was the absence of shared major QTLs for host-plant resistance and abiotic stress tolerance mechanisms. RESISTANCE METHYLATED GENE 1 (RMG1) was one of the candidate genes in this multi-trait GWA study that could be controlling shared resistance mechanisms against many different stresses in Arabidopsis. RMG1 is a nucleotide-binding site Leucine-rich repeat (NB-LRR) disease resistance protein and its potential relation to several resistance/tolerance traits was successfully demonstrated with T-DNA insertion lines.

The 15 stresses were used in a comparison with a metabolomics dataset on this Arabidopsis HapMap population. It was discovered that levels of certain aliphatic glucosinolates correlated positively with the levels of resistance to thrips. This correlation was further investigated with the screening of a RIL (Recombinant Inbred Line) population for resistance to thrips, several knockout mutants and the analysis of co-localization of GWA mapping results between glucosinolates genes and thrips resistance. In a GWA analysis, the C4 alkenyl glucosinolates that correlated the strongest with thrips resistance mapped to the genomic regions containing genes known to regulate the biosynthesis of these compounds. However, thrips resistance did not co-localize with any of the GSL genes, unless a correction for population stratification was omitted. Additional screening of a Cvi x Ler RIL population showed a QTL for thrips resistance on chromosome 2, but no co-localization with any known glucosinolate genes, nor with thrips resistance loci identified by GWA mapping. Knock-out mutants and overexpressors of glucosinolate synthesis genes could also not confirm a causal link between glucosinolates and resistance to thrips. It is possible that the crucial factors that control resistance to thrips may not have been present in sufficient quantities or in the right combinations in the mutants, RILs and NIL screened in this study. Alternatively, the correlation between thrips feeding damage and glucosinolate profiles could be based on independent geographical clines. More research should be conducted to assess which of these explanations is correct.

In the general discussion, the results from this thesis are discussed in a broader perspective. Some prototypes of new phenotyping platforms that could further aid screening for resistance to thrips in the future are presented. Natural variation in host-plant resistance to thrips is compared to the variation in host-plant resistance to aphids and caterpillars. The geographic distribution of host-plant resistance to thrips is not evident in the other insects, in line with the distribution of glucosinolate profiles and other climate factors. The chapter concludes with some suggestions for future research in the field of host-plant resistance to thrips.

Plant responses to multiple herbivory : phenotypic changes and their ecological consequences
Li, Yehua - \ 2016
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 - 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
University. Promotor(en): Marcel Dicke, co-promotor(en): Rieta Gols. - Wageningen : Wageningen University - ISBN 9789462577718 - 191 p.
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 - insectenplagen - parasitoïden - sluipwespen - verdedigingsmechanismen - fytochemie - herbivoor-geinduceerde plantengeuren - insect-plant relaties - diergedrag - multitrofe interacties - plantenziekteverwekkende bacteriën

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.

Unraveling molecular mechanisms underlying plant defense in response to dual insect attack : studying density-dependent effects
Kroes, A. - \ 2016
University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462577756 - 265 p.
016-3953 - arabidopsis thaliana - insect pests - herbivory - pest resistance - defence mechanisms - insect plant relations - molecular plant pathology - density - insectenplagen - herbivorie - plaagresistentie - verdedigingsmechanismen - insect-plant relaties - moleculaire plantenziektekunde - dichtheid

In the field, plants suffer from attack by herbivorous insects. Plants have numerous adaptations to defend against herbivory. Not only do these defense responses reduce performance of the feeding herbivore, they also result in the attraction of natural enemies of herbivores.

The majority of studies investigating plant-insect interactions addressed mainly the effects of attack by a single herbivore species on induced plant defenses. However, because plants are members of complex communities, plants are exposed to different insect attackers at the same time. Moreover, attacks by different herbivores interact at different levels of biological organization, ranging from the level of gene expression, phytohormone production and biochemical changes up to the individual level. Effects of plant responses to feeding by two or more herbivore species simultaneously might cascade through the community and thereby affect insect community composition.

The induction of plant defense responses is regulated by a network of signaling pathways that mainly involve the phytohormones jasmonic acid (JA), salicylic acid (SA) and ethylene (ET). The signaling pathways of the two phytohormones SA and JA interact antagonistically, whereas JA and ET signaling pathways can interact both synergistically and antagonistically in regulating plant defense responses. In general, JA-mediated signaling underlies defense responses against leaf-chewing herbivores, such as caterpillars, whereas phloem-feeding insects, such as aphids, mainly induce SA-regulated defenses.

When caterpillars and aphids simultaneously feed on the same host plant, crosstalk between phytohormonal signaling pathways may affect the regulation of plant defenses. Consequently, multiple insect herbivores feeding on plants interact indirectly through plant-mediated effects. Studies investigating molecular mechanisms underlying interference by multiple attacking insects with induced plant defenses will benefit studies on the ecological consequences of induced plant responses.

The aim of this thesis was to elucidate molecular mechanisms that underlie plant-mediated interactions between attacking herbivores from different feeding guilds, namely Brevicoryne brassicae aphids and Plutella xylostella caterpillars.

Because herbivore density affects the regulation of plant defense responses, it may also influence the outcome of multiple insect-plant interactions. To study if modulation of induced plant defenses in response to dual insect attack depends on insect density, plants were infested with two densities of aphids.

Responses of Arabidopsis thaliana plants to simultaneous feeding by aphids and caterpillars were investigated by combining analyses of phytohormone levels, defense gene expression, volatile emission, insect performance and behavioral responses of parasitoids. To better predict consequences of interactions between plants and multiple insect attackers for herbivore communities, the regulation of defense responses against aphids and caterpillars was also studied in the ecological model plant wild Brassica oleracea.

Transcriptomic changes of plants during multiple insect attack and their consequences for the plant’s interactions with members of the associated insect community take place at different time scales. Direct correlation of transcriptomic responses with community development is, therefore, challenging. However, detailed knowledge of subcellular mechanisms can provide tools to address this challenge.

One of the objectives of this thesis, therefore, was to investigate the involvement of phytohormonal signaling pathways and their interactions during defense responses against caterpillars or aphids at different densities, when feeding alone or simultaneously on the model plant A. thaliana. The studies show that aphids at different densities interfere in contrasting ways with caterpillar-induced defenses, which required both SA- and JA-signal-transduction pathways. Transcriptional analysis revealed that expression of the SA transcription factor gene WRKY70 was differentially affected upon infestation by aphids at low or high densities. Interestingly, the expression data indicated that a lower expression level of WRKY70 led to significantly higher MYC2 expression through SA-JA crosstalk. Based on these findings, it is proposed that by down-regulating WRKY70 expression, the plant activates JA-dependent defenses which could lead to a higher resistance against aphids and caterpillars.

Plutella xylostella caterpillars also influenced plant defense responses when feeding simultaneously with aphids. Caterpillar feeding affected aphid-induced defenses which had negative consequences for aphid performance. Induction of both ET- and JA-mediated defense responses is required for this interference. Moreover, aphid density also played an important role in the modulation by P. xylostella of aphid-induced defenses: P. xylostella caterpillars induced changes in levels of JA and its biologically active from, JA-Ile, only when feeding simultaneously with aphids at a high density.

To study the overall effect of dual herbivory on induced plant defenses, not only interference with induced direct defense, but also with induced indirect defenses was addressed in A. thaliana. We found a significant preference of the aphid parasitoid Diaeretiella rapae for volatiles from aphid-infested A. thaliana wild-type plants and ein2-1 (ET-insensitive) mutants. Interestingly, simultaneous feeding by P. xylostella caterpillars on wild-type plants increased D. rapae’s preference for odors from aphid-infested plants. However, upon disruption of the ET-signaling pathway, D. rapae did not distinguish between ein2-1 mutants infested by aphids or by both aphids and caterpillars. This showed that intact ET signaling is needed for caterpillar modulation of the attraction of D. rapae parasitoids.

On the other hand, attraction of the caterpillar parasitoid Diadegma semiclausum to volatiles emitted by A. thaliana plants simultaneously infested by caterpillars and aphids was influenced by the density of the feeding aphids. Biosynthesis and emission of the terpene (E,E)-α-farnesene could be linked to the observed preference of D. semiclausum parasitoids for the HIPV blend emitted by plants dually infested by caterpillars and aphids at a high density, compared to dually infested plants with a low aphid density.

Transcriptomic changes in the response of A. thaliana wild-type plants to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids compared to plants infested by P. xylostella caterpillars alone were assessed using a microarray analysis. I particularly addressed the question whether the transcriptomic response to simultaneously attacking aphids and caterpillars was dependent on aphid density and time since initiation of herbivory. The data show that in response to simultaneous feeding by P. xylostella caterpillars and B. brassicae aphids the number of differentially expressed genes was higher compared to plants on which caterpillars had been feeding alone. Additionally, specific genes were differentially expressed in response to aphids feeding at low or high density. Cluster analysis showed that the pattern of gene expression over the different time points in response to dual infestation was also affected by the density of the attacking aphids. These results suggest that insects attacking at a high density cause an acceleration in plant responses compared to insects attacking at low density.

As a next step in the study of multiple interacting herbivores, I studied whether plant responses to dual herbivory have consequences for the performance of a subsequently arriving herbivore, Mamestra brassicae caterpillars. The ecological consequences of plant responses to dual herbivory cascading into a chain of interactions affecting other community members have remained unstudied so far. We used wild B. oleracea plants to evaluate dual herbivore-induced plant adaptations for subsequent herbivory. We found that simultaneous feeding by P. xylostella and B. brassicae resulted in different plant defense-related gene expression and differences in plant hormone levels compared to single herbivory, and this had a negative effect on subsequently arriving M. brassicae caterpillars. Differential induction of JA-regulated transcriptional responses to dual insect attack was observed which could have mediated a decrease in M. brassicae performance. The induction of plant defense signaling also affected both P. xylostella and B. brassicae performance. This study further helps to understand herbivore community build-up in the context of plant-mediated species interactions.

Altogether, findings from this thesis reveal a molecular basis underlying plant responses against multiple herbivory and provide insight in plant-mediated interactions between aphids and caterpillars feeding on plants growing in the field or used in agriculture.

Een bij-zonder kleurrijk landschap in Land van Wijk en Wouden : handreiking 2.0 voor inrichting en beheer voor bestuivende insecten
Rooij, S.A.M. van; Cormont, A. ; Geertsema, W. ; Haag, Martijn ; Opdam, P.F.M. ; Reemer, M. ; Spijker, J.H. ; Snep, R.P.H. ; Steingröver, E.G. ; Stip, Anthonie - \ 2016
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2720) - 41 p.
biodiversiteit - insect-plant relaties - regionale planning - ecologische hoofdstructuur - landschap - zuid-holland - bestuivers (dieren) - apidae - lepidoptera - biodiversity - insect plant relations - regional planning - ecological network - landscape - pollinators
Het programma Groene Cirkels (van Heineken) heeft het initiatief genomen tot het realiseren van een duurzaam bijenlandschap in het land van Wijk en Wouden. Deze handreiking wil een impuls geven aan het realiseren daarvan. In Nederland hebben we zo’n 350 verschillende wilde bestuivende insectensoorten. Door variatie in onder andere bloemvormen en kelkdiepte en bloeiseizoen zijn er gespecialiseerde insecten nodig, aangepast op bloeivorm en het bloeiseizoen. Ook moet bestuiving plaats kunnen vinden onder verschillende omstandigheden: bij goed en slecht weer, in vroege en late voorjaren. Nu eens doet de ene soort het goed, dan is er weer een andere die het meeste werk verzet. Diversiteit aan bijen, hommels en zweefvliegen geeft zekerheid voor bestuiving door de jaren heen.
Genetic variation in plant chemistry : consequences for plant-insect interactions
Geem, Moniek van - \ 2016
University. Promotor(en): Wim van der Putten; J.A. Harvey, co-promotor(en): Rieta Gols. - Wageningen : Wageningen University - ISBN 9789462576681 - 141 p.
phytochemistry - plant composition - genetic variation - insect plant relations - interactions - defence mechanisms - soil biology - fytochemie - plantensamenstelling - genetische variatie - insect-plant relaties - interacties - verdedigingsmechanismen - bodembiologie

Plants form the basis of many food webs and are consumed by a wide variety of organisms, including herbivorous insects. Over the course of evolution, plants have evolved mechanisms to defend themselves against herbivory, whereas herbivorous insects have evolved counter-mechanisms to overcome these defences (a.k.a. co-evolutionary arms races). Plant-insect interactions are not restricted to plants and their herbivores (bi-trophic interactions), but also involve natural enemies of the herbivores such as parasitoids and predators (tri-trophic interactions). Plant quality can affect the quality of the host or prey for parasitoids and predators, respectively. In addition, other plant traits are important in providing shelter, alternative food sources, or chemical cues that can be used for host/prey location. Moreover, as plants reside in both soil and air, they mediate interactions between organisms above- and belowground through changes in plant quality. Plant quality is determined by secondary metabolites and morphological traits that may negatively affect the performance of insects, as well as by primary metabolites that plants produce in order to grow, develop and reproduce, which also provide essential nutrients for insects.

Natural plant populations often exhibit genetic variation in various plant traits that include, amongst others, primary and secondary chemistry. Genetic variation in plant defence traits, such as the production of secondary metabolites, can be under selection pressure from a suite of biotic and abiotic factors that vary in space and time. Herbivorous insects may encounter a wide range of plant metabolites because the total concentrations of primary and secondary metabolites and the concentrations of individual compounds vary between genetically different plants. Also as a consequence of genetic variation, plants can respond differently to herbivory in terms of induced defence chemistry and re-allocation of metabolites.

The main aim of this thesis was to study how genetic variation in plant chemistry affects (multi)trophic interactions between wild cabbage plants and associated insects, both above- and belowground. As a model system I used five naturally occurring populations of wild cabbage (Brassica oleracea) located in the Dorset area in the UK. These populations have been shown to genetically differ in their defence chemistry profiles even though they are located in relatively close proximity to each other. Wild cabbages belong to the Brassicaceae, a plant family that is characterized by the production of glucosinolates, a group of secondary metabolites. Together with the enzyme myrosinase they form the chemical defence system of Brassicaceous plants including wild cabbage. Glucosinolates and myrosinases are stored separately in plant tissues but upon tissue damage they come into contact with each other upon which the glucosinolates are hydrolysed into potentially toxic break down products. The wild cabbage populations used in this thesis differ in their total glucosinolate concentrations as well as in the expression of individual glucosinolates.

In chapter 1 I describe plant-insect interactions in a multi-trophic framework, including both the above- and belowground compartments. Genetic variation in plant traits is introduced as the main topic of this thesis, and I present the main aim and outline of my work.

In chapter 2 I discuss how aboveground-belowground interactions influence the evolution and maintenance of genetic variation in plant defence chemistry. I review literature on AG-BG interactions as selection pressures for genetic variation, discuss hypotheses about plant mediation of AG-BG interactions, identify gaps in our knowledge such as the influence of spatial-temporal variation in AG-BG interactions, and in the end present new data on genetic variation in secondary chemistry of wild cabbage and related species.

The co-evolutionary arms race between plants and insects has resulted in adaptations in herbivores to cope with plant defence traits. Some insect herbivore species concentrate or sequester secondary metabolites from their food plant and use them in defence against their own enemies. In chapter 3 I studied whether sequestration of glucosinolates by a specialist herbivore is an effective defence mechanism against a generalist predatory bug. I used the sequestering herbivore Athalia rosae as one prey species, and the non-sequestering herbivore Pieris rapae as the control prey species. I compared the performance of the predatory stink bug Podisus maculiventris on these two prey species. As an extra factor, the two prey species were each reared on three different wild cabbage populations to test if plant population would have an effect on the predator through the sequestering herbivore. I found no consistent effect of plant population on the performance of the predator, and prey species only marginally affected its performance. Based on the results I suggest that in some trophic interactions sequestration is not an effective defence mechanism but merely an alternative way of harmlessly dealing with plant secondary metabolites.

In addition to aboveground plant-insect interactions, belowground interactions were considered as well. To test whether the performance of the belowground specialist herbivore Delia radicum, of which the larvae feed on root tissues, was influenced by population-related variation in defence chemistry, I reared this species on the five wild cabbage populations (chapter 4). Chemical analyses of root tissues revealed that there were differences amongst the populations in plant primary (amino acids and sugars) and secondary (glucosinolates) chemistry, but this did not affect the performance of the root herbivore, suggesting that D. radicum is well adapted to a wide range of total concentrations and concentrations of individual metabolites.

Whereas in chapters 3 and 4 I only focused on one compartment (aboveground and belowground respectively), in chapter 5 I included both compartments in one experiment. I studied the effect of belowground herbivory by larvae of the root fly D. radicum on the performance of an aboveground multi-trophic food chain, and whether this effect differed among three wild cabbage populations. I found that belowground herbivory differentially affected the performances of a specialist aboveground herbivore, the diamondback moth Plutella xylostella, and its parasitoid, Cotesia vestalis, with the parasitoid being more affected than the herbivore. Their performance also differed between the wild cabbage populations, often in interaction with the presence/absence of the belowground herbivore. For both the above- and belowground herbivore I found correlations between performance and plant chemistry, which differed between the insect species and also between males and females.

In chapter 6 I discuss the results of my experiments in relation to other studies. I finish with a general conclusion about my work and provide some ideas for future studies that could contribute to our knowledge in the field of (multi)trophic above-belowground interactions with regard to genetic variation in plant chemistry.

In my thesis I show that genetic variation in plant chemistry can affect the outcome of above-belowground plant-insect interactions. Herbivores and higher trophic levels were differently affected by the wild cabbage populations, and this difference was also influenced by the location of herbivory (i.e. aboveground or belowground). In both chapter 4 and chapter 5 I found no strong, unidirectional links between plant chemistry and insect performance, suggesting that other metabolites may have played a role in the observed differential effects of the wild cabbage populations. I also show that sequestration of plant allelochemicals in some herbivores is an alternative way of harmlessly dealing with plant secondary metabolites instead of an effective defence mechanism against predators (chapter 3).

Mapping moves on Arabidopsis : from natural variation to single genes affecting aphid behaviour
Kloth, K.J. - \ 2016
University. Promotor(en): Marcel Dicke; Harro Bouwmeester, co-promotor(en): Maarten Jongsma. - Wageningen : Wageningen University - ISBN 9789462576483 - 269 p.
016-3933 - arabidopsis thaliana - insect pests - aphidoidea - pest resistance - genetic mapping - gene expression - quantitative traits - functional genomics - feeding behaviour - insect plant relations - insectenplagen - plaagresistentie - genetische kartering - genexpressie - kwantitatieve kenmerken - functionele genomica - voedingsgedrag - insect-plant relaties
Host location by hyperparasitoids: an ecogenomic approach
Zhu, F. - \ 2015
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.

Insecten schadelijk voor naaldhout, vroeger en nu
Hoopen, Jan ten; Moraal, L.G. ; Smits, J. - \ 2015
Entomologische Berichten 75 (2015)3. - ISSN 0013-8827 - p. 86 - 96.
bosecologie - naaldbossen - insect-plant relaties - fauna - historische ecologie - forest ecology - coniferous forests - insect plant relations - historical ecology
In het eerste deel van de Entomologische Berichten besteedt Arie Brants in 1904 aandacht aan de door Staatsbosbeheer in 1903 uitgebrachte plaat 'Insecten schadelijk voor naaldhout'. Wij beschrijven in dit artikel hoe sommige van deze insecten nog steeds als de meest schadelijke in de Europese bosbouw worden beschouwd, maar in Nederland nauwelijks meer een rol spelen. Ook bespreken wij hoe veranderend bosbeheer en veranderend klimaat een verschuiving van plagen liet zien.
Getting prepared for future attack : induction of plant defences by herbivore egg deposition and consequences for the insect community
Pashalidou, F.G. - \ 2015
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 - 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.

Rhizobacterial modification of plant defenses against insect herbivores: from molecular mechanisms to tritrophic interactions
Pangesti, N.P.D. - \ 2015
University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462572836 - 224
planten - rizosfeerbacteriën - insecten - multitrofe interacties - verdedigingsmechanismen - pseudomonas fluorescens - mamestra brassicae - pieris brassicae - plant-microbe interacties - insect-plant relaties - plant-herbivoor relaties - plants - rhizosphere bacteria - insects - multitrophic interactions - defence mechanisms - plant-microbe interactions - insect plant relations - plant-herbivore interactions

SUMMARY

Plants as primary producers in terrestrial ecosystems are under constant threat from a multitude of attackers, which include insect herbivores. In addition to interactions with detrimental organisms, plants host a diversity of beneficial organisms, which include microbes in the rhizosphere. Furthermore, the interactions between plants and several groups of root-associated microbes such as mycorrhizae, plant growth promoting rhizobacteria (PGPR) and plant growth promoting fungi (PGPF) can affect plant interactions with foliar insect herbivores. The beneficial root-associated microbes are able to modify plant physiology by promoting plant growth and induced systemic resistance (ISR), in which the balance between both effects will determine the final impact on the insect herbivores. Using Arabidopsis thaliana Col-0, this thesis explores the molecular mechanisms on how plants integrate responses when simultaneously interacting with the rhizobacterium Pseudomonas fluorescens and the generalist and the specialist leaf-chewing insects Mamestra brassicae and Pieris brassicae respectively.

A literature review on the state-of-the-art in the field of microbe-plant-insect interactions (Chapter 2) explores how root-associated microbes and insect folivores can influence each other via a shared host plant. For more than a decade, both ecological and mechanistic studies mostly focused on exploring these belowground and aboveground interactions using single microbe and single herbivore species. The importance of increasing the complexity of the study system in order to understand the interactions in more natural situations is being emphasized. Furthermore, this review discusses the role of plant hormones in regulating plant growth and defense against folivores, while simultaneously being involved in associations with root-associated microbes.

Experimental evidence has shown patterns on the effects of mycorrhizal colonization on plant interactions with insect herbivores, and raises the question whether plant colonization by different groups of root-associated microbes has similar effects on particular categories of insect herbivores. In Chapter 3, plant-mediated effects of a non-pathogenic rhizobacterium on the performance of leaf-chewing insects, and the underlying mechanisms modulating the interactions, have been examined. Colonization of A. thaliana Col-0 roots by the bacterium P. fluorescens strain WCS417r resulted in decreased larval weight of the generalist leaf-chewing M. brassicae, and had no effect on larval weight of the specialist leaf-chewing P. brassicae. The crucial role of jasmonic acid (JA) in regulating rhizobacteria-mediated induced systemic resistance (ISR) against M. brassicae is confirmed by including plant mutants in the study. Interestingly, I also observed that rhizobacteria can induce systemic susceptibility to M. brassicae caterpillars. Comparison of M. brassicae performance and gene transcription in A. thaliana plants, grown in potting soil or a mixture of potting soil and sand in a 1:1 ratio, shows that in a mixture of potting soil and sand, rhizobacterial treatment had a consistently negative effect on M. brassicae, whereas the effect is more variable in potting soil. Rhizobacterial treatment primed plants grown in potting soil and sand for stronger expression of JA- and ethylene-regulated genes PDF1.2 and HEL, supporting stronger resistance to M. brassicae. Taken together, the results show that soil composition can be one of the factors modulating the outcome of microbe-plant-insect interactions.

Chapter 4 further addresses the mechanisms underlying rhizobacteria-mediated ISR against the generalist leaf-chewing M. brassicae by integrating plant gene transcription, chemistry and performance of M. brassicae in wild type A. thaliana Col-0 plants and mutants defective in the JA-pathway, i.e. dde2-2 and myc2, in the ET pathway, i.e. ein2-1, and in the JA-/ET-pathway, i.e. ora59. Results of this study show that rhizobacterial colonization alone or in combination with herbivore infestation induced the expression of the defense-associated genes ORA59 and PDF1.2 at higher levels than activation by herbivore feeding alone, and the expression of both genes is suppressed in the knock-out mutant ora59. Interestingly, the colonization of plant roots by rhizobacteria alters the levels of plant defense compounds, i.e. camalexin and glucosinolates (GLS), by enhancing the synthesis of constitutive and induced levels of camalexin and aliphatic GLS while suppressing the induced levels of indole GLS. The changes are associated with modulation of the JA-/ET-signaling pathways as shown by investigating mutants. Furthermore, the herbivore performance results show that functional JA- and ET-signaling pathways are required for rhizobacteria-mediated ISR against leaf-chewing insects as observed in the knock-out mutants dde2-2 and ein2-1. The results indicate that colonization of plant roots by rhizobacteria modulates plant-insect interactions by prioritizing the ORA59-branch over the MYC2-branch, although the transcription factor ORA59 is not the only one responsible for the observed effects of rhizobacteria-mediated ISR against leaf-chewing insects.

Taking a step further in increasing the complexity of the study system, Chapter 5 investigates how co-cultivation of P. fluorescens strains WCS417r and SS101 affects direct plant defense to the caterpillar M. brassicae. Inoculation of either P. fluorescens WCS417r or SS101 singly at root tips or simultaneously at two different positions along the roots resulted in a similar level of rhizobacterial colonization by each strain, whereas co-cultivation of both strains at either the root tips or at two different positions along the roots resulted in a higher colonization level of strain WCS417r compared to colonization by SS101. The results suggest that the site of inoculation influences the direct interactions between the two strains in the rhizosphere, as also confirmed by in vitro antagonism assays in the absence of plants. Both upon single inoculation and co-cultivation of both strains at the same or different sites along the roots, the two rhizobacterial strains induced the same strength of ISR against the caterpillar M. brassicae and the same degree of plant growth promotion. In the roots, colonization by the two strains as single or mixed culture resulted in a similar gene expression pattern of up-regulation of MYC2, down-regulation of WRKY70 and no effect on NPR1 expression, genes representing JA-signaling, SA-signaling and the node of crosstalk between the two pathways, respectively. We hypothesize that both rhizobacterial strains use negative crosstalk between JA- and SA-pathways as mechanism to suppress plant immunity and establish colonization. This study shows that competitive interactions between rhizobacterial strains known to induce plant defense in systemic tissue via different signaling pathways, may interfere with synergistic effects on ISR and plant growth promotion.

While the effect of root-associated microbes on direct plant defense against insect herbivores has been studied previously, the effect of these microbes on indirect plant defense to herbivores is much less known. Chapter 6 explores how colonization by the rhizobacterium P. fluorescens strain WCS417r affects indirect plant defense against the generalist herbivore M. brassicae by combining behavioral, chemical and gene transcriptional approaches. The results show that rhizobacterial colonization of A. thaliana roots results in an increased attraction of the parasitoid Microplitis mediator to caterpillar-infested plants. Volatile analysis revealed that rhizobacterial colonization suppressed emission of the terpene (E)-α-bergamotene, and the aromatics methyl salicylate and lilial in response to caterpillar feeding. Rhizobacterial colonization decreased the caterpillar-induced transcription of the terpene synthase genes TPS03 and TPS04. Rhizobacteria enhanced both growth and indirect defense of plants under caterpillar attack. This study shows that rhizobacteria have a high potential to enhance the biocontrol of leaf-chewing herbivores based on enhanced attraction of parasitoids.

Taken together, the research presented in this thesis has shown how single or combined applications of rhizobacteria affect interactions of plants with leaf-chewing insects in terms of direct and indirect resistance. Furthermore, results presented in this thesis have revealed some of the molecular mechanisms underlying plant-mediated interactions between rhizobacteria and leaf-chewing insects that can be used in developing practical approaches by applying beneficial root-associated microbes for improving plant resistance.

Increase of plant resistance with rhizosphere competent entomopathogenic fungi (EPF)
Tol, R.W.H.M. van - \ 2015
gewasbescherming - tuinbouw - entomopathogene schimmels - biologische bestrijding - rizosfeer - natuurlijke vijanden - bodeminsecten - insect-plant relaties - conferenties - melolontha melolontha - bodem-plant relaties - insectenplagen - plant protection - horticulture - entomogenous fungi - biological control - rhizosphere - natural enemies - soil insects - insect plant relations - conferences - soil plant relationships - insect pests
Entomopathogenic fungi are able to kill insects and are as such a potential mean for pest control. Recently it was discovered that these fungi can also colonize plant roots. Most previous work with EPF has ignored the habitat preferences and survival of the fungus outside of the host. It is possible that factors associated with fungal biology outside of the host are more important when selecting an isolate than how pathogenic it is against a particular host in a laboratory bioassay. Poster van PlantgezondheidEvent 12 maart 2015.
Tales on insect-flowering plant interactions : the ecological significance of plant responses to herbivores and pollinators
Lucas Gomes Marques Barbosa, D. - \ 2015
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
Ontwikkelingen in insectenplagen op Nederlandse bomen sinds 1946
Moraal, L.G. - \ 2014
Vakblad Natuur Bos Landschap 109 (2014). - ISSN 1572-7610 - p. 3 - 5.
bomen - struiken - openbaar groen - insectenplagen - insect-plant relaties - klimaatverandering - bosbeheer - inventarisaties - trees - shrubs - public green areas - insect pests - insect plant relations - climatic change - forest administration - inventories
Ruim zestig jaar lang is er onderzoek gedaan aan insectenplagen. Totdat de financiering er van gestopt is. De verzamelde data geven nog steeds een schat aan informatie over oprukkende plaaginsecten, klimaatverandering en slimme manieren van bosverjonging. Dit artikel is gebaseerd op Entomologische berichten 73(2013)1 : 2-24
Het belang van wilde bestuivers voor de landbouw en oorzaken voor hun achteruitgang
Scheper, J.A. ; Kats, R.J.M. van; Reemer, M. ; Kleijn, D. - \ 2014
Wageningen : Wageningen UR Alterra (Alterra-rapport 2592) - 50
bestuivers (dieren) - apidae - fauna - insect-plant relaties - ecosysteemdiensten - landbouw - vruchtbomen - nederland - pollinators - insect plant relations - ecosystem services - agriculture - fruit trees - netherlands
Wilde bestuivers zoals bijen en zweefvliegen leveren een belangrijke bijdrage aan de productie van insect-bestoven landbouwgewassen. Wat de bijdrage van wilde bestuivers is ten opzichte van de diensten geleverd door de honingbij is momenteel onbekend in Nederland. De huidige studie had tot doel meer inzicht te krijgen in (1) welke wilde bestuivers tot soorten behoren die voor de - Nederlandse - landbouw relevant kunnen worden geacht, (2) wat bekend is van hun populatieontwikkelingen en wat waarschijnlijk belangrijke factoren zijn die hun achteruitgang kunnen verklaren en (3) indien de achteruitgang van voedselplanten een belangrijke factor zou zijn bij de achteruitgang van wilde bestuivers, welke (natuur)beheermaatregelen dan eventueel denkbaar zijn om de beschikbaarheid van voedselplanten te bevorderen.
Wilde bijen mede achteruitgegaan door gebrek aan bloemen
Scheper, J.A. - \ 2014
Wageningen UR
apidae - wilde bijenvolken - bloeiende planten - door bijen verzameld stuifmeel - bouwland - waardplanten - rassen (dieren) - insect-plant relaties - vegetatietypen - wild honey bee colonies - flowering plants - bee-collected pollen - arable land - host plants - breeds - insect plant relations - vegetation types
Uit onderzoek van stuifmeel van bijen uit museumcollecties blijkt dat het verlies aan bloemen in het landschap wel eens een belangrijke oorzaak van de achteruitgang van wilde bijensoorten zou kunnen zijn. Dit werd al langer vermoed, maar tot op heden ontbrak hiervoor het bewijs. Dat bewijs is nu geleverd aan de hand van museumcollecties. “Uit ons onderzoek bleek een duidelijke relatie tussen het voorkomen van bijensoorten en hun waardplanten,” zegt Jeroen Scheper in een toelichting op het onderzoek dat zojuist is verschenen in het wetenschappelijk tijdschrift PNAS.
Een bij-zonder kleurrijk landschap in Land van Wijk en Wouden : handreiking voor inrichting en beheer
Rooij, S.A.M. van; Geertsema, W. ; Opdam, P.F.M. ; Reemer, M. ; Snep, R.P.H. ; Spijker, J.H. ; Steingröver, E.G. - \ 2014
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2563) - 16
biodiversiteit - insect-plant relaties - regionale planning - ecologische hoofdstructuur - landschap - zuid-holland - biodiversity - insect plant relations - regional planning - ecological network - landscape
Het programma Groene Cirkels (van Heineken) heeft het initiatief genomen tot het realiseren van een duurzaam bijenlandschap in het land van Wijk en Wouden. Deze handreiking wil een impuls geven aan het realiseren daarvan. In Nederland hebben we zo’n 350 verschillende wilde bestuivende insectensoorten. Door variatie in onder andere bloemvormen en kelkdiepte en bloeiseizoen zijn er gespecialiseerde insecten nodig, aangepast op bloeivorm en het bloeiseizoen. Ook moet bestuiving plaats kunnen vinden onder verschillende omstandigheden: bij goed en slecht weer, in vroege en late voorjaren. Nu eens doet de ene soort het goed, dan is er weer een andere die het meeste werk verzet. Diversiteit aan bijen, hommels en zweefvliegen geeft zekerheid voor bestuiving door de jaren heen.
Whitefly resistance in tomato: from accessions to mechanisms
Lucatti, A.F. - \ 2014
University. Promotor(en): Richard Visser, co-promotor(en): Ben Vosman; Sjaak van Heusden. - Wageningen : Wageningen University - ISBN 9789462570153 - 143
solanum lycopersicum - tomaten - wilde verwanten - insectenplagen - bemisia tabaci - plaagresistentie - verdedigingsmechanismen - plantenveredeling - insect-plant relaties - tomatoes - wild relatives - insect pests - pest resistance - defence mechanisms - plant breeding - insect plant relations

Tomato (Solanum lycopersicum) is affected by a wide range of biotic stresses, of which Bemisia tabaci is one of the most important.Bemisia tabaci affects tomato directly through phloem sap feeding, and indirectly through its ability to be the vector of a large number of viruses. Different methods are available for whitefly control, and although several biological control agents are used against whiteflies in greenhouse cultivation, chemical control still is an essential component in open field tomato production. Breeding for host plant resistance is considered as one of the most promising methods in insect pest control in crop plants, and especially it is a promising alternative in whitefly control. Resistance to whiteflies was found in several wild relatives of tomato like Solanum peruvianum, S. pennellii, S. habrochaites, S. lycopersicum var. cerasiforme, S. pimpinellifolium andS. galapagense. In spite of previous breeding efforts, whiteflies are still a problem in tomato cultivation. The aim of my research was to identify and understand resistance mechanisms targeting specific stages of the whitefly life cycle in order to provide breeders with tools for developing whitefly resistant varieties.

I assessed the natural variation and whitefly resistance in Solanum galapagense and S. cheesmaniae, two wild tomato species endemic to the Galapagos Islands. Previously, Solanum galapagense and S. cheesmaniae were classified as two species based on a morphological species concept, but with molecular markers no clear separation could be made. So far, only a limited number of accessions/populations of S. galapagense and S. cheesmaniae have been evaluated for insect resistance and therefore it was unknown if the insect resistance coincides with the morphological species boundaries. Neither was there any knowledge about the relation between geographical and climatic conditions today on the Galapagos and the occurrence of the two species. We characterized twelve accessions of S. galapagense, 22 of S. cheesmaniae, and as reference one of S. lycopersicum for whitefly resistance using no-choice experiments. Whitefly resistance was found in S. galapagense only and was associated with the presence of relatively high levels of acyl sugars and the presence of glandular trichomes of type I and IV.It is likely that a minimum level of acyl sugars and the presence of glandular trichomes type IV are needed to achieve an effective level of resistance. Genetic fingerprinting using 3316 polymorphic SNP markers did not show a clear differentiation between the two species endemic to the Galapagos. Acyl sugar accumulation as well as the climatic and geographical conditions at the collection sites of the accessions did not follow the morphological species boundaries. Altogether, our results suggest that S. galapagense and S. cheesmaniae might be considered as morphotypes rather than two species and that their co-existence is likely the result of selective pressure.

Plants possess several resistance mechanisms acting at different time points during the interaction with herbivorous insect. Before any contact with the insects, plants emit an array of volatile organic compounds that can act as attractant or repellent of insects.Bemisia tabaci use a set of plant-derived cues in the process of host plant selection. It recognizes mainly monoterpenes (p-cymene, γ-terpinene and β-myrcene, α-phellandrene) and sesquiterpenes (7-epizingiberene and R-curcumene). Previously the line FCN93-6-2, which was derived from a cross between a susceptible tomato cultivar (Uco Plata INTA) and S. habrochaites (FCN3-5) was proved to be non-preferred by the greenhouse whitefly Trialeurodes vaporariorum. We identified chemical cues produced by FCN93-6-2 and S. habrochaites that can affect the preference of the whitefly B. tabaci as well as the potential chromosomal region(s) of S. habrochaites harbouring the genes involved in the preference. Two S. habrochaites accessions (CGN1.1561 and in FCN3-5) and the line FCN93-6-2 were non-preferred by B. tabaci when the whiteflies could get in direct contact with the plant and also when the whiteflies were offered olfactory cues only. The non-preference was independent of trichome type IV and of the presence of methyl-ketones but associated to the presence of monoterpenes in lower concentrations. Functional validation of the candidate metabolites and of the different introgressions is still needed.

Once the insect has landed on a plant, another set of resistance mechanisms enter into action. We have described a 3.06 Mbp introgression on top of Chromosome 5 (OR-5) from the wild tomato species S. habrochaites (CGN1.1561). For the identification of OR-5, we went from the selection of specific F2 plants to the development of F2BC4S1 and F2BC4S2 families. This introgression was sufficient to reduce whitefly fecundity without an evident effect on whitefly survival. The identification of mechanisms exclusively affecting whitefly fecundity and independent of trichomes type IV opens new doors for resistance breeding to whiteflies that may be especially interesting in greenhouse cultivation combination with natural enemies of the whitefly.

As an additional layer of defences, plants can perceive stress signals and respond to them in a specific way through induction of their immune system. This induction can also be triggered by exposing the plants to priming agents like hormones, some xenobiotic chemicals, like benzothiadiazole (BTH), β-aminobutyric acid (BABA), and sugars. Although the effect of priming agents was shown in laboratory and field studies, little is known about the effect of the genetic background of tomato on the extent of the priming, e.g. do genotypes varying in their level of resistance to insects and pathogens respond in the same way to a priming agent. We assessed the effect of selected priming agents on the effectiveness of natural defence in tomato. A set of no-choice and choice bioassays was conducted using tomato genotypes varying in their level of basal resistance to Bemisia tabaci and pathogens. We observed that whitefly survival and oviposition were not affected by the priming treatment in no-choice assays. Overall, in choice assays, fructose treated plants were more preferred by whiteflies than control plants. A genotype specific effect of priming was seen for the line FCN93-6-2. On this tomato line, JA and BABA applications decreased the number of whiteflies, e.g. making them less preferred.

In this thesis, I have gone from the screening of wild relatives of tomatoes to in depth characterization of resistance mechanisms. I have identified resistance mechanisms targeting specific stages of the whitefly life cycle, thus providing new tools for breeding durable whitefly resistance in tomato.

Voedselkwaliteit en biodiversiteit in bossen van de hoge zandgronden
Burg, A. Van den; Dees, A. ; Bijlsma, R.J. ; Waal, R.W. de - \ 2014
Bosschap, bedrijfschap voor bos en natuur - 128
zandgronden - ecosystemen - bosecologie - insect-plant relaties - bodem-plant relaties - bossen - fauna - zure depositie - veluwe - sandy soils - ecosystems - forest ecology - insect plant relations - soil plant relationships - forests - acid deposition
Terrestrische ecosystemen die geen invloed kennen van grondwater en bovendien een van nature matig tot slecht gebufferde bodem hebben, zijn heel erg gevoelig voor verzuring. Hierbij horen bijvoorbeeld de natuurlijke standplaatsen van Oude eikenbossen (H9190) en Beuken-Eikenbos met hulst (H9120), waarvoor het moeilijk is om beheerstrategieën te ontwerpen die de effecten van verzuring en vermesting tegengaan. Er is in dit OBN-project gewerkt aan de volgende drie onderzoeksvragen: (1) Via welk mechanisme kan de bodem-plant interactie bijgestuurd worden, zodat herstel optreedt van de voedingsbalans van planten en vervolgens ook van de daarvan afhankelijke fauna (plant-insect interactie), (2) Onder wat voor omstandigheden (bodem, depositie, evt. maatregelen in verleden) treedt een verstoorde voedingsbalans op en (3) wat zijn mogelijke praktische maatregelen.
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