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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Loopkevers (Coleoptera: Carabidae) in agrarische milieus – een faunakarakteristiek
Turin, H. ; Alebeek, F.A.N. van - \ 2007
Entomologische Berichten 67 (2007)6. - ISSN 0013-8827 - p. 246 - 248.
carabidae - landbouwkundige entomologie - predatoren van schadelijke insecten - natuurlijke vijanden - habitats - akkerbouw - functionele biodiversiteit - agrobiodiversiteit - agricultural entomology - predators of insect pests - natural enemies - arable farming - functional biodiversity - agro-biodiversity
Loopkevers vormen een belangrijk onderdeel van de op-de-bodem-levende fauna in de meest uiteenlopende terreintypen. Het zijn vaak meer of minder gespecialiseerde rovers, maar er zijn ook soorten die zaden eten. Loopkevers hebben een grote invloed op de samenstelling van de lokale ongewervelde fauna en in bepaalde habitats ook op de flora. De soortengroep wordt hier kort gekarakteriseerd, met aandacht voor hun rol in de plaagbestrijding op akkers
Lieveheersbeestjes : heersers van de akkers?
Lommen, S.T.E. ; Cuppen, J.G.M. - \ 2007
Entomologische Berichten 67 (2007)6. - ISSN 0013-8827 - p. 260 - 263.
landbouwkundige entomologie - biologische bestrijding - aphidoidea - coccinella septempunctata - adalia - propylea - akkerbouw - predator prooi verhoudingen - agricultural entomology - biological control - arable farming - predator prey relationships
Aphidofage lieveheersbeestjes zijn predatoren die voornamelijk leven van bladluizen. Deze lieveheersbeestjes worden regelmatig aangetroffen op akkers die geplaagd worden door bladluizen. Over hun effectiviteit als natuurlijke bestrijders van deze plaagsoorten bestaan wisselende rapporten. Een theoretisch model, ondersteunend door veldwaarnemingen en laboratoriumstudies, laat zien dat de biologie van lieveheersbeestjes niet is gericht op het uitroeien van de prooi. Dit maakt het moeilijk om bladluizen via natuurlijke bestrijding met aphidofage lieveheersbeestjes tot onder een economisch acceptabel niveau terug te brengen. Vormen van biologische bestrijding waarbij exotische of inheemse lieveheersbeestjes worden geïntroduceerd zijn soms op korte termijn effectief, maar hebben allebei belangrijke nadelen
Kader 2. Functionele biodiversiteit in boomgaarden
Winkler, K. ; Helsen, H.H.M. ; Wackers, F. - \ 2007
Entomologische Berichten 67 (2007)6. - ISSN 0013-8827 - p. 236 - 237.
fruitteelt - boomgaarden - geïntegreerde plagenbestrijding - natuurlijke vijanden - cacopsylla pyri - eriosoma lanigerum - landbouwkundige entomologie - predatoren van schadelijke insecten - bevordering van natuurlijke vijanden - fruit growing - orchards - integrated pest management - natural enemies - agricultural entomology - predators of insect pests - encouragement
Anders dan akkerbouwgewassen, die meestal (minder dan) een, hooguit twee, jaar op het land staan, worden fruitbomen voor een langere periode geplant. Samen met de rijststroken en de omgevende windhagen vormen fruitbomen een meerjarige ecosysteem, waarvan ook veel insecten- en spinnensoorten deel uitmaken. Van de 1000-2000 insectensoorten die in boomgaarden gevonden worden, is maar 10% als schadelijk voor de fruitproductie te beschouwen. Bijna elk van deze plaaginsecten wordt door meerdere natuurlijke vijanden belaagd. Door het Nederlands Instituut voor Ecologie (NIOO-KNAW) wordt in samenwerking met Wageningen PPO fruit gewerkt aan een tweejarig proefproject, gericht op het gebruik van biodiversiteit ter stimulering van natuurlijke vijanden van perenbladvlo Cacopsylla pyri
Oorwormen (Dermaptera) als belangrijke predatoren in boomgaarden
Helsen, H.H.M. ; Winkler, K. - \ 2007
Entomologische Berichten 67 (2007)6. - ISSN 0013-8827 - p. 275 - 277.
dermaptera - biologische bestrijding - boomgaarden - fruitteelt - forficula auricularia - cacopsylla pyri - eriosoma lanigerum - natuurlijke vijanden - predatoren van schadelijke insecten - landbouwkundige entomologie - biological control - orchards - fruit growing - natural enemies - predators of insect pests - agricultural entomology
Oorwormen zijn alleseters. Omdat ze naast dierlijk voedsel en afval ook wel bladeren en vruchten aanvreten, richt een deel van de landbouwkundige aandacht voor oorwormen zich op hun bestrijding als plaag. In de moderne appel- en perenteelt worden oorwormen echter vooral beschouwd als welkome bestrijders van insectenplagen
Hoe kunnen we plaagonderdrukkende mengteelten ontwerpen?
Bukovinszky, T. ; Lenteren, J.C. van - \ 2007
Entomologische Berichten 67 (2007)6. - ISSN 0013-8827 - p. 231 - 234.
geïntegreerde plagenbestrijding - natuurlijke vijanden - voedselwebben - teeltsystemen - monocultuur - populatie-ecologie - landbouwkundige entomologie - plant-herbivoor relaties - functionele biodiversiteit - agrobiodiversiteit - integrated pest management - natural enemies - food webs - cropping systems - monoculture - population ecology - agricultural entomology - plant-herbivore interactions - functional biodiversity - agro-biodiversity
Plaagpopulaties zijn vaak kleiner in mengteelten dan in monocultures. Met mengteelten kan daarom worden geprobeerd plaagproblemen in agro-ecosystemen te verkleinen. Een grotere vegetatiediversiteit kan plaagorganismen onderdrukken doordat waardplanten minder goed zichtbaar of van geringere kwaliteit zijn en doordat natuurlijke vijanden meer voedsel vinden. Helaas is de respons op mengteelten van zowel plaaginsecten als van hun natuurlijke vijanden. Vaak moeilijk te voorspellen en er is nog onvoldoende kennis om in concrete gevallen de plaagpopulatieverschillen tussen mengteelten die plagen onderdrukken vereist daarom meer studie. In dit artikel laten we zien dat recent verworven kennis van het gedrag en de ecologie van plant-plaag-natuurlijke vijand interacties een nieuw beeld oplevert van het verschil tussen mono- en mengcultures
Synthesis agrobiodiversity - conservation and functionality
Noordijk, J. ; Bruin, J. ; Rijn, P. van - \ 2007
Entomologische Berichten 67 (2007)6. - ISSN 0013-8827 - p. 278 - 283.
insecten - plagenbestrijding - landbouwkundige entomologie - natuurlijke vijanden - habitats - predatoren van schadelijke insecten - voedingsgedrag - nederland - predator prooi verhoudingen - functionele biodiversiteit - landschapselementen - agrobiodiversiteit - insects - pest control - agricultural entomology - natural enemies - predators of insect pests - feeding behaviour - netherlands - predator prey relationships - functional biodiversity - landscape elements - agro-biodiversity
Biodiversity, including that of insects, should be preserve or even enhanced for its own sake, sometimes encouraged by international organizations. In agricultural areas an additional reason for its conservation is the ecological services it can provide to agriculture, including the natural control of crop pests. In this special issue of Entomologische Berichten studies focusing on each of the two aims are discussed. With special attention for the anthropod groups that play a role in pest control. Both aims can partly rely on conserving and improving the network of non-productive landscape elements, but for certain goals and insect groups specific measures will be required
Spinnen (Arachnida: Araneae) op akkers - biologie en plaagbestrijding
Noordijk, J. ; Helsdingen, P.J. van - \ 2007
Entomologische Berichten 67 (2007). - ISSN 0013-8827 - p. 249 - 252.
arachnida - geïntegreerde plagenbestrijding - landbouwkundige entomologie - lycosidae - theridiidae - akkerbouw - habitats - predatoren van schadelijke insecten - roofinsecten - integrated pest management - agricultural entomology - arable farming - predators of insect pests - predatory insects
Spinnen vormen een soortenrijke groep van predatoren. In vrijwel geen terrestrisch habitattype ontbreken soorten uit deze orde. Door hun kolonisatiesnelheid en de diversiteit aan prooivangsttechnieken kunnen spinnen van groot belang zijn voor plaagbestrijding op akkers. In deze bijdrage behandelen wij de levenscyclus van spinnen, het voorkomen op akkers en hun aandeel in plaagbestrijding op basis van recente literatuur. Daarnaast doen we enkele suggesties voor het beheer van de directe omgeving, waardoor het voorkomen van spinnen op akkers gestimuleerd kan worden
Het functionele landschap: de invloed van landschap en bedrijfsvoering op natuurlijke plaagonderdrukking in spruitkool
Belder, E. den; Elderson, J. ; Schelling, G.C. ; Guldemond, J.A. - \ 2007
Entomologische Berichten 67 (2007)6. - ISSN 0013-8827 - p. 196 - 199.
landbouwkundige entomologie - agrarische bedrijfsvoering - brassica oleracea var. gemmifera - ziektebestrijdende teeltmaatregelen - plagenbestrijding - pieris rapae - plutella xylostella - landschapsecologie - biologische landbouw - landschapselementen - landschapsbeheer - agricultural entomology - farm management - cultural control - pest control - landscape ecology - organic farming - landscape elements - landscape management
Speelt de groene dooradering van het landschap een rol bij de natuurlijke plaagregulatie? Op 22 biologische spruitkoolbedrijven verdeeld over diverse landschappen in heel Nederland zijn tellingen gedaan van het klein koolwitje en de koolmot. Het omringende landschap varieerde sterk in de hoeveelheid opgaande begroeiing, zoals hagen, houtwallen en bomenrijen, en in het tuinbouwareaal. Voor deze studie is een indeling gemaakt in vier ruimtelijke schalen, te weten cirkels rond een betreffend perceel met een middellijn van 0.3, 1, 2 en 10 km. We vonden een verband tussen de ruimtelijke structuur van de omgeving en de plaagdichtheid op de akker: de aantallen rupsen van het kleine koolwitje en de koolmot waren kleiner bij een sterkere dooradering van het klein koolwitje en de koolmot waren kleiner bij een sterkere dooradering van het landschap met heggen (op schaal van 2 diameter) en bij een kleiner areaal van tuinbouwgewassen in de omgeving. Dit onderzoek suggereert dat natuurlijke plaagregulatie op een akker beter kan verlopen als er meer heggen en andere lijnvormige landschapselementen staan in het omringende landschap en als daar de tuinbouwgewassen meer ruimtelijk worden gescheiden
Insect-plant Biology
Schoonhoven, L.M. ; Loon, J.J.A. van; Dicke, M. - \ 2005
Oxford, U.K. : Oxford University Press (2nd ed. ) - ISBN 9780198525950 - 421
planten - insecten - gastheer parasiet relaties - insectenplagen - verdedigingsmechanismen - plaagresistentie - chemische ecologie - landbouwkundige entomologie - waardplanten - insect-plant relaties - plants - insects - host parasite relationships - insect pests - defence mechanisms - pest resistance - chemical ecology - agricultural entomology - host plants - insect plant relations
Half of all insect species are dependent on living plant tissues, consuming about 10% of plant annual production in natural habitats and an even greater percentage in agricultural systems, despite sophisticated control measures. Plants are generally remarkably well-protected against insect attack, with the result that most insects are highly specialized feeders. The mechanisms underlying plant resistance to invading herbivores on the one side, and insect food specialization on the other, are the main subjects of this book. For insects these include food-plant selection and the complex sensory processes involved, with their implications for learning and nutritional physiology, as well as the endocrinological spects of life cycle synchronization with host plant phenology. In the case of plants exposed to insect herbivores, they include the activation of defence systems in order to minimize damage, as well as the emission of chemical signals that may attract natural enemies of the invading herbivores and maybe exploited by neighbouring plants that mount defences as well.
Sectie Experimentele en Toegepaste Entomologie van de NEV
Huis, A. van; Bruin, J. de - \ 2003
Entomologische Berichten 63 (2003). - ISSN 0013-8827 - p. 43 - 45.
entomologie - landbouwkundige entomologie - toegepast onderzoek - nederland - entomology - agricultural entomology - applied research - netherlands
The Section Experimental and Applied Entomology (SETE) received its present name in 1988. Its main activity is the organisation of an anual one-day symposium ('Entomologendag') and the production of the associated proceedings volume.
Foraging under incomplete information: parasitoid behaviour and community dynamics
Vos, M. - \ 2001
Wageningen University. Promotor(en): Louise Vet; Joop van Lenteren; A. Hemerik. - S.l. : S.n. - ISBN 9789058084095 - 156
parasitoïden - cotesia glomerata - pieris brassicae - pieris rapae - koolsoorten - trofische graden - voedingsgedrag - populatiedynamica - landbouwkundige entomologie - insectenplagen - parasitoids - feeding behaviour - population dynamics - insect pests - cabbages - trophic levels - agricultural entomology
<p>This thesis describes research on multitrophic interactions between parasitoids, herbivores and plants. These are all involved in a dynamic game of hide-and-seek. Insect herbivores may occur in different spatial distributions across plants. Some species occur in local clusters, while others have a more even distribution. Parasitoids are challenged to deal effectively with such variation in the spatial distribution of their victims. I studied how different species and strains of <em>Cotesia</em> parasitoids make use of chemical information and foraging experience under varying spatial distributions of hosts.</p><p>The parasitoids <em>Cotesia glomerata</em> and <em>Cotesia rubecula</em> show clear interspecific variation in foraging decisions when exploiting patches with herbivores. <em>C. glomerata</em> tunes its foraging decisions to the current environment as it gains experience with hosts during subsequent patch visits. In contrast, foraging decisions in <em>C. rubecula</em> seem insensitive to acquired experience. These <em>Cotesia</em> species prefer different herbivore species, that occur in different spatial distributions across plants. <em>C. glomerata</em> prefers to attack <em>Pieris brassicae</em> , that occurs in rare clusters of highly variable density. The parasitoid <em>C. rubecula</em> specialises on <em>Pieris rapae</em> that mostly feeds solitarily on plants. This leads the parasitoid <em>C. glomerata</em> to experience a more variable environment, with a wider scope for increased efficiency through learning.</p><p>Both <em>Pieris</em> species are present in Europe, but the clustered host is absent in North America. The parasitoid <em>C. glomerata</em> was introduced to North America in 1883 to control solitarily feeding <em>Pieris rapae</em> , and about 350 generations of <em>C. glomerata</em> parasitoids have now foraged there. The experimental results suggest that American <em>C. glomerata</em> have adapted to forage for solitary host larvae, mostly through a loss of costly traits for finding rare clustered larvae. The European parasitoids spend a lot of time on explorative flights, while their American conspecifics seem to minimise travel costs and effectively focus on the exploitation of patches with solitary hosts.</p><p>Herbivores are hard to find victims for parasitoids, and parasitic wasps may use any reliable information from the environment to locate them. Plants play a key role in providing this information. Plants may emit volatile infochemicals, when they are damaged by herbivores. Such volatiles are attractive to parasitoids and may guide them to their hosts. However, this research shows that the reliability of plant infochemicals may be very low when a complex of herbivores feeds on the plant. This is important, as plants are mostly attacked by several herbivore species, both in agricultural and natural ecosystems. The presence of nonhost herbivores causes parasitoids to waste time on damaged plants without hosts. A model study shows that the interaction between this 'wasted time' effect and herbivore diversity stabilises communities of parasitoids and herbivores. However, above a certain diversity threshold parasitoids may waste too much time on nonhost herbivores. This may lead to the local extinction of several parasitoid species. Thus, diversity may promote both stability and extinctions, when plants provide unreliable information.</p><p>This thesis shows that the flow of information between all these actors is crucial for the understanding of insect behaviour and community dynamics. This information flow involves plants, parasitoids and, surprisingly, both host and nonhost herbivores.</p>
Identification and regulation of the juvenile hormone esterase gene in the Colorado potato beetle
Vermunt, A.M.W. - \ 1999
Agricultural University. Promotor(en): Joop van Lenteren; Just Vlak. - S.l. : S.n. - ISBN 9789058080295 - 104
leptinotarsa decemlineata - juvenielhormonen - esterasen - genen - genetica - aminozuren - dierfysiologie - landbouwkundige entomologie - juvenile hormones - esterases - genes - genetics - amino acids - animal physiology - agricultural entomology
<p>A number of important physiological processes in insects is controlled by the titer of juvenile hormone (JH). The juvenile (larval) stage is maintained at a high JH titer, whereas the onset of metamorphosis is induced by a low JH titer. Reproduction by adults requires often a high JH titer. Through synchronization of the reproductive phase with favorable environmental conditions, insects are able to adapt to adverse conditions and to enhance the chance for survival. The Colorado potato beetle uses daylength (photoperiod) as key stimulus for seasonal adaptation.</p><p>In temperate areas the beetle hibernates in the soil and development is arrested. If the adult beetle is exposed to short-day conditions it digs into the soil after 11-12 days, which marks the onset of diapause. This photoperiodic effect is mediated by JH. Long-day conditions result in a high JH titer leading to reproduction. Short-day conditions, however, result in a low JH titer leading to diapause. The JH titer in the hemolymph is the result on the one hand by JH synthesis in the corpora allata and on the other hand by JH degradation in the hemolymph. Hydrolysis of the JH ester by JH esterase (JHE) is the main JH degradation pathway in the beetle. The highest JHE activity occurs in the hemolymph (Chapter 1).</p><p>Surprisingly, the JHE from the Colorado potato beetle (Coleoptera) was found to be a dimer, consisting of two subunits of 57 kDa, whereas lepidopteran JHEs were characterized as monomers. The fact that the beetle JHE occurs as a dimer, is also the reason why the enzyme could be separated from monomeric general carboxyl esterases by nondenaturing polyacrylamide gel electrophoresis (PAGE). After PAGE purification, narrow-range isoelectric focusing and SDS-PAGE were employed to purify JHE from hemolymph of the last larval instar of the Colorado potato beetle. Two forms were found with isoelectric points of 5.5 and 5.6, respectively (Chapter 2).</p><p>To clone the encoding cDNA, the purified JHE was subjected to endoproteinase Lys-C digestion. Based on the amino acid sequence of the separated peptides, degenerate primers were designed to perform RT-PCR in order to clone an internal fragment of the encoding cDNA. The 3'-end was found by screening a cDNA library and the 5'-end by using the 5'RACE technique. The size of the transcript was 1.7 kilobase. The deduced amino acid sequence (515 residues) of the putative JHE cDNA showed limited homology to some functional peptide motifs of other insect esterases (Chapter 3).</p><p>RT-PCR on mRNA and analysis of genomic DNA provided evidence for the existence of two JHE-related genes, JHE.A and JHE.B. Both are intronless in the coding regions. JHE.A with a predicted pI of 5.5 probably codes for hemolymph JHE. The function of JHE.B with a predicted pI of 6.9 is unknown yet, but it may code for cytosolic JHE in the fat body. Both genes lack a conserved motif with a catalytic serine, typical for serine esterases. It was hypothesized that dimerization of the 57 kDa subunits can generate a catalytic site for enzyme activity (Chapter 4).</p><p>In the beetle, the JHE transcript was mainly synthesized during the feeding stage of the last larval instar as well as in pre-diapausing animals (short-day adults). At these stages the JH titer is low and induces pupation and diapause, respectively. JHE activity in the hemolymph correlated with JHE-mRNA levels in the fat body during the development of the beetle. This observation is a strong indication that the probe used to follow JHE-mRNA levels indeed codes for hemolymph JHE. Also after photoperiodic and JH analog treatment the positive correlation was found between JHE-mRNA levels and JHE activity.</p><p>JH analog (pyriproxifen) application to early 4th-instar larvae resulted in a negative feedback as JHE synthesis was enhanced to maintain the JH titer low. In contrast, if the JH analog was applied to early short-day adult beetles, JHE gene expression was suppressed to reprogram the beetles. Instead of preparation for diapause with a low JH titer and a high JHE level, the treated beetles showed reproductive development with a low JHE level to maintain a high JH titer (Chapter 5).</p><p>The putative JHE cDNAs, JHE.A and JHE.B, were expressed in a baculovirus-insect cell system. The JHE-specific transcripts were clearly present in the <em>Spodoptera frugiperda</em> cells, as detected by Northern hybridization. Also a 57 kDa protein was synthesized, as visualized by Coomassie Brilliant Blue staining, although it was at a low level. However, JHE enzyme activity could not be detected. During translation or post-translational modification, other unknown factors may be required for the formation of an enzymatically active dimeric JHE (Chapter 6).</p><p>Finally, following expression of specific genes gives us accurate information about the initiation of a developmental program. In long-day beetles, the JHE gene is switched off and the JH titer increases, leading to reproduction with vitellogenin expression. In contrast, short-days result in switching on of the JHE gene and a low JH titer. This induces the alternative developmental program, diapause, with the expression of diapause proteins. How signal transduction occurs from photoperiodic perception to gene activity is unknown yet (Chapter 7).</p>
Competence and specificity of thrips in the transmission of tomato spotted wilt virus
Nagata, T. - \ 1999
Agricultural University. Promotor(en): R.W. Goldbach; D. Peters. - S.l. : Nagata - ISBN 9789058080769 - 96
tomatenbronsvlekkenvirus - plantenvirussen - plantenziekteverwekkers - plantenziekten - thrips - vectoren - transmissie - landbouwkundige entomologie - tomato spotted wilt virus - plant viruses - plant pathogens - plant diseases - vectors - transmission - agricultural entomology
<p>The study described in this thesis aims to elucidate the fate and pathway of ingested TSWV in thrips during their development from larvae to adult. Insight in this process will contribute to a better understanding of the factors regulating and determining vector competence and specificities.<p>Analysis of the differences in virus susceptibility among thrips species or populations was approached by infection of cell cultures. The methodology developed and the media used to prepare primary cell cultures of the species <em>F. occidentalis</em> and <em>T. tabaci</em> are described and discussed in Chapter 2. The cultures obtained were derived from an efficiently transmitting <em>F. occidentalis</em> population and from a non-transmitting <em>T.</em><em>tabaci</em> population which was not able to transmit the virus. The results obtained by inoculation of these cultures with preparations of purified TSWV particles are described in Chapter 3. To analyse the tissue tropism of TSWV in thrips in relation to its vector competence, a novel histological technique, called whole mount immunofluorescent staining (WMIS) was developed (Chapter 4). Using this technique and other immunohistochemical techniques, infection of the midguts and salivary glands during the development of <em>F. occidentalis</em> thrips was described (Chapter 4). By the combination of all techniques, the temporal development of the virus infection in larvae and adults could be elucidated. To define the various barriers which may regulate the development of virus infection, specific TSWV mutants were used which failed either to infect the thrips or to convert the thrips in a transmitter after infection. Definite barriers were observed at the level of virus entry in the midgut epithelium or virus escape from the midgut to the salivary glands (Chapter 5). The pathway of the virus within the thrips and the mechanism determining the vector specificities were further unravelled by analysing the infection in thrips of a transmitting F. occidentalis population and a nontransmitting T. tabaci population (Chapter 6). Concluding remarks of this study is presented in Chapter 7.
Phylogeny and host-symbiont interactions of thelytoky inducing Wolbachia in Hymenoptera
Meer, M.M.M. van - \ 1999
Agricultural University. Promotor(en): Joop van Lenteren; R. Stouthamer. - S.l. : Van Meer - ISBN 9789058080509 - 118
wolbachia - symbionten - gastheren (dieren, mensen, planten) - hymenoptera - gastheer parasiet relaties - thelytoky - fylogenie - biologische bestrijding - landbouwkundige entomologie - insectenplagen - symbionts - hosts - host parasite relationships - phylogeny - biological control - agricultural entomology - insect pests
<H3>Summary and conclusions</H3><p>Bacteria of the genus <em>Wolbachia</em> (α-Proteobacteria, Rickettsia) are widespread in arthropods and can induce thelytoky (T) in parasitoids (Hymenoptera). Infection with thelytoky inducing <em>Wolbachia</em> (T- <em>Wolbachia</em> ) enables infected females to produce daughters from unfertilised eggs. Thelytokous strains can be maintained without the involvement of males. T- <em>Wolbachia</em> may represent a tool to improve biological control because only female parasitoids attack target pest species. Advantages of thelytokous reproduction of parasitic wasps in biological control programs may include: lower costs of mass rearing; faster population growth after release and easier establishment of thelytokous wasps in pest populations.Therefore, it was suggested to render sexual reproducing parasitoids thelytokous by infecting them with T- <em>Wolbachia</em> . To determine whether this approach was feasible, several experiments were done to improve our understanding of this specific host-symbiont relationship.</p><H3>Phylogeny</H3><p>The phylogeny of <em>Wolbachia</em> has been studied using 16S ribosomal DNA (rDNA) and the cell cycle gene <em>ftsZ</em> but sequence variation of those genes is limited. The spacer 2 region (SR2), the region between 23S rDNA and 5S rDNA, was amplified to determine if this region would improve phylogenetic resolution. The SR2 of <em>Wolbachia</em> is 66 basepairs (bp) long and shows slightly higher sequence differences between strains than <em>ftsZ</em> . Due to the short length of SR2 of <em>Wolbachia</em> , little phylogenetic information could be retrieved. Additional phylogenetic research was done using the sequence of an outer membrane protein ( <em>wsp</em> ) of <em>Wolbachia</em> . Previous research in Yale (USA) showed that this gene evolved at a much faster rate than 16S rDNA or <em>ftsZ</em> and the <em>Wolbachia</em> clade was subdivided into twelve distinct groups based on the proposed 2.5% <em>wsp</em> sequence divergence grouping criterion. We extended this former <em>Wolbachia</em><em>wsp</em> data set with fifteen T- <em>Wolbachia</em> strains and our results showed that: 1)Four new tested thelytokous parasitoids species were as well infected with <em>Wolbachia</em> ( <em>Amitus fuscipennis</em> , <em>Apoanagyrus diversicornis</em> , <em>Coccidoxenoides peregrinus</em> , <em>Eretmocerus staufferi</em> ); 2) T- <em>Wolbachia</em> clones are not closely related; 3) Based on identical <em>wsp</em> sequences of the moth <em>Ephestia kuehniella</em> (Lepidoptera) and its parasitoid <em>Trichogramma</em> , possible horizontal <em>Wolbachia</em> transfer between them was postulated. The exact mechanism of horizontal transfer remains to be clarified.</p><H3>Micro-injection</H3><p>Our goal was to do a T- <em>Wolbachia</em> transfer experiment between hymenopteran species to test whether arrhenotokous wasps could be rendered thelytokous. Infection of a host with <em>Wolbachia</em> can be accomplished by microinjection of the bacteria in an insect egg as shown for <em>Drosophila</em> sp. However, no suitable micro-injection protocol for parasitoids was available. We developed a injection protocol for the gregarious fly pupa parasitoid <em>Nasonia</em><em>vitripennis</em> because with this species, large number of eggs could be collected relatively easy. This facilitated the testing of the different steps of the micro-injection procedure. Different available micro-injection protocols of <em>Drosophila</em> spp. and <em>Tribolium confusum</em> were combined and optimal conditions for each of the different steps were determined. In addition, an <em>in vitro</em> incubation step for the <em>N. vitripennis</em> larvae had to be included. The final protocol enables us to do <em>Wolbachia</em> transfer studies in this species.</p><H3><em>Host</em> Wolbachia <em>interactions</em></H3><p>Different fitness parameters of T- <em>Wolbachia</em> infected and non-infected <em>Trichogramma</em> species were studied. <em>Trichogramma</em> are minute wasps which are widely used in biological control programs against lepidopteran pests. We distinguished two different <em>Trichogramma</em> populations: 1) 'Fixed' populations in which the infection is fully established so that only thelytokous females are present and 2) 'Mixed' populations in which thelytokous females coexist with arrhenotokous ones. In mixed populations thelytokous females are still able to mate and to produce daughters sexually. In mixed populations, a potential cytoplasmic-nuclear conflict exists but in fixed populations, this conflict is absent. It is theorised that fixation of the infection results in a reduction of negative impact of the symbiont on its host. This hypothesis was tested with the egg parasitoid <em>Trichogramma</em> because both mixed and fixed populations exist within this genus.</p><p>Two isofemale lines from fixed populations and four isofemale lines from mixed populations were 'cured' of <em>Wolbachia</em> infection using antibiotics and different lifespan fitness parameters were measured. Daughter production was significantly higher for the thelytokous fixed lines (16-131% more daughters) compared to the conspecific arrhenotokous ones. This is in contrast to the three mixed lines where the opposite was found (6-61% less daughters). Only slight fecundity effects of <em>Wolbachia</em> were found in the fixed lines (varying among 19% less offspring and 6% more offspring) while these effects are clearly negative in the mixed lines (34-49% less offspring).</p><p>Finally, we determined whether thelytokous wasps do equally well as biological control agents as their arrhenotokous counterparts. Theoretically, thelytokous wasps may be better biological control agents than the arrhenotokous ones. However, previous studies, show that <em>Wolbachia</em> can have a negative fecundity impact on their host. Therefore, other fitness parameters such as host searching efficacy, dispersal etc. could also be affected. We assessed whether <em>Wolbachia</em> infection had an impact on the 'parasitization efficiency' of the <em>Trichogramma</em> species <em>T. deion</em> and <em>T. cordubensis</em> in greenhouse compartments. Laboratory studies, to assess the effect of <em>Wolbachia</em> on host fecundity and dispersal were also done to correlate these results with the greenhouse experiment results. Laboratory results showed: 1) The fecundity of the thelytokous wasps species was reduced compared to the arrhenotokous counterparts; 2) Experiments of <em>Trichogramma</em> in a laboratory chamber showed that for both species, the arrhenotokous lines dispersed more than their thelytokous counterparts, suggesting a negative effect of <em>Wolbachia</em> on dispersal.Greenhouse experiments showed for both species that thelytokous wasps parasitize approximately equal number of patches but parasitize fewer eggs per patch than the arrhenotokous females.</p><p>These results correspond with the laboratory fecundity experiments. However, in contrast to laboratory chamber experiments, thelytokous <em>T. deion</em> females dispersed equally well as their arrhenotokous counterparts while thelytokous <em>T. cordubensis</em> females showed significant more dispersal than the arrhenotokous ones. No explanation was found for these dispersal differences in greenhouse or laboratory chamber experimental set-ups. According to calculations, it is still advantageous to use thelytokous parasitoids for biological control when the negative impact of <em>Wolbachia</em> on host fitness is taken into account.</p>
The molecular basis of the interactions between luteoviruses and their aphid vectors
Hogenhout, S.A. - \ 1999
Agricultural University. Promotor(en): R.W. Goldbach; J.F.J.M. van den Heuvel. - S.l. : Hogenhout - ISBN 9789058080523 - 119
luteovirus - plantenvirussen - plantenziekteverwekkers - plantenziekten - vectoren - transmissie - aphididae - landbouwkundige entomologie - interacties - plant viruses - plant pathogens - plant diseases - vectors - transmission - agricultural entomology - interactions
<p>Luteoviruses essentially replicate in the phloem tissue and are transmitted from plant to plant by aphids in a circulative, persistent manner. Virus particles are acquired when aphids feed on phloem sap. Particles are then transported from the midgut or hindgut into the haemolymph and from the haemolymph to the salivary gland, to be eventually released with the saliva to the phloem of uninfected plants. There is no evidence that luteoviruses replicate in the aphid vector. The haemolymph acts as a reservoir in which luteoviruses should persist in an infecting form during the whole lifespan of aphids.</p><p>A virus overlay technique was developed for the characterization of aphid-derived proteins involved in the circulative transmission of luteoviruses by aphids (Chapter 2). Proteins from whole-body homogenates of the aphid species <em>Myzus persicae</em> were separated with a two-dimensional denaturing poly-acrylamide gel (SDS-PAGE) and transferred to nitrocellulose membranes. Subsequently, these membranes were incubated with purified <em>Potato leafroll virus</em> (PLRV; genus <em>Polerovirus</em> ; Family <em>Luteoviridae</em> ) particles. Bound virus particles were detected by incubating membranes with anti-PLRV IgG and phosphatase conjugated goat anti-rabbit IgG. Thus it was demonstrated that PLRV particles bind to five different proteins. A protein of 63 kilodalton (p63) had the highest affinity for PLRV particles and was characterized by N-terminal amino-acid sequencing and immuno-gold labeling studies. These studies revealed that this protein is a homologue of GroEL and is abundantly synthesized by the primary bacterial endosymbiont ( <em>Buchnera</em> sp.) of <em>M. persicae</em> .</p><p>To show whether PLRV particles and <em>Buchnera</em> GroEL also interact <em>in vivo</em> , aphids were fed on diets containing tetracyclin (Chapter 2). This antibiotic acts as bacteriostatic by inhibiting protein synthesis. After a tetracyclin treatment, <em>Buchnera</em> GroEL was not detected in the haemolymph of the aphid, virus transmission was reduced by more than 70%, and the major viral capsid protein was degraded. These observations led to the suggestion that <em>Buchnera</em> GroEL is involved in protection of virus particles against proteolytic breakdown during circulation in the haemolymph.</p><p>To study the interaction of PLRV and <em>Buchnera</em> GroEL of <em>M. persicae</em> (MpB GroEL) in more detail, the gene encoding MpB GroEL and its flanking sequences were characterized and compared to those of <em>Escherichia coli</em> and <em>Buchnera</em> spp. of other aphid species (Chapter 3). The MpB GroEL encoding gene appeared to be part of an operon with a similar organization as the <em>groE</em> operon of <em>E. coli</em> , containing another gene for a 10-kDa protein with sequence similarities to GroES of <em>E. coli</em> . However, a constitutive promoter sequence comparable to that of the <em>E. coli</em><em>groE</em> operon could not be identified; only sequences comparable to the heat shock promoter of the <em>E. coli groE</em> operon were observed. Comparison of the deduced amino-acid sequences disclosed that MpB GroEL is approximately 98% similar to GroELs of other <em>Buchnera</em> spp. and 92% similar to <em>E. coli</em> GroEL. These results demonstrate that MpB GroEL belongs to the family 60-kDa chaperonin or heat shock protein family.</p><p>Several functions of GroEL proteins have been described and the most important one is the folding of nonnative proteins inside the cytosol of prokaryotes, mitochondria and chloroplasts. MpB GroEL and other GroEL proteins have typical double-doughnut structures composed of two stacked rings of seven subunits each. Using the crystal structure of <em>E. coli</em> GroEL, computer-generated structural predictions of the monomer of MpB GroEL was obtained (Chapter 3). Like <em>E. coli</em> GroEL, each subunit of MpB GroEL consists of an apical, an intermediate and an equatorial domain. The apical domain is a continuous domain on the primary MpB GroEL protein structure, whereas the equatorial and intermediate domains are discontinuous with regions located at the N- and C-terminus of the MpB GroEL subunit. The N- and C-terminal regions of the equatorial and intermediate domains assemble in the folded structure of MpB GroEL.</p><p>Functional studies of <em>E. coli</em> GroEL 14-mers have demonstrated that the apical domains are located at both sides of the cylindrical double-doughnut structure and contains amino acids involved in binding of nonnative proteins. The equatorial domains form the waist of the GroEL 14-mer. Intermediate domains function as hinges for moving the apical domain up and down so that amino acids in the apical domain can bind the unfolded protein. Subsequently, unfolded proteins are kept in the cavity of the GroEL 14-mer where they obtain their native structure without being disturbed by cytosolic compounds.</p><p>To investigate which of the domains of MpB GroEL are involved in binding PLRV particles, deletion mutants were designed based on the primary structure of the MpB GroEL protein (Chapter 3). Full-length MpB GroEL and MpB GroEL deletion mutants were expressed in fusion with glutathione-S-transferase (GST) in <em>E. coli</em> and affinity-purified. The GST moiety was removed and similar amounts of recombinant protein were tested for PLRV binding in virus overlay assays. This revealed that recombinant full-length MpB GroEL proteins had a similar affinity for PLRV particles as wild type MpB GroEL proteins isolated from <em>M. persicae</em> . PLRV particles displayed affinity for MpB GroEL deletion mutants only if they still contained the N- or C-terminal regions of the equatorial domain. Strikingly, PLRV-binding to polypeptides containing the apical domain alone or when extended with flanking sequences did not bind PLRV. Furthermore, virus overlay assays with additional MpB GroEL deletion mutants demonstrated that determinants for PLRV binding at the C-terminal part of the equatorial domain are located between residues 408 and 475 of MpB GroEL (Chapter 4). This region comprises threeα-helices.</p><p>Since the N- and C-terminal regions of the equatorial domain assemble in the folded structure of MpB GroEL, the two PLRV-binding regions may become a single PLRV-binding site. The finding that the equatorial domain was involved in binding PLRV particles and not the apical domain is surprising, since studies of <em>E. coli</em> GroEL showed that the apical domain is involved in binding of unfolded proteins in the cytosol of <em>E. coli</em> cells. PLRV particles may have different binding characteristics because of the size limitation of the central cavity of the GroEL molecule and the fact that binding occurs extracellularly in the haemolymph.</p><p>The interaction between PLRV particles and MpB GroEL was investigated in more detail (Chapter 4). Virus overlay studies with additional MpB GroEL deletion mutants revealed that regions between amino acid residues 1 and 57, and 427 and 457 of the N- and C-terminal regions of the equatorial domain, respectively, contain the determinants for PLRV binding. To determine which amino acids are involved in PLRV binding, overlapping decameric peptides of PLRV-binding regions were synthesized and incubated with virus particles in a virus overlay based experiment (Chapter 4). Alanine replacement studies of binding peptides showed that amino acids R13, K15, L17 and R18 of the N-terminal region of the equatorial domain, and R441 and R445 of the C-terminal region of the equatorial domain are responsible for PLRV binding. Alanine replacement of R13, K15, L17 and R18 eliminated PLRV binding of MpB GroEL(1-408) completely, whereas replacement of R441 and R445 reduced, but not eliminated, virus binding of MpB GroEL(122-548). This suggests that besides R441 and R445 other residues in the C-terminus are part of the PLRV-binding site.</p><p>These still unknown residues are likely to be located in the region between amino acids 427 till 474, which comprises oneα-helix located to the outside of GroEL 14-mers. Residues R13, K15, L17 and R18 are located in a longα-helix that is present more internally of GroEL 14-mers. The N- and C-terminal amino acids are positioned behind each other in a cavity, which might be accessible for the readthrough domain (RTD) which protrudes from the surface of a luteovirus particle.</p><p>The luteovirus protein capsid is composed of a major 23-kDa coat protein (CP), and lesser amounts of a ~54-kDa readthrough protein, expressed by translational readthrough of the CP into the adjacent open reading frame encoding the RTD. The RTD is exposed on the surface of the virus particle and contains the determinants necessary for virus transmission by aphids. To study whether the highly conserved major CP or the RTD of the minor 54-kDa protein are involved in GroEL binding, BWYV mutants devoid of the RTD were synthesized and tested for GroEL affinity in a GroEL-ligand assay (Chapter 5). It was found that the BWYV RTD mutants did not bind GroEL, indicating that the RTD contains the GroEL-binding determinants. BWYV mutants lacking the RTD domain were also injected into the haemolymph of aphids and the persistence of these mutants was compared with those of wild-type virus particles (Chapter 5). These studies clearly showed that BWYV mutants devoid of the RTD were more rapidly degraded than wild-type viruses, indicating that the RTD, containing the GroEL-binding sites, is crucial for the persistency in the aphid.</p><p>To reveal whether conserved domains of the RTD are involved in GroEL binding, five luteoviruses belonging to the genus <em>Polerovirus</em> and <em>Pea enation mosaic virus</em> (PEMV; <em>Enamovirus</em> ) were tested for binding to <em>Buchnera</em> GroEL proteins isolated from several aphid species using GroEL-ligand assays (Chapter 5). All luteoviruses displayed a specific but differential affinity for the GroEL homologues isolated from the endosymbiotic bacteria of both vector and non-vector aphid species, and for <em>E. coli</em> GroEL. This indicates that GroEL is not involved in vector specificity. Sequence alignment of the RTDs of different luteoviruses and PEMV revealed that only the N-terminal half of the RTDs is conserved, whereas the C-terminal halves have no global sequence identity. This C-terminal region is also lacking from the PEMV RTD. The highest overall level of sequence similarity in the RTD extends from position 184 to 223 where about 23% of the residues are identical.</p><p>To assess whether the viral determinants required for the interaction of luteoviruses with <em>Buchnera</em> GroEL reside in the conserved region of the RTD, GST-fusions of the RTD and mutants thereof were expressed in <em>E. coli</em> (Chapter 6). After affinity purification, the GST moiety was cleaved and the resulting RTD protein tested for MpB GroEL affinity using a GroEL-ligand assay. This showed that the conserved region of the RTD plays a crucial role in binding GroEL.</p><p>The knowledge derived from the binding studies of GroEL and luteoviruses is valuable for the development of specific control methods. The fact that <em>Buchnera</em> GroEL and luteoviruses directly interact <em>in vitro</em> suggests that this occurs in the haemolymph of aphids as well. Consequently, peptides or antibodies that interfere in this interaction by binding to the equatorial domain of <em>Buchnera</em> GroEL or the RTD of luteoviruses reduce specifically the transmission efficiency of luteoviruses by aphids. It is possible to produce these interfering compounds by plants so that aphids acquire them while feeding. Further studies should reveal whether there are possibilities for transporting peptides or antibodies from the gut to the haemolymph.</p><p>Chapter 7 of this thesis describes an investigation that may lead to an alternative control strategy. In this chapter the effects of neem ( <em>Azadirachta indica</em> A. Juss) seed kernel extracts (NSKE) and its major active compound, azadirachtin, on the ability of <em>M. persicae</em> to transmit PLRV is studied. This secondary plant metabolite has major effects on bacterial symbionts of leafhoppers. Since endosymbiotic bacteria play a major role in the performance of aphids and luteovirus transmission by aphids, it was investigated whether treatments with these compounds would exert an effect on aphid larval growth and mortality, and on the aphid intracellular symbionts. The neem metabolites displayed a 100% mortality at doses higher than 2560 ppm., and morphological aberrations on the bacterial endosymbionts were observed. At doses lower than 160 ppm of NSKE or azadirachtin, the endosymbiont population of <em>M. persicae</em> , and mortality, growth and feeding behavior was similar to that of the untreated groups of aphids. However, PLRV transmission was inhibited by 40-70%. These observations raise the possibility that interfering with the relationship between endosymbionts and aphids may contribute to the control of luteovirus transmission by aphids.</p>
Spiders (Araneae) as polyphagous natural enemies in orchards
Bogya, S. - \ 1999
Agricultural University. Promotor(en): Joop van Lenteren; P.J.M. Mols. - S.l. : Bogya - ISBN 9789058080370 - 189
boomgaarden - araneae - natuurlijke vijanden - insectenplagen - acari - landbouwkundige entomologie - orchards - natural enemies - insect pests - agricultural entomology
<p>Spiders (Araneae) occur in high abundance in all terrestrial ecosystems including agro-ecosystems. They are a very heterogeneous group of animals with different hunting tactics and therefore they play very different ecological roles. At family level these tactics are rather similar thus properties and behaviour found in different species of one family can be seen as characteristic for the whole family. Especially in orchards little is known about their role and probably it is undervalued. Therefore a comprehensive review (based on about 500 articles) of spiders as natural enemies of pest species of different crops was made resulting in information about the expected prey spectrum at family level. A qualitative evaluation of pest-spider relationship was carried out for a whole range of agro-ecosystems and the results are transposed to spider groups inhabiting the orchard ecosystems.</p><p>In a fundamental research project on integrated plant protection in orchards in Hungary (Apple Ecosystem Research) more than 2000 animal species were described for apple orchards. Until now the spiders were not studied in this project. The aim of this study is to describe the species richness and dominance order of spider communities inhabiting the canopy and the herbaceous-layer of apple and pear orchards in Hungary. Altogether 20283 individuals were collected belonging to 165 identifiable species. Considerable overlap has been observed between the spider fauna of apple and pear orchards.</p><p>Special attention is paid to the differences in spider fauna of orchards situated in different growing regions, because this knowledge can contribute to improve regional IPM programs. The great differences indicated that the composition of spider communities is basically determined by geographical locations. Although both the pesticide treatments and the different prey densities can significantly influence the densities of spiders, their effects on the composition of spider communities is limited.</p><p>The effect of conventional (based on broad-spectrum insecticides, e.g. OP's and pyrethroids) and integrated (based on selective chemicals, mainly IGR's) pest management systems on the canopy, herbaceous-layer and ground level inhabiting spider communities was investigated. The results lead to the conclusion that in case of applying integrated pest management there are possibilities to develop more complex spider communities. The negative effect of broad-spectrum compounds on spiders can be observed only on the canopy and to a lesser extent on the herbaceous-layer but not at the ground level. Regardless the pesticide treatments the composition of spider communities was similar.</p><p>The age of the orchards can significantly influence the spider density in the canopy through the prey density. In young (more vigorous) orchards, where the size of the canopy was smaller and the density of the pear lace bug ( <em>Stephanitis pyri</em> ) higher, significantly more complex hunting spider communities were present than in the same treated old orchards. This relationship was not observed in case of the guild web-building spiders. At the same time the diversity of the canopy inhabiting spider communities was higher in the old orchards, regardless of the chemical treatments.</p><p>The effect of the border of orchards on spider communities was investigated and it was found, that if selective insecticides were used the immigration into the orchards was significantly higher. While in case of applying broad-spectrum insecticides the canopy spider densities did not differ significantly between the outer rows and the interior rows of the orchards.</p><p>A considerable overlap exists between the spider communities of the canopy, the herbaceous-layer and the adjacent vegetation. Despite chemical treatments, exchange of individuals occurs and provides possibilities for re-colonization of spiders in the orchards from the herbaceous-layer and from the surroundings after pesticide treatments.</p><p>The most promising group of spiders in orchards is the clubionid spiders (Clubionidae) with as dominant species: <em>Clubiona pallidula</em> , <em>Clubiona phragmitis</em> , <em>Cheiracanthium mildei</em> . These spiders actively hunt on vegetation and never make a web for catching prey. Some species are winter-active, move and even hunt in winter. The low feeding rate in winter months at low temperature indicates that the winter-feeding will be of minor importance for natural pest control. In early spring when most of the other predators and parasitoids are not yet active, these spiders prey on pests that overwintered in the orchard like larvae of leafrollers (Tortricidae) and have a significant effect on suppression of pest populations.</p><p>Considerable predation by spiders was observed of the key pear pest, the pear suckers ( <em>Cacopsylla spp</em> .) and of the pear lace bug ( <em>Stephanitis pyri</em> ) common in IPM orchards in the vegetative period. In the latter case it was observed that the clubionid spider <em>Ch. mildei</em> showed a positive numerical response to prey density in the field, indicating density dependent mortality resulting in a better natural control.</p><p>The predatory capacity of clubionid spiders was estimated to be 3.3 mg at 10 °C to 5.7 mg at 20 °C per day with a model based on digestion and egestion characteristics. This indicates a daily potential killing rate of 3-6 small (L <sub>1</sub> -L <sub>3</sub> ) caterpillars of leafrollers depending on temperature. The size of the population in an untreated apple orchard was estimated to be 60.000 clubionids / ha (22 per tree) by mark-recapture method using double-release protocol in spring. These two findings indicate that spiders can be important in reduction of orchard pests, indeed.</p><p>The data provided in this thesis indicate that the role of spiders as natural control agents in orchards can be augmented. In orchards where Integrated Pest Management is applied, and where the use of broad-spectrum pesticides is minimized, an excellent possibility is available to develop more complex and abundant spider communities, which can contribute to a better suppression of pests.</p>
New Ichneumonidae, parasitic upon the rice borer Rupela albinella (Cr.) (Lep. Pyralidae) in Surinam, with a key to the species of Strabotes (Hym., Ichneumonidae)
Zwart, K.W.R. - \ 1973
Wageningen : Landbouwhogeschool (Celos bulletins no. 21) - 9
suriname - landbouwkundig onderzoek - rijst - rupela albinella - ichneumonidae - parasieten - entomologie - landbouwkundige entomologie - agricultural research - rice - parasites - entomology - agricultural entomology
Venturia ovivenans nov. spec, and Strabotes rupelae nov. spec, are described. Both were reared from the rice stem borer Rupela albinella (Cr.) in Surinam (Sth. America). Strabotes abdominalis obscurus nov. subspec. is described from Columbia and a key is given to the known species of the Neotropic genus Strabotes Townes.
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