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

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

    Induction of indirect plant defense in the context of multiple herbivory : gene transcription, volatile emission, and predator behavior
    Menzel, T.R. - \ 2014
    Wageningen University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462571297 - 146
    planten - plaagresistentie - geïnduceerde resistentie - verdedigingsmechanismen - multitrofe interacties - phaseolus lunatus - mijten - tetranychus urticae - roofmijten - phytoseiulus persimilis - voedingsgedrag - genen - transcriptie - genexpressie - herbivoor-geinduceerde plantengeuren - plants - pest resistance - induced resistance - defence mechanisms - multitrophic interactions - phaseolus lunatus - mites - tetranychus urticae - predatory mites - phytoseiulus persimilis - feeding behaviour - genes - transcription - gene expression - herbivore induced plant volatiles

    Abstract

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

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

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

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

    Verbeterde spintbestrijding door inductie van plantweerbaarheid in komkommer
    Messelink, G.J. ; Groot, E.B. de; Holstein, R. van - \ 2010
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1045) - 22
    tetranychus urticae - komkommers - cucumis sativus - biologische landbouw - biopesticiden - tetranychus urticae - cucumbers - cucumis sativus - organic farming - microbial pesticides
    Samenvatting en vertaling voor internet De biologische bestrijding van spint in komkommer met de roofmijt Phytoseiulus persimilis gaat beter op planten die vooraf behandeld zijn met middelen die resistentie induceren. Plantmetingen (metabolietenanalyses) geven aan dat deze resistentie sterk gekoppeld is aan de aanmaak van flavonoïde afweerstoffen die spint remmen in hun groeisnelheid. Dit onderzoek werd gefinancierd door het Productschap Tuinbouw in samenwerking met het ministerie van Economische Zaken, Landbouw en Innovatie. Abstract Biological control of the spider mite Tetranychus urticae by the predator Phytoseiulus persimilis is significantly enhanced on cucumber plants where resistance was induced by elicitors. Plant metabolomic analyses showed that resistance was strongly correlated with the production of flavonoids, which slow down the population incresae of spider mites. This study was supported by the Dutch Product Board for Horticulture and the Ministry of Economic Affairs, Agriculture and Innovation.
    On-farm evaluation of integrated pest management of red-spider mite in cut roses in Ethiopia : final report to the Ministry of Agriculture and Rural Development
    Belder, E. den; Elings, A. ; Yilma, Y. ; Dawd, M. ; Lemessa, F. - \ 2009
    Wageningen : Wageningen UR Greenhouse Horticulture (Report / Wageningen UR Greenhouse Horticulture 296) - 21
    rosa - rozen - siergewassen - geïntegreerde plagenbestrijding - biologische bestrijding - tetranychus urticae - predatoren van schadelijke insecten - phytoseiulus persimilis - amblyseius - ethiopië - rosa - roses - ornamental crops - integrated pest management - biological control - tetranychus urticae - predators of insect pests - phytoseiulus persimilis - amblyseius - ethiopia
    'Spint dé plaag in glastuinbouw' : Onderzoeker Pierre Ramakers van Wageningen UR Glastuinbouw
    Stijger, H. ; Wageningen UR Glastuinbouw, - \ 2009
    Nieuwe oogst / Magazine tuinbouw 5 (2009)6. - ISSN 1871-0921 - p. 6 - 6.
    tuinbouw - teelt onder bescherming - plagenbestrijding - tetranychus urticae - roofmijten - gewasbescherming - glastuinbouw - horticulture - protected cultivation - pest control - tetranychus urticae - predatory mites - plant protection - greenhouse horticulture
    Vanuit de biologie bekeken is spint de centrale plaag in gewassen onder glas. Volgens entomoloog Pierre Ramakers van Wageningen UR Glastuinbouw zijn de drie hoofdplagen spintmijt, trips en wittevlieg. Van die drie heeft spint het beste aanpassingsvermogen
    Spint in komkommer
    Messelink, G.J. ; Holstein, R. van; Groot, E.B. de - \ 2009
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport / Wageningen UR Glastuinbouw 229) - 20
    cucumis sativus - komkommers - tetranychus urticae - plagenbestrijding - roofmijten - biologische bestrijding - glastuinbouw - gewasbescherming - cucumis sativus - cucumbers - tetranychus urticae - pest control - predatory mites - biological control - greenhouse horticulture - plant protection
    In komkommer worden verschillende soorten roofmijten ingezet voor de biologische bestrijding van trips, witte vlieg en spint. Het is een algemeen verschijnsel in de natuur dat roofdieren niet alleen hun prooi eten, maar ook effect op elkaar kunnen hebben. In dit onderzoek hebben we gekeken of de generalistische roofmijt A. swirskii een effect kan hebben op de spintroofmijten Phytoseiulus persimilis en Neoseiulus californicus, en wat de gevolgen voor de bestrijding van spint kunnen zijn. In een kasproef bleek inderdaad dat A. swirskii de aantallen P. persimilis kan reduceren, maar alleen in kleine spinthaarden. Bij N. californicus kon dit negatieve effect van A. swirskii niet worden aangetoond. De bestrijding van spint met deze roofmijten werd in beide gevallen niet significant verstoord. Een laboratoriumproef liet zien dat A. swirskii belemmerd wordt door het spintweb, waardoor de spintroofmijten, die wel het spintweb ingaan, beschermd zijn tegen predatie door A. swirskii. Er is kortom geen belemmering om de gespecialiseerde spintroofmijten P. persimilis of N. californicus gecombineerd met A. swirskii in komkommer in te zetten. Tijdens dit onderzoek is de merkwaardige ontdekking gedaan dat planten die licht besmet waren met kaswittevlieg de ontwikkeling van spint aanzienlijk kunnen remmen ten opzichte van planten zonder kaswittevlieg en dat de biologische bestrijding daardoor ook significant verbeterd wordt. Kasproeven lieten zien dat alleen de larven van witte vlieg bij dichtheden vanaf 80 per plant deze remming van spint kunnen veroorzaken. Op basis deze geïnduceerde resistentie kunnen we maatregelen ontwikkelen die de bestrijding van spint verbeteren.
    Bonenspint is goed geïntegreerd te bestrijden
    Blok, J.J. de; Dorresteijn, W. - \ 2009
    De Boomkwekerij 22 (2009)2. - ISSN 0923-2443 - p. 10 - 12.
    plantenkwekerijen - tetranychus urticae - organismen ingezet bij biologische bestrijding - geïntegreerde plagenbestrijding - biologische bestrijding - natuurlijke vijanden - nurseries - tetranychus urticae - biological control agents - integrated pest management - biological control - natural enemies
    Bonenspint is te bestrijden door roofmijten in te zetten. Een demo op twee bedrijven maakt duidelijk dat de kosten van een geïntegreerde bestrijding weinig verschillen met die van een chemische aanpak. Nieuwe methoden van inzetten kunnen ertoe bijdragen dat deze vorm van geïntegreerde bestrijding nog aantrekkelijker wordt
    Veelbelovende alternatieven voor spintmijtbestrijding in aardbei
    Kruistum, G. van - \ 2008
    Kennis Online (2008).
    gewasbescherming - biologische bestrijding - aardbeien - tetranychus urticae - roofmijten - tetranychidae - vollegrondsteelt - plant protection - biological control - strawberries - tetranychus urticae - predatory mites - tetranychidae - outdoor cropping
    Resultaten uit lopend onderzoek naar de mogelijkheid roofmijten in te zetten bij de biologische bestrijding van spintmijt in de aardbeienteelt
    Bestrijding aardbeimijt in plantmateriaal: Eindrapport onderzoekfase III & IV
    Kruistum, G. van; Vlaswinkel, M.E.T. ; Spoorenberg, P.M. ; Buddendorf, C.J.J. ; Schaik, A. van; Zouwen, F. van - \ 2008
    Lelystad : PPO AGV (Rapport / PPO-AGV ) - 55
    fragaria ananassa - aardbeien - plantmateriaal - mijten - tetranychus urticae - mijtenbestrijding - nederland - fragaria ananassa - strawberries - planting stock - mites - tetranychus urticae - mite control - netherlands
    Op basis van een jaarlijkse ontheffing werd in Nederland voor de ontsmetting van aardbeiplanten voor vermeerdering tot in het jaar 2007 methylbromide toegepast. Door het gecontroleerd begassen van het basisplantgoed (moederplanten) met methylbromide werd o.a. de gevreesde aardbeimijt zeer effectief bestreden, tot minimaal 99,8%. Hiervoor werd in Nederland jaarlijks 120 kg actieve stof methylbromide ingezet. Vanwege de ongunstige neveneffecten van methylbromide, o.a. op aantasting van de ozonlaag, is internationaal afgesproken om het gebruik van deze stof te beeindigen. Wereldwijd wordt gezocht naar alternatieven voor de toepassing van methylbromide. Dit afsluitende projectrapport gaat in op het onderzoek naar enkele mogelijke alternatieven voor methylbromide en de precieze afstelling en opschalingnaar praktijkniveau van de meest perspectiefvolle methode, de CAwarmtebehandeling.
    Nieuwe ontwikkelingen met roofmijten tegen spint
    Dorresteijn, W. ; Blok, J.J. de - \ 2008
    De Boomkwekerij 21 (2008)29/30. - ISSN 0923-2443 - p. 10 - 11.
    boomkwekerijen - geïntegreerde plagenbestrijding - biologische bestrijding - organismen ingezet bij biologische bestrijding - roofmijten - tetranychus urticae - forest nurseries - integrated control - biological control - biological control agents - predatory mites - tetranychus urticae
    Bonenspintmijt is een lastig te bestrijden plaag. Een aantal boomkwekers heeft goede ervaringen met het inzetten van roofmijten tegen deze plaag. Nieuwe ontwikkelingen, zoals een lagere prijs en andere methoden van inzetten, kunnen ervoor zorgen dat deze vorm van geïntegreerde bestrijding steeds aantrekkelijker wordt.
    Evaluatie spintbestrijding in komkommer
    Messelink, G.J. - \ 2006
    Naaldwijk : Praktijkonderzoek Plant & Omgeving B.V., Sector Glastuinbouw - 23
    cucumis sativus - komkommers - tetranychus urticae - plantenplagen - biologische bestrijding - roofmijten - plantenziektebestrijding - glastuinbouw - vruchtgroenten - cucumis sativus - cucumbers - tetranychus urticae - plant pests - biological control - predatory mites - plant disease control - greenhouse horticulture - fruit vegetables
    Dit korte verslag is het resultaat van een consultancy-opdracht op verzoek van de landelijke komkommercommissie. De opdracht was te evalueren wat de knelpunten zijn bij de bestrijding van spint en wat de mogelijkheden zijn om de bestrijding van spint te verbeteren. Een literatuurstudie heeft laten zien dat er vooral mogelijkheden zijn om de bestrijding van spint te verbeteren met roofmijten. Nagegaan is welke van de toegelaten chemische spintmiddelen integreerbaar zijn. Een tweetal alternatieve maatregelen tegen spint worden genoemd, luchtbevochtiging en resistentieveredeling. Om een helder beeld te krijgen van de spintproblematiek in de Nederlandse komkommerteelt zijn 8 adviseurs van verschillende firma’s en uit verschillende regio’s geïnterviewd. De belangrijke knelpunten zijn benoemd. Opvallend was dat de adviseurs over het gebruik van abamectine (Vertimec) soms tegengestelde meningen ventileren. De één schrijft dit middel standaard voor, terwijl andere voorlichters soms adviseren dit middel weg te laten om zo meer ruimte te geven voor biologische bestrijding. De adviseurs geven diverse suggesties voor onderzoek naar spint in komkommer. Het verslag is afgesloten met een aantal aanbevelingen om methoden te ontwikkelen waarmee de spintbestrijding kan worden verbeterd.
    Hoe roofmijten hun prooi vinden met behulp van plantengeuren
    Boer, J.G. de; Dicke, M. - \ 2005
    Entomologische Berichten 65 (2005)4. - ISSN 0013-8827 - p. 112 - 117.
    phytoseiulus persimilis - tetranychus urticae - phaseolus lunatus - predator prooi verhoudingen - geurstoffen - insectenlokstoffen - phytoseiulus persimilis - tetranychus urticae - phaseolus lunatus - predator prey relationships - odours - insect attractants
    Plantengeuren die de planten afgeven na vraat door een herbivoor insect worden door hun natuurlijke vijanden gebruikt om hun prooi te vinden. Hierover is al meer dan 25 jaar onderzoek gedaan. Recent onderzoek in het tritrofe systeem van limaboonplanten (Phaseolus lunatus), spintmijten (Tetranychus urticae) en roofmijten (Phytoseiulus persimilis) heeft uitgewezen dat roofmijten met behulp van herbivoor-geïnduceerde plantengeuren hun prooi ook kunnen vinden in een omgeving met diverse soorten planten en herbivoren.
    Biologische spintbestrijding in roos : ontwikkeling van de inheemse roofmijt Amblyseius andersoni
    Linden, A. van der - \ 2004
    Boskoop : Praktijkonderzoek Plant & Omgeving, Bomen - 30
    tetranychus urticae - rosa - rozen - biologische bestrijding - organismen ingezet bij biologische bestrijding - roofmijten - plagenbestrijding - plantenziektebestrijding - sierplanten - tetranychus urticae - rosa - roses - biological control - biological control agents - predatory mites - pest control - plant disease control - ornamental plants
    Spint behoort tot de belangrijkste plagen in roos. In de meeste gevallen gaat het om bonespintmijt Tetranychus uticae Koch (Acari: Tetranychidae), maar in mindere mate kan ook fruitspint Panonychus ulmi (Koch) (Acari: Tetranychidae) optreden. Bonespint overwintert als bevruchte vrouwtjes door vanaf september ergens in weg te kruipen. Op een boom kruipen ze bijvoorbeeld in kiertjes in de schors. Bij rozen zoeken ze daarom de basis van de plant, waar de beste overwinteringmogelijkheid te vinden is. In het voorjaar worden de vrouwtjes weer actief en zoeken groen blad om zich te voeden en eieren te gaan leggen. Dikwijls gaan ze daarvoor eerst naar onkruiden omdat er aan bomen en struiken nog geen bladeren zitten. Later gaan ze boom of struik weer in. Als spint tot een plaag uitgroeit, wordt de groei van het gewas benadeeld. Bij aantasting kleuren de bladeren geel en uiteindelijk vallen de bladeren zelfs af. Als een spintaantasting niet wordt behandeld en de spint gaat vanaf september in diapauze, dan komt spint in het volgende voorjaar opnieuw te voorschijn. In stammentrekkers is een spintaantasting vanwege de sterke groei van het gewas meestal geen acuut probleem. Door de ondoordringbaarheid van het gewas is een chemische bestrijding in de zomer ook nauwelijks meer uitvoerbaar. De hoeveelheid aanwezige spint kan erg groot zijn, waardoor voor het volgende jaar een aanzienlijke infectiedruk wordt opgebouwd. Een biologische bestrijder heeft geen moeite met een dicht gewas. Geïntegreerde plaagbestrijding bestaat naast biologische bestrijding uit een bewuste keuze van selectieve chemische middelen. Er worden weliswaar natuurlijke vijanden gekweekt voor de glastuinbouw, maar met ingang van 2005 is een vrijstellingslijst van kracht. De toepassing van exotische natuurlijke vijanden staat onder druk. Staat een organisme niet op de lijst, dan mag die niet worden toegepast. Maar ook afgezien daarvan is het van groot belang om vast te stellen welke inheemse natuurlijke vijanden spontaan op roos voorkomen. Het spontane voorkomen op een bepaalde waardplant is een eerste aanwijzing dat een natuurlijke vijand zich op die plant thuis voelt. Een volgende stap is vast te stellen of deze natuurlijke vijanden op één of andere wijze zijn te bevorderen of op een betaalbare wijze zijn te kweken. r De meest voor de hand liggende kandidaten zijn roofmijten, omdat deze ook bij lagere aantallen spint nog steeds een belangrijke rol spelen bij de regulatie van spint. De kans dat roofmijten zijn te kweken tegen niet te hoge kosten is het grootst.
    Onderzoek naar en ontwikkeling van een nieuw bacterieel biopesticide voor de biologische bestrijding van trips en spint
    Kogel, W.J. de; Ravensberg, W.J. - \ 2004
    Berkel en Rodenrijs : Koppert - 19
    gewasbescherming - insectenplagen - bacteriële insecticiden - insectenpathogene bacteriën - organismen ingezet bij biologische bestrijding - biologische bestrijding - frankliniella occidentalis - tetranychus urticae - plant protection - insect pests - bacterial insecticides - entomopathogenic bacteria - biological control agents - biological control - frankliniella occidentalis - tetranychus urticae
    In dit project worden enkele veelbelovende bacteriestammen gescreend op hun parasitaire werking tegen trips (Frankliniella occidentalis) en spint (Tetranychus urticae). In de loop van het onderzoek zijn verschillende bacterie-isolaten onderzocht en steeds is getoetst of deze isolaten qua werking en veiligheid voldoende perspectief boden als mogelijk nieuw bestrijdingsmiddel. Uiteindelijk zijn de onderzochte bacterie-isolaten om verschillende redenen allemaal afgevallen. Wat deze studie wel heeft opgeleverd is het inzicht dat verschillende soorten bacteriën die in of op de plant kunnen voorkomen een dodend effect op insecten en mijten kunnen hebben. Hoewel het hier beschreven onderzoek niet geresulteerd heeft in een nieuw bestrijdingsmiddel heeft het wel laten zien dat bacteriën in en op de plant in potentie grote effecten op gewasbelagers kunnen hebben.
    Verdedigingsmechanismen van planten in een tritroof systeem
    Boom, C.E.M. van den - \ 2003
    Gewasbescherming 34 (2003)6. - ISSN 0166-6495 - p. 194 - 196.
    fabaceae - solanaceae - tetranychus urticae - phytoseiulus persimilis - tetranychidae - roofmijten - verdediging - aantasting - vluchtige verbindingen - jasmonzuur - plantensamenstelling - lokstoffen - fractionering - fabaceae - solanaceae - tetranychus urticae - phytoseiulus persimilis - tetranychidae - predatory mites - defence - infestation - volatile compounds - jasmonic acid - plant composition - attractants - fractionation
    The spider mite Tetranychus urticae Koch is a serious pest in field crops, glasshouse vegetables and fruit crops. It is a generalist herbivore with several hundreds of host plant species. Phytoseiulus persimilis Athias-Henriot is one of its natural enemies. Investigations of the tritrophic system of plant, T. urticae and P. persimilis will contribute to a better knowledge about the direct and indirect defence defensive strategies of plant species. Host plant acceptance by the spider mite T. urticae, as a measure of the plant’s direct defence, was investigated for eleven plant species. The degree to which the spider mites accepted a plant was expected to depend on differences in nutritive and toxic constituents among plant species. At the level of plant species, a large variation in the degree of acceptance by T. urticae was found. Except for ginkgo (Ginkgo biloba) most plants were accepted or well accepted by the spider mites. At the level of plant family, four plant species from the Fabaceae were compared to four plant species from the Solanaceae. It was shown that all species from the Fabaceae were accepted by the spider mites for feeding, while plant species from the Solanaceae varied in spider mite acceptance from well accepted (tobacco: Nicotiana tabacum) to poorly accepted (sweet pepper: Capsicum annuum)
    Plant defence in a tritrophic context : chemical and behavioural analysis of the interactions between spider mites, predatory mites and various plant species
    Boom, C.E.M. van den - \ 2003
    Wageningen University. Promotor(en): Marcel Dicke; Aede de Groot, co-promotor(en): Teris van Beek. - [S.I.] : S.n. - ISBN 9789058088062 - 148
    fabaceae - solanaceae - tetranychus urticae - phytoseiulus persimilis - tetranychidae - roofmijten - verdediging - aantasting - vluchtige verbindingen - jasmonzuur - plantensamenstelling - lokstoffen - fractionering - fabaceae - solanaceae - tetranychus urticae - phytoseiulus persimilis - tetranychidae - predatory mites - defence - infestation - volatile compounds - jasmonic acid - plant composition - attractants - fractionation

    The spider mite Tetranychus urticae Koch is a serious pest in field crops, glasshouse vegetables and fruit crops. It is a generalist herbivore with several hundreds of host plant species. Phytoseiulus persimilis Athias-Henriot is one of its natural enemies. Investigations of the tritrophic system of plant, T. urticae and P. persimilis will contribute to a better knowledge about the direct and indirect defence defensive strategies of plant species.

    Host plant acceptance by the spider mite T. urticae , as a measure of the plant's direct defence, was investigated for eleven plant species. The degree to which the spider mites accepted a plant was expected to depend on differences in nutritive and toxic constituents among plant species. At the level of plant species, a large variation in the degree of acceptance by T. urticae was found. Except for ginkgo ( Ginkgo biloba ) most plants were accepted or well accepted by the spider mites. At the level of plant family, four plant species from the Fabaceae were compared to four plant species from the Solanaceae. It was shown that all species from the Fabaceae were accepted by the spider mites for feeding, while plant species from the Solanaceae varied in spider mite acceptance from well accepted (tobacco: Nicotiana tabacum ) to poorly accepted (sweet pepper: Capsicum annuum ).

    Some of the plant species that had already been investigated with respect to spider mite acceptance were tested for their degree of indirect defence. After spider mite-infestation the plants attracted the predatory mite P. persimilis . The results showed that plants from all species significantly attracted the predatory mites when infested by spider mites. Experience with the spider mite-infested leaves of the investigated plant species did not affect the predatory mite's choice. Based on the results that spider mites did not survive on ginkgo leaves, these leaves were treated with jasmonic acid to induce a mimic of a spider mite-induced volatile blend. The predatory mites were slightly attracted to the induced volatile blend of jasmonic acid treated leaves. In summary, plants do invest in indirect defence after being attacked by spider mites, even when some plants have already a strong direct defence.

    Subsequently , it was investigated to what degree spider mite-infestation of plants from all species resulted in the emission of novel compounds that were not emitted by undamaged or mechanically damaged plants of the same species. Therefore, the volatiles emitted by T. urticae -infested leaves were analysed and compared to volatiles emitted by clean and mechanically damaged leaves of the same plant species. Almost all of the investigated plant species produced novel compounds that dominated the volatile blend after spider mite infestation, such as methyl salicylate, terpenes, oximes or nitriles. However, spider mite-infested eggplant and tobacco emitted only a few novel compounds and in small amounts. Methyl salicylate was found as dominant compound in six of the investigated plant species and as a less dominant compound in two plant species. However, it was concluded that methyl salicylate alone does not necessarily indicate spider mite-damage of the plant.

    In the introduction (Chapter 1) a hypothesis was postulated that plant species with a weak direct defence would invest in the production of novel compounds after spider mite-infestation, in contrast to plant species that possessed a strong direct defence. However, although plant species that have a weak direct defence can use indirect defence to defend themselves, they do not always emit novel compounds. At the level of plant family qualitative differences in volatile blends from spider mite-infested leaves compared to mechanically-damaged leaves were more prominently found in the Fabaceae than in the Solanaceae.

    A fractionation method was developed for identification of the biologically active compounds in mixtures of volatile compounds (or volatile mixtures), which is more selective and efficient than conventional techniques such as comparison of volatile profiles or the use of synthetic mixtures. With this method bioactive compounds that mediate interactions within and among species can be determined more quickly. First, separation of the volatile mixture was carried out in a gas chromatograph. This made it possible to selectively remove compounds from the mixture. Before the volatiles were tested on bioactivity in an olfactometer, the compounds were revolatilised by thermal desorption and stored in a Teflon bag. Subsequently, the Teflon bag was pressurised and a continuous flow of volatiles was led to the olfactometer.

    Validation of the method showed that most of the investigated compounds that varied in boiling points and in chemical nature showed a high recovery (80-100 %). Only compounds that had a relatively high boiling point (> 300 °C) or contained a phenolic group showed low recoveries (30-50 %). The biological activity of the volatiles emitted by T. urticae -infested lima bean leaves ( Phaseolus lunatus ) and the compounds methyl salicylate and (3 E )-4,8-dimethyl-1,3,7-nonatriene were successfully tested after being processed with the method. An advantage of the method is that volatile blends can selectively be manipulated. Besides, solvent introduction into the bioassay can be circumvented. After processing and revolatilization of the mixture, a known concentration of the volatiles can be led to the bioassay. In potential, the method can be useful to determine biologically active compounds from complex mixtures in the future.

    Plant effects on biological control of spider mites in the ornamental crop gerbera
    Krips, O.E. - \ 2000
    Agricultural University. Promotor(en): M. Dicke; M.W. Sabelis; J.C. van Lenteren. - S.l. : S.n. - ISBN 9789058081889 - 113
    gerbera jamesonii - tetranychus urticae - mijten - plantenplagen - biologische bestrijding - phytoseiulus persimilis - organismen ingezet bij biologische bestrijding - plaagresistentie - resistentie van variëteiten - planteffecten - gerbera jamesonii - tetranychus urticae - mites - plant pests - biological control - phytoseiulus persimilis - biological control agents - pest resistance - varietal resistance - plant effects

    Introduction

    The spider mite Tetranychus urticae Koch is an important pest in many greenhouse crops. In vegetables it can be successfully controlled with the predatory mite Phytoseiulus persimilis Athias-Henriot, a specialist predator of spider mites (Helle & Sabelis, 1985). However, on ornamental crops where aesthetic damage is not tolerated, biological control is more difficult. Pest control on ornamentals mainly relies on the use of pesticides (van de Vrie, 1985).

    In the ornamental crop gerbera, Gerbera jamesonii Bolus, biological control stands a better chance, since gerbera cutflowers are sold without leaves. The leaves stay behind on the plants in the greenhouse, when flowers are harvested. Therefore, zero tolerance for aesthetic damage does apply for gerbera cutflowers but not for the leaves (van de Vrie, 1985).

    In gerbera, spider mites usually only damage leaves and do not feed on flowers. The spider mites only migrate to the flowers when the leaves become overexploitated. Gerbera growers will interfere with control methods long before overexploitation takes place. If they apply biological control, there will be some damage by spider mites on the plant leaves. But spider mite damage on the leaves can be accepted, as long as it does not lead to an intolerable lower flower production by the plants. Therefore, biological control may be a suitable method to control spider mites in gerbera.

    Many cultivars of gerbera are commercially available. At present these cultivars are mainly selected for the colour and shape of the flowers. However, the cultivars also differ in several plant characteristics that have not been selected for, such as leaf shape and density of trichomes on the undersurface of the leaves (Sütterlin and van Lenteren, 1997; Krips et al. , 1999a). Earlier studies showed that the success of natural enemies in biological control can be influenced strongly by characteristics of the host plant (Bergman and Tingey, 1979, Boethel and Eikenbary, 1986;van Lenteren and de Ponti, 1990; Hare, 1992; Walter, 1996). If gerbera cultivars differ in such characteristics, biological control may not be equally successful on all cultivars.

    The objective of this PhD study was to investigate which differences between gerbera cultivars result in differences in the success of biological control of T. urticae with the predatory mite P. persimilis. We have focussed on the following three host plant characteristics:

    1. Host plant resistance to T. urticae
    2. Density of leaf hairs on the under surface of leaves
    3. Production of volatiles by leaves with spider mite damage

    We determined to which extent gerbera cultivars differ in each of these characteristics. In addition, we assessed the effect of these characteristics on certain aspects of the interaction between spider mites and their predators on gerbera.

    1. Host plant resistance to T. urticae

    The intrinsic rate of population increase, r m , of T. urticae was determined on nine gerbera cultivars. The r m differed largely per cultivar and varied from 0.09-0.23/day. Hence, gerbera cultivars differ largely in resistance to T. urticae. However even on the most resistant cultivar additional methods of spider mite control will eventually be necessary. An obvious additional method is biological control with the predatory mite P. persimilis. But this is only possible if plant resistance to spider mites and biological control are compatible in gerbera.

    To investigate whether resistance and biological control of spider mites are compatible in gerbera, we determined the r m of the predatory mite P. persimilis on four gerbera cultivars on which the r m of T. urticae differed largely. Cultivar differences in r m of the predators were negligible, the r m varied from 0.43/day to 0.45/day. This indicates that a combined use of resistance and biological control of spider mites might be possible in gerbera.

    In contrast to what is commonly assumed, the speed at which spider mites are exterminated by P. persimilis is not higher on resistant cultivars than on susceptible cultivars. At first this seems to be an argument against breeding for resistance to spider mites in any crop. However, the advantage of resistant cultivars lies more in the time before predator introduction is necessary, so, to delay the moment that addidtional control methods are necessary, than in the success of biological control after predators are introduced.

    2. Density of leaf hairs on the under surface of leaves

    Gerbera cultivars differ largely in density of trichomes on the undersurface of leaves (Sütterlin & van Lenteren, 1997). We investigated whether prey searching behaviour of P. persimilis is affected on cultivars with a high density of trichomes. We determined the walking speed, walking activity and rate of encounter with prey on three cultivars with trichome densities of 105, 400 and 730 trichomes/cm 2. Furthermore, we assessed the predation rate on these three cultivars at three prey densities.

    Walking speed of the predators was highest on the cultivar with the lowest leaf hair density. Walking activity, defined as the percentage of time the predators spent walking, was not dependent on leaf hair density of the cultivars. The rate of encounter with prey was inversely related to trichome density. Predation rate of adult female P. persimilis was affected negatively by trichome density when prey density was low. However, at high prey density such an effect was absent, because the predation rate is not limited by the rate of encounter with prey at high prey density.

    The results of these experiments showed that the effect of trichome density on the predator-prey dynamics between T. urticae and P. persimilis on gerbera plants will be dependent on the density in which T. urticae occurs on these plants. In a small-scale greenhouse experiment we found indications that the density of T. urticae is limiting the population growth rate of the predators and that trichome density affects the growth of the predator populations on gerbera plants.

    3. Production of volatiles by leaves with spider mite damage

    Many host plant species produce volatiles when herbivores damage the leaves. Natural enemies of the herbivores can use these volatiles to locate plants that are infested with their prey or hosts (see Vet & Dicke, 1992 and Dicke, 1994 for reviews). Such volatiles also are important in the interaction between T. urticae and P. persimilis (Sabelis and van de Baan, 1983; Sabelis et al . , 1984; Dicke and Sabelis, 1988; Dicke et al . , 1990a,b; Sabelis and van der Weel, 1994; Sabelis and Afman, 1994). Plants of several species produce volatiles when spider mites damage their leaves. Phytoseiulus persimilis is attracted to these volatiles (Dicke and Sabelis, 1988). Once the predators have found spider mite-infested leaves, they stay there until all prey is exterminated, which is most likely the result of attraction of the predators to volatiles from the spider mite patch and arrestment by these volatiles (Sabelis & van de Meer, 1986; Sabelis and Afman, 1994).

    We have investigated whether gerbera leaves with spider mite damage also produce volatiles that attract P. persimilis. In contrast to undamaged gerbera leaves that had a low production of volatiles, spider mite-damaged gerbera leaves produced many volatiles in large quantities. However, P. persimilis from our standard culture on Lima bean leaves with T. urticae was not attracted to these volatiles. In contrast, the predators responded strongly to the gerbera volatiles when they were given six days of experience with spider mites on gerbera leaves and therefore were exposed to the spider mite-induced volatiles for six days.

    We have investigated whether the chemical composition of the spider mite-induced volatiles differs between gerbera cultivars. Furthermore, we determined whether cultivar differences exist in attractiveness of the spider mite-induced volatiles to P. persimilis. In a two-choice situation the predators preferred the volatiles of cultivars Rondena and Bianca over those of cultivar Sirtaki. The volatiles from the cultivars Sirtaki and Fame did not differ in attrativeness.

    The blend emitted by spider mite-damaged Sirtaki leaves consisted of a much lower relative amount of terpenes than the blends of the other three cultivars, which was mostly due to a low production of cis-alpha-bergamotene, trans-alpha-bergamotene, trans-beta-bergamotene and (E) -beta-farnesene. Furthermore, the production of (E) -beta-ocimene and linalool was lower by Sirtaki and Fame leaves than by leaves of Bianca and Rondena. These two compounds attract P. persimilis when offered in a Y-tube olfactometer (Dicke et al. , 1990b) . Whether the poor attractiveness of the spider mite-induced volatiles of Sirtaki and Fame is related to the limited production of these compounds should be investigated in future studies.

    Infochemicals in tritrophic interactions : origin and function in a system consisting of predatory mites, phytophagous mites and their host plants
    Dicke, M. - \ 1988
    Agricultural University. Promotor(en): J.C. van Lenteren, co-promotor(en): M.W. Sabelis. - Wageningen : Dicke - 235
    trombidiidae - tetranychus urticae - bryobia - mesostigmata - dermanyssidae - phytoseiidae - lokstoffen - plantenplagen - gastheer parasiet relaties - parasitisme - herbivoren - vleesetende dieren - biologische bestrijding - ongewervelde dieren - nuttige organismen - trombidiidae - tetranychus urticae - bryobia - mesostigmata - dermanyssidae - phytoseiidae - attractants - plant pests - host parasite relationships - parasitism - herbivores - carnivores - biological control - invertebrates - beneficial organisms - cum laude
    What are infochemicals?

    Chemical compounds play an important role in interactions between organisms. Some of these chemicals are to the benefit (e.g. nutrients) or detriment (e.g. toxins) of an organism. Others are of benefit or detriment in an indirect way: through the behavioural response they elicit. The latter chemicals are termed infochemicals (chemicals that, in the natural context, convey information in an interaction between two individuals, evoking in the receiver a behavioural or physiological response that is adaptive to either one of the interactants or both; chapter 2). On an evolutionary time scale, the fate of an infochemical depends on selection pressures on each interactant. Selection pressure is determined by costs and benefits which result from all interactions of an organism in which the infochemical is involved. Yet, for pragmatic reasons, to analyse the function of an infochemical in the biology of an organism, a cost-benefit analysis is made for each interaction between two organisms separately. In this way the cost-benefit analysis is restricted to the smallest number of interactants possible, which ensures its simplicity. Consequently, for each interaction the infochemical is classified according to the corresponding costs and benefits for the two interactants (chapter 2; cf. Nordlund and Lewis, 1976). Moreover, classification also reflects whether the interaction under consideration is between conspecifics or between individuals of different species. This resulted in the terminology represented in Figure 1.1 and Table 1.1 (cf. chapter 2). Its structure and terms are based on those of semiochemicals. However, infochemical terminology differs from semiochemical terminology in two respects (chapter 2):

    (1) Infochemical terminology regards compounds that convey information, whereas semiochemical terminology in addition also includes toxins (Whittaker and Feeny, 1971; Nordlund and Lewis, 1976; Nordlund, 1981). In some instances toxins or nutrients may convey information. If that is the case, these toxins and nutrients are classified as infochemicals when their role as information carrier is considered. When poisonous or nutritious aspects are considered, they are not classified as infochemicals, but as toxins and nutrients respectively.

    (2) Semiochemical terminology is based on origin of the compounds, in addition to the cost-benefit analysis. Although knowledge of the origin is Important to understand the interaction between two organisms, it may be very difficult to elucidate the origin (e.g. Brand et al., 1975; chapter 4). Therefore, application of the origin criterion may lead to ambiguities. Because the cost- benefit criterion by itself is good and useful, infochemical terminology is based on that criterion alone.

    Infochemicals in tritrophic systems.

    Infochemicals play a role in interactions between consecutive trophic levels (e.g plant-herbivore, phytophagous insect- entomophagous insect; Figure 1.2) (e.g. Nordlund et al., 1981; Visser, 1986). Moreover, infochemicals may also mediate interactions between other trophic levels (e.g. plant-entomophagous insect; Figure 1.2) (Price, 1981). Therefore, to understand the selection pressure on an organism, as a result of an infochemical, all trophic levels involved should be regarded. As a consequence, investigations of infochemicals in interactions between herbivores and their predators should also regard involvement of at least the first trophic level, the plant.

    The tritrophic system of this study: predatory mites, phytophagous mites and their host plants.

    The herbivore-predator system investigated most extensively in this thesis consists of phytophagous mites and predatory mites that occur in Dutch orchards. Figure 1.3a,b depicts the two most abundant phytophagous mites that occur as pest organisms in Dutch apple orchards: the apple rust mite, Aculusschlechtendali (Nalepa), and the European red spider mite, Panonychusulmi (Koch) (Van de Vrie, 1973; Van Epenhuijsen, 1981; Gruys, 1982).

    Several species of predatory mites occur in Dutch orchards. The most abundant of these are Typhlodromuspyri Scheuten (Figure 1.3c), Amblyseiusfinlandicus (Oudemans) and A.potentillae (Garman) (McMurtry & Van de Vrie, 1973; Overmeer, 1981; Gruys, 1982). All three species feed on P.ulmi and A.schlechtendali , as well as on other food sources such as several pollens (Overmeer, 1981; Kropczynska, 1970; Overmeer, 1985).

    In this system consisting of two phytophagous prey species and three predator species (Figure 1.4a), prey preference of the predators was investigated. Optimal foraging theory predicts that natural selection favours predators preferring prey species that are most profitable in terms of reproductive success (Krebs, 1978). Reproductive success is determined, among others, by development time, oviposition rate, mortality during development and offspring quality. Each of these components can be affected by the prey species consumed. As a first step in analysing which selection pressures may have moulded prey preference of the predatory mites in the system outlined above, I have tested whether prey preference is matched by the associated reproductive success. If this most simple explanation for prey preference does not hold, other explanations should be considered (see below).

    Do infochemicals play a role in prey preference ?

    Kairomones (Table 1.1, Figure 1.1) may inform predators on presence and identity of prey (Greany and Hagen, 1981) and thereby affect foraging decisions, such as where to search, how long to search at a specific site, which prey to accept and when to disperse on air currents (chapter 3).
    Investigation of the response to kairomones may therefore yield information on prey preference. However, the conclusion on prey preference must be restricted to the foraging phase that was studied. Relative costs involved in finding individuals of each prey species might differ for different foraging phases. Therefore, to obtain a comprehensive view of prey preference, several foraging phases should be investigated. Such analyses should be carried out independently to obtain complementary conclusions. In this study, prey preference was determined in three independent analyses.
    Two laboratory analyses were carried out:
    - Analysis of response towards volatile kairomones. This investigation regards decisions of the predators when prey individuals are not contacted, as is the situation after termination of aerial dispersal or after eradication of a prey patch.
    - Analysis of predation rates at different prey supplies. This relates to acceptance/rejection decisions during contacts with prey items.
    To complement the prey preference analyses carried out in the laboratory, an investigation was made under field conditions: - This was done by determination of diet composition by means of electrophoretic analysis of gut contents of field-collected predators.

    Spider-mite kairomones in a tritrophic context.

    Predatory mites distinguish plants infested by spider mites from clean plants by a volatile kairomone (e.g. Sabelis & Van de Baan, 1983). This kairomone seems to be a product of the interaction between plant and spider mites: after removal of spider mites from an infested plant, the plant remains attractive to the predators during several hours, whereas the mites alone do not remain attractive (Sabelis & Van de Baan, 1983; Sabelis et al., 1984a). Current data on spider mite - predatory mite interactions do not explain the role of this infochemical in the biology of the spider mites (cf. chapter 3 for a review). It may, for instance, be an inevitable byproduct of damage inflicted on the plant by the spider mite, and/or have an indispensable function in the biology of the spider mite. Moreover, the plant may be involved in production of the infochemical. To elucidate the role of this volatile infochemical, its effects in interactions between plant and spider mite, between plant and predatory mite and between spider mites of one species should be investigated. Before this can be done, chemical identification of the infochemical is a necessary first step.

    These investigations were made for a tritrophic system consisting of Lima bean plants, the two-spotted spider mite, Tetranychusurticae Koch and the predatory mite Phytoseiuluspersimilis Athias-Henriot (Figure 1.4b). This system was chosen for practical reasons. The plant and phytophagous mite can be reared throughout the year and therefore, this system is much more suitable to develop a method for the chemical analysis of spider-mite kairomones than a system in which the plant is a perennial.

    Origin and function of T.urticae kairomone in a tritrophic system.

    Two-spotted spider mites distinguish between a clean plant and a plant that is infested by conspecifics on the basis of a volatile infochemical (chapter 4). The spider mites move away from heavily infested leaves. This response is advantageous to spider mites on the infested leaf as well as to spider mites that avoid settling on these leaves: increased competition for food is avoided, cf. Wrensch and Young (1978). In addition, the spider mite that disperses thus avoids settling on a spot that has an increased risk of being detected by predatory mites (Sabelis and Van de Baan, 1983). Therefore, the infochemical in this interaction between conspecific spider mites is called a (+,+)dispersing pheromone. Biological evidence suggests that this pheromone is (at least partly) identical to the volatile kairomone to which predatory mites respond (chapter 4).

    Volatiles emitted from plants infested by T.urticae were identified and subsequent behavioural analyses resulted in identification of four kairomone components that attract the predatory mite P.persimilis : linalool (3,7-dimethyl-1,6-octadiene- 3-ol), methyl salicylate, ( E )-β-ocimene (3,7-dimethyl-1,3( E ),6- octatriene) and 4,8-dimethyl-1,3( E ),7-nonatriene. The structure of these compounds is shown in Figure 1.5. At least two of these (linalool and methyl salicylate) are also components of a kairomone in the interaction between T.urticae and A.potentillae (when reared on V.faba pollen; see below) (chapter 4). Literature data on the behavioural response of T.urticae indicate that one of these kairomone components (linalool) is also a component of the (+,+)dispersing pheromone (Dabrowski and Rodriguez, 1971).

    All identified kairomone components are well-known in the plant kingdom. This suggests that the plant is involved in production of the infochemical, but it is no proof. It may for Instance be that spider-mite enzymes injected into the plant break down a plant compound. Investigation of e.g. site and moment of production and possible storage of precursors are needed as a next step to elucidate the role of the plant in kairomone production. However, suppose that it is the spider mite who produces the infochemical to serve as a dispersing pheromone. Then, it is not clear why this pheromone should necessarily consist of volatiles. As a result of the production of volatiles the spider mites incur more risks of being detected by predators than by production of non-volatile chemicals. Detection by predators inevitably leads to local extermination of spider mites (Sabelis and Van der Meer, 1986). For this reason it seems more likely that the volatiles are plant produced and that the spider mite makes the best of a bad job by using them as information to decide where not to colonize. To understand the evolution of plant-produced volatiles after herbivore attack, it is crucial to assess how they are produced, how much it costs to produce them and what the benefits are in terms of a lowered probability of herbivore attack.

    Involvement of volatile kairomones in prey preference of predatory mites.

    The response of T.pyri and A.potentillae to volatile kairomones is dependent on the diet of the predators. When reared on a carotenoid-poor diet these predators respond to the kairomones of more prey species than when reared on a carotenoid-rich diet (chapters 6, 7 and 8). Carotenoids are indispensable to A.potentillae because of their function in diapause induction (Overmeer, 1985a). The function of these nutrients to T.pyri remains unknown (chapter 8). All prey species to whose kairomones carotenoid-deficient A.potentillae and T.pyri respond can relieve the lack of carotenoids. Carotenoid-containing A.potentillae and T. pyri only respond to the P.ulmi kairomone. The above observations were made for predators that were starved for 20 h. Longer starvation of predators reared on a carotenoid-rich diet also enlarges the number of prey species responded to. Investigations of the response to volatile kairomones indicates that A.potentillae and T.pyri (whether carotenoids are available or not) prefer P.ulmi to A.schlechtendali (chapters 6, 7 and 8) and that A.finlandicus has a reverse preference (chapter 11).

    This corresponds to conclusions from predation experiments performed at different composition of prey supply (chapters 9 and 11). The observed predation rates when mixed prey supplies were offered, were compared with a model provided with parameters estimated from experiments with each of both prey species alone. Amblyseiuspotentillae and T.pyri fed more on P.ulmi and A.finlandicus fed more on A.schlechtendali than was predicted by the model. This difference between observed and predicted predation rates cannot be explained by a change in behaviour of the prey species as a result of being together, nor by a change in walking behaviour of the predator. Therefore, these data indicate that A. potentillae and T.pyri prefer P.ulmi and that A.finlandicus prefers A.schlechtendali , in terms of a change in acceptance/rejection ratio ('success ratio').

    Analysis of prey preference under field conditions showed that most T.pyri collected from apple leaves that widely varied in P.ulmi : A.schlechtendali numbers contained P.ulmi esterase, whereas A.schlechtendali esterase was present in a minor fraction of predators (chapter 10). Rust-mite esterase and P.ulmi esterase were found equally frequent in A.finlandicus . The data for A.finlandicus , obtained over a narrower range of prey-number ratios than for T.pyri , do not allow a definite conclusion on prey preference. However, they certainly do not cause rejection of the conclusion on prey preference as obtained in the laboratory analyses (chapter 11). No field data are available for A.potentillae .
    Because the conclusions on prey preference as determined in these independent analyses are consistent for each predator species, the inference on prey preference is firmly established.

    Prey preference and reproductive success of predatory mites in an orchard system with two species of phytophagous prey mites.

    Analysis of reproductive success of these three predator species, when feeding on either P.ulmi or A.schlechtendali , indicates that A.finlandicus selects the best prey species in terms of reproductive success. This predator species suffers high larval mortality on P.ulmi , but not on A.schlechtendali . This results in a much higher intrinsic rate of population increase when feeding on apple rust mites (chapter 12).

    Amblyseiuspotentillae and T.pyri would also do better by feeding preferentially on A.schlechtendali : development times when feeding on this prey species are shorter than when feeding on P.ulmi , whereas these prey species do not differentially affect mortality or oviposition rate (chapter 12). For A.potentillae this may not be the case at the end of the season because P.ulmi is a better prey species in terms of diapause induction. Thus, on the basis of current data, optimal prey-choice theory cannot satisfactorily predict actual prey peference of A.potentillae and T.pyri . Future investigations should concentrate on e.g. (1) possible effect of competition between prey species on prey availability, (2) possible effect of competition between predator species on prey availability, and (3) possible shift in prey preference during the season.

    Studies on population dynamics of the scarlet mite, Brevipalpus phoenicis, a pest of tea in Indonesia
    Oomen, P.A. - \ 1982
    Landbouwhogeschool Wageningen. Promotor(en): J. de Wilde, co-promotor(en): P. Gruys. - Wageningen : Oomen - 89
    plantenplagen - camellia sinensis - thee - trombidiidae - tetranychus urticae - bryobia - gewasbescherming - plagenbestrijding - ziektebestrijding - dieren - populatiedichtheid - populatie-ecologie - mortaliteit - populatiegroei - indonesië - plant pests - camellia sinensis - tea - trombidiidae - tetranychus urticae - bryobia - plant protection - pest control - disease control - animals - population density - population ecology - mortality - population growth - indonesia

    Tea is the national drink of Indonesia. The habitual consumption prevents intestinal infections; the production provides many Indonesians with a living. The production is affected by scarlet mites (Brevipalpus phoenicis GEIJSKES), an important pest of tropical and subtropical crops. It is one of the main pests of tea in Indonesia and inhabits virtually all tea bushes. The factors restricting the development of this mite on tea in West Java were studied by observations and experiments in the laboratory and the tea gardens of the Research Institute for Tea and Cinchona.

    Scarlet mites multiply fast under favourable conditions. The intrinsic rate of increase (r m = 0.0610) however is far less than that of some spider mites. The scarlet mite populations develop continuously in the field, without synchronization. The mites stay on the undersurface of the tea maintenance leaves and are rather sedentary. A deteriorating leaf quality triggers off migration with a positive phototactic orientation, i.e. towards younger leaves of the bush.

    Different tea clones and seedlings sustain significantly different mite densities as a consequence of differences in host plant resistance. Tea bushes are pruned once in four years in West Java. This strongly reduces the abundance of scarlet mites. The populations build up slowly and exponentially to a mean equilibrium level which is attained around two years after pruning. Most populations have a low and rather stable density during the second two years of the pruning cycle; some populations have high and fluctuating densities. Generally speaking, the populations especially increase during the dry seasons and decrease during the transitory periods. Maxima are reached usually at the end of the dry season. The fluctuations are not directly related to the average minimum or maximum temperature, average minimum relative humidity or the total rainfall. Application of copper fungicides (copperoxychloride) increases the average mite densities and especially the seasonal maxima. The numerical multiplication of field populations always remained much below that of populations in the laboratory under favourable growing conditions.

    Many other arthropods beside scarlet mites inhabit tea leaves. Predators of scarlet mites were collected from tea estates in Java and Sumatra. The diversity of predatory mite species appeared to be particularly rich. A considerable number of species probably has not been described and is identified provisionally in this paper by a code name. The predatory behaviour of most species (Phytoseiidae and Stigmaeidae), the reproduction of three typical species and the capacity of three stigmaeid species to keep scarlet mites in check were confirmed in laboratory experiments.

    A series of pesticides was screened in the laboratory for (undesired) toxicity towards scarlet mites, DDT was screened for toxicity towards predators. Most Phytoseiidae appeared to be susceptible, and most Stigmaeidae appeared to be tolerant to DDT. DDT, maneb and PH 60-42 were selected as exclusion pesticides with the intention of killing respectively: all the predators, the predatory mites and the predatory insects, without affecting the scarlet mites in a predator cheek experiment.

    These exclusion pesticides were frequently applied in the field during the 16 months period of the predator check experiment. The effects deviated from the expectation in various respects but resulted in a sufficiently diversified predatory fauna to analyze the importance of several predator species as a factor restricting the development of scarlet mites. The effect of DDT was most unexpected. It killed the most common Phytoseiidae and permitted the Stigmaeidae and Amblyseius z to develop high densities. The density of scarlet mites decreased to a rather constant level below that of the (untreated) control, probably as a consequence of predation. The predators that made the most impact were the Stigmaeidae. They suppressed the level of abundance of scarlet mites in the DDT-treated and the untreated fields to 13% and 27% respectively of the abundance without these predators.

    The more effective control by predators in the DDT-treated fields was interpreted by a selective killing with DDT of the less efficient predators (Ambly seius x and A. deleoni). The disappearance of these probably benefitted the other, more effective predators of scarlet mites (Stigmaeidae and Amblyseius z ). The diversity of the ecosystem at the trophic level of the predators appeared not to be related to the effectiveness of the control of scarlet mites. Suggestions for control, especially the planting of resistant clones, conclude this paper.

    Biological control of two-spotted spider mites using phytoseiid predators
    Sabelis, M.W. - \ 1982
    Landbouwhogeschool Wageningen. Promotor(en): C.T. de Wit, co-promotor(en): J. de Wilde; R. Rabbinge. - Wageningen : Pudoc - ISBN 9789022007761
    rosaceae - sierplanten - biologische bestrijding - ongewervelde dieren - nuttige organismen - plantenplagen - trombidiidae - tetranychus urticae - bryobia - predatie - vleesetende dieren - rosaceae - ornamental plants - biological control - invertebrates - beneficial organisms - plant pests - trombidiidae - tetranychus urticae - bryobia - predation - carnivores
    The searching behaviour of individual predators of four phytoseiid species ( Phytoseiulus persimilis , Amblyseius p o tentillae , Amblyseius bibens , Metaseiulus occidentalis ) is investigated in relation to the two-spotted spider mite ( Tetranychus urticae ), which infests greenhouse roses. Especially the role of spider- mite webbing in the predator-prey relation is studied. Webbing interferes with searching, decreasing the rate of encounter per unit prey density. Low walking speeds and activity in webbing ensure that the predator is rarely disturbed after contact with other mites. Webbing also positively influences searching, as spider mites aggregate within the webbed area: prey density, defined here as the number of prey per square centimetre of webbed leaf area, is high, as is the rate of encounter with prey. The ability to capture a prey after tarsal contact depends on the food content of the gut, the prey-stage and, in two specific cases, the webbing; the success ratio of P. persimilis increased on a webbed substrate, that of A. potentillae decreased.
    Models to simulate rate of predation on the basis of the dynamics of the motivational state and the state dependent rate of successful encounter are proposed. The food content of the gut is chosen as an indicator of the motivational state. A stochastic queueing model simulates predation as accurately as a Monte Carlo model or a compound simulation model. The queueing model is preferred because of its economic use of computer time and the relatively few variables used. The model was validated in predation experiments.
    Systems analysis showed that the effect of temperature on the rate of predation is largely determined by its relation with the relative rate of food conversion into egg biomass and not by behavioural changes related to temperature. Also, it was shown that webbing has an important influence on the predation rate. A new model for the analysis of prey-stage preference is proposed.
    Predators invade the webbed leaf area after contact with the silk strands, irrespective of the presence of prey. The residence time in the prey colony is determined by prey density. Simulation of experimentally defined walking behaviour shows that predators remain in profitable prey patches by turning at the edge of the webbed leaf area. However, when predator density increases, the tendency to leave the prey colony also increases, even at high prey densities. Only A. potentillae avoided the webbed leaf area, preferring the thickest parts of the leaf ribs or other protected places on the plant.
    A survey of references on life history data is presented; emphasis is given to the role of food, temperature and relative humidity. Experiments by the author show that oviposition history of predatory females is a major factor in determining the actual rate of food conversion into egg biomass; and that the egg stage of the predators is very vulnerable to relative humidities below 70%, though the evapotranspiration of the plant and the hygroscopic properties of the webbing buffer this to some extent. As the juvenile mortality of the phytoseiids increases above 30°C, and that of the two-spotted spider mites above 35°C, spider-mite control at temperatures above 30°C is not effective.
    The four phytoseiid species are ranked on their capacities for numerical increase and predation: P. persimilis , A. bibens , M. occidentalis and A. potentillae . On capacity to survive on alternative foods they are ranked: A. potentillae , A. bibens , M. occidentalis and P. persimilis . Some trials with alternative food supply did not improve survival rates established for prevailing greenhouse conditions.
    The rate of increase of the webbed area per individual spider mite is quantified by experiment. This knowledge will enable continuous monitoring of the prey density during simulations of the predator-prey interactions on the population level.

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