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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Alternatieven voor neonicotinoïden in de sierteelt onder glas : bestrijding van tabakswittevlieg en bladluis in kuipplanten en perkgoed
    Messelink, Gerben ; Vijverberg, Roland ; Bloemhard, Chantal ; Leman, Ada - \ 2016
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1418) - 42
    tuinplanten - containerplanten - insectenplagen - bemisia tabaci - aphididae - kasgewassen - glastuinbouw - biologische bestrijding - insecticiden - lecanicillium muscarium - entomopathogene schimmels - roofinsecten - bedding plants - container grown plants - insect pests - bemisia tabaci - aphididae - greenhouse crops - greenhouse horticulture - biological control - insecticides - lecanicillium muscarium - entomogenous fungi - predatory insects
    The control of phloem feeding insects such as aphids, whiteflies, cicadas, mealybugs, scales and plant feeding bugs in greenhouse crops still largely depends on the use of neonicotinoids. However, the increased found negative effects on the environment will soon results in a total ban on the use of these pesticides. In this project we summarized the possible alternative control measures with pesticides and biological control agents. Furthermore, a number of preventive and curative control measures was evaluated for the control of aphids in bedding plants and the tobacco whitefly in container plants, with Calibrachoa and Mandevilla as model plants. An endophytic application of an isolate of the entomopathogenic fungus Lecanicillium gave a clear trend of 25% reduced population growth of aphids on Calibrachoa. Curative control of aphids with lacewings was not effective. Mullein plants enhanced tobacco whitefly control by the predatory bug Macrolophus pygmaeus in Mandevilla and increased predator survival and reproduction. Among the tested alternative control measures, we found 5 products that controlled tobacco whiteflies effectively in Mandevilla.
    A multidisciplinary approach to study virulence of the entomopathogenic fungus Beauveria bassiana towards malaria mosquitoes
    Valero Jimenez, C.A. - \ 2016
    Wageningen University. Promotor(en): Bas Zwaan; Willem Takken, co-promotor(en): Sander Koenraadt; Jan van Kan. - Wageningen : Wageningen University - ISBN 9789462578548 - 131
    beauveria bassiana - entomogenous fungi - virulence - vector control - mosquito-borne diseases - malaria - anopheles - culicidae - beauveria bassiana - entomopathogene schimmels - virulentie - vectorbestrijding - ziekten overgebracht door muskieten - malaria - anopheles - culicidae

    Although globally malaria mortality rates have fallen by 48% between 2000 and 2015, malaria is still killing an estimated 438,000 people each year. An effective way to alleviate the burden of malaria is to control its vector (malaria mosquitoes) using insecticides. This can be achieved either with insecticide-treated bed nets (ITNs) or through indoor residual spraying of insecticides (IRS). However, because of rapidly expanding insecticide resistance, there is a need to find alternatives to control the mosquitoes. Entomopathogenic fungi (EPF) could constitute an effective biological control tool, as is able to reduce malaria transmission under laboratory and field conditions. However, fundamental knowledge on the mechanisms and regulation of the infection process of the fungus, as well as insights into the defensive responses of the host insect to EPF, is limited. Therefore, the main goal of this thesis was to study virulence of the entomopathogenic fungus B. bassiana towards malaria mosquitoes using a multidisciplinary approach.

    Chapter 2 provides an overview of existing knowledge of genes influencing virulence in EPF, with a special focus on B. bassiana. The infection cycle and virulence mechanisms are discussed, and put in a framework of novel strategies and experimental methods that are needed to better understand virulence and improve the usage of EPF as a biocontrol agent.

    The study of natural variation in fungal virulence is a first step towards understanding the genetic mechanisms involved, because it reveals the extent of variation in the different components of virulence and their overall role. Chapter 3 describes the natural variation in virulence for 29 B. bassiana isolates that were tested on malaria mosquitoes. Furthermore, the phenotypic characteristics of the fungal isolates such as sporulation, spore size and growth were evaluated and their relationship with virulence analysed.

    Based on the ample natural variation observed in fungal virulence, in Chapter 4, a comparative genomics analysis was performed on five selected isolates of contrasting virulence. In order to understand mechanisms underlying contrasting virulence, a comparison on gene gain/loss, single nucleotide polymorphisms (SNPs), secreted proteins, and secondary metabolites was performed. Insight is provided to the magnitude of the complexity of a trait such as virulence and suggests candidate genes that can be further studied using a functional analysis approach.

    Chapter 5 focuses on an experimental evolution approach in which B. bassiana was solely using insects as a nutritional source for ten consecutive passages through malaria mosquitoes. Two isolates of B. bassiana that differed in virulence were compared to their respective ancestors, and they were assayed in virulence, fungal outgrowth, mycelial growth rate (MGR), and sporulation. Passage of the entomopathogenic fungi B. bassiana through the insect host resulted in an altered capacity to grow on different substrates while maintaining the ability to kill insects.

    Chapter 6 presents a discussion on the main findings of this thesis and describes future perspectives to study virulence of the entomopathogenic fungi Beauveria bassiana in the context of biological control of malaria mosquitoes.

    Mogelijkheden voor bladluisbestrijding met schimmels
    Messelink, G.J. ; Holstein-Saj, R. van; Dinu, M.M. ; Bloemhard, C.M.J. - \ 2015
    gewasbescherming - tuinbouw - glastuinbouw - capsicum - plagenbestrijding - biologische bestrijding - aphididae - natuurlijke vijanden - kasproeven - entomopathogene schimmels - conferenties - plant protection - horticulture - greenhouse horticulture - capsicum - pest control - biological control - aphididae - natural enemies - greenhouse experiments - entomogenous fungi - conferences
    Doelstelling: Bepalen welke soorten entomopathogene schimmels het meest kansrijk zijn voor de bestrijding van bladluizen in kasteelten en wat de randvoorwaarden zijn voor een geslaagde bestrijding. Poster van PlantgezondheidEvent 12 maart 2015.
    Increase of plant resistance with rhizosphere competent entomopathogenic fungi (EPF)
    Tol, R.W.H.M. van - \ 2015
    gewasbescherming - tuinbouw - entomopathogene schimmels - biologische bestrijding - rizosfeer - natuurlijke vijanden - bodeminsecten - insect-plant relaties - conferenties - melolontha melolontha - bodem-plant relaties - insectenplagen - plant protection - horticulture - entomogenous fungi - biological control - rhizosphere - natural enemies - soil insects - insect plant relations - conferences - melolontha melolontha - soil plant relationships - insect pests
    Entomopathogenic fungi are able to kill insects and are as such a potential mean for pest control. Recently it was discovered that these fungi can also colonize plant roots. Most previous work with EPF has ignored the habitat preferences and survival of the fungus outside of the host. It is possible that factors associated with fungal biology outside of the host are more important when selecting an isolate than how pathogenic it is against a particular host in a laboratory bioassay. Poster van PlantgezondheidEvent 12 maart 2015.
    Bouwstenen voor een systeemaanpak voor tripsbestrijding : rapportage toplagen, instandhouden roofwantsen en Lure & Infect
    Grosman, A.H. ; Linden, A. van der; Bloemhard, C.M.J. ; Holstein, R. van; Tol, R.W.H.M. van; Messelink, G.J. ; Balk, P. - \ 2014
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport / Wageningen UR Glastuinbouw 1330) - 46
    sierteelt - glastuinbouw - snijbloemen - frankliniella occidentalis - roofmijten - entomopathogene schimmels - kweekmedia - afdeklagen - bestrijdingsmethoden - geïntegreerde plagenbestrijding - ornamental horticulture - greenhouse horticulture - cut flowers - frankliniella occidentalis - predatory mites - entomogenous fungi - culture media - coatings - control methods - integrated pest management
    Californische trips, Frankliniella occidentalis, is een groot probleem in de sierteelt onder glas. In dit rapport zijn de resultaten weergeven van onderzoek aan toplagen voor roofmijten, bankerplanten voor Orius en een “Lure & infect-systeem” voor volwassen tripsen. Toplagen van een mix van bark, zemelen en gist verhoogden populatiedichtheden van roofmijten in zowel de bodem als op het gewas. Dit resulteerde bij alstroemeria en roos in een betere bestrijding van trips ten opzichte van roofmijten zonder toplagen. Inzet van toplagen bij een hoge tripsdruk leidde tijdelijk tot verhoogde tripsdichtheden. Scherpe peper, rode amaranthus en korenbloemen waren geschikte bankerplanten voor Orius. In een situatie waarbij de roofwantsen geen keuze hebben, blijken ze zich het beste te ontwikkelen op korenbloem. In een keuzesituatie bleken de wantsen naast korenbloem ook veel eieren af te zetten op peperplanten. De bestrijding van trips met entomopathogene schimmels was niet succesvol. Bij het testen van een Lure & Infect-systeem met de schimmel Beauveria bassiana, bleek bij terugvangsten van trips niet meer dan 10% van de volwassen tripsen geïnfecteerd te zijn en er werd géén significante bestrijding van trips behaald. Verder liet laboratoriumonderzoek zien dat volwassen tripsvrouwtjes die besmet zijn met schimmels nog enkele dagen eieren blijven leggen, waardoor het effect minder is dan bij directe afdoding door bijvoorbeeld een vangplaat.
    Lure & Infect trips
    Messelink, G.J. ; Holstein, R. van; Kok, L.W. - \ 2013
    sierteelt - frankliniella occidentalis - thrips - alternatieve methoden - entomopathogene schimmels - bestrijdingsmethoden - ornamental horticulture - frankliniella occidentalis - thrips - alternative methods - entomogenous fungi - control methods
    Californische trips, Frankliniella occidentalis , is een groot knelpunt in de sierteelt waar de bestrijding leunt nog sterk op inzet van pesticiden. Een goed alternatief systeem voor pesticiden kan alleen bereikt worden met een systeemaanpak, waarbij verschillende maatregelen en methoden tegen trips gecombineerd worden. Een belangrijk onderdeel van die aanpak kan de inzet van entomopathogene schimmels tegen trips. Het doel van het onderzoek is het verbeteren van de bestrijding van trips met entomopathogene schimmels in de sierteelt door middel van een nieuw 'Lure & Infect'-systeem.
    Optimalisatie toepassing entomopathogene schimmels tegen trips in chrysant
    Messelink, G.J. ; Holstein, R. van - \ 2012
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1142) - 18
    chrysanthemum - insectenplagen - thripidae - entomopathogene schimmels - biologische bestrijding - chrysanthemum - insect pests - thripidae - entomogenous fungi - biological control
    De californische trips, Frankliniella occidentalis , is een groot knelpunt in de teelt van chrysant. In dit onderzoek is beoor-deeld in hoeverre de verschillende tripsstadia (larven poppen en adulten) vatbaar zijn voor de entomopathogene schim - mels Beauveria bassiana (Botanigard®), Metarhizium anisopliae (BIO 1020®), Lecanicillium lecanii (Mycotal®) en Isaria fumosorosea PreFeRal®. De larven en poppen van trips bleken nauwelijks vatbaar te zijn voor de geteste entomopatho - gene schimmels. Bij het direct in contact brengen met schimmelsporen werd slechts incidenteel infectie waargenomen. Een mogelijke verklaring is dat deze tripsstadia een infectie van een schimmelspore weer kwijtraken bij een vervelling naar het volgende stadium. Een preventieve grondbehandeling met B. bassiana of M. anisopliae had géén meetbaar effect op de overleving van trips in deze gronden. Bij alle geteste schimmelpreparaten was er wel een duidelijk effect op de volwassen tripsen. De schimmel M. anisopliae was met een doding van 96% het meest effectief. Het is dan ook aan te bevelen om de bestrijding van trips met entomopathogene schimmels zo veel mogelijk te richten op het volwassen tripsstadium.
    Integrating fungal entomopathogens in malaria vector control
    Farenhorst, M. - \ 2010
    Wageningen University. Promotor(en): Louise Vet; M.B. Thomas. - [S.l.] : S.n. - ISBN 9789085858034 - 129
    culicidae - vectoren, ziekten - vectorbestrijding - entomopathogene schimmels - geïntegreerde plagenbestrijding - biologische bestrijding - chemische bestrijding - culicidae - disease vectors - vector control - entomogenous fungi - integrated pest management - biological control - chemical control
    Widespread and long-term pesticide use has caused a selection and spread of resistance in malaria mosquito populations, which endangers the effectiveness of contemporary malaria control strategies that are based on chemical insecticides. The fungal entomopathogens Metarhizium anisopliae and Beauveria bassiana show potential as alternative and more sustainable malaria vector control agents. These hyphomycetes can effectively infect anophelines and potentially reduce malaria transmission by killing the mosquitoes within several days before they can transmit malaria parasites.
    The aim of this thesis was to evaluate the potential of fungal entomopathogens for integration in chemical-based malaria interventions. Its objectives were to evaluate fungal spore application methods, to develop novel field delivery tools with potential for integrated use, to measure fungal efficacy against insecticide-resistant anophelines and to test the compatibility of fungi and chemical insecticides.

    The first part of the work (Chapter 3-5) focused on evaluating fungal spore application methods and developing novel delivery systems that could potentially be effective in tropical field settings and integrated into existing malaria control strategies. Spraying, dipping and coating were effective methods for applying an infective layer of fungal spores on mosquito resting surfaces. A coating method, involving the application of uniform spore layers on papers, was developed to enable accurate laboratory evaluations, and a rotating spray apparatus to standardize the application of oil suspensions inside clay pots. The combination of formulation and substrate was shown to have a high impact on spore infectivity, with viscous suspensions being only effective on porous substrates. Spore application dose, exposure time and type of mosquito contact were key factors of fungal virulence, as they influenced the number of spores effectively picked up by a resting mosquito. Two novel delivery methods were developed and tested in the laboratory. Clay pots showed potential for use as indoor and outdoor point-source objects to target resting mosquitoes with fungal spores. Oil-based Metarhizium suspensions were effective in infecting and killing mosquitoes after spray application inside clay pots and did not affect their attractiveness to resting male and female anophelines. Fungus-impregnated netting showed potential for use as house screens to target host-seeking mosquitoes. Spores of Metarhizium and Beauveria were most effective applied by spraying nets with evaporative suspensions. Fungi were infective on small- and large-meshed polyester and cotton nets, with spores being more viable on cotton. These two fungus delivery systems offer multiple deployment options and could potentially be used complementary to chemical-based malaria control measures such as insecticide-treated bednets (ITNs) or indoor residual spraying (IRS).
    The second part of the work (Chapter 6 & 7) focused on evaluating the efficacy of fungi against insecticide-resistant Anopheles mosquitoes and their compatibility with public health insecticides. Metarhizium and Beauveria were highly effective against a diverse suite of insecticide-resistant Anopheles mosquitoes. Four metabolically resistant anopheline strains were equally susceptible to B. bassiana infection as their baseline counterparts. Both fungi were also highly effective in killing a laboratory strain and field population of West African An. gambiae s.s. with genetically conferred knockdown resistance (kdr) to public health insecticides. Moreover, fungi and insecticides were highly compatible and enhanced each other’s efficacy. Fungal infection increased the sensitivity of resistant mosquitoes to the neurotoxic insecticides permethrin and DDT. Fungus-infected mosquitoes with metabolic resistance mechanisms showed a significant increase in mortality after insecticide exposure compared with uninfected control mosquitoes. Reciprocally, permethrin increased subsequent fungus-induced mortality rates in a laboratory and field population of kdr-resistant An. gambiae. Several combinations of insecticide and fungus were shown to induce synergistic effects on mosquito survival. Synergy was highest after simultaneous co-exposure to both agents. These findings suggest that integrated control tools that induce contact to fungi and insecticides within a single feeding episode would have the highest impact on mosquito survival and may enable control at more moderate levels of coverage. Moreover, the synergistic and resistance breaking properties of fungi show potential for augmenting current malaria interventions and managing the further spread of insecticide resistance.

    Several factors still remain to be optimized before fungus-based malaria mosquito control can be realised. Cost-effective field deployment will require the development of high quality, low cost mass-production of mosquito-pathogenic fungi, persistent formulations and efficient delivery systems. The laboratory studies in this thesis provide useful knowledge and tools for future implementation research on these novel biological vector control agents. The potential field delivery systems that were created will, however, still need to be further evaluated in field settings under realistic environmental conditions.
    In this thesis it was, for the first time, shown that fungi are effective against insecticide- resistant malaria vectors and induce the highest impact on mosquito survival when used in combination with chemical insecticides. These findings make a compelling case for viewing novel fungus-based and existing chemical-based control measures not as mutually exclusive, but as complementary interventions that would reach the greatest malaria control benefit once successfully integrated.
    Optimization of formulation and delivery technology of entomopathogenic fungi for malaria vector control
    Mnyone, L.L. - \ 2010
    Wageningen University. Promotor(en): Willem Takken; Marcel Dicke. - [S.l.] : S.n. - ISBN 9789085857877 - 125
    culicidae - vectoren, ziekten - malaria - vectorbestrijding - entomopathogene schimmels - biologische bestrijding - toepassing - formuleringen - culicidae - disease vectors - malaria - vector control - entomogenous fungi - biological control - application - formulations
    Vector control is one of the most effective means of controlling mosquito-borne diseases such as malaria. The broad goal of this strategy is to protect individuals against infective mosquito bites and, at the community level, to reduce the intensity of disease transmission. With the deployment of mainly insecticide-treated nets (ITN) and indoor residual spraying (IRS), aided by effective drug treatment, certain countries particularly those within the low endemic zones have documented more than 50% reduction in malaria cases over the past decade. To keep up the pace and expand effective malaria control, in line with the global effort to eliminate malaria, IRS and ITN need to be complemented with alternative control methods. Indeed, neither long lasting insecticide nets (LLINs) nor IRS alone will be sufficient to achieve and maintain interruption of transmission in malaria holoendemic and hyperendemic areas. Besides, the sustainability of both methods is inescapably threatened by mosquito resistance to insecticides. Scientific evidence indicates that biological control based on entomopathogenic fungi has the potential to complement existing vector control methods. Two species of entomopathogenic fungi, Metarhizium anisopliae and Beauveria bassiana, have demonstrated ability to infect and kill adult malaria vectors.

    This thesis describes the results of a series of laboratory investigations followed by small scale field trials in Tanzania in an area of high malaria endemicity, with abundant populations of the malaria vector Anopheles gambiae sensu lato. The overall aim was to optimize fungal formulations, develop delivery techniques that maximize fungus infection rates in wild malaria populations, evaluate impact on survival of these mosquitoes and asses the impact on malaria transmission levels. A series of variables that we hypothesized affect the efficacy and persistence of the fungal isolates Metarhizium anisopliae ICIPE-30, M. anisopliae IP 46 and Beauveria bassiana I93-825 against adult An. gambiae were assessed. These included a) conidia concentration (1×107- 4×1010 conidia m-2), b) exposure time (15 min - 6 h), c) delivery substrates (netting, cotton cloth & mud wall), d) mosquito age (2 - 12 d), e) time since blood meal (3 - 72 h) as well as f) mosquito behaviour (repellency by conidial formulations). Co-formulations of M. anisopliae ICIPE-30 and B. bassiana I93-825 in ratios of 4:1, 2:1 & 1:1 were also tested. Metarhizium anisopliae IP 46 was exposed to An. gambiae and An. arabiensis to determine its pathogenicity on these mosquito species before being used for the field trials. Mosquitoes were exposed to fungal formulations applied on paper inside holding tubes, except when different delivery substrates were assessed. For the delivery substrates, sections of netting and black cotton cloth were joined using Velcro strips to fit over 20 × 20 × 20 cm wire frame cages; and mud-lined plywood panels were similarly assembled into 20 × 20 × 20 cm cages. Laboratory experiments were performed using laboratory reared mosquitoes at the Ifakara Health Institute, Ifakara, Tanzania. Following the laboratory experiments, fungal formulations were assayed in experimental hut trials in a field setting at Lupiro village (Ulanga District, Tanzania), a rural hamlet 30 km south of Ifakara. Five different techniques that each exploited the behaviour of mosquitoes when entering (eave netting, eave curtains, eave baffles), host-seeking (cloth strips hung next to bed nets) or resting (cloth panels) were assessed.

    The degree at which mosquito survival was reduced varied with conidia concentration; 2×1010 conidia m-2 was the optimum concentration above which no further reductions in survival were detectable. Co-formulations exerted neither synergistic nor additive effect in reducing mosquito survival. The exposure of mosquitoes to fungal formulations for time periods as short as 15 and 30 min was adequate to achieve 100% mortality of mosquitoes within 14 d post exposure. Longer exposure times did not result in a more rapid killing effect. Conidia impregnated on papers remained infective up to 28 d post application, and such trait did not seem to be influenced by the conidia concentration. Mosquitoes of the age between 2-12 d equally succumbed to fungus infection, with them, however, being relative more susceptible when non-blood fed. Oil-formulations of the fungi did not exhibit any repellency to mosquitoes. Metarhizium anisopliae IP 46 was pathogenic to both An. gambiae and An. arabiensis. Conidia were more effective when applied on mud panels and cotton cloth compared with polyester netting. Cotton cloth and mud, therefore, represent potential surfaces for delivering fungi to mosquitoes in the field.
    Two delivery techniques, cotton cloth eave baffles and strips hung next to the bed net were successful in exploiting the behaviour of wild anopheline mosquitoes. Up to 75% of house-entering mosquitoes became infected with fungus applied with either technique. By contrast, eave netting, eave curtains and cotton panels placed next to the bed net were ineffective in infecting mosquitoes with sufficiently high doses of fungi to affect their survival. Based on the survival data of the mosquitoes infected with fungus by means of eave baffles, model estimates indicated that fungus alone can reduce EIR by more than 75%.

    In conclusion, these findings indicate that with well-optimized fungal formulations and correctly-designed delivery techniques, a high proportion of house-entering wild malaria mosquitoes can be infected with entomopathogenic fungi to achieve considerable reduction in their survival and possibly malaria transmission. More importantly, these findings provide baseline information that is highly relevant for designing and conducting large-scale field trials to validate the projected impact of fungal infection under realistic field situations.

    Schimmels als nieuw wapen tegen malariamuggen
    Knols, B.G.J. ; Takken, W. - \ 2008
    In: Natuur als Bondgenoot / Osse, J.W.M, Schoonhoven, L.M., Dicke, M., Buiter, R., Leiden : Stichting BWM (Cahiers bio-wetenschappen en maatschappij 4) - ISBN 9789073196490 - p. 69 - 75.
    malaria - antimalariamiddelen - plasmodium - ddt - pyrethroïden - entomopathogene schimmels - parasitisme - ziektepreventie - ziektebestrijding - culicidae - ziekten overgebracht door muskieten - malaria - antimalarials - plasmodium - ddt - pyrethroids - entomogenous fungi - parasitism - disease prevention - disease control - culicidae - mosquito-borne diseases
    Er gaat ieder jaar veel geld om in de - chemische - bestrijding van malariamuggen. Maar dankzij een veelbelovende schimmel staat een heel nieuwe, duurzame aanpak voor de deur, zeggen medisch entomologen Bart Knols en Willem Takken. 'Het is toch schrijnend dat we aan het begin van de eenentwintigste eeuw nog steeds afhankelijk zijn van DDT.'
    Geïntegreerde tripsbestrijding chrysant
    Beerling, E.A.M. ; Stolk, J. - \ 2006
    Gewasnieuws Chrysant 9 (2006)3. - p. 3 - 3.
    geïntegreerde plagenbestrijding - chrysanthemum - thrips - plaagbestrijding met natuurlijke vijanden - biopesticiden - roofmijten - entomopathogene schimmels - gewasbescherming - glastuinbouw - integrated pest management - chrysanthemum - thrips - augmentation - microbial pesticides - predatory mites - entomogenous fungi - plant protection - greenhouse horticulture
    Berichten over de huidige stand van zaken van een roofmijten-proef en een GNO-proef uitgevoerd in proefkassen door PPO Glastuinbouw, en van het praktijkonderzoek op vijf chrysantenbedrijven door van Iperen en Syngenta bioline.
    Biologische bestrijding van varroa met behulp van schimmels
    Gerritsen, L.J.M. ; Cornelissen, B. - \ 2006
    Bijen : maandblad voor imkers 15 (2006)2. - ISSN 0926-3357 - p. 35 - 36.
    bijenhouderij - honingbijen - varroa - mijten - mijtenbestrijding - biologische bestrijding - organismen ingezet bij biologische bestrijding - entomopathogene schimmels - beekeeping - honey bees - varroa - mites - mite control - biological control - biological control agents - entomogenous fungi
    Sinds enkele jaren wordt er volop onderzoek gedaan naar de bestrijding van de varroamijt. Doordat de varroamijt steeds resistenter wordt tegen chemische middelen, wordt er steeds vaker gekeken naar biologische manieren om deze te bestrijden. PPO-Bijen deed een onderzoek naar bestrijding door middel van schimmels
    Bestrijding van de champignonvlieg met behulp van entomopathogene schimmels: nader onderzoek
    Baar, J. ; Rutjens, A.J. - \ 2004
    Horst : PPO Paddestoelen (Rapport PPO 2004-30) - 11
    megaselia halterata - biologische bestrijding - insectenpathogenen - entomopathogene schimmels - megaselia halterata - biological control - entomopathogens - entomogenous fungi
    Bestrijding van de champignonvlieg Megaselia haltera met behulp van entomopathogene schimmels
    Baar, J. ; Rutjens, A.J. - \ 2004
    Horst : PPO Paddestoelen (Rapport PPO 2004-13) - 15
    agaricus bisporus - paddestoelen - megaselia halterata - biologische bestrijding - insectenpathogenen - entomopathogene schimmels - agaricus bisporus - mushrooms - megaselia halterata - biological control - entomopathogens - entomogenous fungi
    The entomopathogenic fungus Metarhizium anisopliae for mosquito control. Impact on the adult stage of the African malaria vector Anopheles gambiae and filariasis vector Culex quinquefasciatus
    Scholte, E.J. - \ 2004
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): Willem Takken; B.G.J. Knols. - Wageningen : S.n. - ISBN 9789085041184 - 183
    culicidae - anopheles gambiae - culex quinquefasciatus - biologische bestrijding - metarhizium anisopliae - entomopathogene schimmels - anopheles gambiae - culex quinquefasciatus - culicidae - biological control - metarhizium anisopliae - entomogenous fungi
    Insect-pathogenie fungi for mosquito control (Chapters 1-3)Malaria and lymphatic tilariasis impose serious human health burdens in the tropics. Up to 500 million cases of malaria are reported annually, resulting in an estimated 1.5-2.7million deaths, of which 90% occur in sub-Saharan Africa. Malaria is caused by protozoa of the genus Plasmodium and is transmitted through bites of mosquitoes belonging to the genus Anopheles. Lymphatic filariasis is caused by helminths, the most widespread species being Wuchereria bancrofti, and is transmitted through bites of mainly Culex quinquefasciatus and certain Anopheles species. Worldwide, approximately 146 million people are infected with the disease.Mosquito vector control is an important way to tight these diseases. In Africa, vector control is almost exclusively based on chemical insecticides, used predominantly to impregnate bed nets and for indoor residual spraying. Growing concerns about their negative impact on human health, on the environment, and about insecticide resistance are the reasons for increasing interests in vector control methods that are not based on chemicais, such as biological contro!.veral biological control agents are known to be effective against mosquitoes such as predatory tish (e.g. Gambusia ajfinis and Poecilia reticulata), nematodes (e.g. Romanomermis culicivorax), microsporidia (e.g. Nosema algerae), bacteria (e.g. Bacil/us thuringiensis israelensis and B. sphaericus), and insect- pathogenie fungi (e.g. Lagenidium, Coelomomyces and Culicinomyces).All of these, however, target the larval stages of mosquitoes. To date, there is no biological control agent for use against the adult stage of mosquitoes. However, reduction in survival of adult mosquitoes is considered to have a much higher impact on transmission than a reduction in the number of mosquito larvae. The objective of this PhD thesis was therefore to search for a biological control agent for adult mosquitoes, and to develop a method to use such an agent in integrated vector management (IVM) in Africa. The primary targets for this research were the major malaria vector Anopheles gambiae s.l., and, to alesser degree, the lymphatic tilariasis vector Culex quinquefasciatus. In Chapter 2 the most important insect-pathogenic fungi for (mostly) larval mosquito control are reviewed. Of these, the Hyphomycetes possess a characteristic that gives them a major advantage over other biocontrol agents to be used for killing adult mosquitoes: Unlike with bacteria, nematodes or microsporidia, the infectious propagules of these fungi do not need to be ingested. Instead, contact with the cuticle is enough for the infective propagules (conidia) to infect the mosquito. A conidium penetrates the insect cuticle by secreting cuticle­degrading enzymes. Once inside, the fungus grows rapidly and secretes toxins, which kill the mosquito. Depending on temperature, fungal dosage, and susceptibility of the mosquito to the fungus, the process from inoculation to host death may take between approximately three and ten (or even more) days. After host death, and under favourable conditions of high humidity, the fungus will grow out of the cadaver and produce conidia asexually (sporulation).The strategy envisaged to infect and kill wild mosquitoes in sub-Saharan Africa is based both on the characteristic of Hyphomycetous fungi to infect insects through contact by penetrating the cuticle, and on the behavioural characteristic of An. gambiae mosquitoes to blood feed predominantly inside houses during the night, and remain indoors for at least several hours afterwards to rest and digest the blood mea!. If conidia are applied indoors on so-called 'mosquito resting targets' (see Chapter 9), mosquitoes are expected to acquire an infection ofthe fungus by resting on those targets.In Chapter 3, five different Hyphomycetous insect pathogenie fungi were tested on adult An. gambiae, including Beauveria bassiana, a Fusarium sp. and three isolates of Metarhizium anisopliae. Four of these fungi were isolated from insects in western Kenya, an area of endemie malaria. Isolate ICIPE30 of M. anisopliae proved to be highly virulent for the tested mosquito species, and it was decided to continue further studies with this isolate.The effect of the insect-pathogenie fungus Metarhizium anisopliae on African mosquito vectors (Chapters 4-7)As described in Chapter 4, M. anisopliae was tested both on An. gambiae as weil as on Cx. quinquefasciatus, and a standard contamination technique to infect adult mosquitoes was developed. Using this technique, the effect ofthe fungus on An. gambiae was quantified in more detail by a dose-response bioassay. This experiment showed that at a dose of 1.6 x 1010 conidia m-z, >83% were infected (i.e. mosquito cadavers with sporulating fungus), with a mean LT50 value of 5.6::1: 0.4 days. Later experiments (Chapters 6 and 8) showed that the fungus could be even more effective at that same dose, with infection levels up to 96.4%, and all mosquitoes dead by day 6, whereas uninfected female An. gambiae lived much longer with L T 50 values > 18 days.Apart from the principal effect of the fungus, causing mosquito death by direct contact with conidia, infection with M. anisopliae also caused at least two secondary effects (Chapter 5). One ofthose secondary effects is a reduction in feeding propensity. In one ofthe experiments of Chapter 5, individual female An. gambiae s.s. were offered a total of 8 blood meals. It was found that mosquitoes, inoculated with a moderately high dose of fungal conidia (1.6 x 109 conidia mOz), exhibited reduced appetite upon increasing effects of fungal growth. Of the fungus-infected females, the proportion of mosquitoes taking a second blood meal was reduced with 51 %. This was further reduced to 35.3% for the 4th blood meal. The other observed secondary effect was that infected females took smaller blood meals, resulting in fewer eggs per gonotrophic cycle.In order to achieve the highest possible impact on mosquito populations, it is desirabIe that other contamination pathways besides the primary mode of contamination are utilized to spread the fungus through the population, such as horizontal transmission. The results of experiments described in Chapter 6 showed that, under laboratory conditions, conidia can be transferred from an inoculated female to a 'clean' male during the process of mating, with mean male infection rates between 10.7::1: 302% and 33.3 ::I: 3.8%.Since the mosquito inoculation method described above is based on mosquitoes that rest on conidia-impregnated sheets, it is desirabIe that mosquitoes are not repelled by conidia. To test this, behavioural effects of female An. gambiae in close vicinity of the fungus were investigated (Chapter 7). The results showed that dry conidia have a significant repellent effect (p<0.05). However, when conidia were applied in a suspension of 8% adjuvant vegetable-oil formulation and impregnated on paper, this effect ceased (p=0.205). The results suggest that if the fungus is to be applied as a biological control agent against Afrotropical mosquitoes, conidia should be impregnated on e.g. cotton sheets in an oil-based formulation to avoid repellency effects.Practical approach to mosquito vector control in Africa using M. anisopliae (Chapters 8-10).From a practical and economic point of view, the interval between applications ofthe control agent should ideally be as long as possible, without the agent losing too much efficacy. In the case of commonly used chemical residual insecticides such as permethrin this is about 6 months. Laboratory experiments (Chapter 8) showed that M. anisopliae conidia impregnated on paper and on netting material remained virulent to An. gambiae up to one month after impregnation. Experiments on conidial shelf life under different conditions showed that conidia kept in 8% vegetable oil remained viabie up to at least I month. Conidia stored in 0.05% Tween 80 exhibited only slightly reduced viability after 3 months at 27° and after 6 months at 4°C. Dry conidia stored with silica gel retained viability for at least 6 months. The results suggest that, if applied in the field, re-impregnation should be carrPractical approach to mosquito vector control in Africa using M. anisopliae (Chapters 8-10).From a practical and economic point of view, the interval between applications ofthe control agent should ideally be as long as possible, without the agent losing too much efficacy. In the case of commonly used chemical residual insecticides such as permethrin this is about 6 months. Laboratory experiments (Chapter 8) showed that M. anisopliae conidia impregnated on paper and on netting material remained virulent to An. gambiae up to one month after impregnation. Experiments on conidial shelf life under different conditions showed that condidia kept in 8% vegetable oil remained viable up to at least 1 month. Condidia stored in 0.05% Tween 80 exhibited only slightly reduced viability for a least 6 months. The results suggest that, if applied in the field, re-impregnation should be carried out monthly, but dry conidia can be stored for at least 6 months under conditions of very low relative humidity. Chapter 9 of this thesis describes a field study of domestic application of M. anisopliae in houses in south east Tanzania, a region holoendemic for malaria and lymphatic filariasis. The fungus was applied on black cotton sheets, attached to ceilings as indoor mosquito resting targets. Indoor resting catches of mosquitoes were carried out daily and collected mosquitoes were kept alive in small containers as long as possible to determine survival. Almost 90% of all collected mosquitoes were An. gambiae s.l. (of which 94.7% were An. gambiae s.s. and 5.3% An. arabiensis). In total, 181 wild An. gambiae s.l. and 6 wild Cx. quinquefasciatus were infected with the fungus. Infected mosquitoes died significantly sooner than uninfected mosquitoes, with an average daily survival rate of 0.722 for infected female An. gambiae, against 0.869 for uninfected females. Calculated from the total number of An. gambiae s.l. and Cx. quinquefasciatus that were caught from the fungus­impregnated resting targets, respectively 33.6 and 10.0% had acquired fungal infection. Of the total number of 580 female An. gambiae collected from the houses containing fungus­impregnated sheets, 132 were infected, which is an effective coverage of22.8%. Ifthis same coverage level is assumed at village level, and, together with the reduced daily survival rate, is introduced into a malaria transmission model, the total number of infectious bites per person per year (Entomological Inoculation Rate; EIR) drops from 262 to 14 (Chapter 10). Although the field experiment was on a relatively small scale and of short duration, the predictions of the malaria transmission model strongly indicate that application of M. anisopliae, aimed at the adult stage of African mosquito vectors can have a high impact on transmission intensity. It is argued that large-scale application of this method, implemented as part of an integrated vector management (IVM) strategy including larval control using biological control agents, the use of repellent plants and of unimpregnated bednets, malaria can effectively be controlled without the use of chemical insecticides. This thesis may form a first step towards such a strategy. Further research is necessary, especially in 1) searching for a fungal isolate that has even higher virulence against the targeted mosquito species, 2) testing of non-target effects and safety of the most effective fungal strain for registration, 3) searching for the most optimal formulation and application method to increase infection percentages.
    Entomopathogenic fungi against whiteflies : tritrophic interactions between Aschersonia species, Trialeurodes vaporariorum and Bemisia argentifolii, and glasshouse crops
    Meekes, E.T.M. - \ 2001
    Wageningen University. Promotor(en): J.C. van Lenteren; J.J. Fransen. - S.l. : S.n. - ISBN 9789058084439 - 181
    insectenplagen - aleyrodidae - entomopathogene schimmels - aschersonia - trialeurodes vaporariorum - bemisia argentifolii - gastheer parasiet relaties - biologische bestrijding - insect pests - aleyrodidae - trialeurodes vaporariorum - bemisia argentifolii - entomogenous fungi - aschersonia - host parasite relationships - biological control

    Many horticultural and agricultural crops are good host plants for the greenhouse whitefly, Trialeurodes vaporariorum, and the silverleaf whitefly, Bemisia argentifolii . Their damage to crops is manifold. When present in sufficient numbers they can cause leaf drop and inhibit fruit maturation. They are efficient vectors of economically important plant viruses. In addition, whiteflies produce honeydew, which soils and damages crops, and serves as a substrate for sooty moulds, thus reducing leaf photosynthesis and renders plants and fruits unsightly.

    As more environmentally responsible agricultural strategies are adopted, natural enemies of both whitefly species, will play an increasing role. Screening for natural enemies which are able to kill both pest insects quickly, without affecting other natural enemies, is an important line of research. Entomopathogenic fungi can meet these requirements and can therefore be a valuable asset to existing biological and chemical control measures. Our attention is directed towards the entomopathogenic fungi of the genus Aschersonia , which are specialised on whitefly and scale insects. Previous research indicated that Aschersonia aleyrodis is a promising whitefly control agent because of its tolerance to relative humidities as low as 50%, its long persistence on leaf surfaces and its compatibility with the parasitoid Encarsia formosa , but little is known about other species within the genus.

    This project consisted of two components: 1) to identify virulent isolates of Aschersonia spp. for the use against greenhouse and silverleaf whitefly, and 2) to study factors which influence the effectivity of entomopathogenic fungi, with special reference to host plant, humidity and their interaction.

    Forty-four isolates of Aschersonia spp. were tested for their ability to sporulate on semi-artificial media and to infect the insect hosts, both important criteria for selection of biocontrol agents. Seven isolates sporulated poorly (less than 5.10 7 conidia/culture) and ten were not able to infect either of the whitefly species. After a selection based on spore production and infection, virulence of 31 isolates was evaluated on third instar nymphs of both whitefly species on poinsettia ( Euphorbia pulcherrima ). Infection levels varied between 2 to 70%, and infection percentages of B. argentifolii correlated with that of T. vaporariorum . Several isolates, among which unidentified species of Aschersonia originating from Thailand and Malaysia, A. aleyrodis from Colombia, and A. placenta from India showed consistent results in their ability to infect both whitefly species. Of these isolates LD 50 and LT 50 values were compared to select the most virulent isolate for control of B. argentifolii and T. vaporariorum . Bioassays were carried out on intact poinsettia plants under glasshouse conditions and the dosage ranged from 14 to 1.4 x 10 5 conidia/cm 2 . On B. argentifolii LD 50 's varied between 1600 and 4800 conidia/cm 2 and LT 50 's between 4.6 - 8.7 days and on T. vaporariorum LD 50 's varied between 700 and 5300 conidia/cm 2 and LT 50 's between 4.5 and 9.9 days. For two isolates the optimum mortality did not occur at the highest dosage, which was also reflected in the speed of kill.

    To obtain better insight into the infection process of A. aleyrodis , A. placenta and an unidentified Aschersonia sp. scanning electron microscopy and bioassays were carried out. Conidia of Aschersonia spp. germinated readily on the cuticula of host insects as well as on water agar. On water agar A. placenta also produced capilliconidia. No germination was observed on poinsettia leaf surface, except on the leaf veins. On B. argentifolii the fungi formed large amounts of mucilage to attach themselves to the insect. Appressoria were formed before penetration, but also direct penetration was observed. This seemed not related to a specific site on the insect. For both whitefly species, first to third instar nymphs were most susceptible. If the population existed of fourth instar nymphs for more than 50%, infection levels dropped from 90 to 50%. Infected whitefly nymphs usually died in the stage following the treated stage. The fungus protruded from the insect via the margins or via the emergence folds of pupae, if humidity levels were high enough.

    Persistence of A. aleyrodis was studied on cucumber ( Cucumis sativus ), gerbera ( Gerbera jamesonii ) and poinsettia. Germination capacity and infectivity of conidia, which stayed on the different plants over a period of up to one month, were assessed. Average germination of conidia on the leaves was low (< 14%), whereas it was shown that most of the conidia transferred from the leaf to water agar were viable, even after having been present on the leaf surface for one month. Germination capacity was influenced by host plant species: it was highest on cucumber, followed by poinsettia and lowest on gerbera. On cucumber leaves, conidia stayed viable and were able to infect 90% of the whitefly nymphs, even at 31 days after spore application. On gerbera, germination capacity decreased considerably from 80% (day 0) to 40% (day 31). This was reflected in nymphal mortality, which declined from 75% to 40%. Despite the high germination capacity (60%) of conidia on poinsettia after a one month on the leaf surface, nymphal mortality decreased from 70% at the day of spore application to 10% after three days at leaf surface, and remained low throughout the monitoring period. The phyllosphere microflora, secondary plant metabolites and microclimate can play a role in these findings.

    Can phyllosphere humidity explain differences in insect mortality due to entomopathogenic fungi on different crops? This was tested for cucumber, gerbera, tomato ( Lycopersicon esculentum ) and poinsettia on which mycosis of T. vaporariorum and cotton aphid ( Aphis gossypii ) were determined in relation to host-plant climate. Phyllosphere humidity was estimated using climate and host-plant parameters. Hydrophobicity of the leaves and crop density were also taken into account. On cucumber, gerbera and tomato, the fungi A. aleyrodis and A. placenta caused over 90% mortality in whitefly, while another entomopathogenic fungus, Verticillium lecanii , caused 50% mortality. On poinsettia, whitefly mortality was significantly lower for all three fungi (ca. 20%). The phyllosphere of cucumber was more humid than that of the other crops. This cannot the lower whitefly mortality on poinsettia. The fact that poinsettia leaves were more hydrophobic than the other leaves may offer an explanation for the observed lower whitefly mortality, but chemical host-plant aspects may also play a role. Our results underline the importance of the first trophic level (plant) for entomopathogenic fungi in integrated pest management programs.

    The influence of relative humidity (RH) and host-plant species and their interaction on mycoses of T. vaporariorum by A. aleyrodis , A. placenta and V. lecanii was studied. Experiments conducted on poinsettia, gerbera and cucumber at 50% and 80% RH showed a clear host-plant effect. On cucumber and gerbera all fungi caused significantly higher mortality compared with the control and a higher humidity resulted in higher mortality by the fungus, whereas whitefly mortality on poinsettia remained low and was not significantly different from the control. Both Aschersonia spp. performed significantly better than V. lecanii . In following experiments an additional period of 0, 3, 6, 12, 24 or 48 hours of high RH was applied after treatment with A. aleyrodis and V. lecanii . Mortality caused by the fungus increased with a longer additional period of additional high RH and higher ambient humidity. However, the host-plant species effect exceeded the effect of ambient or additional high RH period; whitefly mortality was highest on cucumber and lowest on poinsettia. On poinsettia both fungi had hardly any effect on whitefly mortality, except after a 48 hrs additional high RH period. On gerbera and cucumber all fungal treatments were significantly different from the control and A. aleyrodis performed better than V. lecanii .

    The influence of cultivar differences on the efficacy of entomopathogenic fungi is also tested. The experiment was conducted in a glasshouse (semi-practice) using two gerbera cultivars, 'Bourgogne' and 'Bianca' with different plant structure and trichome density on the leaf: 'Bianca' having more and larger leaves and fewer trichomes/cm 2 than 'Bourgogne'. A. aleyrodis and V. lecanii were applied for the control of T. vaporariorum , in two concentrations, 10 6 and 10 7 conidia/ml. In 'Bianca', both fungi caused a whitefly mortality up to 80%. Whitefly mortality was higher for 10 7 than for 10 6 conidia/ml. In 'Bourgogne', V. lecanii caused a significantly lower mortality than A. aleyrodis . Although no cultivar differences in whitefly development time were found, other characteristics, like natural mortality and build-up of the whitefly population, seemed to differ. Differences in mortality levels in relation to cultivar (humidity, hit-probability) and whitefly characteristics may explain the differences between the efficacy of the fungal species.

    The host plant is the most important factor in this tritrophic system, exceeding the influence of ambient humidity. However, although entomopathogenic fungi are less successful in controlling whiteflies on poinsettia, these problems may be circumvented by use of formulation. Aschersonia spp. are highly virulent against whitefly pests, can cause natural epizootics in the field, can be grown on artificial media, are well adapted to survive in the canopy environment, and are compatible to/or even complementary with other natural enemies.

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