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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    Atomization of dilute oil-in-water emulsions during application of crop protection products
    Hilz, E. - \ 2013
    Wageningen University. Promotor(en): Martien Cohen Stuart; Frans Leermakers, co-promotor(en): A.W.P. Vermeer. - S.l. : s.n. - ISBN 9789461735416 - 199
    drift - spuiten - druppelstudies - verstuiving - druppelgrootte - formuleringen - pesticiden - emulsies - drift - spraying - droplet studies - atomization - droplet size - formulations - pesticides - emulsions

    Crop protection products are usually applied as sprays. These spray droplets have a certain size distribution. Fine droplets are often required to achieve a good coverage of the plant and to guarantee the biological efficacy of an agrochemical product. At the same time very fine droplets in spray are not desirable. Due to their low mass and velocity, these droplets can be carried from the application site by crosswind and e.g. can contaminate surface water. Droplet drift can be minimized by reducing the number of very fine droplets in spray. Dilute emulsions produce coarser sprays compared to water when atomized through a standard flat fan nozzle. For this reason dilute emulsions can reduce drift risk.

    The mechanism of spray formation of dilute emulsions has been investigated in this thesis. The proposed mechanism also describes spray formation in more complex mixtures of dilute emulsions with surfactants or polymers.

    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.

    The development of microbial pest control products for control of arthropods: a critical evaluation and a roadmap to success
    Ravensberg, W.J. - \ 2010
    Wageningen University. Promotor(en): Joop van Lenteren. - [S.l.] : S.n. - ISBN 9789085856788 - 348
    plagen veroorzaakt door geleedpotigen - biopesticiden - ontwikkeling - potentie - screenen - biologische productie - formuleringen - experimenteel veldonderzoek - kwaliteitscontroles - vercommercialisering - planning - toelating van bestrijdingsmiddelen - arthropod pests - microbial pesticides - development - potency - screening - biological production - formulations - field experimentation - quality controls - commercialization - planning - authorisation of pesticides
    Microbial pesticides have been developed for a hundred years, but many of these biological crop protection products have not been successful in the market. This is illustrated in chapter 1 by the history of microbial pest control products and the biopesticide companies producing those. In this thesis I recognize the need for a model that would facilitate the development and commercialization of biopesticides based on entomopathogenic bacteria, fungi, viruses, and nematodes. The aim of this thesis was to develop a rational and structured approach that will increase the chances of achieving success with microbial pest control products for control of arthropods.
    The initial step is finding a microbial pest control agent which has the potential to control the pest (chapter 2). The search for a novel agent is directed by an elaborate description of the pest problem. The first level of selection is the type of entomopathogen: bacteria, fungi, viruses, protozoa, and entomopathogenic nematodes. The second level is at the species and strain level. This study identified three decisive selection criteria for a commercial microbial insecticide: mortality, production efficiency, and safety to humans and the environment. The consecutive steps in the screening process have been identified as the collection of isolates, laboratory screening on efficacy in well-standardized bio-assays, and on production efficiency, assessment of mode of action and toxicological properties, and efficacy in small glasshouse trials. This selection process should deliver determinative information on which one or at the most three to four strains are chosen for further development.
    The next phase is the investigation of the feasibility of economic mass production of the selected strain(s) and the development of a stable product (chapter 3). Two phases are distinguished, the development of the production process, including medium development and downstream processing, and the development of the product, including formulation, packaging and field testing. Mass production is preferably an in vitro process because that offers more control than an in vivo process. Bacteria, fungi and entomopathogenic nematodes are generally produced in vitro, whereas baculoviruses must be produced in vivo. The critical technical and economic factors are identified and evaluated for these four types of pathogens. The goal is to produce the greatest number of infective propagules for the lowest cost.
    A stable product requires a formulation. The four main objectives in formulating the infective propagules are: to stabilize the propagules for reasons of packaging, shelf-life and shipping; to create a user-friendly product that can be effectively delivered to the target; to protect the propagule, once applied, to improve its persistence at the target site; and to minimize risks of exposure to the applicator. Formulation considerations and recommendations are presented per formulation function as well as per type of pathogen.
    Field testing links all steps in the developmental process. It provides information on the efficacy of the selected strain, on the quality of the produced propagules, on the formulation, and on the optimal application strategy. Results from field tests provide a continuous circle of feedback that allows improvement of each of the steps of the entire developmental process.
    The price of a product is an essential element and a cost price model for biopesticides is presented. The model provides a perspective on the makeup of the end-user’s price. Economy of scale, full use of the production capacity, and capacity planning are pivotal factors to keep the costs low. Key elements to successful biopesticides are both production efficiency and product efficacy.
    Quality control (chapter 4) provides feedback on the production and formulation processes, and on the final product. The continuous process of improvements will ultimately decrease costs and improve performance of the production system and the product. Products must meet product specifications. Parameters checked per batch are the number of effective propagules, microbial purity, presence of toxins, technical properties and efficacy. Standardization and comparison with a reference product are prerequisites for proper quality control. Quality control is also required for registration, but standard methods and criteria are lacking. Therefore, guidance documents need to be developed. Biocontrol companies should ensure that product quality is maintained through the whole distribution chain and that end-users receive high quality products. I showed that in that way, both the biocontrol industry and its customers benefit from proper quality control.
    In chapter 5 regulations for microorganisms are reviewed. Microorganisms, except nematodes, need to be registered as plant protection products for crop protection. Registration is perceived as the main hurdle to the development of a biopesticide. The procedures in the EU are presented and difficulties discussed. The issues relate to inappropriate data requirements, lack of guidance for applicants and regulators, testing methods for microbials, lack of experience in regulators, national registration procedures, and the inexperienced small biopesticide companies. Registration is expensive and takes many years. I presented registration cost estimates for each type of entomopathogenic product. Initiatives for improvements from the EU-REBECA project, from the OECD BioPesticides Steering Group, and some national projects are presented. I also provided recommendations for improvements for data requirements and regulatory procedures. New regulations may offer improved procedures in the near future. Various import and export regulations affect the use of microorganisms, and the need for harmonization is emphasized. The Convention of Biodiversity may, through Access and Benefit Sharing, create a further impediment for biocontrol.
    The patentability of an entomopathogen is discussed as well as the criteria for granting a patent: novelty, inventive step, and industrial applicability. I also discussed costs and other considerations whether to apply for a patent for a biopesticide.
    The implementation strategy of the product in an IPM programme is a basic element of the use of any microbial pest control product (chapter 6). Three phases are distinguished: the optimal application strategy of the product, the incorporation of the microbial pest control product in an IPM system, and a carefully designed adoption strategy. Determinative parameters for each phase, and for each type of product are identified. For instance, for a successful use, the compatibility with chemical pesticides and with natural enemies and pollinators needs to be investigated. Furthermore, knowledge transfer and training are pivotal elements. All stakeholders need to participate in this process.
    These phases require a considerable amount of research which should be conducted before market launch. Recommendations are provided for a tiered approach which results in reliable information for commercial conditions. Many companies underestimated or even neglected this part of product development. In my opinion, these phases are paramount for good market introduction. I reported the most relevant requirements for successful use of a microbial pest control product. Successful implementation of a microbial pest control product depends on how well relevant interactions are studied and translated into practical recommendations for the grower. This phase continues after market introduction. It requires a continuous effort from producer, distributor and customer to ensure that product adoption will increase and satisfied customers will remain using the new product in their IPM system.
    In chapter 7, I noted that commercialization is the final and most difficult step in the development and the market introduction of a microbial pest control product. The factors that determine success or failure are identified for a company as well as for a product, and recommendations are provided that will facilitate success.
    Figures on the global biopesticide market are reviewed. The European market is estimated to be €57 million at end-user level, and the market in the Netherlands at €5-6 million. The European biopesticide market comprises less than 1% of the total European crop protection market. Biopesticides are predominantly used in protected crops and in orchards.
    Companies which contemplate the development and commercialization of a biopesticide need realistic data on five key aspects to make their decision: market demand, market size, profit margin, time to market, and time to volume. The biggest mistake companies still make today is a misjudgement of the potential market size and the expected market adoption rate. I proposed the use of a stage-gate process with objective, quantifiable, and transparent tools in decision-making. Examples of scorecards are presented to quantify decisions. The business model that performs best at present seems to be a small company which follows an incremental and manageable growth of the organization. Total developmental costs and time to market are significant factors of a company’s success. Costs amount to € 10-15 million for a company that still needs to be built; while in an existing company, costs may reach € 5-10 million for a biopesticide project. Time to market including registration is five to seven years. I have identified five determinants for successful commercialization: 1) acceptable expenses and time to market; 2) a high quality product; 3) a sufficiently large market; 4) a profit margin that allows expansion in new markets and products; and 5) the appropriate business approach.
    A new product development project is extensive and it is difficult to oversee. In chapter 8 I have made an analysis of the various phases and I highlighted the most important topics in the development and commercialization of a microbial pest control product. This study demonstrated that the development of a microbial pest control product requires a structured project plan. The building blocks of the entire process are defined and essential factors emphasized. From this, I have divided the process in phases and steps, and designed the roadmap to a successful product. Three diagrams illustrate the stepwise approach of the entire process, the selection phase, the product development phase, and the implementation phase. Registration and commercialization are processes that relate to these phases during the entire developmental process.
    A future perspective on the biopesticide market is presented with limiting and promotional factors and trends. The significant drivers for success are food safety concern, changes in the regulatory climate, biodiversity and environmental issues, new research and technology, and the occurrence of new invasive pests. The biopesticide industry has reached a sufficient level of maturity and critical mass to form a base for further expansion. This will allow the biopesticide market to steadily grow. The roadmap proposed in this study will assist developers of biopesticides in accomplishing their goals in a cost- and time-effective way, which will result in successful and sustainable products and expanding biocontrol companies.


    Toedieningswijze en formulering cruciaal voor effectiviteit van GNO's
    Zande, J.C. van de; Stevens, L.H. ; Spits, H.G. - \ 2006
    gewasbescherming - pesticiden - plantaardige pesticiden - biopesticiden - toedieningswijzen - doseringseffecten - formuleringen - bladbespuiting - aardappelen - lelies - appels - toelating van bestrijdingsmiddelen - plant protection - pesticides - botanical pesticides - microbial pesticides - application methods - dosage effects - formulations - foliar spraying - potatoes - lilies - apples - authorisation of pesticides
    Succesvolle introductie van GNO’s in de praktijk is in hoge mate afhankelijk van een juiste toedieningswijze en daarmee samenhangende formulering. Verbetering van de effectiviteit verlaagt de benodigde hoeveelheid GNO’s, waardoor de kans op introductie wordt verhoogd. Onderzoek naar toediening en formulering is daarom een integraal onderdeel van de ontwikkeling van GNO-produkten voor de praktijk
    Foliar absorption of crop protection agents: influence of cpa properties, formulation and plant species : a literature study for the Dutch research programme pesticides and the environment (DWK-359) theme B-2
    Ruiter, H. de; Kempenaar, C. ; Blom, M. - \ 2004
    Wageningen : Plant Research International (Report / Plant Research International 77) - 26
    4-cpa - opname via bladeren - formuleringen - veldgewassen - eenzaadlobbigen - tweezaadlobbigen - 4-cpa - foliar uptake - formulations - field crops - monocotyledons - dicotyledons
    Influence of adjuvants and formulations on the emission of pesticides to the atmosphere : a literature study for the Dutch Research Programme Pesticides and the Environment (DWK) theme C-2
    Ruiter, H. de; Holterman, H.J. ; Kempenaar, C. ; Zande, J.C. van de - \ 2003
    Wageningen : Plant Research International (Report / Plant Research International 59) - 42
    pesticiden - formuleringen - hulpstoffen - emissie - pesticides - formulations - adjuvants - emission
    Volatilization patterns of tri-allate formulations : a report for Monsanto Europe, Bruxelles and Monsanto USA, St. Louis
    Ruiter, H. de - \ 2002
    Wageningen : Plant Research International (Note / Plant Research International 181) - 26
    thiocarbamaatherbiciden - tri-allaat - vervluchtiging - formuleringen - thiocarbamate herbicides - tri-allate - volatilization - formulations
    Hulpstoffen maken onkruidbestrijdingsmiddelen efficienter
    Schans, D.A. van der - \ 2001
    PPO-bulletin akkerbouw 2001 (2001)4. - ISSN 1385-5301 - p. 6 - 9.
    onkruidbestrijding - onkruiden - herbiciden - herbicidenmengsels - onkruiddodende eigenschappen - hulpstoffen - toevoegingen - formuleringen - dosering - doseringseffecten - toedieningshoeveelheden - gewasbescherming - chemische bestrijding - bestrijdingsmethoden - weed control - weeds - herbicides - herbicide mixtures - herbicidal properties - adjuvants - additives - formulations - dosage - dosage effects - application rates - plant protection - chemical control - control methods
    In kasproeven testte PPO de werkzaamheid van contactherbiciden in verschillende doseringen, en bij toevoeging van hulpstoffen, bij de bestrijding van de onkruiden melganzevoet en hanepoot. Uit de sterk verbeterde werking blijkt dat bij een verstandig gebruik van hulpstoffen de grenzen van LageDoseringsSystemen (LDS) nog niet zijn bereikt. In veldproeven werd de werking onderzocht van hulpstoffen bij lage doseringen van verschillende tankmixen herbiciden voor de bestrijding van perzikkruid en hanepoot in suikerbieten en maïs
    De grondwaterstroming naar diepe putten bij twee watervoerende lagen in een concentrisch binnengebied met droge sloten
    Ernst, L.F. - \ 1972
    Wageningen : I.C.W. (Nota / Instituut voor Cultuurtechniek en Waterhuishouding 660) - 10
    grondwaterstroming - watervoerende lagen - putten - formuleringen - groundwater flow - aquifers - wells - formulations
    Een nadere uitwerking van formules is gegeven, waarbij een stelsel van 3 vergelijkingen werd overgehouden voor grondwaterstroming naar putten bij 2 watervoerende lagen
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