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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.

    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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    Lessons from paradise: AESOP Lecture Series / Lecture 14
    Needham, Barrie ; Leeuwen, Eveline van - \ 2019
    The fairphone approach dealing with spatial and temporal dynamic
    Planning, law and economics : The rules we make for using land
    Needham, Barrie ; Buitelaar, E. ; Hartmann, T. - \ 2018
    New York : Routledge - ISBN 9781138085572 - 180 p.
    Data challenges and opportunities for environmental management of North Sea oil and gas decommissioning in an era of blue growth
    Murray, Fiona ; Needham, Katherine ; Gormley, Kate ; Rouse, Sally ; Coolen, Joop W.P. ; Billett, David ; Dannheim, Jennifer ; Birchenough, Silvana N.R. ; Hyder, Kieran ; Heard, Richard ; Ferris, Joseph S. ; Holstein, Jan M. ; Henry, Lea-Anne ; Mcmeel, Oonagh ; Calewaert, Jan-Bart ; Roberts, J.M. - \ 2018
    Marine Policy 97 (2018). - ISSN 0308-597X - p. 130 - 138.
    Maritime industries routinely collect critical environmental data needed for sustainable management of marine ecosystems, supporting both the blue economy and future growth. Collating this information would provide a valuable resource for all stakeholders. For the North Sea, the oil and gas industry has been a dominant presence for over 50 years that has contributed to a wealth of knowledge about the environment. As the industry begins to decommission its offshore structures, this information will be critical for avoiding duplication of effort in data collection and ensuring best environmental management of offshore activities. This paper summarises the outcomes of a Blue Growth Data Challenge Workshop held in 2017 with participants from: the oil and gas industry; the key UK regulatory and management bodies for oil and gas decommissioning; open access data facilitators; and academic and research institutes. Here, environmental data collection and archiving by oil and gas operators in the North Sea are described, alongside how this compares to other offshore industries; what the barriers and opportunities surrounding environmental data sharing are; and how wider data sharing from offshore industries could be achieved. Five primary barriers to data sharing were identified: 1) Incentives, 2) Risk Perception, 3) Working Cultures, 4) Financial Models, and 5) Data Ownership. Active and transparent communication and collaboration between stakeholders including industry, regulatory bodies, data portals andacademic institutions will be key to unlocking the data that will be critical to informing responsible decommissioning decisions for offshore oil and gas structures in the North Sea.
    A Dutch perspective on urban growth boundaries : From containing to stimulating growth
    Janssen-Jansen, Leonie ; Tan, Wendy - \ 2018
    In: Instruments of Land Policy Taylor and Francis - ISBN 9781138201514 - p. 137 - 141.
    Within international planning educational circles, the Netherlands has long been held up as an exemplar of effective national and regional land use planning practices. Well-known examples are the water management policies (van der Cammen and de Klerk 2012). The clearly defined administrative hierarchies, the policy consistency, and the management of the land resource with governmental controls in planning have been praised in planning literature. The Dutch planning system is seen as a great example for other countries, just as Sullivan’s Portland example (Bontje 2003; Fainstein 2005). The urban growth boundary (UGB) of the Regional Framework Plan of Portland is likewise one of the most outstanding elements of the land use planning system in State of Oregon. This is an example of an instrument accompanied by many other complementary ordinances, regulations, and rules that together result in a desired planning outcome. The UGB is therefore often compared to national planning instruments in the Netherlands intent on enforcing a strict boundary between the urban and the rural. In the Netherlands, this divide has always been a keystone concept of the land use planning system, which is to keep as much open space ‘open’ as possible, while concurrently address the need for expansion and growth by ensuring enough land for residential development in a context of land scarcity in the upcoming decades. This is a similar situation to Portland where the growth necessary for the next 20 years needs to be balanced by the geographical constraints of the nature and agricultural areas. Although the regional UGB enjoys statutory status in Portland, regional coordination is considered an informal norm within the Netherlands. For example, certain provinces keep to an 80–20 rule, whereby the majority of new developments should take place within existing urban contours. The regional focus of Portland’s planning system is relevant for international planners as most land use issues tend to cross administrative borders in nature and involve more than a single government level. On the surface, the Dutch planning system might not have much to offer as compared to Portland as the legal force is maintained mostly at the local level in the form of municipal land use plans (Needham 2016). Although the 2008 revision of the planning law (WRO 2008) does enable regional and inter-municipal zoning plans 138that can be brought forward by multiple municipalities or proposed by the Dutch regional government – the province – this instrument has been hardly implemented. From the provincial perspective, ‘overthrowing’ municipalities is politically not popular; municipalities – and their governors – focus on the land in their municipality as they are accountable for planning within the municipality, not outside.
    Community gardens in urban areas: a critical reflection on the extent to which they strenghten social cohesion and provide alternative food
    Veen, E.J. - \ 2015
    Wageningen University. Promotor(en): Han Wiskerke, co-promotor(en): Andries Visser; Bettina Bock. - Wageningen : Wageningen University - ISBN 9789462573383 - 265
    publieke tuinen - tuinieren - stedelijke gebieden - bewonersparticipatie - buurtactie - stadslandbouw - alternatieve landbouw - volkstuinen - voedingsmiddelen - biologische voedingsmiddelen - sociologie - public gardens - gardening - urban areas - community participation - community action - urban agriculture - alternative farming - allotment gardens - foods - organic foods - sociology
    Summary

    Introduction

    The aims of this thesis are twofold; firstly, it aims to increase the understanding of the extent to which community gardens enhance social cohesion for those involved; secondly, it aims to gain insight into the importance community gardeners attach to food growing per se, and the extent to which participants perceive community gardens as an alternative to the industrial food system.

    I define community gardens as a plot of land in an urban area, cultivated either communally or individually by people from the direct neighbourhood or the wider city, or in which urbanites are involved in other ways than gardening, and to which there is a collective element. Over the last years, community gardens have sprung up in several Dutch cities. Although there are various reasons for an increasing interest in community gardens, there are two that I focus on in this thesis in particular. The first is the assumption made that community gardens stimulate social cohesion in inner-city neighbourhoods, to be seen in the light of the ‘participatory society’. The second is community gardens’ contribution to the availability of locally produced food, in the context of an increased interest in Alternative Food Networks (AFNs).

    The Dutch government aims to transform the Dutch welfare state into a participatory society in which citizens take more responsibility for their social and physical environment. This way the government not only hopes to limit public spending, but also wishes to increase social bonding and the self-organisational capacity of society. Community gardens fit the rhetoric around the participatory society, as they are examples of organised residents taking responsibility for their living environment. Moreover, the literature suggests that gardens are physical interventions that may decrease isolation by acting as meeting places. However, both the extent to which community gardens enhance social cohesion and under what conditions they may do so are unclear, especially as gardens come in various designs, shapes and sizes.

    The popularity of community gardens also seems to be related to an overall increasing societal interest in food, and can be discussed in relation to Alternative Food Networks. AFNs are food systems that are different in some way from the mainstream, and are seen as a reaction to consumer concerns about the conventional food system. They are often considered to be dictated by political motivations and injected with a ‘deeper morality’. The category ‘AFN’ is however a heterogeneous category, as is the conventional food system; neither can be easily defined. The degree to which community gardens can be seen as AFNs is therefore unclear. While they do improve the availability of local food and operate outside of the market economy, we do not know how much and how often people eat from their gardens, nor do we know to what extent they are involved in the gardens in order to provide an alternative to the industrial food system. Hence, there is a lack of knowledge about the sense in which community gardens are alternative alternatives.

    Research questions

    The overall research question of this thesis is:

    What is the significance of community gardening in terms of its intention to promote social cohesion as well as its representation as an alternative food system?

    This broad question is instructed by the following sub-questions:

    Why do people get involved in community gardens? What are their motivations?How, to what extent, and under which conditions does community gardening promote the development of social relations between participants? How do participants value these social effects? To what extent do the diets of community garden participants originate from the gardens in which they are involved? What is the importance of food in community gardens?What is the importance of growing or getting access to alternative food for participants of community gardens? Methodology

    An important theoretical lens in this research is the theory of practice. Practices are defined as concrete human activity and include things, bodily doings and sayings. By performing practices people not only draw upon but also feed into structure. Routinisation – of practices, but also of daily life – therefore plays a central role in practice theory. Practice theory allows for an emphasis on practical reality as well as a study of motivations. This focus on how people manage everyday life, and how gardening fits within that, makes it particularly useful for this thesis.

    I define social cohesion as the way in which people in a society feel and are connected to each other (De Kam and Needham 2003) and operationalised it by focusing on ‘social contacts, social networks, and social capital’, one of the elements into which social cohesion is often broken up. This element was operationalised as 1) contacts (the width of social cohesion) and 2) mutual help (the depth of social cohesion).

    This research has a case study design; I studied four Dutch community gardens over a two-year period of time, and later supplemented these with an additional three cases. As practices consist of both doings and sayings, analysis must be concerned with both practical activity and its representation. I used participant observations to study practical activities, and interviews, questionnaires and document study to examine the representation of these activities.

    Findings

    Chapters 3 to 7 form the main part of this thesis. They are papers/book chapters that have been submitted to or are published by scientific journals or books. All of them are based on the field work.

    In chapter 3 we compare two of the case studies and determine to what extent they can be seen as ‘alternative’. We argue that although reflexive motivations are present, most participants are unwilling to frame their involvement as political, and mundane motivations play an important role in people’s involvement as well. By using the concept of ‘food provisioning practices’ we show that participants of community gardens are often required to be actively involved in the production of their food. This means that participants are both producers and consumers: the gardens show a ‘sliding scale of producership’. This chapter also shows that political statements are not a perfect predictor of actual involvement in community gardening. This finding was one of the main reasons for starting to use the theory of practice, which is the main topic of the next chapter.

    In chapter 4 we compare one of my case studies with an urban food growing initiative in New York City. By comparing the internal dynamics of these two cases and their relations with other social practices, we investigate whether different urban food growing initiatives can be seen as variations of one single practice. We also study the question of whether the practice can be seen as emerging. In particular, we take the elements of meaning, competences and material (Shove et al. 2012) into account. We found both similarities and differences between the two cases, with the main difference relating to the meanings practitioners attach to the practice. We conclude, therefore, that it is not fully convincing to see these cases as examples of the same social practice. We also argue that urban food growing may be considered an emerging practice, because it combines various practices, both new and established, under one single heading.

    In chapter 5 we use the theory of practice to explore how urban food growing is interwoven with everyday life. We compare four community gardens - two allotments and two cases which we define as AFNs. We found that participants of the allotments are involved in the practice of gardening, while members of the AFNs are involved in the practice of shopping. The gardening practice requires structural engagement, turning it into a routine. The produce is a result of that routine and is easily integrated into daily meals. As AFNs are associated with the practice of shopping, they remain in competition with more convenient food acquisition venues. Eating from these gardens is therefore less easily integrated in daily life; every visit to the garden requires a conscious decision. Hence, whether members are primarily involved in shopping or in growing has an impact on the degree to which they eat urban-grown food. This shows that motivations are embedded in the context and routine of everyday life, and ‘only go so far’.

    Chapter 6 concerns the organisational differences between the seven case studies in this thesis and the extent to which these influence the enhancement of social cohesion. We study people’s motivations for being involved in the gardens and compare these with the three main organisational differences. This comparison reveals that the gardens can be divided into place-based and interest-based gardens. Place-based gardens are those in which people participate for social reasons – aiming to create social bonds in the neighbourhood. Interest-based gardens are those in which people participate because they enjoy growing vegetables. Nevertheless, all of these gardens contribute to the development of social cohesion. Moreover, while participants who are motivated by the social aspects of gardening show a higher level of appreciation for them, these social aspects also bring added value for those participants who are motivated primarily by growing vegetables.

    In chapter 7 we present a garden that exemplifies that gardens may encompass not only one, but indeed several communities, and that rapprochement and separation take place simultaneously. While this garden is an important meeting place, thereby contributing to social cohesion, it harbours two distinct communities. These communities assign others to categories (‘us’ and ‘them’) on the basis of place of residence, thereby strengthening their own social identities. Ownership over the garden is both an outcome and a tool in that struggle. We define the relationship between these two communities as instrumental-rational – referring to roles rather than individuals - which explains why they do not form a larger unity. Nevertheless, the two communities show the potential to develop into a larger imagined garden-community.

    Conclusions

    This thesis shows that the different organisational set-ups of community gardens reflect gardeners’ different motivations for being involved in these gardens. The gardens studied in this thesis can be defined as either place-based or interest-based; gardens in the first category are focused on the social benefits of gardening, whereas gardens in the second category are focused on gardening and vegetables. Nevertheless, social effects occur in both types of gardens; in all of the gardens studied, participants meet and get to know others and value these contacts. Based on this finding, I conclude that community gardens do indeed enhance social cohesion.

    Place-based community gardens specifically have the potential to become important meeting places; they offer the opportunity to work communally towards a common goal, and once established, can develop into neighbourhood spaces to be used for various other shared activities. Most interest-based gardens lack opportunities to develop the social contacts that originated at the garden beyond the borders of the garden. These gardens are often maintained by people who do not live close to the garden or to each other, and those who garden are generally less motivated by social motivations per se. Important to note is that community gardens do not necessarily foster a more inclusive society; they often attract people with relatively similar socio-economic backgrounds and may support not one, but several communities.

    Most participants from place-based gardens eat from their gardens only occasionally; others never do so. This type of community garden can therefore hardly be seen as a reaction to the industrialised food system, let alone an attempt to create an alternative food system. Nevertheless, certain aspects of these gardens are in line with the alternative rhetoric. By contrast, most gardeners at interest-based gardens eat a substantial amount of food from their gardens, and to some of them the choice to consume this locally-grown food relates to a lifestyle in which environmental considerations play a role. However, this reflexivity is not expressed in political terms and participants do not see themselves as part of a food movement. Participants who buy rather than grow produce showed the greatest tendency to explain their involvement in political terms, but many of them have difficulty including the produce in their diets on a regular basis. I therefore conclude that community gardens cannot be seen as conscious, ‘alternative’ alternatives to the industrial food system. Nonetheless, the role of food in these gardens is essential, as it is what brings participants together – either because they enjoy gardening or because the activities which are organised there centre around food.

    Theoretical contributions

    In this thesis I used and aimed to contribute to the theory of practice. Using participant observations to study what people do in reality was particularly useful. It turned research into an embodied activity, enabling me to truly ‘live the practice’, and therefore to understand it from the inside.

    Deconstructing the practice of food provisioning into activities such as buying, growing and cooking was helpful in gaining an understanding of how people manage everyday life, and how food acquisitioning fits into their everyday rhythms. It sheds light on how and to what extent people experience the practice of community gardening as a food acquisitioning practice, and to what degree they relate it to other elements of food provisioning such as cooking and eating. The focus on the separate elements of food provisioning practices helped me realise that acquiring food from community gardens represents a different practice to different people; some are engaged in the practice of growing food, others in the practice of shopping for food.

    This thesis showed that motivations delineate how the practice ‘works out in practice’; the way in which a practice such as community gardening is given shape attracts people with certain motivations, who, by reproducing that practice, increase the attractiveness of the practice for others with similar motivations. This implies that while community gardening appears to be one practice, it should in fact be interpreted as several distinct practices, such as the practice of food growing or the practice of social gathering. Motivations therefore influence a garden’s benefits and outcomes. This thesis thus highlights that motivations should not be overlooked when studying practices.

    Apprehending the motivations of community gardeners is also an important contribution to the literature around AFNs, since it helps us to understand the extent to which urban food production is truly alternative. By studying motivations, this thesis reveals that AFNs do not necessarily represent a deeper morality, or that not all food growing initiatives in the city can be defined as alternative. However, participants of community gardens are often both producers and consumers (there is a ‘sliding scale of producership’); the gardens are thus largely independent from the conventional food system. Moreover, for participants who buy produce, the meaning of the gardens often goes beyond an economic logic (there is a ‘sliding scale of marketness’). Hence, while the gardens studied in this thesis are no alternative alternatives, most of them can be qualified as ‘actually existing alternatives’ (after Jehlicka and Smith 2011).

    This thesis showed that even those gardens in which the commodification of food is being challenged do not necessarily represent a deeper morality, which is contrary to what is argued by Watts et al. (2005). This implies that understanding whether or not initiatives resist incorporation into the food system is insufficient to be able to determine whether or not they can be defined as alternative food networks. However, determining whether or not deeper moral reflection is present is not a satisfactory way of defining food networks as alternative either, as this neglects the fact that motivations do not always overlap with practical reality. This suggests that establishing whether a food network can be regarded as alternative requires studying both motivations and practical reality. The thesis also raises the question to what extent the label AFN is still useful. Since it is unclear what ‘alternative’ means exactly, it is also unclear whether a given initiative can be considered alternative. Moreover, the world of food seems too complex to be represented by a dichotomy between alternative and conventional food systems; the gardens presented in this thesis are diverse and carry characteristics of both systems. I therefore suggest considering replacing the term AFN with that of civic food networks, as Renting et al. (2012) advocate.

    Reducing aggression among chronic psychiatric inpatients through nutritional supplementation
    Schat, A.A. ; Hubers, M.M. ; Geleijnse, J.M. ; Rest, O. van de; Hout, W.B. van den; Bogers, J.P.A.M. ; Mouton, C. ; Hemert, B.M. van; Giltay, E.J. - \ 2014
    In: Book of abstracts Fourth International Conference on Violence in the Health Sector. - www.icn.ch - p. 360 - 360.
    Q fever in humans and farm animals in four European countries, 1982 to 2010
    Georgiev, M. ; Alfonso, A. ; Neubauer, H. ; Needham, H. ; Thiéry, R. ; Rodolakis, A. ; Roest, H.I.J. ; Stärk, K.D. ; Stegeman, J.A. ; Vellema, P. ; Hoek, W. van der; More, S.J. - \ 2013
    Eurosurveillance 18 (2013)8. - ISSN 1025-496X - 13 p.
    burnetii-inactivated vaccine - coxiella-burnetii - seroepidemiologic survey - hospitalized-patients - sheep flock - dairy herds - goat herds - netherlands - outbreak - germany
    fever is a disease of humans, caused by Coxiella burnetii, and a large range of animals can be infected. This paper presents a review of the epidemiology of Q fever in humans and farm animals between 1982 and 2010, using case studies from four European countries (Bulgaria, France, Germany and the Netherlands). The Netherlands had a large outbreak between 2007 and 2010, and the other countries a history of Q fever and Q fever research. Within all four countries, the serological prevalence of C. burnetii infection and reported incidence of Q fever varies broadly in both farm animals and humans. Proximity to farm animals and contact with infected animals or their birth products have been identified as the most important risk factors for human disease. Intrinsic farm factors, such as production systems and management, influence the number of outbreaks in an area. A number of disease control options have been used in these four countries, including measures to increase diagnostic accuracy and general awareness, and actions to reduce spillover (of infection from farm animals to humans) and human exposure. This study highlights gaps in knowledge, and future research needs.
    The Formative Years of the Dutch Town Planning Movement (1850-1950)
    Valk, A.J.J. van der - \ 2013
    In: A Centenary of Spatial Planning in Europe / Teixeira, J., Brussels : ECTP-CEU; Editions Outre Terre - ISBN 9789994931484 - p. 215 - 223.
    Spatial planning is planned government intervention in the use of private and public land. In the Netherlands this activity has a long history going back to the middle of the nineteenth century. The notion currently used for this practice i.e. spatial planning (in Dutch: ruimtelijke ordening), became common only after the Second World War. Before that time ‘urban expansion’ (in Dutch: stadsuitbreiding) and ‘town planning’ (in Dutch: stedenbouw) respectively were used. (Faludi & Van der Valk, 1994; Needham, 2007). In this paper a number of milestones in the history of government policy and the discipline will be considered. In addition, attention will be paid to the ideals of professionals and the development of a programme for proper town (and country) planning in practice. Planning is the work of mankind. Plans and projects reflect opinions and decisions of administrators, ordinary people and experts. The thoughts and deeds of Dirk Hudig, the pioneer of modern spatial planning in the Netherlands, are sketched out by way of illustration. Being a spider in a web of international experts he was the driving force behind the landmark 1924 international town planning conference in Amsterdam. (Dings, 2010, 32; De Ruijter, 1987, 152) In this paper Hudig is portrayed as an exponent of a movement that flew the flag for ‘make-ability’ of society. The starting point for this treatise is the topical question of assessing the current and future role of spatial planning in large societal projects in the Netherlands, e.g. the management of urban growth and sustainable spatial adaptation strategies to climate change. The question implies contemporary dissatisfaction with and doubt about the possibilities of manageability of spatial developments in the country formerly known as ‘Planner’s Paradise’. (Faludi & Van der Valk, 1994, xiii) Part of the answer is rooted in the history of the profession
    Introduction why reconsider planning by law and property rights?
    Hartmann, Thomas ; Needham, Barrie - \ 2012
    In: Planning By Law and Property Rights Reconsidered Ashgate Publishing Ltd - ISBN 9781409437215 - p. 1 - 19.
    Planning by law and property rights reconsidered
    Hartmann, Thomas ; Needham, Barrie - \ 2012
    Ashgate Publishing Ltd - ISBN 9781409437215 - 233 p.

    Countries which take spatial planning seriously should take planning law and property rights also seriously. There is an unavoidable logical relationship between planning, law, and property rights. However, planning by law and property rights is so familiar and taken for granted that we do not think about the theory behind it. As a result, we do not think abstractly about its strengths and weaknesses, about what can be achieved with it and what not, how it can be improved, how it could be complemented. Such reflections are essential to cope with current and future challenges to spatial planning. This book makes the (often implicit) theory behind planning by law and property rights explicit and relates it to those challenges. It starts by setting out what is understood by planning by law and property rights, and investigates - theoretically and by game simulation - the relationships between planning law and property rights. It then places planning law and property rights within their institutional setting at three different scales: when a country undergoes enormous social and political change, when there is fundamental political debate about the power of the state within a country, and when a country changes its legislation in response to European policy. Not only changing institutions, but also global environmental change, pose huge challenges for spatial planning. The book discusses how planning by law and property rights can respond to those challenges: by adaptive planning), by adaptable property rights, and by public policies at the appropriate geographical level. Planning by law and property rights can fix a local regime of property rights which turns out to be inappropriate but difficult to change. It questions whether such regimes can be changed and whether planning agencies can make such undesirable lock-ins less likely by reducing market uncertainty and, if so, by what means.

    Conclusion
    Needham, Barrie ; Hartmann, Thomas - \ 2012
    In: Planning by Law and Property Rights Reconsidered Ashgate Publishing Ltd - ISBN 9781409437215 - p. 219 - 228.
    Needham's Question
    Stigter, C.J. - \ 2011
    Meteorologica / Centro Argentino de Meteorl¿ogos 20 (2011)3. - ISSN 0325-187X - p. 30 - 30.
    Parasite-host interactions between the Varroa mite and the honey bee : a contribution to sustainable Varroa control
    Calis, J.N.M. - \ 2001
    Wageningen University. Promotor(en): J.C. van Lenteren; M.W. Sabelis. - S.l. : S.n. - ISBN 9789058084460 - 144
    honingbijen - bijenziekten - varroa jacobsoni - gastheer parasiet relaties - mijtenbestrijding - honey bees - bee diseases - varroa jacobsoni - host parasite relationships - mite control

    Introduction

    Varroa mites as parasites of honey bees

    Varroa destructor (Anderson & Trueman, 2000), is the most important pest of European races of the Western honey bee, Apis mellifera L., weakening bees and vectoring bee diseases (Matheson, 1993). Over the past decades it has spread all over the world and control measures are required to maintain healthy honey bee colonies.

    Originally, this mite only occurred in colonies of the Eastern honey bee, Apis cerana Fabr., in Asia. Varroa destructor was formerly known as V. jacobsoni Oud. (Anderson & Trueman, 2000). The Varroa mite was described in 1904 by Oudemans as a parasite of Eastern honey bees in Indonesia. Although the actual damage inflicted by the mite to the Eastern honey bee has never been determined, the Varroa mite is not considered to be a problem in colonies of its original host. However, Varroa turned into a serious pest of Western honey bees when beekeepers moved the Western honey bee into the area of distribution of the Eastern honey bee. The mite appeared to be a harmful parasite on its new host, but before this was realised it had already spread over the world through shipments of colonies and queens (De Jong et al., 1982; Matheson, 1993).

    Varroa mites may ruin Western honey bee colonies because parasitised bees suffer from malformations and a shortened life span (Beetsma et al., 1989). The Varroa mite feeds on both adult bees and brood, but reproduction is restricted to brood cells, which mites invade during the final larval developmental stage of the honey bee. Offspring is produced during the period that the immature bee develops in the capped brood cell and the mother and her progeny emerge together with the young bee. In addition to direct damage to bees through feeding, mites act as vectors of honey bee pathogens and increase the incidence of honey bee diseases (Ball, 1994). This threat of Varroa mites to beekeeping resulted in the development of acaricides and nowadays several effective acaricides are available which are applied world-wide (Koeniger & Fuchs, 1988; Ritter, 1990). However, the use of acaricides has important disadvantages. Acaricides contaminate bee products like honey and wax (De Greef, 1994) and thus the use of these acaricides is in conflict with the status of honey and wax as natural products. Another disadvantage is that mites have become resistant to these acaricides and this resistance is spreading world-wide, which implies the need for alternative ways of control.

    Towards sustainable Varroa control

    In this thesis, I present studies on biotechnical methods of Varroa control and studies on how variation in the honey bee's susceptibility to Varroa affects the mite population growth. In theory, biotechnical control methods in which mites are trapped in brood cells and removed from the colony, so-called trap-comb methods, are simple. In practice, however, these methods may become complicated because timing of application needs to be integrated in other activities of the beekeeper, such as swarm prevention. In addition, application of these methods is usually labour intensive. Effective trap-comb methods are available, but reduction of labour intensity is still needed. Much research is therefore directed to breed honey bees that are less susceptible to Varroa mites (Woyke, 1989; Büchler, 1994; Moritz, 1994). In this field, I investigated whether reduced developmental time of bee brood and attractiveness of bee brood to mites are suitable traits for selection aiming at reduced susceptibility of honey bees to Varroa mites. If less susceptible honey bees are available, the high effectiveness of control methods needed for successful control may be relaxed. This in turn may allow simplification of biotechnical control methods. The aim of my thesis is to develop acaricide-free beekeeping by using alternative methods for effective control of Varroa .

    Objectives and research questions

    Applying knowledge on invasion behaviour in the development of biotechnical control methods and population modelling

    The parasite-host interactions between the mite and the honey bee have been intensively studied, because such knowledge may lead to new ways of control. In earlier work, I collaborated with Beetsma and Boot (1995) to study invasion behaviour of mites into brood cells. Varroa mites survive on adult bees, but reproduction is restricted to the capped brood cell (Ifantidis & Rosenkranz, 1988). The rate of brood cell invasion defines the distribution of mites over bees and brood and, therefore, the population dynamics of the mite. The rate of invasion appeared to depend mainly on the ratio of brood cells that are being capped per bee in the colony, as reviewed in Chapter 1. In this thesis I applied this knowledge to design control methods that are based on trapping mites in bee brood. I investigated if it is possible to predict the effectiveness of trap-comb methods using a model based on the calculated invasion rate of the mites in brood cells from the ratio of capped brood cells per bee (Chapters 2&3). Using this model, concepts of trap-comb-methods were evaluated (Chapter 4). I also applied knowledge on invasion behaviour to gain more insight in the mite's population dynamics in general (Chapter 5).

    Towards less susceptible honey bees

    Differential reproduction of mites in both host-species, A. cerana and A. mellifera , seems to be a key factor in susceptibility of honey bees to Varroa (Büchler, 1994; Rosenkranz & Engels, 1994). In European A. mellifera colonies mites reproduce in both worker and drone brood and mite numbers increase rapidly. In colonies of its original host, A. cerana , mites invade both types of brood cells but refrain from reproducing in worker cells (Boot et al., 1997). Thus, in A. cerana mite numbers can only increase when drones are being reared. In African and africanised A. mellifera races a high percentage of mites that invade worker brood also refrain from reproducing (Camazine, 1986; Ritter, 1993). Therefore, like A. cerana, African and africanised honey bees are less susceptible to Varroa . I studied whether refraining from reproduction in worker brood is due to a trait of the honey bee or due to a trait of the mite (Chapter 6). By transferring Varroa mites originating from A. mellifera colonies to A. cerana worker brood and vice versa there appeared to be two distinct mite populations with a different reproductive strategy. Mites originating from A. mellifera reproduced in worker brood in both species of honey bee, whereas mites originating from A. cerana reproduced in drone brood only. Later, genetic studies of Varroa mites (Anderson & Trueman, 2000) made clear that the two populations in fact belong to different species. The mites that parasitise Western honey bees originate from Korea and Japan and were erroneously called V. jacobsoni and have been recently named V. destructor (Anderson & Trueman, 2000).

    Selection for honey bee traits that reduce reproductive success in worker brood is reminiscent of the situation we in the original host-parasite relationship where mites reproduce exclusively in drone brood. I studied honey bee traits that may play a role in the reproductive success of Varroa mites in worker brood: the duration of the capped brood stage and attractiveness of the brood cells. A short duration of the capped brood stage will limit the development of nymphs (Chapter 7). Reduced attractiveness will decrease the rate of invasion and hence the rate of reproduction (Chapter 8).

    Summary

    Structure of the thesis

    The chapters in this thesis are articles in which a separate part of the work is introduced and results are presented and discussed. The first six chapters have been published in periodicals and the final two chapters are submitted for publication.

    Invasion behaviour of Varroa mites: from bees into brood cells (Chapter 1)

    Varroa mites may invade worker or drone brood cells when worker bees bring them into close contact with these cells. The attractive period of drone brood cells is two to three times longer than that of worker brood cells. The attractiveness of brood cells is related to the distance between the larva and the cell rim and the age of the larva. The moment of invasion of the mite into a brood cell is not related to the duration of its stay on adult bees. The fraction of the phoretic mites that invade brood cells is determined by the ratio of the number of suitable brood cells and the size of the colony. The distribution of mites over drone and worker brood in a colony is determined by the specific rates of invasion and the number of both brood types. Knowledge of mite invasion behaviour has led to effective biotechnical control methods and increased insight in the mite's population dynamics.

    Control of Varroa mites by combining trapping mites in honey bee worker brood with formic acid treatment of the capped brood outside the colony: Putting knowledge on brood cell invasion into practice (Chapter 2)

    Biotechnical Varroa control methods are based on the principle that mites inside brood cells are trapped and then removed from the bee colony. Initially, methods were studied in which worker brood was used for trapping. Trapped mites were killed with a formic acid treatment that left the worker brood unharmed. The observed percentage of mites trapped and killed by formic acid treatment was 87% and 89% in two experiments which matched predictions based on knowledge on brood cell invasion. Hence, knowledge on the mites' behaviour with respect to brood cell invasion proved to be a useful tool for designing and improving trap-comb methods for Varroa control.

    Effective biotechnical control of Varroa mites: Applying knowledge on brood cell invasion to trap mites in drone brood (Chapter 3)

    Trapping mites in brood cells is most efficient when drone brood is used while the colonies are otherwise broodless. In theory, one trap-comb using drone brood is enough to achieve effective control. I designed and tested two methods using trap-combs with drone brood. To reduce labour intensity, application of trap-combs was integrated in swarm prevention techniques. In the first method, effectiveness of the control method varied considerably, from 67% to 96%. Effectiveness depended on the number of drone cells that had been available for mite trapping. The observed effectiveness in each separate colony could be predicted from the numbers of bees and brood cells, thereby showing the validity of our approach. In the second method, we adjusted the method to improve production of drone brood on the trap-combs, because this appeared to be crucial for trapping efficiency. The observed effectiveness of 93.4 % demonstrates that trap-combs with drone brood can effectively trap mites, thereby offering a non-chemical method of Varroa control.

    Model evaluation of methods for Varroa mite control based on trapping in honey bee brood (Chapter 4)

    The trap-comb model that was used to predict mite-trapping effectiveness in our experiments was used to estimate and compare effectiveness of different trap-comb methods described by several authors. Predictions of the model showed that for effective control by trapping with worker brood is labour intensive because a large amount of brood is needed to trap a sufficient number of mites. An extra input of labour is the demand for treatment of the capped worker brood to selectively kill the mites, because beekeepers want to save the brood. The model predicted that trapping with drone brood demands much less brood cells for effective mite control. Labour intensity is less compared to trap-combs with worker brood. This is because drone brood with trapped mites is usually destroyed instead of saved and preparation of trap-combs with drone brood can be integrated into swarm-prevention-techniques.

    Population modelling of Varroa mites (Chapter 5)

    To understand population dynamics of the mite, Fries et al. (1994) incorporated knowledge on Varroa mite-honey bee interactions into a mite population model. I updated and extended this model by incorporating more recent data, in particular on mite invasion from bees into brood cells. This allowed predictions of invasion into and emergence from brood cells, and hence the distribution of mites over bees and brood. As mite control treatments usually only affect mites either in brood cells or on adult bees, the model can be used to evaluate their effectiveness and timing. Mite population growth proved to be especially sensitive to the length of the brood period, the number of drone cells and reproductive success in the brood cells.

    Natural selection of Varroa explains the different reproductive strategies in colonies of Apis cerana and Apis mellifera (Chapter 6)

    In colonies of European A. mellifera, Varroa reproduces both in drone and in worker brood. In colonies of its original Asian host, A. cerana, the mites invade both drone and worker brood cells, but reproduce only in drone cells. Absence of reproduction in worker cells is probably crucial for the tolerance of A. cerana towards Varroa because it means that the mite population can only grow during periods of drone rearing. To test whether the absence of mite reproduction in worker brood of A. cerana is due to a trait of the mites or of the honey bee species, mites from bees in A. mellifera colonies were introduced into A. cerana worker brood cells and vice versa. Approximately 80% of the mites originating from A. mellifera reproduced in worker cells of both A. mellifera and A. cerana. Conversely, only 10% of the mites originating from A. cerana colonies reproduced in worker cells of A. cerana and A. mellifera. Hence, absence of reproduction in worker cells is due to a trait of the mites. Additional experiments showed that A. cerana removed 84% of the worker brood that was artificially infested with mites from A. mellifera colonies. Brood removal started 2 days after artificial infestation, which suggests that the bees responded to behaviour of the mites. Because removal behaviour of the bees will have a large impact on the mite's fitness, it probably plays an important role in selection for differential reproductive strategies. These findings have large implications for selection programmes to breed less-susceptible bee strains. If differences in mites (i.e. whether they reproduce in worker brood or not) are mite-specific, we should not only look for mites not reproducing as such, but for colonies in which mites are selected for not reproducing in worker cells. Hence, in selection programmes reproductive success of mites that reproduce in both drone and worker cells should be compared to the reproductive success of mites that reproduce exclusively in drone cells.

    Reproductive success of Varroa mites in honey bee brood with differential development times (Chapter 7)

    Reproduction of Varroa mites has been extensively studied and many aspects of its life history such as number of eggs laid, timing of egg laying, and mortality of immature mites, are well known. However, estimates of the actual reproductive success after one brood cycle, i.e. how many mites can be found alive on the bees after emergence of an infested cell, are still fairly theoretical. Because this parameter is crucial for understanding population growth of the mites, several methods were used to measure the actual reproductive success. To evaluate how development time of the capped brood stage may affect population growth of the mites, measurements were done in bee strains with different development times of worker brood. In brood with a relatively short developmental time, reproductive success of mites was lower. Increased developmental time resulted in higher egg production and lower mortality of offspring before or shortly after emergence of the mites from the brood cell. The results show that the number of mites emerging alive from worker cells with relatively short development times, may become lower than the initial number that invaded the cells. This results in a decline of the mite population if only worker cells are available. In addition, the low reproductive success in worker brood with a short development time, explains that the phenomenon of mites not reproducing in worker cells, as found in A. cerana and in several A. mellifera races, evolves if these mites survive to reproduce in drone brood the next brood cycle.

    Attractiveness of brood cells of different honey bee races to Varroa mites (Chapter 8)

    Reproduction of the Varroa mite only occurs inside capped brood cells of honey bees. Therefore, invasion into brood cells is crucial for the mite's reproduction and the rate of invasion will affect the growth of the mite population. I investigated the invasion response of the mites to drone or worker larvae of different honey bee races, because selection for less attractive brood may help Varroa control. The observed differences in invasion response of Varroa mites to worker brood of the tested colonies were not statistically significant. The results suggest that not the racial origin of the worker brood, but the distance between the larva and the cell rim affects the invasion response of the Varroa mites to worker brood cells. Because measuring the distance between the larva and the cell rim in drone brood cells is inaccurate due to curved cell caps of neighbouring cells, the results for drone brood cells are difficult to interpret. Possibilities to obtain less attractive brood via selection or comb manipulation are discussed.

    Epilogue

    Towards a future in which beekeeping does not depend on the use of acaricides for effective control of Varroa

    Considering the conflict between the use of synthetic acaricides and the status of honey bee products as natural products and the spreading resistance of Varroa to these acaricides, there is a clear need for alternative ways of Varroa control. Our research on biotechnical control methods and susceptibility of honey bees to Varroa contributes to sustainable Varroa control. Knowledge on invasion behaviour of mites into brood cells proved to be useful to understand the possibilities and limitations for improvement of biotechnical control methods. Using drone brood on trap-combs, an effective biotechnical control method has become available providing a non-chemical way of controlling the mite population. Integration of knowledge on invasion behaviour into a population model of the Varroa mite allows us to gain more insight in the mite's population dynamics and evaluate traits of honey bees that via selection may decrease susceptibility of honey bee colonies. Selection for honey bee traits that reduce reproductive success in worker brood in A. mellifera may lead to selection of mites towards the situation we know from the original host-parasite relationship were mites only reproduce in drone brood. The duration of the capped brood stage seems a good candidate because selection for a short development time will reduce reproductive success of the mites. Attractiveness of brood cells is a less suitable trait because differences in attractiveness of brood of different race were not detected. Although less susceptible honey bees are not available yet, selectable traits have been identified that may reduce the effect of Varroa infestation on honey bee colonies. Nowadays, beekeeping is not dependent on the use of synthetic acaricides to control the Varroa mite. Next to trap-comb methods, much research has been successfully directed towards Varroa control using organic acids and essential oils (Imdorf, 1999). Reducing susceptibility of honey bees together with effective control by means of biotechnical and other 'organic' control methods provides a perspective for beekeeping that does not rely on synthetic acaricides to kill Varroa mites.

    Acknowledgements

    I thank M. Beekman, WJ Boot, JC van Lenteren and M.W. Sabelis for their valuable comments on the manuscript.

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