Research Interest

I work as senior scientist at the Evolutionary and Population Biology (EPB) research group of IBED.

My research focuses on population-dynamical consequences of omnivory in plant-herbivore-carnivore interactions, with emphasis on biological pest control.

Short CV

• I studied Biology at Leiden University with emphasis on the organism and population levels (ethology, systematics, evolution, ecology). I had additional courses in mathematics and geology, and spent quite some time outdoors learning to recognise plants, birds and insects. I was active in political and environmental organisations. I graduated in 1986 based on studies in Environmental Science, Environmental Biology and Animal Ecology.

• In 1988 I became Junior Researcher at the University of Amsterdam at the Population Biology section headed by Prof. Dr M.W. Sabelis. Here I started on a research project on the predator-prey interactions of thrips and predatory mites, with emphasis on the impact of alternative food. I studied the life histories of predator and prey species, predator functional and numerical responses and comparative studies on various predatory mite species. The latter study resulted in the discovery of Iphyseius degenerans as potential new biocontrol agent of thrips, and a request to develop a more efficient rearing method for this species by the biocontrol company Ciba Bunting BC Ltd.
• Subsequently, I worked for 7 months as Visiting Associate in Research at Washington State University in Vancouver, WA, with Dr. L.K. Tanigoshi, on the life history, diet range and pesticide-resistance of this and related predator species.
• In 1996 I returned to the University of Amsterdam on a self-attained grand to continue my research on thrips, predatory mites andsupplementary food.  Now the emphasis was on behavioral studies and large-scale population experiments (the latter at the greenhouse research station in Naaldwijk). Mathematical models were formulated to link lab results with greenhouse experiments. This all resulted on the 14th of February 2002 in a PhD.

• In 2001 and 2002 I worked as post-doc ecological modeller at the NERC Centre for Population Biology and CABI Bioscience (both at Silwood Park, Ascot, UK) on the effect of cannibalism and intraguild predation on predator coexistence, as part of EU project on environmental risks of biological control introductions (ERBIC). In addition, I worked on evolutionary models for insect-killing fungi.
• From 2003 until 2008 I had a research position at the Netherlands Institute of Ecology (NIOO-KNAW) in Heteren. Here I initially worked on (the evolution of) direct and indirect defence in plants and (with Dr F.L. Wäckers) on the publication of a book on plant-provided food for predators. From 2005 onwards I could bring my views on the importance of supplementary food into practice by participating in different projects on 'Functional Agrobiodiversity' (FAB).
• In 2008 I again returned to the University of Amsterdam to continue with a second FAB project (see seperate page).
• From 2012 until 2015 I received a grand from the Netherlands Science Foundation (program "Biodiversity Works!") to underpin the ideas and results from the FAB projects with population-dynamical models and develop better theory on how to support biodiversity and natural pest control in agriculture-dominated landscapes.
• In 2016 I worked (as freelancer) on the optimisation of flower strips to support pollination and natural pest control in blueberries. I also modelled the effects of different food-supply scenario’s on the biological control of thrips in greenhouses, on request by WUR-Greenhouse Horticulture.
• In 2017-2018 I coordinated a two-season study monitoring the effects of flower strips on insect diversity, aquatic macrofauna, pest control and pollination in the Hoeksche Waard, funded by the Dutch Ministry of Infrastructure and the Environment (Min. I&M).
• From 2019 onwards I am appointed permanently as senior researcher at the UvA-IBED, with the following tasks:
• Supervising practical for BSc students and research projects for MSc students related to natural pest control.
• Local project manager of the NW Europe Interreg project ‘FABuleus Farmers’ (2019-2023), with Hoeksche Waard as pilot area and RIVM and local organisations in the Hoeksche Waard as sub-partners. As part of this project we continue the aforementioned monitoring on the effects of flower strips for an additional 4 years and quantify all the ecosystem services related to flowering field margins and other FAB measures.
• I analysed the effects of organic farming measures on soil arthropod fauna and natural pest control in organic greenhouse vegetable crops, as part of the EU CORE project ‘GreenResilience’ (2018-2022).
• Local project manager of the EU Horizon-2020 project 'FRAMEwork-biodiversity' (2020-2025) on improving on-farm biodiversity by supporting farmer cluster collaboration, with a farmer cluster in Flevoland as pilot area.
• Supervisor of PhD student Laura Mansier on the design and analysis of habitat-structured population-dynamical models of natural pest control and pollination (as part of the FRAMEwork project).

My Expertise

• Ecology of thrips, predatory mites and hoverflies
• Life history evolution
• Foraging behaviour & predation
• Modeling predator-prey dynamics
• Plant-provided food supplements
• (Conservation) biological control
• Functional Agrobiodiversity
• Landscape ecology

Links

For more information about  

• my publications
• my research on thrips and mites
• Functional Agrobiodiversity (FAB) projects

check the links below.

My Publications

• Edited publications
• Book chapters
• Scientific papers
• Popular articles and reports (in Dutch)

See lists below. Some papers are available through links on the research pages (links below) or through DARE.

Bevordering van nuttige organismen voor plaagbestrijding en bestuiving in open teelten

[Support of beneficial organisms for pest control and pollination in field crops]
Zilva A. van Rossum, Felix L. Wäckers, Arne Janssen & Paul C.J. van Rijn.
Rapport in opdracht van het Ministerie van Landbouw, Natuur en Voedselveiligheid (LNV).  IBED Amsterdam 2022. 66p.

In dit rapport evalueren we de effecten van gericht samengestelde landschapselementen op natuurlijke plaagbestrijding en bestuiving. Deze gerichte biodiversiteitsverhoging kan op verschillende manieren worden bereikt, zoals door de aanleg van specifiek samengestelde bloemrijke akkerranden of houtige landschapselementen zoals hagen, maar ook door bv mengteelten, strokenteelten en bosakkerbouw. Door deze maatregelen af te stemmen op de functionele groepen die de ecosysteemdiensten leveren, kunnen deze effectiever ondersteund worden, een concept dat Functionele Agrobiodiversiteit (FAB) is gaan heten.

Plant-provided Food for Carnivorous Insects:

A Protective Mutualism and its Applications
Edited by:
Felix L. Wäckers
Paul C.J. van Rijn
Jan Bruin
Cambridge University Press 2005,365 pages
Within a carnivore's lifecycle, there is often at least one stage that relies on plant-provided food, e.g., nectar. In fact, carnivore omnivory is far more common than first thought. Contributed by an international team of experts, this book suggests, among other ideas, that presence, or lack of, plant-provided foods for carnivores could determine the success or failure of agricultural ecosystems using Integrated Pest Management systems relying on predators as biological control agents.

Agrobiodiversity - Conservation and Functionality

Biodiversiteit - Nut en Natuur

Edited by:
Paul C.J. van Rijn
Jinze Noordijk
Jan Bruin

Themanummer Entomologische Berichten 67(6), Nederlandse Entomologische Vereniging 2007, 102 pagina's

Link voor downloads: https://secties.nev.nl/pages/publicaties/eb/eb_inhoud.php?nummer=67-6

Book Chapters

• Sabelis, M.W. and P.C.J. van Rijn. 1997. Predation by insects and mites. In: T. Lewis (Ed.), Thrips as Crop Pests, CAB-International, London , pp. 259-354.
• Sabelis, M.W., M. van Baalen, F.M.Bakker, J. Bruin, B. Drukker, M. Egas, A.R.M. Jansen, I.K. Lesna, B. Pels, P.C.J. van Rijn and P. Scutareanu. 1999. The evolution of direct and indirect defence against herbivorous arthropods. In:Olff, H.,V.K. Brown and R.H. Drent (Eds.) Herbivores: between plants and predators. Blackwell Science, Oxford.
• Van Lenteren, J.C., D. Babendreier, F. Bigler, G. Burgio, H.M.T. Hokkanen, S. Kuske, A.J.M. Loomans, I. Menzler-Hokkanen, P.C.J. vanRijn, M.B. Thomas, and M.G. Tommasini. 2003. Regulation of import and release of mass-produced natural enemies: a risk-assessment approach. In: Van Lenteren, J.C. (Ed.)Quality Control and Production of Biological Control Agents. Theory and Testing Procedures. CAB International, London , pp. 191-204.
• Wäckers, F.L. and P.C.J. vanRijn. 2005. Food for Protection: an Introduction. In:F.L. Wäckers, P.C.J. vanRijn & J. Bruin (eds.), Plant-provided Food for Carnivorous Insects: A Protective Mutualism and its Applications. Cambridge University Press, Cambridge, pp. 1-14.
• Sabelis, M.W. , P.C.J. van Rijn and A. Janssen. 2005.Fitness consequences of food-for-protection strategies in plants. In: Plant-provided Food for Carnivorous Insects: A Protective Mutualism and its Applications. F.L. Wäckers, P.C.J. van Rijn & J. Bruin (eds.), Cambridge University Press, Cambridge, pp. 109-134.
• Van Rijn, P.C.J. and M.W. Sabelis. 2005. The impact of plant-provided food on herbivore-carnivore dynamics. In: F.L. Wäckers, P.C.J. van Rijn & J. Bruin (eds.), Plant-provided Food for Carnivorous Insects: A Protective Mutualism and its Applications. Cambridge University Press, Cambridge, pp. 223-266.
• Wäckers, F.L. and P.C.J. van Rijn. 2012. Pick and mix: selecting flowering plants to meet the requirements of target biological control insects. In: G.M. Gurr, S.D. Wratten, W.E. Snyder & D.M.Y. Read (eds.). Biodiversity andInsect Pests: Key Issues for Sustainable Management. John Wiley & Sons, pp. 139-165.

Scientific Papers

• Van Houten, Y.M., P.C.J. van Rijn, L.K. Tanigoshi, P. van Stratum and J. Bruin. 1995. Preselection of predatory mites for year-round control of Western Flower Thrips ( Frankliniella occidentalis), in greenhouse crops. Entomologia Experimentalis et Applicata 74: 225-234.
• Van Rijn, P.C.J., C. Mollema and G. Steenhuis. 1995. Comparative life history studies of Frankliniella occidentalis and Thrips tabaci (Thysanoptera: Thripidae) on cucumber. Bulletin of Entomological Research 85: 285-297.
• Van Rijn, P.C.J. and L.K., Tanigoshi. 1999. The contribution of extrafloral nectar to survival and reproduction of the predatory mite Iphiseius degenerans on Ricinus communis . Experimental and Applied Acarology:23: 281-296.
• Van Rijn, P.C.J. and L.K., Tanigoshi. 1999. Pollen as food for the predatory mites Iphiseius degenerans and Neoseiulus cucumeris (Acari: Phytoseiidae): dietary range and life history. Experimental and Applied Acarology 23: 785-802.
• Van Rijn, P.C.J. and M.W. Sabelis. 1999. Should plants provide food for predators when it also benefits the herbivores? The effects of pollen on a thrips-predatory mite system.  In: R. Mitchell, D.J. Horn, G.L. Needhamand W.C. Welbourn (Eds), Acarology IX, Vol 2, Symposia. Ohio Biological Survey, Columbus, Ohio, pp. 227-231.
• Van Rijn,P.C.J., Y.M. Van Houten and M.W. Sabelis. 1999. Pollen improves thrips control with predatory mites. IOBC-WPRS Bulletin, 22(1): 209-212.
• Faraji, F., A. Janssen, P.C.J. van Rijn and M.W. Sabelis. 2000. Kin recognition by the predatory mite Iphiseius degenerans: discrimination among own, conspecific, and heterospecific eggs. Ecological Entomology 25: 147-155.
• Van Baalen, M., V. Krivan, P.C.J. van Rijn andM.W. Sabelis. 2001. Alternative food, switching predators and the persistence of predator-prey systems. American Naturalist 157: 512-524.
• Van Rijn, P.C.J. 2002. The Impact of Supplementary Food on a Prey-Predator Interaction. PhD Thesis, University of Amsterdam. 267 pp.
• Van Rijn, P.C.J., Y.M. van Houten andM.W. Sabelis. 2002. How plantsbenefit from providing food for predators even when it is also edible to herbivores. Ecology 83: 2664-2679.
• Van Lenteren, J. C., D. Babendreier, F. Bigler, G. Burgio, H.M.T. Hokkanen, S. Kuske, A.J.M. Loomans, I. Menzler-Hokkanen, P.C.J. van Rijn, M.B.Thomas, M.G. Tommasini, and Q.Q. Zeng. 2003. Environmental risk assessmentof exotic natural enemies used in inundative biological control. Biocontrol 48:3-38.
• Van Rijn, P.C.J., Bakker, F. M., van der Hoeven,W. A. D. and Sabelis, M.W. 2005. Is arthropod predation exclusively satiation-driven? Oikos109: 101-116.
• Wäckers, F.L. and P.C.J. van Rijn. 2005. Plantfood to enhance the performance of natural enemies in mass rearing and in the field. Encyclopedia of Pest Management. D. Pimentel (ed.), Marcel Dekker, New York.
• Van Rijn, P.C.J. , G. Burgio and M.B. Thomas 2005. Impact of intraspecific and intraguild predation on predator invasion and coexistence. Can exotic ladybeetles displace native species? In: Second International Symposium on Biological Control of Arthropods. M.S. Hoddle (ed.), USDA Forest Service Publication, pp. 38-47.
• Sabelis, M.W. and P.C.J. van Rijn. 2005. When does alternative food promote biological pest control? In: Proceedings Second International Symposium on Biological Control of Arthropods. M.S. Hoddle (ed.), USDA Forest Service Publication, pp. 428-437.
• Sabelis, M.W. and P.C.J. van Rijn. 2006. When does alternative food promote biological pest control? IOBC-WPRS Bulletin Vol. 29(4): 195-200.
• Van Rijn, P.C.J., J. Kooijman and F.L. Wäckers. 2006. The impact of floral resources on syrphid performance and cabbage aphid biological control. IOBC-WPRS Bulletin Vol. 29(6): 149-152.
• Van Alebeek, F., M. Wiersema, P.C.J. van Rijn, F.L. Wäckers, E. den Belder, J. Willemse and H. van Gurp. 2006. A region-wide experiment with functional agrobiodiversity (FAB) in arable farming in the Netherlands. IOBC-WPRS Bulletin Vol. 29(6): 141-144.
• Magalhães, S., P.C.J. van Rijn, M. Montserrat, A. Pallini and M.W. Sabelis. 2006. Population dynamics of thrips prey and their mite predators in a refuge. Oecologia 150(4): 557-568.
• Wäckers, F.L., P.C.J. van Rijn, K. Winkler and D. Olson. 2007. Flower power? Potential benefits and pitfalls of using (flowering) vegetation for conservation biological control. Aspects of Applied Biology 81: 135-140.
• Wäckers, F.L., J.Romeis and P.C.J. van Rijn. 2007. Nectar and pollen-feeding by insect herbivores and implications for tri-trophic interactions. Annual Review of Entomology 52: 301-323.
• Wäckers, F.L., P.C.J. van Rijn and G. Heimpel. 2008. Honeydew as a food source: Making the best of a bad meal? Biological Control 45(2): 176-184.
• Langoya, L.A. and P.C.J. van Rijn. 2008. The significance of floral resources for natural control of aphids. Proc. Neth. Entomol. Soc. Meet.19: 67-74.
• Van Rijn, P., F. van Alebeek, E. den Belder, F.Wäckers, J. Buurma, J.Willemse & H. van Gurp.2008. Functional agro-biodiversity in Dutch arable farming: results of a three year pilot. IOBC-WPRS Bulletin Vol. 34: 125-128.
• Van Rijn, P., E. den Belder, J. Elderson, M. Vlaswinkel, F. van Alebeek. 2008. Perspectives for functional agro-biodiversity in Brussels sprouts. IOBC-WPRS Bulletin Vol. 34: 121-124.
• Van Rijn,P.C.J. and F.L. Wäckers. 2010. The suitability of field margin flowers as food source for zoophagous hoverflies. IOBC-WPRS Bulletin Vol. 56: 125-128.
• Van Rijn, P.C.J. 2012. The suitability of field margin flowers as food source for Chrysoperla lacewings. IOBC-WPRS Bulletin Vol. 75: 213-216.
• Wäckers, F.L. and P.C.J. van Rijn. 2012. Pick and mix: selecting flowering plants to meet the requirements of target biological control insects. In: Biodiversity and Insect Pests: Key Issues for Sustainable Management (Edited by G.M. Gurr, S.D. Wratten, W.E. Snyder and D.M.Y. Read), John Wiley & Sons, pp. 139-165. 
• Van Rijn, P.C.J., J. Kooijman and F.L. Wäckers. 2013. The contribution of floral resources and honeydew to the performance of predatory hoverflies (Diptera: Syrphidae). Biological Control 67: 32–38.
• Van Rijn, P.C.J. 2014. Which shrubs and trees can conserve natural enemies of aphids in spring? IOBC-WPRS Bulletin Vol. 100: 137-141.
• Van Rijn, P.C.J. & F.L. Wäckers. 2016. Nectar accessibility determines fitness, flower choice and abundance of hoverflies that provide natural pest control. Journal of Applied Ecology 53 (3): 925–933. doi: 10.1111/1365-2664.12605.
• Geertsema, W., Rossing, W.A.H., Landis, D.A., Bianchi, F.J.J.A., van Rijn, P.C.J., Schaminée, J.H.J., Tscharntke, T. & van der Werf, W. 2016. Actionable knowledge for ecological intensification of agriculture. Frontiers in Ecology and the Environment 14 (4): 209–216. doi:10.1002/fee.1258.
• Van Rijn, P.C.J. 2017. Natural pest control requires a complete landscape. IOBC-WPRS Bulletin 122: 107-111.
• Van Rijn, P.C.J., M. Klompe, S. Elzerman, M.E.T. Vlaswinkel & H. Huiting. 2019. The role of flower-rich field margin strips for pollinators, natural enemies and pest control in arable fields. IOBC-WPRS Bulletin 143: 56-60.

Book:  Biodiversity and Insect Pests: Key Issues for Sustainable Management

Edited by Geoff M. Gurr, Stephen D. Wratten, William E. Snyder & Donna M. Y. Read. 2012 John Wiley and Sons Ltd, Chichester, UK.

Biodiversity offers great potential for managing insect pests.  It provides resistance genes and anti-insect compounds; a huge range of predatory and parasitic natural enemies of pests; and community ecology-level effects operating at the local and landscape scales to check pest build-up.  The new book 'Biodiversity and Insect Pests: Key Issues for Sustainable Management' brings together world leaders in theoretical, methodological and applied aspects to provide a comprehensive treatment of this fast-moving field.  Chapter authors from Europe, Asia, Africa, Australasia and the Americas ensure a truly international scope.  Topics range from scientific principles, innovative research methods, ecological economics and effective communication to farmers, as well as case studies of successful use of biodiversity-based pest management some of which extend over millions of hectares or are enshrined as government policy. Written to be accessible to advance undergraduates whilst also stimulating the seasoned researcher, this work will help unlock the power of biodiversity to deliver sustainable insect pest management.

Chapter 9 by Felix L. Wäckers and Paul C.J. van Rijn on "Pick and mix: selecting flowering plants to meet the requirements of target biological control insects" 

reviews the various methods to study flower exploitation and summarizes the floral food requirements for the main groups of pest natural enemies.

Nederlandstalige Publicaties

• Van Rijn, P.C.J.& F.L. Wäckers. 2004. Goede insecten klaar aan zijlijn. Groenten en Fruit 42:49.
• Van Rijn, P.C.J.& F.L. Wäckers. 2005. Wie niet sterk is, moet zoet zijn. De Levende Natuur - nov. 2005: 275.
• Van Rijn, P. & F.Wäckers. 2007. Akkerranden als wegrestaurant. Natuurlijke vijanden een handje helpen. Nieuwe Oogst 23 juni 2007.
• Van Rijn, P. 2007. Hulptroepen in onze akkers. Strijd tegen plagen win je niet alleen. Nieuwe Oogst 23 juni 2007.
• Van Rijn, P., J. Noordijk &  J. Bruin. 2007. Agrobiodiversiteit -nut en natuur. EntomologischeBerichten 67 (6): 183.
• Van Rijn, P.C.J. & F.L.Wäckers. 2007.Bloemrijke akkerranden voeden natuurlijke vijanden. Entomologische Berichten67(6): 226-230.
• VanAlebeek, F., P. van Rijn, E. den Belder, J. Willemse & H. van Gurp. 2007.FAB projecten in de akkerbouw.Entomologische Berichten67 (6):235-236.
• Van Rijn, P.C.J.& J.T. Smit. 2007. Zweefvliegen (Diptera: Syrphidae) voor de natuurlijke bestrijding van bladluizen. Entomologische Berichten 67 (6): 253-256.
• Van Schelt, J. & P. van Rijn. 2007. Gaasvliegen (Neuroptera): vraatzuchtige larven voorde goede zaak. EntomologischeBerichten 67 (6): 268-270.
• Noordijk, J., P. van Rijn & J. Bruin. 2007. Synthesis: Agrobiodiversity - conservation and functionality. Entomologische Berichten 67 (6): 278-283.
• Van Rijn, P., J. Willemse & F. van Alebeek. 2011. FAB en Akkerranden - voor natuurlijke plaagbeheersing. FAB2 Brochure, DLO Wageningen, 46p.
• Van Alebeek, F., B. Schaap, J. Willemse & P. van Rijn. 2011. FAB en Omgeving. Het belang van groen en blauwe netwerken. FAB2 Brochure, DLO Wageningen, 50p.
• Van Alebeek, F., M.P. Vijn,  J. Willemse & P. van Rijn. 2012.  Een mooier landschap met minder plagen. Ekoland 32 (2012) 5:   26-27.
• Van Rijn, P.C.J. 2016. Completeer het landschap voor een betere plaagbeheersing. Landschap 33: 41-43.
• Geertsema, W., Bianchi, F.J.J.A, Pulleman, M.M., van Rijn, P.C.J., Rossing, W.A.H., Schaminée, J.H.J. & van der Werf, W. 2016. Kennisontwikkeling samen met Stakeholders. Ecosysteemdiensten in agrolandschappen. Landschap 33: 63-65.

• Van Rossum, Z.A. , F.L. Wäckers, A. Janssen & P.C.J. van Rijn. 2022. Bevordering van nuttige organismen voor plaagbestrijding en bestuiving in open teelten. Rapport voor LNV, IBED Amsterdam, 66p.

My research on thrips and predatory mites

My research at the Universities of Amsterdam and Washington State focussed on plant-feeding thrips (especially Frankliniella occidentalis ) and its natural enemies, especially predatory mites ( Amblyseius s.l.) and bugs ( Orius spp.). Using this model system I studied many different aspects, ranging from life history and behaviour to population dynamics, in order to answer both fundamental and applied research questions. Some of these topics are discussedbelow. (Forreferences see >links or separate 'Publications' page.)

Behavioural responses of predators to multiple food sources

Functional and numerical responses are traditionally described by Holling's disk equation which is based on time budget considerations. For many arthropod predators, however, it is much more likely that their consumption is limited by the rate of digestion rather than by prey-handling time, and this has important ecological implications. In contrast with the predictions of a time budget model, a satiation-driven mixed-food model, experimentally validated for predatory mites, indicated that reproduction is not a linear but an asymptotic function of predation, due to partial prey consumption at higher satiation levels (see Van Rijn et al. 2005). It also showed that mixing foods that differ in particle size will lower consumption on the larger prey, even when abundantly available, when consumption of smaller food items bring satiation beyond the level where it will no longer feed on larger prey.
The way predators distribute themselves in response to the distribution of its food sources can be modeled with the Ideal Free Distribution approach. However, in the absence of strong interference such models predict that the population always fully concentrated at the location with the highest overall food density (Van Baalen et al. 2001).
Relaxing the assumptions, by assuming that not the location but only the direction of movement can be chosen, based on local information on food distribution, results in the simple prediction that predator distribution equal to the distribution of the value-weighted overall food density. My population-dynamical observations with predatory mites feeding on thrips and pollen showed strong congruence with these predictions (Van Rijn et al. 2002).

The impact of supplementary food on predator-prey dynamics

Arthropod predators and parasitoids play an important role in reducing herbivore pressure on plants.The majority of these principally carnivorous arthropods also use plant-provided foods as a source of nutrients during at least part of their life cycle. In the field, parasitoids and predators can frequently be found feeding on nectar or pollen. These plant-provided foods can have dramatic impact on longevity, fecundity, and distribution of their consumers, and consequently on the population dynamics of herbivore-carnivoresystem( Wäckers et al. 2005, Van Rijn & Tanigoshi 1999).
Spatial distribution. Plants, as well as growers, have only limited control over these supplies and often cannot prevent other, non-beneficial species consuming them as well. By greenhouse experiments and model analysis I showed that misuse by the herbivores (thrips) can be restricted by limiting the supply to a small part of the plant, as this allow the predators to monopolise the food sources (Van Rijn et al. 2002).  Other means to minimise misuse are restricting supply in time and maximising food specificity.
Time scale. The profits of plant-provided food are also affected by the time and spatial scale of the herbivore-natural enemy interactions. Experiments with food provision are typically performed at single-generation time scales, thereby missing the major effects through enhanced natural enemy reproduction. Stage-structured models have been used to explore multi-generation effects on herbivore suppression by carnivores that differ in lifestyle and size, and provided with different types of plant-provided foods (Van Rijn & Sabelis 2005, Sabelis & Van Rijn 2005).

Selecting better biocontrol agents

 One of the basic elements in biological control research is the search for natural enemies that are the most effective as biocontrol agents for specific pests. Science can contribute to this search and selection process in two ways.
Firstly, it should indicate which features of natural enemies determine its success in pest suppression, and are therefore important to measure and consider. System-specific predator-prey models can be of great importance for this process. These show e.g. for the thrips-predatory mite system that a higher reproduction rate can quickly compensate for a lower predation rate (Sabelis & Van Rijn 1997; Van Rijn et al. 2002).
Secondly, science can design and perform the experiments that are suitable for measuring these features, as well as for testing the expectations under real cropping conditions. To find more effective predators for the control of thrips in greenhouses a number of predatory mite species has been compared on the following features: Predation rate, Oviposition rate with thrips as prey,Oviposition rate on a pollen diet, Draught tolerance, and Diapause incidence under short-dayconditions.Inthis study (Van Houten et al. 1995) three species ( T. limonicus, N. cucumeris, I. degenerans ) clearly performed better than the other species and these have subsequently been tested in greenhouse cucumber crops (e.g. Van Rijn et al. 1999). I. degenerans is now widely available for commercial use, and is especially affective in pollen-rich crops (Van Rijn & Tanigoshi 1999). The absence of an efficient rearing method has halted the commercial use of T. limonicus . 
Potential negative side-effects of biocontrol introductions have to be considered in the selection process as well (Van Lenteren et al. 2003; Van Rijn et al. 2005).

Leaf domatia of European scrubs and trees

Plants can improve the effectiveness of beneficial arthropods not only by providing them with food or information but also by providing shelter. Leaves of many trees and scrubs have small structures that are used by carnivorous and fungivorous mites to hide and reproduce. These leaf domatia (or 'acarodomatia') appear to improve the suppression of fungi (mildew) and leaf feeding artropods. Leaf domatia have been described systematically for only some parts of the world, such as Australia. My aim is to describe the domatia of all trees and scrubs of Western Europe, and dominant species that inhabit these structures. With now half of the woody plant species sampled, domatia seems to be present on more that half of the species, and mainly utilised by phytoseiid and tydeiid mites.
Comparative and experimental studies are needed to reveal the ecological significance of domatia in plant arthropod interactions. Such knowledge may be of practical relevance as well, e.g. when selecting species and genotypes supporting biological control or agrobiodiversity.

Functional AgroBiodiversity and Conservation Biological Control

The Functional Agrobiodiversity (FAB) project aims at enhancing the natural control of insect pests, by taking away limitations for natural enemies in the agricultural landscape with respect to hibernation habitat, alternative prey and plant-provided food. In this way we try to reinstall a sufficient top-down control of pests in arable crops, so that insecticides are no longer required as a standard treatment. My specific contribution to this project is to design and study field margins (annual and perennial) that optimally support natural enemies, especially by providing the right kind of food (pollen, nectar, alternative prey).
The project is managed by the Dutch farmers' organisation LTO, and supported by the ministries of agriculture (LNV) and environment (VROM), the province of Zuid-Holland and several agricultural production boards.
Final reports on the FAB projects (in Dutch):

Natural enemies and plant-provided food sources

Hoverflies, lacewings and parasitoids are likely to be the most important (winged) natural enemies of aphids and other pest in arable crops. All these insect groups require some sugar source (and some also pollen) during their adult life stage for survival and reproduction (Wäckers and Van Rijn 2005). Providing these resources in the agricultural landscape may therefore be an essential element of conservation biological control (CBC). In contrast to common belief, only al limited range of plant species can offer this food source to the predators and parasitoids. The plants should not only be attractive, flower morphology should also allow these insects to feed on the nectar or pollen, and the quality of the food should match the nutritional requirements. To learn the specific requirements and find the plants that can meet these requirements, lab studies are performed (using Episyrphus balteatus as a model organism) on:
•    Suitability of different sugar sources (including honeydews and nectars) for adult survival,
•    Importance of pollen for adult survival and reproduction,
•    Suitability of various flower species as source of nectar and pollen for hoverflies (based on morphology, behavior and survival).

How to design functional field margins?

In modern, large scale agricultural landscapes several resources are likely to be in short supply for natural enemies, such as winter habitat and adult food. For some of the natural enemies field margins can potentially provide these resources, if properly designed and maintained.
In order to support biological control field margins should contain plants that flower in the right period, and that are attractive and suitable for the various natural enemies (see former paragraph). Moreover, food provision should be relatively selective: natural enemies should benefit more than potential pest insects that may also use these plants as food or host plants. The vegetation should provide sufficient cover in winter and prey for ground-dwelling predators (such as beetles and spiders). The composition should be well-balanced and no source for weeds. In addition, other functions of field margins (landscaping, nature conservation, barrier for water pollution) should if possible be included as well.
Suitable annual plant mixtures have been developed to support natural enemies of aphids in especially wheat and potato fields. In the FAB2 project (2008-2011) also perennial mixtures have been developed that provide winter cover as well as floral resources .
The suitability of various plant species for functional field margins can be found in the brochure below.

Developing FAB in practice

To test the efficacy and applicability of field margins (in addition to the existing semi-natural landscape elements) farmers were asked to create  perennial field margins as well as annual flower strips. Potato and wheat fields were regularly monitored (at different positions from the field margins) on various pests and natural enemies. Mean densities were directly communicated to the farmers to support pest management decisions. In the period between 2005 and 2011 densities of aphids were mostly well below threshold levels. Natural enemies in the crop were mainly hoverflies, lacewings, predatory bugs and parasitoids, mostly in numbers of one for each10 aphids or more. Based in this information the particpating farmers refrained from insecticide applications in 4 out of 5 years on average.
Natural enemies were most abundant in the field within 100 meter from the flowering field margin.

The role of shrubs and trees

In addition to field margins many other landscape elements can play a role in supporting populations of natural enemies of pests.
Shrubs and trees are especially important for natural enemies, since they provide 
+ shelter of overwintering stages of winged insects, 
+ floral resources for adults in spring, and
+ aphids as prey in spring.
In this sense, woody landscape elements are complementary to field margins which mainly flower in summer and provide shelter mainly to ground-dwelling insects.
About 20 different shrub and tree species bordering arable land have been monitored during spring In the period 2010-2013, checking the presence of natural enemies and recording the amount of resources these plants provide. This study showed that all species flower in late winter or springbut are highly different in the numbers of aphids they support. Species that develop high numbers of aphids generally show the highest numbers of ladybeetles and hoverflies, while (with each subperiod) the number of ladybeetles is also related to the presence of flowers. Aphid species are with few exceptions highly specific and unharmful for agriculture. This information (see IOBC paper) can be used to make combinations of plant species that are likely to support natural enemies by flowers and prey during the full spring period. Other valuable information on how to improve the landscape surrounding arable fields for the support of natural pest control can be found the the brochure 'FAB en Omgeving' (in Dutch).