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.
For more information about
check the links below.
See lists below. Some papers are available through links on the research pages (links below) or through DARE.
[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.
A Protective Mutualism and its Applications
Felix L. Wäckers
Paul C.J. van Rijn
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.
Biodiversiteit - Nut en Natuur
Paul C.J. van Rijn
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
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.
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 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.)
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
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).
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 &
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).
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).
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
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.
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):
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).
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.
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
Natural enemies were most abundant in the field within 100 meter from the flowering field margin.
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).