Main research interests
(1) Intra-interspecific variation in plant quality and its effects on herbivores, parasitoids and hyperparasitoids; linking above- and below ground multitrophic interactions via plant defense.
Related plant species with different spatial and/or temporal life-history characteristics often possess differences in secondary chemistry and thus direct defensive capability. These differences are often attributed to a range of divergent selection pressures from herbivores and pathogens. Most studies of insect-plant interactions have examined the effects of plant defence on herbivore performance, with less attention being paid to higher trophic levels, such as parasitoid wasps. Ultimately, the net effect of secondary plant compounds on plant fitness depends on how each trophic level separately responds to them. Many parasitoids (in the third trophic level) are attacked by one or more species of obligate hyperparasitoids (in the fourth trophic level) which may in turn be attacked by facultative (or tertiary) hyperparasitoids. Most importantly, the dynamics of tri-trophic interactions involving plants, herbivores and parasitoids may be profoundly affected by hyperparasitoids. They may exert a significant negative effect on plant-fitness by removing parasitoids or predators of the herbivores, (top-down regulation) or else plant allelochemicals may be transferred vertically through herbivores feeding on plants to the third trophic level and perhaps higher (bottom-up regulation). At present this research explores interactions between (a) wild cruciferous plants (Brassicaceae), insect herbivores, parasitoids and hyperparasitoids. Crucifers produce inducible glycoside toxins known as glucosinolates. Although glucosinolates are known to be synthesized by plants in several plant families, they are best studied in the family Brassicaceae. Glucosinolates and their breakdown products play a role in mediating plant-phytophage interactions. For example, they have been shown to act as feeding deterrents or to exhibit detrimental effects on the growth and development of herbivores, pathogens and nematodes. Alternatively, they are known to act as oviposition and feeding stimulants for specialist herbivores. Current research (with R. Gols, Wageningen University, Nicole van am, NIOO, J. Bullock, UK) is examining development and plant selection in several generalist and specialist herbivores and their endoparasitoids on wild and cultivated populations of Brassica nigra and Brassica oleracea. Moreover, PhD student (R. Soler), is also investigating indirect interactions between above- and below ground herbivores as mediated by differential effects of herbivory on primary and secondary chemistry in the two Brassica species.
Collaborations: Nicole van Dam (NIOO), Martijn Bezemer (NIOO and Wageningen University), Arjen Biere (NIOO), Rieta Gols (Wageningen Uniersity), James Bullock (Institute of Ecology and Hydrology, Dorset, UK), Karen Kester (Virginia Commonwealth University, USA) Pedro Barbosa (University of Maryland, USA), Anne-Marie Cortesero (University of Rennes, France).
(2) Life-history, foraging and developmental strategies in hyperparasitoids.
Hyperparasitoids are a fascinating group of insects that attack primary parasitoid hosts. Hyperparasitoids may be primary (e.g. they attack their hosts as larvae within a secondary host, usually a herbivore) or secondary (e.g they attack the primary parasitoid host after it has emerged from the secondary host). With the exception of hyperparasitoids of aphidiine braconds, very little is known about the biology and ecology of most hyperparasitoids. Virtually nothing is known (beyond some basic taxonomic information) of the hyperparasitoid complex of even well-studied tritrophic systems, such as the crucifer-Pieris-Cotesia interaction. At present I am examining lifetime reproductive success and development of Lysibia nana and Gelis agilis, secondary ichneumonid hyperparasitoids that attack cocooned pre-pupae and pupae of several microgastrines in the genus Cotesia. Recent work has shown that differing plant quality, as mediated through the herbivore (secondary host) and parasitoid (primary host) affects developmentof both species, even though there were no effects on the host. Furthermore, Lysibia has a much higher reproductive success than many other hyperparasitoids, reflecting an adaptation to gregarious parasitoid hosts. Offspring sex ratio is highly female-biased, also reflecting selection pressures on its host (via local mate competition). By contrast, reproductive success and daily patterns of progeny allocation in Gelis are much lower.
Collaborations: Jacques Brodeur (Laval University, Canada), Mark Jervis (University of Cardiff, UK).
(3) Spatial and temporal effects on multitrophic interactions.
It is well established that higher trophic levels occupy only a subset of habitats occupied by lower trophic levels. Much recent attention has focussed on evaluating the effects of habitat fragmentation on multitrophic interactions, and parasitoid wasps and their hosts have been increasingly employed as model systems in this research. However, hyperparasitoids have been virtually ignored in this research, even though (as stipulated above) they may play an important role in mediating the strength of community modules. Furthermore, the 'enemies hypothesis' predicts that more complex habitats will harbour a greater number of natural enemies than simple habitats. Most tests of this hypothesis have been based on agricultrual systems, which usually exhibit considerable homogeneity compared with semi-natural self-organized environments. Using extreme ends of a continuum, I am comparing (1) levels of predation, (2) parasitism, and (3) secondary hyperparasitism in a simple habitat (mown field margin) and a complex habitat (dense stands of Brassica nigra along the River Rhein) in order to test both the 'enemies hypothesis' and to establish how parasitoids and hyperparsitoids respond to such extreme variation in the spatial structure and plant diversity of the two locations.
(4) Science, ecology and advocacy.
Scientists are currently faced with the immense challenge of better informing the public and policy makers as to the underlying causes and potential consequences of human-induced simplification of the biosphere. Although our knowledge of factors shaping the evolution, assembly and functioning of ecosystems is poorly understood, we do know that over large spatial and temporal scales, conditions and processes (‘ecosystem services’) which nurture life and humanity are generated. At the same time, sophisticated techniques are being employed around the world by powerful, vested interests that are aiming to change the way the public thinks about the environment. For example, a number of dubious sources are invoking science as a tool to influence and reshape public opinion, to attack the consensus view held amongst the scientific community, and to ultimately influence politicians into reducing environmental regulations. In the face of this new threat from the political right, scientists are faced with the immense challenge of better informing the public and policy makers as to the underlying causes and potential consequences of human-induced changes to the biosphere and their consequent effects on the delivery of ecosystem services. Over the past several years I have become actively involved in discussions based on bridging economics and ecology, in an attempt to stem the relentless flow of disinformation emanating from a number of surprisingly well-endowed think tanks and public relations firms that are distorting science to support a political agenda and pre-determined worldview on environmental issues.
Anne-Marie Cortesero, University of Rennes, France
Saskya van Nouhuys, Cornell University USA
Mark Jervis, University of Cardiff, UK
James Bullock, Department of Ecology and Hydrology, Wool, Dorset, U.K.
Heiko Vogel, Department of Chemistry and Evolution, Max Planck Institute, Jena, Germany
Toshiharu Tanaka, Department of Bioagricultural Sciences, Nagoya University, Japan
Caroline Muller, Bielefeld, Germany
Royal Society Postdoctoral Fellow, 1995-1997
ALW grant for PhD, 2001-2005, co-supervising Linde Hess
ALW grant for PhD, 2003-2007, co-supervising Joanneke Talsma
ALW grant for PhD, 2003-2007, senior supervisor for Roxina Soler