Abstract
Plants can defend themselves against herbivores by direct and indirect defence mechanisms. Direct defence mechanisms include a.o. the production of deterring or toxic secondary metabolites. Indirect defence mechanisms include the attraction of parasitoids of herbivores by emitting specific volatile compounds. Potential conflict between these two types of plant defence has been a concern to integrated pest management: plant defence chemicals that are sequestered by herbivores have potential harmful effects on natural enemies, and hence could lead to incompatibility between breeding for herbivore-resistant crops (based on selection for increased levels of defence compounds) and biocontrol of herbivores by natural enemies. Insight in mechanisms and conditions under which such conficts arise is of prime importance to understand the evolution of plant defence in natural, multitrophic systems. Yet evolutionary studies of natural systems that address this issue are extremely rare. Current knowledge of indirect plant defence by the emission of volatiles involved in attracting parasitoids is almost exclusively based on studies of crop species, while inferences about its importance and evolution clearly require studies from natural plant-herbivore-parasitoid systems. In this project therefore use a natural plant species and its herbivore-parasitoid complex to assess (i) naturally occurring genetic variation in this type of indirect defence, (ii) its compatibility or conflict with direct chemical defence under different biotic conditions, and (iii) consequences of genetic differences in the levels of the two types of defences for plant fitness. Five specific hypotheses will be tested, using a combination of laboratory, mesocosm, and field studies. The project will contribute to our understanding of both the evolution of plant defence in complex natural ecosystems and the compatibility of pest control strategies.
Netherlands