Résumé
By cultivating diverse crop species that make different demands on the soil and water, one mitigates the adverse impacts of climatic hazards on crop production in agrosystems, especially in the context of climate change. Likewise, cereal and legume combinations or use of cover crops that reduce erosion bolster food security (Malézieux et al., 2008). However, little is known about the effects of such plant diversification on populations of bio-aggressors (pests and pathogens), and the damage they cause to crops. On the other hand, wide diversity of plant species, or plant species diversity (PSD), which characterizes natural ecosystems, generally results in much lower bio-aggressor incidence than in mono-specific (or even worse mono-genotypic), agrosystems. With a view to economic and environmental sustainability, setting up an "ecologically intensive" agriculture by modifying agrosystems to mobilize natural regulation mechanisms taking ecological processes as a source of inspiration, has become a major challenge. Gaining a clearer understanding of interactions and using them to minimize any negative impacts and limit synthetic pesticide use will help the necessary shift from a "tactical" curative approach with chemical treatments (agrochemistry) to bioaggressor management, to a "strategic" prophylactic approach (agroecology)(Deguine et al., 2008). This is particularly relevant in the tropics were fanners are faced with plant protection issues resulting in food insecurity and low-income due to crop losses in low-input traditional agrosystems, and to pesticide-induced adverse impacts on human health and the environment in intensive systems. In this context, Cirad and its partners are implementing in the tropics since 2008 the Omega3 project, whose acronym in French stands for "Optimizing Ecological Mechanisms of bio-Aggressor Management, for sustainable Improvement of Agrosystem productivity". It is analysing how pest and pathogen populations and impacts are affected by the introduction of spatial and temporal PSD in cropping systems, with a view of gaining robust and generic results namely: i) knowledge on ecological bio-aggressor regulation processes that can be mobilized in agrosystems; ii) tools & methods for incepting & evaluating novel bio-aggressor-resilient cropping systems.