Keywords :

Organized diversity and pest and disease dynamics

Communities of biological organisms living in cultivated terrestrial ecosystems have an impact on their productivity and sustainability, either directly, e.g. pests and diseases, or indirectly, e.g. ‘soil engineers’ or litter processors. The working hypothesis is that the reintroduction and promotion of biodiversity in relatively nondiversified agrosystems can help to improve the functioning and self-regulation capacities by strengthening the ecological functions, or ecological services, without regular massive pesticide treatments.

Diversity associated with plant communities is a key factor in curbing the development of pests and structuring biological communities via resources and the habitat. The introduction of gaps in monocropping systems has varying effects on pest and disease abundance, dispersion and development. The unit has thus selected several nonhost plants of the nematode banana pest Radopholus similis, which could be grown as cash, forage or cover crops. Fallows were found to be efficient in controlling R. similis, but promoted spatial dissemination of the weevil Cosmopolites sordidus on a farm scale. Studies were thus carried out to investigate the dispersion of this latter pest according to the spatial layout of the cropping system (CS), and a mass trapping campaign was conducted using pheromone traps in fields left fallow for sanitization purposes.

Diversity associated with fauna and flora present in an agrosystem has beneficial impacts on plants and could be essential in improving the biological quality of soils. Soil-eating Pontoscolex corethurus earthworms can stimulate banana leaf and root growth, while also having an impact on their nitrogen and mineral nutrition. This associated diversity can also facilitate management of some pests and diseases.

Hampering pest and disease dispersal by changing the spatial layout of CS could be an effective way of controlling their development. This study will be conducted on different scales starting from the simplest systems based on the spatiotemporal organization of a single variety and crop, and then investigating multi-variety and -species mixtures. Potential trophic links between pathogens and other functional entities of the communities will also be studied. The knowledge gained will be integrated into a trophic network simulation model designed to represent the interactions and regulations involved, with the aim of optimizing them and developing more sustainable CS.