Regulating to manage pesticide resistance development. The question of the sustainability of pest and disease sensitivity to pesticides and resistant varieties[Réguler pour contrôler le développement de la résistance aux pesticides: La durabilité de la sensibilité des bioagresseurs aux pesticides et aux variétés résistantes]

Using pesticides in agriculture and introducing varieties that are resistant to some pests and diseases (insects, fungus, virus and bacteria) exerts selection pressure on the populations of those pests and diseases. In the course of time, the efficiency of this technology may decrease if resistances (to pesticides or resistant varieties) develop. Therefore, the sustainability of pesticides and resistant varieties is largely dependent on their use. The more systemic and intensive the use of the technology, the higher the selective pressure, the quicker the selection of the resistance gene in the population and the faster the technology becomes obsolete. Sustainable management of resistance requires parsimonious use of the preventive means, which is not necessarily compatible with the users' economic interests in the short run. From an economic point of view, the sensitivity of pests or diseases to pesticides or varietal resistances is a natural resource. Sustainable resistance-management strategies aim to extract it in an optimal way in the course of time, that is to say to delay the adaptation of these pest or disease populations1. In order to control the development of resistance to pesticides, the "regulator" has various environmental policy tools. Our study helps to understand the determinants in the arbitration between two of these tools: compulsory refuge areas and a tax on pesticides or seeds of resistant varieties. A spatially and temporally explicit bio-economic model was used to compare the performance of the two tools according to various assumptions on pest mobility. This analysis followed on from a previous pluri-disciplinary exercise of bio-economic simulations on the example of European Corn Borers (Vacher et al., 2007).