First, we conducted a detailed analysis of farmers pesticide use decisions in the Zone Atelier Plaine et Val de Sèvre over the last decade. We find that pesticide use practices of farmers have remained remarkably stable in the main field crops over the last decade, despite the ambitious pesticide policies in France. Interestingly, when analyse how these changes translate to the regional level, we find that pesticide use and risks have decreased over the last decade. Importantly, decreases were not driven by a change in pesticide management practices (number of applications), but by i) the substitution of toxic insecticides and fungicides that were banned in France and ii) changes in farmers land use decisions, planting crops that are less intensive in pesticide use.
Second, we conceptually analysed potential drivers of "optimal" pesticide use and how they differ across different scales (field, farm, landscape, national level) and from viewpoints of actors (farmers, consumers, and policymakers).
We show how underlying assumptions on the effects of pesticides and their connection with agroecosystems drive those differences. Moreover, we show how extending perspectives can lead to new solutions to reduce pesticide use, by considering non-linearity in effects, uncertainty in decisions, and multiple outputs of agricultural production.
Third, based on the developed conceptual model we empirically analysed farmers pesticide use decisions in oilseed rape (which is the most intensive crop for insecticide use in France) and their interactions with predator-prey interactions in the agro-ecosystem (natural pest control). To this end, we use detailed data on farmers pesticide use decisions, as well as levels of natural pest control and landscape characteristics. More specifically, we empirically analyzed the hypothesis that intensive use of insecticides can lead to a "lock-in" effect of pesticides, through the reduction of the effectiveness of pesticide substitutes, consisting of natural pest control in this case. in line with our hypothesis, we find that pesticide use reduces pest but also predator populations. Our main finding, confirming our hypothesis, is that the positive effect on pests dominates for low levels of pesticide use (pesticides increase yields), but is outbalanced by the negative effects on predators for high levels of pesticide use (pesticides decrease yields).
Since the project has been terminated earlier than planned, the articles are not yet published and has thus not been widely exploited and disseminated yet. However, I have already presented results to the resilience group at CEBC-CNRS and they will be further exploited for research on farmers pesticide use decisions and the ecological impacts of pesticide use by me and the Resilience group at CEBC-CNRS. Results have further already been disseminated in invited presentations to Master students in agronomy and pest management sciences at the Universities of Angers and Nice.
