Best organic farming expansion scenarios for pest control: a modeling approach

Abstract

Organic Farming (OF) has been expanding recently around the world in response to growing consumer demand and as a response to environmental concerns. Its share of agricultural landscapes is expected to increase in the future. The effect of OF expansion on pest abundance and Conservation Biological Control (CBC) in organic and conventional fields is difficult to predict. Given the inherent complexity of CBC and the lack of CBC data across situations of OF expansion, and the probable interactions with landscape context, modeling is a useful tool to understand and forecast how pests and their control may vary during OF expansion. Here, we used a neutral spatially explicit landscape model simulating pests and predators interacting on an agricultural landscape to investigate the impact of different organic deployment strategies on the CBC. We modeled three spatial strategies of conversion of conventional fields to organic fields (Random, Isolated fields first, and Grouped fields first) in landscapes contrasting in terms of semi-natural habitat areas fragmentation. We performed simulations considering organic farming deployment, different initializations of population dynamics and various combinations of pesticides effects on pests and predators depending on the land use. Our results showed that the organic farming deployment affected more predator densities than pest densities for most combinations of landscape types and deployment strategies. Its impact was also generally stronger in organic than conventional fields and in landscapes with large amounts of fragmented seminatural habitats. Based on pest densities and the predator to pest ratio, our results suggest that a progressive organic conversion with a focus on isolated conventional fields could help promote CBC. Careful landscape planning of OF deployment appeared most necessary when OF pesticides had a low efficiency, and in landscapes with low quantities of semi-natural habitats.