Identifying the landscape drivers of agricultural insecticide use leveraging evidence from 100,000 fields

Background/Question/Methods: Over the past 50 years, agricultural systems have become more simplified with fewer, high-yielding crops grown in shorter rotation cycles on larger fields with less non-crop habitat interspersed. While such agricultural intensification has undoubtedly led to increases in yields, there are concerns that more simplified agricultural landscapes result in increased use of pesticides and associated environmental degradation. This is because simplified agricultural landscapes have reduced natural enemy populations and more homogeneous crop resources, both of which are thought to lead to increased pest problems. Despite robust ecological theory, empirical studies evaluating the effect of landscape simplification on insect pests or insecticide use have been equivocal. In part this may be due to the limitations on the spatio-temporal extent of field studies and the coarse nature of data-driven approaches in parsing apart the importance of different components of simplified landscapes. Here we seek to bridge the gap between detail and scale to elucidate how different aspects of landscape simplification drive insecticide use. Using a fixed-effects panel data approach and unique data on crop production and insecticide use from over 100,000 field-level observations encompassing 2005-2013, we parse apart if and how crop diversity, field size and cropland extent affect insecticide use in practice.

Results/Conclusions: Overall, we find that higher crop diversity does reduce insecticide use, but the relationship is strongly influenced by the selection of crop types into diversified landscapes. Further, we find insecticide use decreases with increasing crop diversity and increases with increasing field size. The effect of cropland extent is distance dependent with nearby cropland decreasing insecticide use while cropland further away increases insecticide use. This refined spatial perspective provides novel understanding of how different components of landscape simplification influence insecticide use over space and for different crops. Our results indicate that neither the traditionally conceived ‘simplified’ nor ‘complex’ agricultural landscape is most beneficial to reducing insecticide inputs; reality is far more complicated.