Crop spatiotemporal dominance is a better predictor of pest and predator abundance than traditional partial approaches

Abstract

Landscape-scale agricultural intensification can concentrate pest resources (high host density) and impede natural enemy populations through a reduction in non-crop resources or disturbance events. Current approaches examine the impacts of crop dominance on pest pressure through a simple lens, either spatially (i.e. landscape complexity), or temporally (i.e. diversity of crop rotation schedules). However, these partial approaches are inadequate because they do not take into account the impact of multiple years of non-rotation, or the impacts of the surrounding landscape, respectively. In this study, we use a unique method that allows land use in both space and time to be quantified simultaneously with a single metric, “spatiotemporal dominance”. We examined the impact of spatiotemporal dominance of sweet corn on populations of a key insect pest, Ostrinia nubilalis, and its potential predators. Additionally, we evaluated site-specific variables such as crop rotation, percent agriculture in the landscape, cover crop use, and frequency of insecticide applications, to determine their relative importance in predicting pest pressure, alongside our metric of spatiotemporal crop dominance in the landscape. Ostrinia nubilalis adult abundance was positively associated with spatiotemporal dominance of sweet corn in the landscape (space and time) and high proportional agricultural land use (space), but was unrelated to the previous year’s crop (time). Predatory soldier beetle abundance was negatively associated with sweet corn spatiotemporal dominance (space and time), but not associated with the previous year’s crop (time) nor percent agricultural land use (space). Our contrasting results between the new spatiotemporal dominance metric and either crop rotation history or percent agricultural land use or both emphasized that the new method predicts impacts of agricultural intensification on arthropods that were not captured by traditional techniques. In general, pest populations were more abundant in areas with high host dominance, whereas certain predators were less abundant when high disturbance management practices were used (e.g. no cover crop, high insecticide use). Therefore, quantifying spatiotemporal crop dominance refines and strengthens our ability to implicate intense agricultural land use in creating high pest pressure situations through simultaneous bottom-up and top-down effects.