As agricultural production has intensified on the local scale over the last century, landscapes have also become increasingly homogenized. Herbivorous and predatory arthropods respond to land-use intensity at varying scales. This study analyzes the effects of land-use intensity at both landscape and local scales on the main insect herbivores, Spodoptera frugiperda and Rhopalosiphum maidis and on the most abundant predators, Coccinellidae, in grain sorghum in the southern hemisphere. Landscape intensity was evaluated using the proportion of annual agriculture within 1km of field sites. Local intensity included a multi-year component, a less intense grazing-agriculture rotation versus a more intense continuous agriculture rotation, and a within-year component based on insecticide use and winter crop cultivation prior to summer sorghum. Piecewise structural equation models were used compare the direct and indirect effects of land-use intensity at these different scales over a two-year period in 59 sorghum fields in western Uruguay.
Results/Conclusions
Greater landscape intensity increased densities of both pest species and provided evidence that they may interact indirectly through apparent commensalism leading to decreased coccinellid abundance. At a local scale, grazing-agriculture rotational systems had lower coccinellid species richness, winter crop cultivation caused a higher proportion of non-native coccinellid individuals, and insecticide use increased R. maidis density. In contrast to other studies, coccinellid species evenness was reduced with greater land-use intensity. The use of structural equation models provided a robust analysis of the effects of land-use intensification on insect communities in a lesser known multi-year management system in an under-studied region.