Abstract
Agricultural production has intensified over the last century both across increasingly homogenized landscapes and at the field level. This study analyzes the effects of land-use intensity at both landscape and local scales on the main insect pests, predators and yield of grain sorghum as a summer crop in Uruguay. It represents one of very few landscape studies focused on a reduced intensity production system other than organic agriculture and adds information from an under-studied subtropical region. Piecewise structural equation models were used to compare the direct and indirect effects of intensification at landscape scales and more sustainable practices at a local scale on densities of Spodoptera frugiperda (fall armyworm) and Rhopalosiphum maidis (corn leaf aphid), coccinellid abundance and yield over a two-year period in sorghum fields in western Uruguay. Greater landscape intensity resulted in increased S. frugiperda densities. Lower intensity crop-grazing rotation production systems reduced R. maidis densities compared to continuous cropping systems. Additionally, S. frugiperda and R. maidis interacted indirectly through apparent commensalism in continuous cropping systems, but not in crop-grazing rotational systems. Single cropping management resulted in lower S. frugiperda density, while insecticide use had no effect on pest or predator species. Our analysis affirms that agricultural intensification benefits herbivorous arthropod pests at the landscape scale, but that local management practices can mitigate some of these effects.
Highlights
Agricultural crops and livestock pastures cover approximately 38 % of the ice-free land surface globally (Smith et al, 2014), and agricultural production has continued to increase in intensity over the past 300 years (World Resources Institute, 2005)
Though 1,255 Orius sp. were caught on yellow sticky traps no linear model explained more than 6% of the variation so they were excluded from the Piecewise SEMs (pSEMs)
Landscape and/or local intensity factors had significant effects on four of the five component linear models used for the sorghum yield piecewise structural equation models (SEMs), the exception being the model for chlorophyll content (Table 1)
Summary
Agricultural crops and livestock pastures cover approximately 38 % of the ice-free land surface globally (Smith et al, 2014), and agricultural production has continued to increase in intensity over the past 300 years (World Resources Institute, 2005). Landscape homogeneity has been shown to increase habitat connectiv ity, leading to greater population densities of pest species (Balzan et al, 2016; Meehan et al, 2011; Rand et al, 2014) and altering food web structure (Tylianakis et al, 2007). It can reduce the biological control services provided by natural enemies (Bianchi et al, 2006; Gardiner et al, 2009; Perovic et al, 2010). Landscape intensification is often correlated with local intensification (Meehan et al, 2011; Norton et al, 2009)
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