Effects of agricultural intensification on ability of natural enemies to control aphids

Abstract

Agricultural intensification through increasing fertilization input and cropland expansion has caused rapid loss of semi-natural habitats and the subsequent loss of natural enemies of agricultural pests. It is however extremely difficult to disentangle the effects of agricultural intensification on arthropod communities at multiple spatial scales. Based on a two-year study of seventeen 1500 m-radius sites, we analyzed the relative importance of nitrogen input and cropland expansion on cereal aphids and their natural enemies. Both the input of nitrogen fertilizer and cropland expansion benefited cereal aphids more than primary parasitoids and leaf-dwelling predators, while suppressing ground-dwelling predators, leading to an disturbance of the interspecific relationship. The responses of natural enemies to cropland expansion were asymmetric and species-specific, with an increase of primary parasitism but a decline of predator/pest ratio with the increasing nitrogen input. As such, agricultural intensification (increasing nitrogen fertilizer and cropland expansion) can destabilize the interspecific relationship and lead to biodiversity loss. To this end, sustainable pest management needs to balance the benefit and cost of agricultural intensification and restore biocontrol service through proliferating the role of natural enemies at multiple scales.

Agroecology: Principles for the Conversion and Redesign of Farming Systems

“…Reduced biological control cost soybean farmers about $58 million per year due to reduced yield and increased pesticide use [4]. Similarly, Chinese researchers found in a two-year study of seventeen 1500 m-radius sites in China, that input of nitrogen fertilizer and cropland expansion compromised the ability of natural enemies to control cereal aphids leading to a disturbance of interspecific relationships thus enhancing reliance on pesticides [5].…”

Agroecological Principles for the Conversion of Farming Systems

“…For example, Zhao et al (2015) found in a two-year study of 17, 1500 m-radius sites in China, that input of nitrogen fertiliser and cropland expansion compromised the ability of natural enemies to control cereal aphids leading to a disturbance of the interspecific relationships and enhancing reliance on pesticides.…”

Cropland expansion facilitated the outbreak of cereal aphids during 1951–2010 in China

“…In previous study, we found that agricultural intensification can destabilize the interspecific relationship and lead to biodiversity loss. Additionally, increasing nitrogen fertilizer input could benefit cereal aphids more than their natural enemies, leading to biocontrol loss in agroecosystem [7]. Now, we found that another factor, cropland expansion (landscape change) could lead to pest outbreak at large spatiotemporal scale.…”