Shifts in natural enemy assemblages resulting from landscape simplification account for biocontrol loss in wheat fields

In recent decades, landscape simplification due to agricultural intensification has resulted in biocontrol loss within agroecosystems leading to an increase in pest outbreaks. Empirical experiments have focused on the relationship between landscape pattern and the abundance of specific species. However, fewer studies have examined the varied responses of multiple natural enemy modules to landscape simplification. In the present study, 23 landscapes were examined to determine the effects of landscape simplification on cereal aphids and their natural enemies. Results showed that landscape simplification can increase cereal aphid populations with no significant effects on the total abundance of natural enemies. For each natural enemy module, it was found that the abundance of parasitic wasps was greatly increased by landscape simplification while the abundance of ground-dwelling predators was significantly reduced. In contrast, the abundance of leaf-dwelling predators was not significantly altered by landscape simplification. Therefore, the varied response of the three natural enemy modules to landscape simplification can result in major fluctuations in natural enemy–pest ratios and ultimately disrupt the top-down control of natural predators and biocontrol services within agroecosystems. In conclusion, quantitative food-web analysis could be a promising technique in clarifying the varied response of the three natural enemy modules to landscape pattern changes and species-specific abundance, a field of biological pest control that requires further study.