Land-use effects on aphid-parasitoid-hyperparasitoid food web structure and function

Abstract

Understanding the impact of land-use intensity on aphid-parasitoid food web structure and biological control services is crucial for managing landscapes in a way that supports natural pest regulation. However, few studies have directly linked the structure of these food webs to actual pest control outcomes. In this study, we analyzed how the structure of aphid-parasitoid food webs and the ecosystem services they provide varied across a land-use intensity gradient in 24 alfalfa fields during three years in China. Beta diversity result indicates that the regional species pools play a key role in local food web assembly. Species in plain regions (intensive agricultural areas) were subsets of those found in mountainous region (more diverse landscapes), indicating that land-use intensity filtered out species from the broader regional pool rather than creating unique local assemblages. Land-use intensity, particularly mowing and insecticide application, negatively impacted both primary parasitoid and hyperparasitoid richness and abundance. Conversely, noncrop areas positively influenced primary parasitoid richness. Food web structures varied across regions and sampling dates. Hyperparasitism was significantly correlated with food web structural metrics, showing a negative relationship with modularity and a positive relationship with nestedness in primary-hyperparasitoid food webs. It suggests that hyperparasitoids may be more effective in suppressing primary parasitoids and thereby aphid biocontrol in less modular and more interconnected food webs. These findings highlight the importance of food web structure in shaping parasitoid dynamics and emphasize the need for landscape management strategies that promote biodiversity and ecosystem functions.