Ecological and management drivers of pest regulation via multitrophic pathways in tropical insular agroecosystems

Abstract

Natural pest regulation services provided by arthropod natural enemies are a cornerstone of ecological intensification. While vegetation diversification is known to support natural enemy communities, its relative contribution and interactions with other drivers for pest regulation services remains unclear, especially in dynamic and diversified smallholder agroecosystems under the tropics. In this study, we investigate how crop and non-crop field vegetation diversity, farming practices, climatic and landscape parameters jointly shape arthropod community structure and their services in the aerial and ground strata in tropical market gardening systems on La Réunion Island. We surveyed 22 open-field market gardening systems during two seasons. Using a multitrophic, piecewise structural equation modeling approach, we assessed direct and indirect cascading effects of local and landscape factors on arthropod diversity and pest regulation services. Results show that in aerial communities, non-crop vegetation richness generated a positive bottom-up trophic cascade. It enhanced herbivore diversity which, in turn, increased natural enemy richness, ultimately reducing pest abundance and crop damage, particularly during the dry season. In contrast, insecticide use suppressed natural enemy richness and reduced the effectiveness of pest regulation. Ground-dwelling communities were more strongly influenced by landscape fragmentation, semi-natural habitat cover, and temperature, with less evidence for structured trophic cascades. Overall, beneficial cascading effects of vegetation on pest regulation services in above-ground communities may outweigh the impacts of other management and landscape drivers. These findings underscore the potential of promoting vegetation diversity and reducing pesticide use as key strategies for enhancing natural pest regulation in tropical smallholder agroecosystems.