Vegetation complexity and regional differences impact ant-coffee berry borer interactions in Hawaiian coffee

Climate change and land management alter ecological complexity, impacting species interactions in tropical agroforests. Complex shade-grown coffee agroecosystems support diverse natural enemies that contribute to key ecosystem services, including pest control. However, agricultural intensification and climate change may impact vegetation complexity and disrupt natural enemy populations. Ants are well-known biological control agents of the coffee berry borer (CBB, Hypothenemus hampei ) pest in many coffee-growing regions, but their role in Hawaiian coffee farms is unexplored. We examined the relationship between coffee farm vegetation management, ant richness and abundance, and CBB predation and fruit damage across three climatically distinct coffee-growing regions of Hawai‘i Island. Specifically, we assessed how shade tree diversity, ground vegetation cover, and regional differences influence ant diversity, and related effects on ant-CBB interactions. On 16 coffee farms, we quantified shade tree richness and abundance, estimated percentages of groundcover types, and surveyed ants using tuna baits. We assessed CBB fruit damage through visual surveys and conducted a CBB prey removal experiment to observe ant-CBB interactions. We recorded 20 ant species and found that shade tree species richness, but not abundance, increased ant richness. Farms with higher tree species richness and higher ant abundance had fewer coffee fruits damaged by CBB, as well as increased CBB predation by ants. Herbaceous ground cover was associated with lower fruit damage but also lower CBB predation by ants, possibly due to movement barriers for ground-foraging ants. Ant richness and ant-CBB interactions varied significantly between regions. We identified four ant species that were associated with CBB removal: Pheidole megacephala, Linepithema humile, Brachymyrmex obscurior, and Plagiolepis alluaudi . Our findings underscore the importance of diverse shade tree assemblages and complex vegetation structures to support ant diversity and pest control services in coffee and other agroecosystems. • Ant richness increases with shade tree richness on coffee farms. • Higher tree richness and ant abundance reduce coffee berry borer (CBB) fruit damage. • Higher shade tree richness and greater ant abundance support ant predation on CBB. • Herbaceous ground cover reduces CBB damage but also reduces ant predation on CBB. • Four key ant species were associated with CBB removal.