Field-scale plant diversification of agroecosystems is a promising way to enhance ecological pest regulation. Existing studies, however, have provided inconsistent results and have generally focused on only a few trophic groups or a few levels of plant diversification. Using field data from banana agroecosystems and structural equation modelling, we assessed (i) the effects of plant species richness (two height strata) and soil cover (% of living plant cover and% of litter cover) on a multitrophic arthropod food web, (ii) the links among five trophic groups of arthropods (detritivores, herbivores, non-ant omnivores, omnivorous ants, and predators) and (iii) the effect of natural enemies on the abundance and the damage of the banana weevil, Cosmopolites sordidus. Plant species richness of low strata (<1.5 m high) had a positive bottom-up effect on herbivore prey abundance, which in turn enhanced the abundance of non-ant omnivores and of predators. Litter cover promoted the abundance of detritivore prey, which in turn enhanced predators and omnivorous ants. The latter two trophic groups were negatively related to weevil damage and probably reduced damage by consuming weevil eggs and larvae. Finally, on the basis of our results, we suggest how the plant community and soil cover within the field could be managed to enhance ecological regulation of the banana weevil.