Honeydew-producing pest enhances density and predation behavior of ants: a case study in erva-mate agroecosystems

Ant-plant interactions are diverse and complex, with their effects on plants largely determined by the species involved and the ecological context. Most ants are omnivorous, preying on arthropods (e.g., pests) for protein, while deriving carbohydrates from plant-based sources and honeydew from hemipterans. Ants can benefit plants by preying on pests, but when they interact with honeydew-producing pests and start to defend these pests (e.g., attacking natural enemies), ants may become detrimental. In this study, we investigated the role of ants as predators in erva-mate, a key crop in Southern Brazil, and studied how fruit presence and the honeydew-producing pest Gyropsylla spegazziniana, influenced ant densities and predation. Using sticky barriers to exclude ants and termites as prey models, we found that termite survival was significantly lower in branches with ants, suggesting an important role of ants as predators in erva-mate plants. Plants infested by G. spegazziniana and plants containing fruits, exhibited higher ant densities. Additionally, survival of termites was significantly lower in plants with the pest. As no evidence for ant predation on G. spegazziniana was observed, we suggest that ants visit colonies of G. spegazziniana on erva-mate plants to collect honeydew, and in doing so, they prey more aggressively on termites and possibly other arthropods that either, compete for honeydew or threaten G. spegazziniana. Despite our study was conducted in a single erva-mate plantation, the observed ant—G. spegazziniana interactions revel clear ecological and potential biocontrol implications for erva-mate cultivation.