Resource-dependent mutual association with sap-feeders and a high predation rate in the ant Crematogaster scutellaris: help or harm in olive pest control?

Crematogaster scutellaris is a common tree-nesting ant in Mediterranean olive groves, where it acts as both predator and soft scale insect tender. We aimed to quantify the predatory action of this species and assess whether it influences the distribution of soft scale insects. Predation was investigated through experiments using live prey. The mutualistic relationship between ants and soft scales was assessed by supplementing sugar, amino acids or water to ant colonies, then monitoring for changes in scale tending activity. The probability of soft scale infestation on trees hosting or not hosting ant nests was also estimated. Predation rates on trees hosting a C. scutellaris nest were significantly higher than on trees without nests. Tending activity was affected by carbohydrate and, surprisingly, water availability. While the presence of C. scutellaris was significantly correlated to soft scale infestation, it also favoured predation towards other insects, suggesting a potential role in influencing different insect pests.