Influence of ant-exclusion on generalist predators in a citrus orchard

Formicids have been observed to protect honeydew-producing Homoptera from their natural enemies by disturbing or killing parasitoids and predators, thereby reducing natural enemy effectiveness. In field studies carried out over two growing seasons (1998-1999) in an organic citrus orchard in Sardinia, Italy, sticky trunk barriers were used to exclude ants from orange tree canopies in order to enhance the biological control of the mealybug Planococcus citri Risso. The influence of antexclusion on the abundance of four groups of generalist predators (spiders, true bugs, lacewings and ladybirds) was examined. Predators and ants were collected every ten days, on randomly selected fruits, for about five months per year. Four species of ants were found and Lasius niger (L.) was the most common species (> 80%). The total number of generalist predators was significantly higher in the ant-excluded plot relative to the undisturbed one (P < 0.000). The same result, with the only exclusion of Neuroptera (P = 0.1022), was obtained considering each predator group singularly.