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


Abstract: Formicids have been observed to protect honeydew-producing Homoptera fromtheir natural enemies by disturbing or killing parasitoids and predators, thereby reducingnatural 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 toexclude ants from orange tree canopies in order to enhance the biological control of themealybug Planococcus citri Risso. The influence of ant-exclusion on the abundance of fourgroups 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 fivemonths per year. Four species of ants were found and Lasius niger (L.) was the mostcommon species (> 80%). The total number of generalist predators was significantly higherin the ant-excluded plot relative to the undisturbed one (P < 0.000). The same result, with theonly exclusion of Neuroptera (P = 0.1022), was obtained considering each predator groupsingularly.

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