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Eight years of ant-exclusion from citrus canopies: effects on the arthropod assemblage and on fruit yield


Josep Piñol. Tel.: +34 93 581 1312; fax: +34 93 581 4151; e-mail:


  • 1Ants are important generalist predators in most terrestrial ecosystems. However, because many ant species are also hemipteran mutualists, their role in agriculture has generally been considered to be negative for plants.
  • 2In the present study, we report an experiment in ant-exclusion from tree canopies in an organic citrus grove with two main objectives: (i) to examine whether the absence of ants increased the abundance of some beneficial arthropods and reduced the attack of some pests such as aphids and (ii) to examine whether ant-exclusion increased the fruit yield of citrus trees.
  • 3The exclusion of ants from tree canopies had positive effects on the arthropod assemblage and on fruit yield. However, the 8-year duration of the experiment can be divided into two periods with contrasting results. In the first period, the arthropod assemblage was only slightly affected, except for a greater density of aphids in ant-excluded trees; in addition, fruit yield was higher in ant-excluded trees than in the control ones. In the second period, ant-exclusion increased the abundance of most arthropod groups, although the previous positive effect on fruit yield was no longer observed.
  • 4There are two main conclusions of the present study. First, from an applied perspective, ant-exclusion from tree canopies is not a sound management alternative in citrus plantations in the Mediterranean. Second, the 8-year duration of the experiment highlighted the importance of long-term experiments in community ecology and biological control because the effects observed in the first 4 years of the experiment were very different from what occurred subsequently.