Ant-aphid mutualism may increase or decrease plant yield. This depends on the relative cost of damage by ant-tended aphids versus the relative benefit of ant suppression of other (non-aphid) herbivores and associated yield losses. To evaluate the effect of mutualism between cotton aphid Aphis gossypii Glover and Lasius brunneus Latreille on productivity of cotton plant, a field experiment with the presence or absence of ants was conducted in cotton research center of Golestan province in 2014. During the test (three months), the numbers of cotton aphid and visiting ants, Coccinella septempunctata (Linnaeus) and Helicoverpa armigera (Hubner) on each plant were weekly counted and the yield of cotton plants was finally measured. Statistical analyses for abundance of insects and yield of plant were performed using one-way repeated measure ANOVA and non-pair t-student in the presence or absence of ants, respectively. Our results indicated that ant presence resulted significant increased on abundance of cotton aphid and significant reduction on abundance of C. septempunctata and H. armigera with ant suppression of presence them. The presence of ant increased aphid density but reduced density of C. septempunctata and H. armigera. Despite increase in abundance of cotton aphid, cotton yield significantly enhanced in the presence of ants. This finding could be caused by the effect of ant presence in reduction of H. armigera abundance and associated yield losses on cotton plant. In general, the results of current study showed that indirect benefit of ant-aphid mutualism influence cotton plants by the suppression of H. armigera damage. Since this pest causes serious damage on cotton plant, attention to the increasing role of ant predation is economically useful.

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