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, and brown ant, Lasius brunneus, on the productivity of cotton plant, a field experiment was conducted in the presence or absence of ants in the Cotton Research Center of Golestan province -Iran-, in 2014. During the two-month test, the numbers of A. gossypii and visiting ants L. brunneus as well as Coccinella septempunctata and Helicoverpa armigera on each plant were counted in four-day intervals and, finally, the yield of cotton plants was measured. Ant presence significantly increased the abundance of cotton aphid, whereas the ant with suppression in presence of C. septempunctata and H. armigera significantly reduced their abundance. Regardless of the increase in the abundance of A. gossypii, cotton plant yields significantly increased in the presence of L. brunneus. This could be due to the effect of ant presence and the reduction of H. armigera abundance and the associated yield losses on cotton plant. In general, the results of the current study showed that indirect benefits of ant-aphid mutualism influence cotton plants by suppression of H. armigera damage. Since this pest causes serious damage on cotton plant, increasing attention to the role of ant predation is economically useful.

Keywords