ABSTRACT

We investigated the effect of a fire ant-aphid mutualism on the efficacy of red imported fire ants as predators of insect pests in cotton fields. In a series of greenhouse and field experiments we found that honeydew produced by aphids prompted fire ants to forage on cotton plants. This microhabitat shift resulted in more frequent encounters between fire ants and insects feeding on cotton plants. Consequently, fire ants reduced the densities of herbivorous arthropods in the canopy of cotton plants when aphids were present. In a caged greenhouse experiment we found reduced beet armyworm caterpillar survival in the presence of fire ants and aphids compared to fire ants alone. In our field experiment, the interaction between fire ants and aphids helped explain the distribution and abundance of caterpillars. Furthermore, this interaction and its resultant impact was density-dependent (i.e., greater aphid densities resulted in greater fire ant impact). Our results indicate that the fire ant-cotton aphid interaction may have a beneficial effect on cotton production and allow growers to predict the impact of fire ants on pests. This conclusion has far-reaching significance for understanding the efficacy of biological control in fire ant-infested areas.