Texas A&M University College Station, Texas, United States
Abstract: Mutualisms are ubiquitous in nature and contribute to the origin, maintenance, and organization of biological diversity. For example, by altering the behavior, activity and local abundance of ants on plants, food-for-protection mutualisms between ants and honeydew-producing hemipterans (e.g., aphids, scales, leafhoppers and their relatives) can alter the structure of arthropod assemblages and indirectly affect host plant fitness. Honeydew-producing hemipterans (HPH) provide a reward to ants in the form of a sugar-rich excrement called honeydew. In return, some ant species “tend” and protect HPH from natural enemies (e.g., predators and parasitoid wasps). Some tending ants, however, also attack non-hemipteran herbivores (e.g., caterpillars, beetle larvae, etc.) as well as natural enemies while tending hemipterans. If these non-hemipteran herbivores cause more damage to host plants than the HPH’s, then plants indirectly benefit by hosting ant-HPH mutualisms. Here I present the first evidence of how the replacement of native ants by a more “aggressive” invasive ant (Solenopsis invicta, the Red Imported Fire Ant) has resulted in increased ant protection of aphids and a corresponding increase in ant protection of plants from damaging herbivores. I found that fire ants recruited to honeydew-producing aphids in larger numbers than common species of native ants, were more likely to attack and remove natural enemies of aphids than native ants, and, most importantly, far more likely to attack and remove non-aphid herbivores when tending aphids than native ants. These data suggest that the invasion of the southeastern United States by Red Imported Fire Ants has significantly altered the evolution of plant-herbivore interactions in multiple wild plant species and may have resulted in significant changes in the arthropod biodiversity associated with aphid-infested plants.
