The primary objective of this experiment was to assess the impacts of ant tending by the Argentine ant, Linepithema humile, on myrmecophilous and nonmyrmecophilous herbivores of Baccharis halimifolia, through field manipulations of ant attendance levels. High and low levels of ant attendance were established for a 5-mo evaluation of the densities of ant attended aphids, aphid predators, and leaf miners, which are subject to ant-induced damage of the mines. High levels of ant attendance resulted in significantly higher densities of both aphids and their predators over the course of the 5-mo experiment. A complementary short-term (20-d) experiment revealed that (1) aphid populations in ant-attended colonies increased in size and persisted longer than those in non–ant-attended colonies, and (2) aphid predators remained more abundant on non–ant-attended aphid colonies until the colonies went locally extinct. There were no significant effects of ants on the densities of the two common leaf miners, Amauromyza maculosa and Liriomyza trifolii, despite a significantly greater number of ant-damaged mines on trees in the high ant density treatment. The results of this experiment suggest that ant tending by L. humile on B. halimifolia may only impact those insects normally involved in the ant–aphid mutualism and not all herbivores of this host plant.