While there is some evidence showing that invasive ants promote homopteran population growth, comparisons between invasive and native ants on the same homopteran population had not previously been performed. We monitored numerical changes in a population of the black citrus aphid Toxoptera aurantii tended by adjacent colonies of the Argentine ant, Linepithema humile and Odorous house ant, Tapinoma sessile. Both ant species maintained significantly greater aphid numbers than that of the controls where ants were excluded. However, L. humile sustained higher overall levels of aphid numbers over time than T. sessile. Implications for competitive exclusion, foraging efficiency, predator defense and aphid augmentation will also be discussed.