Red imported fire ants, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), are an invasive species found in high densities throughout southeastern agricultural systems. We tested the hypothesis that fire ants tend cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), and thus release them from predation by lady beetle larvae, Coccinella septempunctata L. and Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae), and green lacewing larvae, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae). Fire ants preferentially foraged on aphid-infested cotton, Gossypium hirsutum L., plants (x̄ = 103 ± 47 ants per plant) compared with plants without aphids (x̄ = 5 ± 3 ants per plant). In caged greenhouse experiments, fire ants reduced survival of lady beetle larvae by 92.9% and green lacewing larvae by 83.3%. Furthermore, strong mortality imposed on aphid predators by fire ants affected aphid survival. With the addition of fire ants to aphid-predator treatments, aphid survival approximately doubled. In a field experiment, predator larvae were more abundant in cotton plots with experimentally suppressed densities of fire ants (0.62 ± 0.11 lady beetle larvae per sample; 0.06 ± 0.02 lacewing larvae per sample) than in plots with high fire ant densities (0.23 ± 0.06 lady beetle larvae per sample; 0.01 ± 0.01 lacewing larvae per sample). Conversely, cotton aphids were more abundant in high fire ant density field plots (x̄ = 6.83 ± 0.03 aphids per leaf) than in low fire ant density plots (x̄ = 4.04 ± 0.03 aphids per leaf). These data suggest that red imported fire ants enhance cotton aphid survival and density in the field through predator interference.
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