Disruption of Cotton Aphid (Homoptera: Aphididae)—Natural Enemy Dynamics by Red Imported Fire Ants (Hymenoptera: Formicidae)

Abstract

Red imported Þre ants, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), are an invasive species found in high densities throughout southeastern agricultural systems. We tested the hypothesis that Þre 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 cot- ton, Gossypium hirsutum L., plants (x 103 47 ants per plant) compared with plants without aphids (x 5 3 ants per plant). In caged greenhouse experiments, Þre 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 Þre ants affected aphid survival. With the addition of Þre ants to aphid-predator treatments, aphid survival approximately doubled. In a Þeld experiment, predator larvae were more abundant in cotton plots with experimentally suppressed densities of Þre ants (0.62 0.11 lady beetle larvae per sample; 0.06 0.02 lacewing larvae per sample) than in plots with high Þre 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 Þre ant density Þeld plots (x 6.83 0.03 aphids per leaf) than in low Þre ant density plots (x 4.04 0.03 aphids per leaf). These data suggest that red imported Þre ants enhance cotton aphid survival and density in the Þeld through predator interference.