Mutualism of the red imported fire ant, Solenopsis invicta Buren, with honeydew-producing homoptera

Abstract

The red imported fire ant, Solenopsis invicta Buren, was observed to associate mutualistically with the following Homoptera in Brazos Co., Texas: the corn leaf aphid, Rhopalosiphum maidis (Fitch), on sweet corn and johnsongrass; the buffalo treehopper, Stictocephala bubalis (Fab.), on greeen beans, blackeyed peas, and cowpen daisy; the cotton aphid, Aphis gossypii Glover, on okra, wild sunflower, and cotton; and a treehopper, Thelia bimaculata (Fab.), on wild sunflowers. Fire ants in the field collected pollen from sweet corn, cotton, summer squash, okra, and wild sunflowers. Laboratory colonies of fire ants fed more heavily on cotton and sunflower pollen than pollen from summer squash and okra. S. invicta feeding damage to corn leaves and kernels, bean plants, okra pods, blackeyed pea plants, and okra pods was observed in the field. Field bioassays demonstrated that cotton aphid honeydew attracted fire ants and increased the ant's searching movements. In August, 1980, 38% of cotton plants naturally infested with cotton aphids also were infested with fire ants. A significant positive correlation between fire ant and cotton aphid abundances and a significant negative correlation for fire ant and predator abundances were found in August and September, 1981. Greenhouse experiments demonstrated that fire ants had no effect on nonalate cotton aphid densities but reduced alate aphid production. The fire ant transferred 48% of the corn leaf aphids from dying sorghum to vigorous sorghum in another greenhouse test. Interspecific behavioral interactions of the fire ant and Hippodamia convergens (Guerin-Meneville) adults and third instar larvae, Scymnus louisianae Chapin third instar larvae, Chrysopa carnea Stephens third instar larvae, and Lysiphlebus testaceipes Cresson were qualified and quantified in the field and the greenhouse. In these tests the fire ant significantly reduced the effectiveness of the aphid predators and significantly reduced the number of L. testaceipes produced on sorghum.