RED IMPORTED FIRE ANT (RIFA): Solenopsis invicta (Buren) Order - Hymenoptera: Family - Formicidae

DISTRIBUTION: Narrow corridor Brazil to Argentina, southeastern United States, and portions of California and Porte Rico.

DESCRIPTION: Eggs (Fig 1a) are white in color and at 0.22 mm each look somewhat like finely ground meal. Larvae (Fig 1b) are dirty white in color, legless, and kidney shaped with recurved hairs like tiny Velcro. As they grow, body segments and mouthparts appear. Pupae (Fig 1c) are pale, shiny white in color and about the same size as they will be as adults.

Adultworkers (Figs 2 and 3) range from 1.6 mm (minims) to 6 mm (majors), are wingless and possess stingers. The pedicel (waist) consists of two segments. The mandible (mouthpart) has four distinct teeth and the antennae are 10-segmented, ending in a two-segmented club. Workers do not reproduce. Queens are abut 9 mm long. Males are dark colored and have a much smaller head than queens. Both sexes have wings before mating; queens remove theirs prior to nest building.

HOSTS: Omnivorous, feeding on almost any plant or animal material; although insects seem to be preferred.

DAMAGE: The major problem with RIFA is that the worker ants sting and inject venom that causes blisters (Fig 4) or allergic responses in people. RIFA causes significant damage to agricultural crops and upsets the ecological balance reducing the numbers of native ant species, birds and mammals. They discourage hand harvesting of crops. Mounds damage farm equipment. Attracted by electrical currents they cause damage to heat pumps, air conditioners, transformers, etc.

INSPECTION TIPS: When inspecting nursery stock, nests may be located by vigorously striking containers with an ax. Moving small plants (flats, etc.) a few inches will also trigger a defensive swarming that will make detection easier. Large boxed trees that have not been moved recently may need to be tipped to inspect underneath for ants that have begun to tunnel under the box. With large boxes the reaction may not be immediate. Food bates (Spam) can be used to detect foragers. RIFA seeks shelter as far as possible from excessive heat and water. Foraging in hot areas occur primarily at night and early morning.

LIFE CYCLE: Colony reproduction and nuptial flights occur throughout the year, usually after a rain when temperatures are warm enough. After swarming, the mated female drops to the ground, sheds her wings and begins burrowing into the soil. The first adults (minims) beg food from the queen, but begin foraging after three days. The minims then assume responsibility for brood care. As the colony size increases, improved feeding causes a greater proportion of larvae to become majors, stabilizing with 35 percent of the workers as majors in mature colonies. A colony matures sexually and produces winged adults at the end of the second year. Colonies average 27,000 workers after two years and 53,000 workers after three years. Very large, mature mounds may seasonally fluctuate between 120,000 and 230,000 workers. Workers live from two to four months and queens approximately seven years. Two or more ovipositing queens may occupy the same colony. Hybridization with S. richteri (black imported fire ant) may occur. Mounds of mature colonies may be as high as 12 inches, but mounds may be absent in very warm localities. A single colony may forage over an area of about 1,900 square feet. Only 10 to 20 percent of the workers are foragers.

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