Red imported fire ant

Scientific name

Solenopsis invicta (Hymenoptera: Formicidae)

Other common names

RIFA

Similar species

native fire ant, Solenopsis geminata
Colonies of the native fire ant, Solenopsis geminata, will contain workers with square-shaped heads that are larger in proportion to the rest of their body. Workers of S. invicta do not have workers with disproportionate headhead:
one of the three main body segments in insects; the anterior-most segment containing the many sensory structures including the eyes, antennae, and mouthparts
to body ratios.

desert fire ants, Solenopsis aurea
Found in western states.

black imported fire ant, Solenopsis richteri
Confined to northeastern Mississippi and northwestern Alabama.

Distribution

United States: Alabama, Arkansas, California, Florida, Georgia, Louisiana, Maryland, Mississippi, New Mexico, North Carolina, South Carolina, Oklahoma, Tennessee, Texas, and Virginia. The infestations in Maryland and Virginia are sparse and still not formally recognized on USDA maps.

Worldwide: Australia, Brazil, the Caribbean, Hong Kong, Malaysia, Singapore, and Taiwan.

Native to Brazil.

Diagnostic characteristics

Nests

• Found in open and or disturbed areas like lawns, roadsides, pastures, and abandoned cropland.
• Often build their nests at the base of young trees in citrus orchards.
• Vary in shape and size; appear as loose dome-shaped mounds of dirt or sand with no obvious entrance or exit.
• Mound may not be evident; ants will also nest in downed logs, rotten wood, and debris.

Adults

• Red to brown in color with a black gastergaster:
  the bulbous part of the ant abdomen located behind the waist (petiole)
  (last segment of abdomenabdomen:
  one of the three body segments in insects; the most posterior segment containing the heart, reproductive organs, and digestive organs
  ).
• Workers come in many sizes (polymorphic); individuals range from 2.4 - 6 mm (0.12 - 0.24 in.).
• Antennae have ten segments and end in a two-segmented club.
• Pedicel pedicel:
  from the base, the second segment of the antenna, located between the scape and the flagellum
  (waist) consists of two segments.
• Mandible has four distinct teeth.
• Sting (modified ovipositorovipositor:
  a tubular structure extending from the abdomen of female insects that is used to lay eggs
  ) present at the tip of the gastergaster:
  the bulbous part of the ant abdomen located behind the waist (petiole)
  (last segment of abdomenabdomen:
  one of the three body segments in insects; the most posterior segment containing the heart, reproductive organs, and digestive organs
  ).

Pupae

• Occur in underground nest, only seen when mound is disturbed.
• Resemble adults with legs and antennae held close to body.
• Initially appear white with black eye-spots.
• Color of pupae darkens with age.

Larvae

• Occur in underground nest, only seen when mound is disturbed.
• Four larval stages.
• White, grub-like larvae.
• Fourth instarinstar:
  immature stages (larva or nymph) of insects in between molts
  larvae are the only stage capable of ingesting solid food.

Eggs

• Occur in underground nest, only seen when mound is disturbed.
• White in color.
• Difficult to see without magnification.

Hosts

Citrus hosts

All Citrus species and their hybrids.

Non-citrus hosts

Not a direct pest but is disruptive in agricultural production.

Host damage

Flowers

• Feed on flowers.

Fruits

• Feed on young, developing fruit.

Trunk

• Chew on the bark and cambium of young trees to feed on sap.
• Can girdle and kill young trees.

Twigs

• Chew twigs of newly planted, young trees.
• Chew off new growth.

Other

• May nest in and plug irrigation lines.
• Indirectly harm citrus by protecting honeydew-secreting insect pests from natural enemies. This protection can disrupt biological control programs targeting honeydew-secreting insects and result in larger populations of pest species including scales, aphids, whiteflies, etc.
• Shown to preferentially attack some parasitized pest species, resulting in disruption of biological control programs of pest species like the citrus leafminer.

Biology

Red imported fire ants can occur invery high densities in citrus orchards and other human-modified agricultural systems. They are also highly aggressive and can out-compete other ant species for resources. Mating flights are the primary means of ant colony propagation. However, RIFA has both single and multiple queen forms, so a portion of a colony can branch off to become an autonomous unit.

Colonies generally contain a few large workers (major workers), many medium-sized workers (media workers), and a majority of small workers (minor workers). The three types of workers are all sterile females and serve to perform tasks necessary to maintain the colony. The queen (or queens) is the single producer of eggs. Mature colonies may contain as many as 80,000 - 240,000 workers.

The diet of foraging workers consists of dead animals, including insects, earthworms, and vertebrates. Workers also collect honeydewhoneydew:
the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
. Larvae are fed only a liquid diet until they reach the third instarinstar:
immature stages (larva or nymph) of insects in between molts
. When the larvae reach the fourth instarinstar:
immature stages (larva or nymph) of insects in between molts
, they are able to digest solid foods. Worker ants will bring solid food rich in protein and deposit it in a depression in front of the mouth of the larvae. The larvae will secrete digestive enzymes that break down the solid food and regurgitate it back to worker ants.

Comments

Identification of fire ants in the genus Solenopsis is difficult and requires evaluating a series of different-sized workers. In addition, members of this genus are known to interbreed.

The red imported fire ant is a generalist predator. Therefore, the presence of the ant may be beneficial when consuming other pest species. However, the red imported fire ant is viewed as a pest based on other negative impacts they may have on agricultural operations.

RIFA is capable of both biting and stinging. The sting is composed of an alkaloid-based venom with necrotoxic activity. The sting is responsible for both the pain and the pustule.

References

University of Calilfornia Agriculture and Natural Resources. 2009. UC Pest Management Guidelines. (http://www.ipm.ucdavis.edu/PMG/r107300211.html).

Banks, W.A. and C.S. Lofgren. 1991. Damage to young citrus trees by the red imported fire ant, Solenopsis invicta (Hymenoptera: Formicidae). J Econ Entomol 84(1): 241-246. (http://ddr.nal.usda.gov/bitstream/10113/23162/1/IND92044417.pdf).

Collins, L. and R.H. Scheffrahn. 2008. Featured creatures fact sheet: red imported fire ant, Solenopsis invicta Buren (Insecta: Hymenoptera: Formicidae). Publication EENY-195. University of Florida.(http://entnemdept.ufl.edu/creatures/urban/ants/red_imported_fire_ant.htm).

Department of Entomology, Texas A & M University. 2011. Texas imported fire ant research and management project. (http://fireant.tamu.edu/).

Stuart, R.J., I.W. Jackson, and C.W. McCoy. 2003. Predation on neonate larvae of Diaprepes abbreviatus (Coleoptera: Curculionidae) in Florida citrus: Testing for daily patterns of neonate drop, ant predators, and chemical repellancy. Florida Entomologist 86(1): 61-72. (http://www.fcla.edu/FlaEnt/fe86p061.pdf).

Zappala, L., M.A. Hoy, and R.D. Cave. 2007. Interactions between the red imported fire ant, the citrus leafminer, and its parasitoid Ageniaspis citricola (Hymenoptera: Encyrtidae): Laboratory and field evaluations. Biocontrol Science and Technology 14(4): 353-363. (http://www.tandfonline.com/doi/abs/10.1080/09583150701213612).

Authors

Weeks, J. A., A.C. Hodges, and N.C. Leppla