Red Imported Fire Ants: Where did they come from and what are my options?

They are everywhere. They came from South America in the 1930s and were first reported entering ports in the Panhandle coming in from Brazil. It is the red imported fire ant (RIFA).

There are two types of fire ants in this state: the native fire ant (Solenopsis geminata) and the RIFA (S. invicta). As of August 2008, the RIFA had been reported as established in the states of Alabama, Arkansas, California, Florida, Georgia, Louisiana, Maryland, Mississippi, New Mexico, North Carolina, South Carolina, Oklahoma, Tennessee, Texas and Virginia. It also has colonized places like Malatya, Singapore, Taiwan and many Caribbean Islands.

Map of imported fire ant quarantine areas, including areas infested by hybrid fire ants. Photo credit: USDA.

 

Fire ant populations have spread rapidly in the U.S. due to the absence of natural enemies. In fact, fire ant density in the U.S. is reported to be five to ten times the density in their native Brazil, where natural enemies keep fire ant populations in check.

Correct identification of fire ants

The pedicel, or “waist” in S. invicta consists of two segments. Workers consist of many sizes (polymorphic) between 1/8 to 1/4 inches. The mandible has four distinct teeth and the antennae are 10-segmented, ending in a two-segmented club. A sting is present at the tip of the gaster (abdomen or third segment). Body color is usually red to brown in color with a black gaster.

Mounds are built of soil and are seldom larger than 18 inches in diameter. When a mound is disturbed, ants emerge aggressively to bite and sting the intruder. subsequently, a white pustule usually appears the next day at the site of the sting. It is important to distinguish between the RIFA and the native fire ant in order for appropriate control measures to be taken. Mounds of S. geminata will contain workers with square-shaped heads that are larger in proportion to the rest of their body.  These workers collect and mill seeds for the colony. Workers of S. invicta do not have workers with disproportionate head to body ratios.

External anatomy of Red Imported Fire Ants. Photo credit: eXtension.org

Colonies of both species of fire ants consist of eggs, brood, polymorphic workers, winged males, winged females and one or more reproductive queens. New colonies are formed when a mated queen burrows into the ground and lays eggs. Once the first generation of workers emerges they begin foraging above ground for food to feed the queen and the developing brood. Within 30 days, larger workers have emerged and the colony begins to grow. Within six months several thousand workers can occupy the colony and a “mound” is readily visible. The queen can live up to seven years and produces an average of 1,600 eggs per day throughout her life. At maturity, a fire ant colony can consist of over 250,000 ants.

Nuisance on the Farm

Fire ants can present particular challenges in an agricultural setting. They feed on germinating seeds and can girdle the stems and trunks of young fruit trees. Tunneling fire ants can damage potato tubers and peanuts. During drought, crop damage can increase as fire ants seek alternate water sources. Also, in farms that use drip irrigation systems, fire ants will build their mounds over the emitters, reducing or blocking the flow of water to crops. Moreover, fire ants are attracted by electrical currents and have caused considerable damage to pumps and other electrical equipment.

So, how do I get rid of them?

Individual mound treatments

There are many methods of treating individual mounds. Some of these include: mound drenches, surface dusts, mound injections and baits.

Broadcast treatments

Currently there are few products available for treatment of large areas. These products are either granular insecticides or baits. Baits are composed of soybean oil and a toxicant on a corn grit carrier. These granules can be broadcasted over large areas upon the discovery of RIFA. Worker ants will harvest these baits and bring them in the colony to feed the queens and larvae.

Biological control

Biological control agents for imported fire ants include predatory mites, parasitic nematodes, parasitic flies, and the fungus Beauvaria bassiana. Scientific studies are being conducted to evaluate the effectiveness of some of these natural enemies, but others remain untested or have not been shown to be highly effective.

An adult Pseudacteon litoralis emerges from an ant head. Photo credit: Sanford D. Porter, USDA-ARS. http://entnemdept.ufl.edu/creatures/beneficial/flies/ant_decapitating_phorids.htm

Fire Ant Decapitating flies (also known as scuttle flies, hump-backed flies, and phorid flies; Pseudacteon spp.) are parasitoid flies of ants in the genus Solenopsis, which includes RIFA. In 1997 a species of Fire Ant Decapitating fly (Pseudacteron tricuspis) was released in the US followed by a release of five other species. Currently their effects on the RIFA populations across Florida and the Southern United States.

Depending on your operation you will be able to use specific insecticides which have been labeled for your crop or situation. For additional details, please contact us on how to manage populations in your farm or home.

Treatment considerations for best results:

  1. Follow the product labels before applying.
  2. If using baits, use fresh product, preferably from an unopened container.
  3. Apply baits with a spreader or other suitable equipment rather than by hand.
  4. Don’t apply baits mixed with seed or fertilizer.
  5. Broadcast apply when there is small to no chance of rain for the next 24 to 48 hours.

Proper identification and familiarity with product labels can improve the control of RIFA in your farms. Further information on this subject can be obtained by calling the UF/IFAS Extension Hardee County office at 863-773-2164.

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