A Florida golfer dies as a result of massive fire ant stings; a 91-year-old bedridden woman was bitten more than 600 times in a Texas nursing home. Although rare, fire ant horror stories do happen. If you are managing grounds in the southeastern United States or even in California or New Mexico, fire ants are a concern.
In 1998 surveys led by Dr. Curtis Lard, economist at Texas A&M University, the annual cost of fire ants to major Texas metropolitan areas (Austin, Dallas, Ft. Worth, Houston and San Antonio) was $526 million. Of that, $47.1 million (9 percent) was spent for medical care and $280 million (53 percent) was spent on insecticide treatments and other controls.
Although the bulk of this money was spent for control at residential households, fire ants also cost big bucks on golf courses ($29 million) and on fixed sites such as schools ($25 million) and cities ($612,500). Fire ants cost each golf course almost $65,000. This figure includes replacement of equipment such as irrigation systems ($53,000), insecticides and other controls ($7,000), repair of electrical equipment and physical damage to the course ($4,000) and medical treatments. Nationally, fire ants cost well over a billion dollars a year.
Imported fire ants include the red imported fire ant (Solenopsis invicta) and, around Mississippi and Alabama, the black imported fire ant (S. richteri) and a hybrid between the two. Worker ants sting and inject a venom that burns “like fire,” causes localized sterile blisters, whole-body allergic reactions, anaphylactic shock and, occasionally, death. Where ants are abundant, people tend to modify their behavior — like not sitting on the grass or having picnics — to avoid contact with fire ants or their nests.
Colonies can contain more than 200,000 ants and build unsightly mounds — mostly in open, sunny areas and at the base of trees. However, under hot, dry conditions, the ants may not produce mounds at all. Taller mounds can cause damage to mowing equipment and interfere with golf games. Foraging workers exit through underground tunnels radiating up to 10 yards away from the nest. Like stepping on biological land mines, disturbance of mounds or food sources results in a rapid defensive response by worker ants, which quickly run up vertical surfaces to bite and sting any object encountered.
Fire ant foraging and nesting activities often result in failure of many types of irrigation and electrical systems. Entire colonies have been known to move into buildings or vehicles, seeking favorable nesting sites and stinging residents, particularly during flooding and very hot, dry conditions.
On the plus side, fire ant mound and tunneling activities reduce soil compaction, and foraging fire ants prey on ticks, many caterpillars and other pests. They can, however, also aggravate populations of aphids and scale insects that produce sugary honeydew that ants love.
Fire ants spread and re-infest treated grounds through mating flights or through movement of entire colonies by ground migration, on flood water. It is also possible to spread these insects in shipments of landscape plants, sod and infested soil. During mating flights, females land within a mile or so of the nest, unless the wind carries them farther. Afterwards, they remove their wings and burrow into the ground to begin laying eggs. Queen ants can live for more than seven years and lay about 800 eggs per day. It may take a month or two before the first worker ants appear to begin building a new mound. If you use only mound treatments for control, you will miss these undetectable colonies.
Worker ants develop from egg to adult in 22 to 37 days. Larva are legless, cream-colored and grub-like with a distinct head capsule. Pupae resemble worker-ant “mummies” and are initially creamy white, turning darker before they emerge as adult ants. Insect growth regulator (IGR) ant bait products, which include fenoxycarb (Award and Logic), pyriproxifen (Distance) and methoprene (Extinguish), prevent worker-ant development for many months following application.
Most worker ants live 60 to 150 days, with larger ants living longer; but during cooler weather, workers can survive for eight months or more. This is why IGR products work more slowly under cooler conditions. These products do not kill adult ants, which must die off naturally before the colony is eliminated.
Young workers tend and move the queen and brood, while older workers defend the colony, construct and maintain the mound. Only the oldest worker ants — a small percentage of the ants in a colony — become foragers. For this reason, control strategies that kill only foragers are ineffective at eliminating colonies.
Under favorable conditions, new colonies develop winged “reproductive” ants after about six to eight months. Larvae developing into these forms are much larger (up to ⅜ inch long) than worker-ant larvae, and pupae have distinct wing pads. In colonies treated with IGR baits, these will be the only stages present after about three to six weeks of treatment — an indication that the treatment was successful and you can wait for colonies to die off.
Winged males are black and shiny, and females or “queens-to-be” are reddish-brown. They stay in the colony until they leave on nuptial flight, which they do after rainy periods under mild temperatures.
Two forms of imported fire-ant colonies exist: the single-queen (monogyne) and the multiple-queen (polygyne) forms. Worker ants from multiple-queen colonies are not territorial and can produce three to 10 times as many ant mounds — sometimes more than 1,000 mounds per acre. Areas infested with the single queen normally have up to about 150 mounds per acre. Mound treatments alone are not a good control option when mounds are this numerous.
The good news is that you can win the war on fire ants in urban landscapes using currently-available technology. You can find in-depth discussions of integrated pest management (IPM) treatment program options for imported fire ants on the Web site http://fireant.tamu.edu. For grounds maintenance, considerations for choosing the “best” strategy include abundance of fire ants and other ant species, cost and level of control desired through the season.
If fire ant mounds are few and where preservation of native competitor ants is desired, you can treat mounds with granular, dust or drench-mound applications. Cost of treating individual ant mounds can range from about 10 cents to several dollars per mound, not including time and labor.
You can achieve better, longer-lasting control of more heavily-infested land by treating entire areas or even entire communities. A major source of re-infestation is from fire ant colonies migrating into treated areas from adjacent untreated land. Therefore, control lasts longer in larger treatment areas. One treatment of an acre of land can range from a product cost of about $10 for a broadcast-applied bait to more than $200 for a surface-applied contact insecticide.
For larger areas such as parks and landscape areas with a history of 20 or more fire ant mounds per acre, the most cost-effective, environmentally-sound approach is the two-step method. In this program, you apply a bait-formulated product one to three times per year, generally in the fall and again in the spring (step 1). These treatments can maintain a level of about 90 percent suppression. The goal is to reduce or eliminate the need for mound treatments, which you should use conservatively to treat “nuisance” mounds only (step 2).
The fastest-acting bait products are those containing hydramethylnon (Amdro Pro, Seige Pro, MaxForce or ProBait) or spinosad (Justice and others), providing control in two to six weeks of treatment. Abamectin baits (Ascend, Varsity) provide slower, prolonged control, much like IGR baits. These IGR products provide control in two to six months that lasts for six to 18 months. The combination of faster-acting baits like Amdro in addition to an IGR has proven to produce the fastest-acting and longest-lasting control.
In cases where your goal is near-absolute control of the ants, a long-acting contact liquid or granular insecticide applied to the grounds is the better option. Pyrethroid insecticides like bifenthrin (Talstar) applied as granules or liquids to the surface can quickly eliminate surface activity for four to six months. The new fipronil granular products such as Chipco TopChoice Insecticide or Over'n Out Fire Ant Killer Granules require more extensive application, but provide control in about four weeks of treatment that lasts the entire season. There are, however, restrictions when using these products near water.
To customize a control program that works best for your specific needs, you can implement different approaches in different areas of your grounds. If you maintain a golf course, for instance, you may require absolute control of fire ants in high-traffic areas, but the two-step method might be satisfactory in fairways and other areas. Be careful not to apply baits where there are lingering effects of a surface-applied contact insecticide that prevents ant foraging. In athletic fields, you should also consider seasonality. If you want to use IGR baits for fire-ant control in the fall for the football season, for instance, you should apply treatments in spring or early summer.
If there are buildings on the grounds you manage, communicate with the managers or professional pest-control operators who manage indoor pests. Ants easily penetrate walls and can cause serious problems indoors if not managed around the building. Also, many states now have regulations for pest management in and around public schools.
Research efforts continue as we try to develop better control options and improve existing IPM program options in the southeastern United States. Among these are studies surrounding biological control agents such as parasitic phorid flies that suppress fire ant foraging and are being mass produced and released. These, in addition to other natural enemies of fire ants, such as diseases that include the protazoan Thelohania, show promise for providing some level of sustainable suppression of these pests. It is unlikely, however, that these biological controls will achieve the near-absolute levels of control desired in urban landscapes. For that reason, it is up to grounds managers to implement smart control programs to keep fire ants in check.
Bastiaan “Bart” M. Drees is project director for the Texas Imported Fire Ant and is an entomologist professor and extension entomologist at Texas A&M University (College Station, Texas). You can reach him by e-mail at firstname.lastname@example.org.
Fire ants are sensitive to vibration or movement and tend to sting when the object they are on moves. The ants can swarm up your leg and when one ant stings you jerk or move. This triggers many of the other ants to sting in response. Thus, it appears they all sting at the same time, and most do.
Fortunately, only a very small portion of the population experiences severe allergic reactions. If you are bitten by one of these pests, there really isn't much you can do, except watch the area for excessive swelling, itching or redness or other symptoms like shortness of breath, thickening of the tongue, sweating, etc. that could indicate a systemic allergic reaction. If you suspect you are having an allergic reaction, seek professional medical treatment immediately. Otherwise, treat stings as you would stings of other insects and keep stings clean and intact to avoid getting secondary infections.
COMING TO AMERICA
Fire ants are from South America. They entered the United States through Mobile, Ala., probably in soil used for ships' ballasts. They were accidentally introduced around the 1930s and have been spreading ever since.
Red imported fire ants are very aggressive, efficient competitors. You can find them throughout the southeastern United States as well as in New Mexico and California. Their northward spread depends on temperature. Cold winters tend to push them back. Western spread is largely dependent on water. You can find them mostly in urban areas, creek bottoms, irrigated land, etc. The entire Pacific Coast is fertile ground for infestation. The bad news is that they are probably here to stay. The good news is that with relatively little cost and effort, you can prevent most of the problems they cause using currently available methods. Research efforts can result in even more cost-effective, environmentally-sound fire-ant management systems.
WANT TO KNOW MORE?
To find out more about fire ants, visit these Web sites:
Texas Imported Fire Ant Research and Management Plan
The University of Minnesota
The University of Texas
The University of Florida
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