Red Imported Fire Ants
The red imported fire ant (RIFA), Solenopsis invicta, is native to the state of Mato Grosso in Brazil. It was introduced into the United States at Mobile, Alabama during the 1930’s. It spread rapidly through the southeastern U.S. during the 1940’s and ’50’s and is presently found in 13 states that include NC, SC, GA, FL, AL, MS, TN, LA, AR, OK, TX, NM, and CA. The RIFA has the potential for continued spread to uninfested areas where climatic conditions are favorable. While RIFA can spread naturally, many new infestations are thought to be associated with movement of nursery stock and grass sod. These ants can also be moved in soil adhering to soil-moving equipment and in hay bales.
The RIFA is a small ant with workers varying from 1/8 to 1/4 inch long. It is usually dark reddish brown in color and has two nodes on the petiole and a two-segmented antennal club. They are similar in appearance to many of our common house and field ants and are especially difficult to distinguish from a native species, the Southern fire ant, Solenopsis xyloni.
Life Cycle & Life History
New colonies are formed by one (or more) winged, mated females (queens) following a mating flight. The mated queens find suitable nesting sites, shed their wings, and begin digging underground chambers in which to lay eggs. The first eggs and larvae are cared for by the queen. They emerge as small workers after three to four weeks. Thereafter, workers care for the queen and the brood, forage for food, and expand the nest. An undisturbed colony can increase in size rapidly and may contain 10,000 or more workers after one year. Winged reproductives will also be produced sometime in the second half of the first year. A mature colony (3 years old) may contain 100,000 to 500,000 workers and several hundred winged forms.
Imported fire ants spread naturally during their mating flights. This spread is usually one mile or less but flights of up to 12 miles have been recorded. Flights occur most commonly in spring or early summer, one or two days after a rain when the weather is warm and sunny and the wind is light. Ants can also float downstream in masses or on debris during floods.
These ants do not directly feed on turfgrass, but they are a nuisance pest due to their sting. The mounds can impede turf management practices.
The most important problem with RIFA is its sting. Workers can sting repeatedly and attack anything that disturbs their mounds or food sources. Symptoms of the sting include burning and itching, followed by the development of a pustule that may take a week or more to heal. Scratching these pustules can lead to secondary bacterial infections. As usual with insect stings, certain people are hypersensitive to fire ant venom and may suffer a severe allergic reaction prompting immediate medical attention.
Inspection & Control
As workers extend the nest, excavated soil is brought to the surface and a mound begins to develop. The mound may be small and inconspicuous for the first year or more, especially in sandy areas. In soils with considerable clay content, the mounds often reach 12 inches high and 12 or more inches across. Mounds in sandy soils are flatter and wider. The mounds are not denuded of vegetation and may have grass growing up through them. Each mound has several foraging tunnels that extend in all directions away from the mound just under the soil surface. These have openings to the surface at irregular intervals and may extend outward for 200 to 300 feet. The RIFA will nest in almost any type of soil but mounds are not common in heavily wooded areas. They prefer open, sunny areas such as pastures, parks, lawns, meadows, and cultivated fields.
In general, nonchemical methods are ineffective against fire ants. Digging up or tilling mounds usually results in dispersal of ants or movement of nests. Several recommended treatment options are available that utilize chemical control methods for managing fire ants. Any of the treatment options discussed below can be used on specific sites within a managed area where different levels of fire ant control are desired.
Program 1: The "Two-Step Method"
This program suppresses ants in ornamental/athletic turf and non-agricultural lands, including roadsides. It is also suitable for pasture and rangeland if the products selected are specifically registered for use in these sites. This approach is best suited to medium-sized or large areas, and the cost is moderate. It is not suggested for use in previously untreated areas with few fire ant mounds (20 per acre or fewer, or 0.46 or fewer per 1,000 square feet). Some bait products may affect native ants that compete with imported fire ants. The goal of this program is to reduce fire ant problems while minimizing the need to treat individual mounds.
The two steps involve: 1) broadcast application of a bait product, followed by 2) treating nuisance mounds with a faster-acting individual mound treatment or with a mound re-treatment of the bait.
Once or twice per year, usually in spring and fall, broadcast a bait-formulated insecticide or use an outdoor bait station product as directed on the label. The speed and duration of ant suppression differs with the product used. Hydramethylnon, fipronil, indoxacarb, and spinosad baits provide maximum control one to four weeks after application, while insect growth regulator (IGR) bait products (i.e., those containing fenoxycarb, methoprene, or pyriproxyfen) provide maximum suppression two to six months after treatment depending on environmental conditions. Abamectin baits act more slowly than hydramethylnon, fipronil, indoxacarb, and spinosad but more quickly than IGR products. Using higher rates of an IGR bait does not eliminate colonies more quickly. Also, a late summer IGR application produces maximum suppression the following spring. The blending of half rates of a faster-acting bait plus an insect growth regulator (such as hydramethylnon plus methoprene) can provide faster and longer lasting suppression. Where there are many mounds per acre (200 or more), a second application may be needed after the maximum effects of the first treatment have occurred because not all mounds are affected by a single bait application.
Wait several days or more after broadcasting the bait before treating nuisance ant colonies (such as those in sensitive or high-traffic areas) with an individual mound treatment method (see Program 2, Step 1 below). Otherwise, be patient and wait for the bait treatment to work. Any nuisance mounds that escaped the effects of bait treatment, and any colonies migrating into treated areas, should be treated as needed. In large areas, individual mound treatment may not be feasible and routine broadcast bait treatments alone may provide sufficient control.
Repeat the bait application when ants re-invade the area and mound numbers reach about 20 per acre or exceed the tolerance level for a situation. Bait products do not protect against re-invasion by ant colonies from surrounding land or by newly mated queens. Ant populations can fully recover within twelve to eighteen months of the last bait treatment. Low-lying, moist and flood-prone areas are more prone to re-infestation.
Program 2: Individual Mound Treatment
This approach is best used in small areas of ornamental/athletic turf (usually 1 acre or less) where there are fewer than 20 to 30 mounds per acre or where preservation of native ants is desired. This program selectively controls fire ants, but rapid re-invasion should be anticipated. It generally requires more labor and monitoring than other programs, and is not suggested for large or heavily infested areas.
Treat undesirable fire ant mounds using an individual mound treatment. Products are applied as dusts, dry granules, granules drenched with water after application, liquid drenches, baits, or aerosol injections. Non-chemical treatment methods such as drenching mounds with very hot water also may be used. Mound treatments may need to be repeated to eliminate the colony if any queen ants survive initial treatment. When treating an ant mound with a liquid product or watering a product into a mound, begin on the outside of the mound and circle into the center of the mound.
Continue treating undesirable mounds that appear, as needed.
Program 3: The Long-Residual Contact Insecticide Treatment Method
This program eliminates many ant species in treated areas and it reduces re-invasion of treated areas as long as the contact insecticide remains effective. However, these products are more expensive, use more insecticide, and have greater environmental impact than other methods. This approach is frequently used by commercial applicators for treating ornamental turf. Long-residual products that contain a pyrethroid insecticide usually work most rapidly. Fipronil granular products eliminate ant colonies more slowly but have longer residual effects.
(Optional) Broadcast a bait-formulated insecticide in areas where there are many mounds (more than 20 per acre), or individually treat fire ant mounds. Wait two to three days after applying a bait before conducting the next step.
Apply a contact insecticide with long residual activity (i.e., fipronil or a pyrethroid such as bifenthrin, cypermethrin, lambda-cyhalothrin, or permethrin) to turfgrass as directed (generally every four to eight weeks for most products, or once per year using a granular fipronil product). Liquid or granular products (which are usually watered in after application) that can be evenly applied to an area are appropriate for this use. With most products, the initial surface treatment may not eliminate ants located deep in mounds, but routine re-application will eventually eliminate most colonies. Fipronil, a non-repellent contact insecticide that can be used with bait products, will eliminate ant colonies within four to ten weeks of treatment, even those nesting well beneath the surface. However, ants migrating into treated areas may take more than a week to be eliminated.
Any of the three programs can be used on specific sites within a managed area where different levels of fire ant control are desired. On golf courses, for instance, Program 3 might be suitable for high-use areas such as putting greens and tee boxes. In fairways and rough areas, Program 1 might be sufficient. Program 3 should be used on athletic fields, where as many ants as possible must be eliminated, and the program should begin early enough to attain maximum suppression by the time the field is in full use. People with severe allergies to fire ant stings should follow Program 3 for their lawns or use a bait on a calendar schedule. For grounds around schools, day care centers, mental health facilities, and other sensitive sites, broadcast application of a fire ant bait product twice per year is one of the safest methods of control. Control should be monitored with routine surveillance for re-invading ant mounds that need to be treated.
All chemical information is given with the understanding that no endorsement of named products is intended, nor is criticism implied of similar products that are not mentioned. Before purchasing or using any pesticide, always read and carefully follow the directions on the container label.