History-Introduction into U.S., Spread and Early Control Efforts

 

The fire ant, by best estimates, was introduced into the United States in 1918 or 1919 through the Port of Mobile; however, it was not until about 1926 or 1927 that the ant was identified as a species within the fire ant group (Solenopsis). It is thought that the ant came into the port on ships from South America (parts of Brazil and Argentina are the main fire ant areas of S.A.), and as ballast or goods were removed, fire ants were also inadvertently removed.

After its introduction, the fire ant began to expand its range. By the end of 1939, it is estimated to have infested nine counties in Alabama and three in Mississippi -- Jackson, George, and Green. From this point within Mississippi, the ant spread west and north, and by the late 50's, about 50% of the counties were infested to some degree. Some 25 to 30 years later, all 82 counties had some level of fire ant infestation

Black (BIFA) + the Red Imported Fire Ant (RIFA) = Hybrid Fire Ant (HFA). In actuality, two different species of fire ants were imported during the early days of the fire ant: the black imported fire (Solenopsis richteri) and the red imported fire ant (Solenopsis invicta). The black was probably the first species introduced, followed by the red. As the two species expanded their ranges, the RIFA appeared to be more aggressive in foraging for food and defending its territory, hence it displaced the BIFA. However, the two species did interbreed and in the mix there is a hybrid, a cross between the two species. At the present time, the true BIFA is found mostly in the Northeast corner of the state, with some scattered colonies along the Mississippi/Tennessee border. The HFA is present in a band that runs somewhere between Macon and West Point. The RIFA is present in the area south of the above band, and it is thought that, given time, the RIFA will displace both the BIFA and the HFA and will eventually become the only fire ant species in the state.

Question: How do fire ants spread? There are two major methods of ant movement (1) natural and (2) man-assisted. Man-assisted movement is probably responsible for large-scale "jumps" in ant infestations. In other words, if ants are located in one state and they suddenly show up in an adjacent state with no connecting infested sites, then this infestation is probably associated with man's activities. Some ways that this may happen are the movement of nursery stock, either containerized or ball and burlap plant material, movement of sod, construction equipment, hay bales, agricultural equipment, etc. Natural movement may be in the form of swarming, walking or floating. Movement of this type typically occurs in small increments and takes much longer for a large area to become infested. Walking is simply the movement of an ant colony from one area to another. This may happen due to disturbance or competition in an area. Floating happens when there is flooding in an infested area. Under this circumstance, large balls of ants have been observed to float from a flooded area to a dry area. Swarming will be covered under biology.

Early Control Efforts. Since its introduction, a number of federal, state and county programs have been initiated in an effort to control imported fire ants. Baldwin County Alabama personnel began the first program of this nature in 1937. This program used Cyanogas as the method of treatment, and approximately 2,000 acres of vegetable cropland were treated. With the appropriation of $15,000 to fight the fire ant, Mississippi initiated a control and research program in the spring of 1947 using 5% chlordane dust.

Following these programs, a number of cooperative programs were started in various states. Some examples are: North Carolina, 1952, found an infestation and eradicated it; Louisiana, 1952, appropriated funds for the purchase of chlordane; Arkansas, 1957, conducted a program on 12,000 acres in Union County using granular heptachlor at 2 lb/acre applied by aircraft. Each of these programs achieved some success, but the problem remained. A more ambitious program was started in July 1957 with the appropriation of $2.4 million by Congress that was to be matched by participating states. The field phase of this program kicked off in November 1957 using 2 lbs of granular dieldrin or heptachlor per acre. The rate was reduced to 1.25 lb in 1959 and was soon reduced to 0.25 lb/acre as concerns for wildlife and residue problems begin to mount. The tolerances for heptachlor residues were eventually reduced to zero after it was discovered that heptachlor epoxide had been found in meat and milk.

The program switched to mirex as the product of choice in 1962. The application rate in the latter phases of the program was 1.25lb/acre, which translated to 0.06 oz of actual toxicant per acre. It was not long before it became evident that this material was extremely persistent and accumulated in the tissues of animals as it progressed up the food chain. In 1971 EPA limited its use to one application in a 12-month period and further stipulated that estuaries, coastal counties, and similar areas could not be treated with mirex. The first notice of cancellation came in 1971; aerial application was disapproved in 1977, and the final cancellation came in 1978. This was also the end of USDA eradication efforts, if in fact that was the goal of these programs.

By the end of the federal program (1957 to 1977), millions of acres had been treated (one of the largest community programs on record) using aircraft of different types, including modified World War II bombers. In one year alone (1972), 18.7 million acres were treated with mirex bait. Some 28 or 29 years later the fire ant still persists and is likely to for the foreseeable future. Imported fire ant management has become the responsibility of the individual homeowner, landowner or land manager, as it is with cockroaches, budworms/bollworms, termites, pine beetles, etc. As one progresses through these pages, fire ant management methods (insecticides and applications techniques) will be described, and, if they are followed, a certain degree of control will be obtained. Fire ant management is an on-going process, it is not something that can be done one time and the problem is ended. It must be done each and every year.

References:

Collins, Homer. 1992. Control of imported fire ants: A review of current knowledge. USDA, APHIS. Tech. Bull. No. 1807.

Green, H.B. 1967. The imported fire ant in Mississippi. Miss. State. Univer., Agri. Exp. Stat. Bulletin 737.

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