Linda M. Hooper-Bui
Red imported fire ants are ubiquitous in Louisiana. They inhabit pastures, fields, playgrounds, lawns, flowerbeds and even potted plants. These ants are called imported because they were accidentally brought here from South America in the early 1930s. In such countries as Brazil and Argentina, the ants are held in check by other organisms and environmental factors. In Louisiana, however, there are no natural controls, resulting in an ever-growing population.
In infested urban areas, red imported fire ants can cause many problems. If stung, some people suffer allergic reactions, secondary infections and unsightly skin damage. The ants can cause structural damage in houses and industrial buildings. Some infestations lead to damage of waste containers, electronic circuitry, ground-placed industrial lighting and even traffic control lights.
Fire Ant Biology
Red imported fire ants are omnivorous and opportunistic in their food gathering. They will gather practically anything, including dead animals and plants, and will kill other arthropods. Fire ants can remove seeds, developing and ripe fruit, and feed on sap flows.
Reproduction in fire ant colonies is accomplished by winged “sexuals.” These winged individuals fly out of the colony and mate in the air. The males die, and the mated females return to the ground (often after flying several miles) to find a suitable place to start a nest. The mating flight is one way fire ants infest previously noninfested or treated areas. Another way is by splitting the colony (budding) or moving the colony after it has been disturbed.
The fire ant queens lay eggs that hatch into balloon-like, helpless larvae. Worker ants use these larvae to process the solid food they gather into a form easily consumable by the colony. Larvae eventually transform into adults. The adult ants function as workers who build the nest, feed other workers and larvae, and most important, care for and feed the queen. The workers that provide the colony with food will exit the colony or mound through tunnels and forage for food on the soil surface.
How Baits Work
Because of the way worker ants feed the rest of the colony, baits make an appropriate and effective means of control. Baits consist of a food item desirable to the target ants combined with either a slow-acting toxicant or a growth regulator. The worker ants pass the food around to the various members of the colony, who will eventually succumb to the effects of the toxicant or be rendered sterile from the growth regulator. Either way, the population of affected ants will die.
Homeowners have used bait for years, but results are usually short-lived. The baits were probably working and controlling the ants in the treated yards, creating an “ant-free zone.” Because of their mobility, ant colonies from the neighboring yards may move into areas where the baits had not been used.
LSU AgCenter Research
The LSU AgCenter began focusing research efforts on fire ant control in urban areas in 1998. Researchers wanted to test the effectiveness of large-scale, community-based management techniques as compared to individual homeowner efforts. Traditionally, large-scale bait treatments of red imported fire ants have been applied to agricultural or grazed fields. The practice of managing fire ants using a large-scale technique in urban areas has been tried in other southern states, beginning in Arkansas in 1991. Texas made popular a two-step technique in which insecticidal bait is broadcast followed by individual mound treatments with a contact insecticide.
To study fire ant control in an urban area, LSU AgCenter scientists selected for the large-scale portion of the study an 85-acre subdivision near downtown Baton Rouge called Spanish Town. Nine homes within the neighborhood were selected for more intense study of the ants, and three nontreated areas adjacent to the subdivision were monitored.
For the small-scale portion of the study, 30 individual homes scattered in Baton Rouge close to Louisiana State University were chosen for treatment. Three homes were used as nontreated controls.
Large-scale Study in Spanish Town
LSU AgCenter personnel worked with Spanish Town residents to develop the plan, which was nicknamed “Put the Fire Out.” The homeowners were to broadcast bait in their individual yards all on the same day at three times six months apart—April 17 and Oct. 16, 1999, and April 22, 2000. The residents were instructed to measure the area of their property and subtract the area of their house’s footprint. LSU AgCenter personnel then distributed the appropriate quantity of bait and a hand-held spreader to each of the homeowners on the three days.
Each homeowner received one of three baits—Amdro, Distance or Award—randomly assigned and recorded on a data sheet. The spreader with the correct amount of bait was checked out to the individual, who then treated his or her yard. When the resident returned the spreader, he or she was asked to mark on a map the area treated to ensure that the entire area was covered.
LSU AgCenter employees broadcast monthly each type of bait at three of the nine houses (for three replicates) in conjunction with the community effort. The type of bait each of the study houses received was randomly assigned but remained the same throughout the study.
Small-scale Treatment of Individual Homes
Thirty homes were treated with the same three baits—10 per bait. Using a hand-held spreader, a pest control technician applied all of the broadcast bait treatments to the 30 houses. This ensured that the bait was spread correctly and consistently. The individual homes were treated in April 1999. However, this treatment method was not as effective as the areawide treatment.
Numbers Go Down
Before the initiation of the study, mounds were counted in the yards of the areas set for treatment and the nontreated controls. After the initial treatment, the mounds were counted monthly in each homeowner’s yard and the nontreated control areas.
All three baits used were successful in reducing the number of fire ant mounds in all homeowners’ yards in the study. Large-scale fire ant control using baits was more efficacious than individual homeowner efforts. Small-scale treatments initially were effective with a reduction in fire ant mounds for the first month and then gradually increased, supporting the hypothesis that the fire ants were moving from the neighbors’ yards. Results from the large-scale application demonstrate that granular baits are effective in controlling red imported fire ants. Ant movement from nontreated adjacent areas into the treated area thwarted the small-scale efforts. Because baits offer little or no residual, there is no protection from re-invasion from neighboring nontreated areas.
This LSU AgCenter study demonstrated that large-scale treatment in urban areas may slow the re-invasion of red imported fire ants and reduce the number of treatments needed, cost of treatments and the amount of chemicals released in the urban environment. Treatment for fire ants with the large-scale broadcast approach, in which bait is bought in bulk, would have cost each resident of Spanish Town about $2 to $10 per year all together, depending on the size of their yards. (For participating in the study, residents received the bait free.) This is compared to an estimated $20 to $100 each homeowner would have to pay per year to treat for red imported fire ants on his or her own. With large-scale fire ant treatments using broadcast granular baits, residents can expect to reduce ant control costs tenfold, reduce fire ant populations and experience more success.
Linda Hooper-Bui, Associate Professor, Department of Entomology, LSU AgCenter, Baton Rouge, La.
(This article appeared in the spring 2001 of Louisiana Agriculture.)