Getting to bottom of ant world

Reforesting the South was big in the 1950s, but a tiny insect that grew in great numbers was thwarting those efforts in western Louisiana and East Texas by stripping pine seedlings of their needles and destroying them.

Foresters involved with the restoring of millions of bare, cutover acres were in a dilemma to control the leaf-cutting town ants and were hopeful that anything discovered could be applied to the region under siege.

The technology for this reforestation effort was being developed in the newly established Alexandria Forestry Center of the Forest Service’s Southern Forest Experiment Station. The officer in charge of this quasi-military operation was William “Bill” F. Mann, who was leading a cadre of a dozen forestry-related specialists, recently returning from serving as officers during World War II.

These men had the assignment of developing the technology to reforest the South and they were approaching the effort with military precision. Their efforts were being guided by an advisory committee consisting of the most prominent and knowledgeable foresters in the State who were providing technical and political support for the operation.

The leaf-cutting ants (Atta texana), known as town ants because of their colony development, became an obstacle to the foresters achieving their goal — successful plantation establishment. The ants were not a wide-spread issue, but a problem, nevertheless.

Town ants live in large colonies of up to 2 million insects and the mounds of one colony could occupy several acres on sandy to sandy-loam soils. Foraging on green plant material, young pine seedlings became a favorite target in winter months when other green vegetation is scarce. The needles of pine seedlings are clipped off in a day or two.

Interestingly, the ants do not eat the needles, but chew them into tiny particles, “glue” them together, and inoculate the plant material with a fungus. The fungus grown in this “garden” provides the only food for the ants.

The worker ants are 1/8 to 3/4 inch in length. The queen ants are several times larger with long, blackish wings. The queens are seen only during spring when mating flights of the reproductive ants occur.

Above ground, a colony is recognized by numerous crater-shaped mounds that are 5 to 15 inches high and 1 to 1 1/2 feet in diameter. Each mound has an entrance hole which leads to a multitude of underground chambers. The town ants were considered the second most important pest in pine plantations, following only that of the southern pine beetle. It was estimated town ants damaged as much as 12,000 acres of pine seedlings each year.

Not Conventional

The ants became an interesting challenge. Because they only ate the fungus they cultivated, they did not respond well to conventional ant baits, including sugar- or oil-based baits typically used for controlling ants. To deal with this issue, the Southern Forest Experiment Station advertised for a technician with entomological experience. This person would need to develop methodologies to protect young pine seedlings.

Bill Mann and his colleagues were greatly surprised when a Ph.D.-trained scientist applied for the position. John C. Moser, a new doctoral graduate with training from Ohio State and Cornell universities, arrived with the assignment to study the ants and develop control methods.

He arrived in Louisiana on July 1, 1958, and was the first doctor of entomology hired by the Southern Forest Experiment Station. Moser would serve more than 55 years as a Forest Service employee and volunteer.

Moser came with excellent credentials, having been trained by some of the country’s leading entomologists. He began an aggressive research effort to learn all he could about town ants and soon his interests conflicted with those of his supervisor Bill Mann.

Mann wanted Moser to perfect methods of killing the ants and anticipated a solution to the problem in a couple of years. Moser convinced Mann that real control would not be accomplished without knowing something about the biology of the insect. Moser soldiered on, collaborating with elite scientists, and continued to study all that went on below ground.

The Big Dig

One of the most notable, logistically and visually impressive efforts was the excavation and mapping of a large colony.

In 1960, a colony was excavated using a bulldozer that cut a swath 25 feet wide, 100 feet long and 12 feet deep. Fungus-garden cavities were the heart of the nest and averaged a foot in diameter. Occasionally, the cavities were much larger and a person could actually stand within the cavity. They were as much as 8 feet below the surface and were connected by a series of tunnels used for movement to the surface.

Material depleted of nutrients was found deposited in dump or detritus cavities. Other cavities were found packed with material such as ants, eggs, larvae and pupae. The data Moser obtained from this expansive dig allowed him to construct a 3-D model of a town ant colony and gave great insight into these underground creatures.

The study of the underground life of the ants gained Moser national and international recognition, but did not provide any ant control methodology. With the establishment of a forest insect research work unit at Pineville in 1962, Moser transferred from Mann’s unit and began research on problems related to the southern pine beetle. He was allowed, however, to continue some involvement with town ant ecology. Through these efforts he determined the trail marking chemicals used by the ants and established the timing of mating flights of the reproductive ants. He also studied the ecology of mites and other insects, like flies and roaches, associated with the ants.

In some entomology circles, Moser is fondly remembered as “Father Town Ant.”

With the loss of Moser to the southern pine beetle unit, Bill Mann recruited another entomologist, Hamp Echols, to develop the desired town ant control technology.

In 1966, Echols published data providing a control of the ants with a formulation of pelleted Mirex bait. Mirex is an organochloride and a very effective pesticide for the control of ants.

The U.S. Department of Agriculture coordinated an eradication program for fire ants beginning in 1969 using a somewhat different formulation of Mirex. The program called for the aerial application treatment of 120 million acres, to be repeated three times. All areas of the South where fire ants were located were to be treated. During these applications, data became available demonstrating environmental concerns about the chemical’s use.

In the mid-1970s, Mirex was banned in the United States.

Ironically, although the application of Mirex to the rural regions of the South was not effective in eradicating fire ants, it did greatly reduce the population of native ants, including town ants.

The large mounds of the town ants disappeared, and it has taken nearly 50 years for their mounds to again become familiar sights in western Louisiana and eastern Texas.

Foresters and others including those living near cities are now facing issues on how to control the ants when the ants encroach in areas dedicated for other use.

Some ant control formulations are available, but these are not nearly as effective as older chemicals that have been removed from the market. For help in control issues, see your county agent or nearby LSU AgCenter Extension specialist.

Fortunately for the town ants, foresters now are more likely to share portions of their forests with the ants. The work of John Moser allows us to understand and appreciate these amazing leaf-cutters from the underworld.

(Dr. James Barnett is emeritus science researcher. Stacy Blomquist is public affairs specialist, USDA Forest Service, Kisatchie National Forest.)

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