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MAFES Agronomist Studies Ant Problem

By Rebekah Ray

MISSISSIPPI STATE -- They are chemists, architects, engineers -- and invaders.

"I don't know of anything that has been such an unstoppable force in the South like fire ants. Not only are they harmful to humans and animals, they are changing our environment," said Dr. David Pettry, Mississippi Agricultural and Forestry Experiment Station agronomist. Pettry's research has investigated the impact fire ants are having on the environment.

More than 50 years ago, they probably "stowed away" on a ship and landed in Mobile, Ala. Since then, imported fire ants have spread across the Southeast. Now they infest more than 200 million acres in 11 states and Puerto Rico.

Two species of imported fire ants are found in Mississippi, the red or light species and the black or dark species. These tiny intruders can seriously impact agricultural production. Their mounds alter vital soil characteristics, damage crops, and interfere with cultivation, grazing and harvesting.

"Not only are they dangerous, their venom can be poisonous," Pettry said. "When bitten, humans may develop allergic reactions to the venom. And, if a newborn calf falls into one of the mounds, the results can be serious."

The battle between humans and fire ants rages on.

"The materials used to fight fire ants are staggering. People have tried a number of approaches, including gasoline, motor oil, insecticides, boiling water, Clorox, Tide and even grapefruit halves. These could seep underground into the water table, so we need to know about fire ants to protect the environment," Pettry said.

For the last four years, Pettry and Mississippi State University scientists William Green and Richard Switzer have examined the impact fire ants have made on a wide variety of Mississippi soils. In consultation with MSU's Department of Entomology and Plant Pathology and U.S. Department of Agriculture researchers, the team hoped to uncover some long-term implications regarding structure, composition and function of ant beds on Mississippi soils.

Studies conducted on 12 soil sites throughout the state examined the effects fire ant beds may be having on Mississippi's soils. Researchers measured and compared the structure, composition and other physical components like temperature and water.

Research showed that ant beds are very porous and are composed of particles of excavated soil and plant material mixed and assembled by the ants. The mounds are typically higher in clay, phosphorous and potassium, and lower in organic matter, sand and silt than the surrounding undisturbed topsoil.

The pH of the inhabited mound and submound is usually higher than that of the uninhabited bed and has very different temperatures and moisture levels. The mounds also heat up faster than surrounding soil in the spring and summer, and they dry out more quickly than adjacent soils.

The ant beds allow more water infiltration and leaching through the fragile crust and porous channel network. Additionally, active ant mounds have increased populations of bacteria and fungi.

Perhaps the most obvious long-term effect of fire ants is the blending of the upper part of the soil, which changes the nutrient and water retention in the soil. In their mound-construction process, ants bring subsoil to the surface and mix it with topsoil. When these mounds collapse, the materials backfill the channels, so that the chemical composition of the soil is altered.

This could result in result in noticeable increases in the need for agricultural fertilizer as elements such as nitrogen, phosphorus and potassium may be lost from the soil through concentration and leaching.

As colonies relocate, die or develop, ants may alter 100 percent of a given landscape in less than 100 years.

Imported fire ants have taken hold of soils that have never before experienced such destructive forces. As they take over these new environments, the fire ants are changing soil composition and format.

"We don't yet have an environmentally friendly way to control imported fire ants," Pettry said. "In their native habitats of Central and South America, the ants are controlled by naturally occurring mechanisms. The more we know about fire ant lifestyles and habitats, the closer we will be to controlling them and saving our environment as we know it."

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Released: June 21, 1999
Contact: Dr. David Pettry, (662) 325-2770

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