Dec. 21, 1998 CLEMSON - In the ongoing war to control fire ants, a new, biological approach is being tested at Clemson University. Entomologists here have introduced a naturally occurring disease into fire ant colonies as a means to reduce their population growth.
The disease keeps fire ant populations under control in their native South America, but was only recently found in this country. Without any natural predators, imported fire ants have run rampant across the southern states and are now spreading to colder climates.
"Using natural means to control fire ant populations restores balance to the environment," said Mac Horton, a Clemson entomologist and one of the project leaders for fire ant research, along with entomologist Clyde Gorsuch. "Fire ants are having as harsh an impact on the environment as anything man could do. They dominate many native plants and animals and cause the natural plant and animal systems to break down."
The ants also have a major economic impact. Throughout the southern states, damage estimates are in the billions as the aggressive ants invade electrical equipment, agricultural fields, homes and gardens. Their painful sting sends thousands of people to the doctor each year, and can be deadly for about five out of every 1,000 people.
Clemson scientists are working with the Agricultural Research Service of the U.S. Department of Agriculture (USDA) to test the new biological control method. This is one of just seven approved test sites in the country.
The disease that has been introduced is carried by a micro-organism, called Theolohania, that reduces the ability of the queen to lay eggs so the colony slowly dies over a period of six to eight months. Although it does not affect any other insects, the disease still required regulatory approval to be used in the tests.
The scientists introduced infected fire ant larvae into a number of test mounds this summer. The mounds are being monitored every two months over a two-year period to track fire ant population activity, using satellite technology. Researchers are overlaying the ant population data with other activity, such as human traffic and plant species, to track impact. Findings will be shared with other states to generate data across a wide range of climates and conditions, accelerating the pace of research nationwide.
"The disease agent is one of several strategies that we are testing to control the pests," said James R. Fischer, director of the South Carolina Agriculture and Forestry Research System based at Clemson. "Our scientists are also searching for other environmentally sensitive management strategies, such as competition and predation by native ants, other potential parasites and predators, and tests to determine the ecological peculiarities of the ants in North America."
This work is funded by the state General Assembly and the USDA through the research system.
The most common method of controlling fire ants is the use of bait that the ants discover while foraging and then take back to the colony. The bait technology has been tested by Clemson scientists since the 1960s and refined in partnership with the USDA and various commercial manufacturers.
"It took 30 years to understand the biological complexity of fire ants," said Horton. "The adults use juveniles to convert solid food to liquid food that passes through several adults before it1s given to the queen. They do this to protect the queen, so we had to develop a very slow-acting bait."
Since the queen lays up to 1,000 eggs per day for as long as seven years, fire ant colonies in South Carolina can include more than 250,000 ants, compared to fewer than 1,000 for the native ants. This is one reason why some treatments require several weeks to show results.
When the fire ants detect some pesticides, they often build a new nest before the treated colony completely dies out. As a result, Clemson entomologists recommend broadcasting the bait rather than simply treating the visible mound.
Clemson Extension agents work closely with Clemson Regulatory and Public Service specialists to educate homeowners, agricultural producers and others on the various methods and regulatory requirements for controlling fire ants.
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