Linda Benedict, Fuxa, James R. | 4/19/2005 10:29:06 PM
It may be a while before their work bears fruit, but researchers at the LSU AgCenter and others across the South are investigating how to assist the spread of a microscopic parasite that could reduce the number of red imported fire ants.
The parasite, called "microsporidia Thelohania," was first discovered in fire ant colonies from Brazil in the 1970s, according to Dr. Jim Fuxa, an insect pathologist with the LSU AgCenter and part of the Red Imported Fire Ant Management Task Force.
Now, LSU AgCenter researchers are investigating ways to use this biological agent to control red imported fire ants in Louisiana and across the South.
Fuxa says social insects such as ants have defenses against spreading diseases, so the introduction of any pathogen must be "very subtle." Microsporidia, a type of parasite of arthropods and fishes that invades and destroys host cells, "is not devastating but weakens the colony."
At one site, infected colonies had about 900 ants while uninfected colonies had about 5,000 ants, Fuxa says. If the scientists are successful, introducing Thelohania will lower the number of colonies and reduce their strength.
"Red imported fire ant colonies can have well into the tens of thousands of ants, and the effects of Thelohania are variable," he says.
Once queens become infected, the disease spreads to all their offspring, Fuxa says. Eventually, whole colonies become infected and weakened.
A weakened ant colony is more susceptible to chemical treatments or to dying out in harsh winter weather, the LSU AgCenter scientist says, cautioning, however, "But it takes a lot of study to utilize microsporidia to the best advantage."
The parasites weren’t identified in the United States until 1998 and were common in Florida and Texas by 2000. Now, they’re turning up in Louisiana. "We’re finding it does occur in Louisiana, but only in limited spots," Fuxa says.
Fuxa says microsporidia Thelohania probably came into Louisiana with ants from Texas and Florida and that it is slowly spreading – although "very, very slowly."
LSU AgCenter researchers are "trying to speed it up a bit," Fuxa says.
Their research began by sampling 165 Louisiana locations – at least one in each parish – and up to 10 ant colonies in each location. They now have data on almost 1,600 colonies.
The researchers have found that some fire ant colonies have a single queen while others have multiple queens, but single-queen colonies are much harder to infect than multiple-queen colonies.
"It’s easier to infect a multiple-queen colony, but it’s easier to destroy a single-queen colony," says Fuxa, who was first to discover and document an epidemic in a population of single-queen colonies.
"Now we know for certain we can infect single-queen colonies. It happens in nature," he says. "If you know there’s a target, you know you can do it."
One of the challenges the researchers face is that Thelohania lives only inside fire ants.
"The microsporidia have to live inside the cells of hosts," Fuxa says. "They’re very host specific."
Thelohania’s life cycle and transmission are complex, he adds. Understanding these factors – the key to using the microsporidium – is a prime objective of Fuxa’s research.
To get the disease into existing ant colonies, researchers are trying to introduce immature, infected ants into uninfected colonies. Then, it can spread slowly until it reaches the queens.
Using infected ants they maintain in their laboratory, Fuxa and his colleagues – researchers Dr. Julia Sokolova and Dr. Maynard Milks, technician Art Richter and graduate student Casey Barocco – have successfully introduced Thelohania into three sites with multiple-queen colonies.
The first was near St. Joseph in June 1998, and the researchers have been monitoring that site since then.
Only one colony was infected until the spring of 2002, Fuxa says, "Then, there were two to three dozen."
Now well-established, the parasite has spread about 100 yards from the initial St, Joseph colony. A release at Clinton, on the other hand, spread 200 yards in two years.
"It could take decades on its own," Fuxa says of the speed the parasite spreads. "We’re trying to speed up the process."
The researchers have tested Thelohania against other ants and found it’s only effective against red and black imported fire ants – not native ants.
Funding for Fuxa’s research has come from the Louisiana Legislature’s earmarked fire ant research funds along with grants from the state of Texas for cooperative work with Texas A&M and from the U.S. Department of Agriculture for cooperative work with Florida.