Twenty years of figuring-out fire ants

Thursday, September 21, 2006

Red imported fire ants being attacked by a phorid fly (in right corner).

Ranchers from Bee County, Texas learn how to control their fire ants with phorid flies during a workshop at BFL.

When the wave of red imported fire ants rolled into Austin in the early 1980s, Larry Gilbert knew in no time flat. Students who were studying ants at the Brackenridge Field Laboratory found colonies of the invaders on the property in 1981.

It had been 60 years since the thousand-legged fire ant hurricane smashed into Mobile, Alabama. The ants arrived aboard a ship sometime in the 1920s, likely stowed in the soil of exotic plants coming from South America. From there, they spread slowly, but surely, throughout the southeastern and central western United States.

By 1983, thousands of the imported ants’ mounds dotted the verdant fields at Brackenridge Field Lab (BFL). After seeing a student’s map showing how the imported ants were spreading at BFL, Gilbert, a professor of integrative biology, says he “became fascinated and obsessed with understanding the mechanism of the invasion.”

“Instead of appearing in random hotspots across the landscape,” he says, “imported fire ants at BFL were invading as one massive army, spreading like honey poured on a plate. Behind the invasion boundary no native fire ants survived.”

Gilbert realized that we needed to know more about these non-native fire ants, why they spread, and most importantly, how to control them without nasty pesticides. He set out to create a fire ant research program at The University of Texas at Austin, and with the arrival of researchers Sanford Porter and Ed Vargo in September 1986, the fire ant lab was born.

Twenty years of fire ants

The fire ant lab, celebrating 20 years of research this month, is nestled in the heart of Austin, secreted behind a fence tangled with greenery along Lake Austin Boulevard. It’s there at BFL (and throughout Texas and South America) that Gilbert and his colleagues—an army of postdoctoral researchers, scientists and students—have been studying the imported fire ants.

Porter and Vargo began the fire ant work by finding that the imported ant colonies in Texas had multiple queens and that these colonies reproduced primarily by “budding.” Normally, queens fly away from their natal nest to establish a new colony from scratch. But in the Texas multiple queen fire ant colonies, several queens will leave their home to set up new mounds with an army of workers in tow.

This helped explain why fire ants were denser in Texas than other southeastern states. Colonies with multiple queens are less territorial (they fight less with each other), so they can live at higher densities.

Phorid fires

One of the largest success stories of the fire ant research lab has been the discovery and introduction of a parasitic fly that targets and controls imported fire ant populations. The fly larvae develop inside the ants and kill their host. BFL researchers also found that when the flies are buzzing around, the imported ants stay inside their nests to avoid being parasitized. This lessens their ability to collect food and grow the colony.

When the BFL fire ant project was initiated 20 years ago little was known about phorid flies. In 1994, Gilbert and his colleagues brought many species of phorid flies from Brazil and Argentina to BFL and have since engaged in many studies and release programs with them.

“This was the first place that the USDA granted permission to release phorids for North America,” says Gilbert. “The first attempt to initiate naturalized populations of exotic phorids anywhere in the world took place at BFL in late 1995.”  While that attempt failed, persistence paid off. The initial species of phorid released at BFL has since spread widely, now covering over more than 3.5 million acres in Texas.

In 2005, scientists at the fire ant lab trained ranchers in Bee County, Texas to dig up fire ant mounds, separate the ants, and transport them to areas where naturalized phorid flies could attack them. The method led to the first successful introduction of a phorid fly in South Texas and inspired a new approach to establishing and spreading the flies that doesn’t rely on governmental assistance.

Fire ant research continues at BFL with scientists using new remote sensing and GIS technology to better understand the colonization of fire ants and the spread of the phorid flies.

Using molecular genetic techniques, researchers in the lab have also found that a species of phorid fly previously thought to be one species is in fact two. The laboratory has studied attack behavior and host specificity in more that ten phorid fly species known to victimize the red imported fire ant in its South American home and is searching for even more potential ant-controlling fly species with Argentine and USDA collaborators.

The war at home

Dr. Larry Gilbert pokes a fire ant mound at BFL. Photo: Marsha Miller

Many people might say that it’s been Gilbert and his hard work and devotion that has led to these advances in fire ant research, but Gilbert is more likely to reflect the credit back on his colleagues and to one place: BFL. It’s the field lab, he insists, that has served as the incubator for all of this ant research.

“Thanks to the availability of BFL near campus and the research talent attracted to UT-Austin, we now know many details of this fascinating system,” says Gilbert, who is also director of BFL. “Moreover, a large group of fire ant researchers, including undergraduate and graduate students, were inspired by being at BFL or have been influenced by those who were.”

Porter, for example, now studies fire ant biological control for the USDA in Gainesville, Florida, and according to Gilbert “he leads the way in developing ways to culture and introduce phorid flies to North America.” Vargo is currently researching pest termites as a  professor at North Carolina State University.

“BFL Fire Ant Laboratory’s army is too large to name all the individuals,” says Gilbert. “But each member of the team was absolutely critical to the success of the venture to date.”

The battle against the stinging beasts is not yet won, but Gilbert and his colleagues at the Fire Ant Lab will continue their quest in collaboration with colleagues in South America, at Texas A&M, at the USDA in Gainesville, and with concerned land managers and ranchers across the region. To learn more about fire ant research at the university, visit http://uts.cc.utexas.edu/~gilbert/