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Tiny phorid flies attack imported fire ants in biological control experiments at UT Austin

Researchers at UT Austin this year have been collecting heads of dead imported fire ants as part of a biological experiment to help bring the pesky insects under control.

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AUSTIN, Texas–Researchers at UT Austin this year have been collecting heads of dead imported fire ants as part of a biological experiment to help bring the pesky insects under control.

What the researchers find valuable is not the heads themselves, but what’s inside these heads–the larvae of tiny phorid flies, a natural enemy of fire ants, that have devoured the fire ants’ bodies from within and which soon will fly out seeking to attack other fire ants.

Like a tiny airplane, a phorid fly will swoop down from above and inject its eggs into the thorax of an imported fire ant. When the eggs hatch into the larval stage, they migrate from the body to the head where they become pupae. At that point, the tissue connecting the head and body degenerates and the head falls off. Researchers then put the heads into containers, and about 20 days later the flies emerge.

“We are producing flies on a daily basis in the lab now and are beginning to introduce them into our facility to help culture them,” said Dr. Lawrence Gilbert, director of the Brackenridge Field Laboratory at UT Austin as well as of the zoology department at the University. He said the experimental space dedicated to fire ant research at the laboratory has nearly doubled during the past year to include room for phorid fly breeding facilities. In the early stages of his research, Gilbert said it was necessary for researchers to keep bringing additional replacement phorid flies from South America due to the short life span of the flies.

The biological experiments at UT Austin are part of its cooperative efforts with Texas A&M University, Texas Tech University and the Texas Department of Agriculture in a statewide program to reduce the impact of fire ants in Texas. The Texas Imported Fire Ant Research and Management Plan is administered through the Texas Experiment Station in College Station.

It is estimated that fire ants, which researchers suspect came to this country decades ago from South America on cargo ships, cost Texans about $300 million annually. In urban areas, residents spend more than $90 million each year trying to control fire ants in their lawns and gardens, repairing damage done by the pests and obtaining medical treatment for bites.

Additionally, rural Texans suffer as well. Fire ants feed on seeds and young plants. They can damage electrical and irrigation systems and prevent harvesting by hand. Fire ants may attack calves and other animals, resulting in increased veterinary expenses, decreased animal quality and at times, cause blindness and even death.

Gilbert said the effectiveness of phorid flies in helping to reduce the imported fire ant population depends, to a great extent, on the survival of the less damaging native fire ant, which has drastically declined in numbers since the introduction of the imported fire ant.

The theory is that as phorid flies and chemicals reduce the number of imported fire ants, the native fire ants, which are not bothered by phorid flies, can become more competitive and drive out many of the imported fire ant colonies.

Gilbert suggests the best way for homeowner to deal with fire ants is to first determine whether the insects in their yards are native or imported fire ants. The native fire ants have heads larger than their bodies, while the heads of imported fire ants are about the same size as their bodies.

“There’s no point in poisoning native ants. They actually help foster the phorid fly effect because the phorid fly works by shifting the balance of competition. You need the native ant to step in when you diminish the imported ant,” he said. Gilbert said he hopes pesticide companies will cooperate in this process by having pictures of native and imported fire ants printed on their labels, so people will recognize the difference and know whether or not to apply poison to the mound.

Gilbert said that to deal with fire ants adequately and sustainably, we must take advantage of our knowledge of biology and rationally use the chemistry that’s available, for the short term. We also must be more sophisticated than we have been in the past in dealing with insects.

The “Any ant is a dead ant” thinking must change, he said. Now we must get to a point where we discriminate in the kinds of ants we kill because the effectiveness of the controls we are talking about depend upon our maintaining the integrity and fabric of our native ant in the insect community.

Texas A&M researchers said one proven method of reducing imported fire ant populations in heavily infested home lawns and ornamental turf is called the”Two-Step Method” of fire ant control.

It involves the once or twice per year broadcast application of a bait and waiting several days to a week before treating nuisance mounds, using an individual mound treatment, such as a dust, granule, bait or drench insecticide. Otherwise, wait for the bait treatment to take effect.