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February 2010 cover image canoe on Bois d'Arc Creek

Scout: Dawn of the living dead ants

Phorid flies may wipe out fire ant populations.

By Cameron Dodd

Fire ants can quickly ruin a barefoot traipse through the woods or a picnic in the park. Now, studies show that South American phorid flies, which feed on the brains of these pesky creatures, could play a significant role in quelling fire ant populations.

Since the 1930s, when cargo ships from Brazil accidentally brought populations of red imported fire ants (Solenopsis invicta), or RIFA, into the country, the invasive species has spread rapidly across the southern United States.

In North America the ants have no predators, and thus their population has increased, unhindered, at a tempestuous rate. As invasive species typically do, these troublesome ants have caused numerous problems for native plants and animals. Fire ants have been reported to invade homes and ­buildings, causing damage to electrical equipment. They also damage grasses, flowers and other plants. It is estimated that every year they cause hundreds of millions of dollars in damages in Texas alone.

So how do you stop an exotic species with no natural predators? Bring in an exotic predator.

That’s where the South American phorid fly enters the picture. Like their North American cousins, the genus Pseudacteon are parasitic flies that resemble fruit flies, but their reproductive method and diet make them much more valuable to us. The phorid fly’s larvae require a living body in which to develop, and a fire ant makes an ideal incubator.

After being laid in the neck of the ant, the larva feeds on the ant’s body fluids, eventually making its way to the head, where it eats part of the brain. Then, as if becoming a zombie, the ant simply begins walking away from the colony, continuing its aimless journey for up to two weeks. Once the fly is fully developed it releases an enzyme that causes the ant’s head to fall off, and the fly escapes through the neck.

Researchers have been experimenting with phorid flies since 1997, and in April 2009, AgriLife researchers released a species that was raised by a team at the University of Texas at Austin. Previously released species would attack only disturbed mounds, but the new species also targets undisturbed mounds and foraging ants. Other than a minimal amount of nectar consumption by adults, the phorid flies eat only fire ants, and each species of fly exclusively eats a certain species of ant.

“For RIFA control, a more long-term solution like this is needed,” says Mike Warriner, Texas Parks and Wildlife Department entomologist, “especially for control of these ants in areas where use of chemicals could be damaging to natural systems.”

Since their introduction, the phorid flies have begun to spread throughout the entire RIFA-infested range in Texas. The damage done to the red imported fire ant population so far remains minimal. However, researchers believe that the flies’ stalking of foraging ants is causing the ants to hide in their mounds rather than forage for food — resulting in food shortages and starvation in the colonies.

Researchers have reported that the older introduced species of phorid flies have spread to 97 counties and that the new species has already become established in 10 sites throughout Texas.

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