Brain-Controlling Flies to Triumph Over Alien Ants?

May 15, 2009
A decades-long battle against invasive fire ants in the southern U.S. might be turning a corner, thanks to a nightmarish little fly.

(Pictures: "Zombie" Ants Controlled, Decapitated by Flies.)

Fire ants are widely hated, because they bite people's feet, kill infant birds, short out electrical units, and outcompete native ant species.

But as punishing as fire ants can be, they've got serious competition in parasitic phorid flies.

Plentiful in fire ants' South American home ranges, phorid fly females inject their eggs into the fire ants.

The egg develops into a maggot, which appears to control the ant's behavior. The maggot "directs" the ant to a moist, leafy place—phorid larvae are vulnerable to drying out—a safe distance from other fire ants.

The larva then eats the ant's brains, causes the ant's head to fall off, then finally "hatches" from the ant's hollowed-out head about 40 days later.

"Not only is it decapitating it, but it turns the ant into a zombie," said Sanford Porter, a research entomologist with the U.S. Department of Agriculture's Agricultural Research Service.

Fighting Fire With Phorids

Since 1997 researchers have been importing and releasing several species of phorid flies in Florida and Texas, one of the hardest-hit areas. Finally, researchers say, the flies are approaching a critical mass and could begin actually to control fire ant populations.

Previously released species attack at ant mounds. But this year scientists are planning new releases of a phorid fly species that attacks fire ants on their foraging trails—,meaning, if all goes well, the fire ants will be vulnerable to phorids both in the mound and on the trail.

"The more [phorid species] we have, the better," said entomologist Scott Ludwig of the Texas A&M University's AgriLife Extension Service and his colleagues.

All-Out War

Rob Plowes, a research associate at the University of Texas, said fire ants first emigrated from Argentina to Mobile, Alabama, in early 1930s, probably on an agricultural-produce boat, then began moving through Texas around 1950.

"They're still spreading," Plowes said.

There's a "huge history of efforts to remove the ants, ranging from physical removal to pesticides and, most recently, biological control," Plowes added.

Though one phorid species didn't take hold, two others have expanded to cover almost half the U.S. fire ant range and will probably make it the rest of the way in the next several years, the USDA's Porter said.

Ludwig and his colleagues released the foraging-ant-attacking species, Pseudacteon obtusus, last year in southern Texas, though the species has failed to spread.

This year the researchers will release P. obtusus in two new locations—one near previously released species in southern Texas so that, hopefully, the different species' ranges will one day overlap, resulting in a multipronged attack on the ants.

The second set is headed to eastern Texas, where no other phorid flies have yet been released. Eastern Texas is moister than southern Texas, making the east more conducive to phorid survival, the researchers hope.

Besides the phorid flies, several labs are working to develop fire ant-fighting fungi and viruses—perhaps to be delivered via phorid fly eggs.

"It will take a community of natural agents to control them," Porter said.

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