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Phorid flies possible fire ant control

Dr. Charles Barr excitedly pointed to activity less than a foot above a recently disturbed red imported fire ant mound. Standing up, a visitor doesn't see much but angry, milling fire ants.

However, crouching close to the mound reveals tiny, gnat-like creatures darting in and out of the swarm of ants.

“That may not excite many people, but to us, a half-dozen phorid flies showing up is great news,” said Barr, a Texas Cooperative Extension program specialist.

He and his Texas A&M University graduate student, Alejandro Calixto, have headed up an experiment in which Brazilian phorid flies establish, overwinter and expand their range to an area about one-half mile wide and one mile long near Caldwell.

The researchers are finding that phorid flies, in combination with baits and another naturally-occurring parasite called Thelohania solenopsae, are keeping fire ant numbers manageable on about 300 acres at a working ranch near here.

Stops foraging

The phorid flies used in the project are a natural enemy of the red imported fire ant, Barr said. The life span of adult flies is only two or three days. After mating, the females will inject eggs into worker fire ants that are foraging for food. After hatching, the fly “eats” its way through the ant's body — paralyzing it — and emerges 40 days later from the host's head.

“Females can lay about 200 eggs, which means (a possible) 200 paralyzed ants,” Barr said. “But more importantly, the fire ants recognize the flies and for protection, will stop foraging for food. That makes life hard for the ants.”

The phorid flies — reared and released in a cooperative project with the U.S. Department of Agriculture — are specific to the red imported fire ant and are not known to attack anything else, insect or otherwise.

Therefore, the chance of the population mushrooming out of control is small, Barr said.

In the last several years, phorid flies have been released and populations established near Austin and Vidor by either University of Texas or Texas A&M researchers, he said.

Thriving populations — introduced by the USDA — can also be found in Florida, where they are expanding their range at a rate of 10 to 15 miles per year. If that rate of expansion happens in Texas, Barr estimated the phorid flies introduced in the Vidor and Caldwell areas could expand to the Houston area in the next 10 or 15 years.

The red imported fire ant was accidentally introduced into the United States around the 1930s and has spread to infest more than 260 million acres of land in nine southeastern states. Because it had few natural enemies here, it spread quickly and displaced many native ant species.

Cost estimates of damage by red imported fire ants to the cattle industry alone range anywhere from $50 million to $200 million, Barr said. Fire ants can overwhelm and kill newborn calves, clog hay baling machines, infest hay or ruin feed. They also have an unusual attraction to electrical systems and can clog or short out water pumps or breaker boxes, he explained.

Often too costly

Bait-formulated insecticides are commonly used to control fire ant populations in urban areas, but the cost — about $10 per acre per year — often keeps farmers and ranchers from applying it to their land.

But Barr said a combination of several control measures makes fire ant control less expensive.

“Ranchers can treat large areas with the bait, knocking populations to manageable numbers,” Barr said. “Then other natural controls — like the phorid flies and Thelohania — have a chance to keep the number of fire ants down, thus spreading the cost of baits out over a longer period and making it affordable.”

The naturally occurring Thelohania makes the fire ant queen slowly lose her reproductive ability, he explained.

Barr and Calixto are still collecting data from the ranch, but he, the ranch owner and the manager have noticed considerably fewer mounds in the treated area.

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