Oct. 31, 2005

DALLAS – Entomologists have achieved another milestone in the war against the red imported fire ant. This month phorid flies, a natural enemy of fire ants, were found on the county line between Denton and Wise counties.

The first population of the fire ant's natural enemy in North Texas, this colony is also the northernmost establishment of a phorid fly population in Texas to date. The same phorid fly species, P. curvatis, was found in Oklahoma after a release and has since crossed the Texas/Oklahoma state line.

This milestone didn't occur naturally or by accident. In the fall of 2004, Texas Cooperative Extension entomologists Kim Engler and Dr. Bart Drees, with help from local Master Gardeners and Master Naturalists, spent three weeks collecting fire ants.

The ants were then shipped to Gainesville, Fla., for one week. The U.S. Department of Agriculture's Animal and Plant Health Inspection Service deposited the ants into chambers that also contained phorid flies. Over the course of that week, the female flies laid their eggs inside the thoracic region of the fire ants.

The ants were then flown back to North Texas and re-released into the colonies from which they were originally collected.

"This parasitic fly lays its eggs inside a fire ant worker," Engler said. "The larvae eats its way into the head capsule and eventually decapitates the ant. It then completes its development in the fire ant's head and emerges from there fully grown. If it's a female, it will mate then start the whole process over again. The entire process takes about one month."

The red imported fire ant is originally from South America, where it has a number of natural enemies and is not considered to be a serious pest. It gained entry to the U.S. via cargo ships unloading in a port at Mobile, Ala. in the late 1920s to early 1930s. With no natural enemies, the ants quickly spread. Today, they infest the Eastern two-thirds of Texas and many other Southern states.

Other phorid fly populations in Texas have been established near Vidor in Orange County, Caldwell in Burleson County, Austin in Travis County and in Polk County. But the population discovered in North Texas means the fire ant's enemy may spread to whole new area. It also means a new opportunity for researchers to study how cold temperatures and drought affect the phorid fly's life and reproductive cycles.

"Little is known about how the conditions here in North Texas affect the process, Engler said.

"Phorid flies are not social insects, even though they will congregate next to a mound in order to produce offspring. They don't live together as a unit. They kind of do their own thing, so just getting a population established was very exciting. A lot of sweat, stings and tears went into collecting the ants, so finally getting some payoff from that was fantastic!"

Another release of phorid flies will probably happen next year, Engler said.

"This will not only decrease the fire ant populations, but it will also keep many of the worker ants from foraging for food," she said. "The phorid fly basically stalks the worker ants to lay their eggs, which prompts the ants to hide. If they're hiding, they're not taking food back into the colony. That hurts the colony and also benefits the native ant species, because there's more food for them. The native ant species are far less aggressive and harmful. So there's a positive domino effect."

Engler hopes the phorid fly population will spread in a 1- to 2-mile radius from its original population by next year.

"This is one of the most rewarding projects I've worked on so far, because it's a biological approach to controlling fire ants, and we had the success of getting a phorid fly population established," she said.