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Ant-attacking flies adapting to Texas climate

An important milestone has been reached in an effort to initiate biological control of imported fire ants in Texas, according to Dr. Larry Gilbert, director of the Brackenridge Field Laboratory (BFL) at The University of Texas at Austin.

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AUSTIN, Texas— An important milestone has been reached in an effort to initiate biological control of imported fire ants in Texas, according to Dr. Larry Gilbert, director of the Brackenridge Field Laboratory (BFL) at The University of Texas at Austin.

Gilbert said that during the Memorial Day weekend, he and Post-doctoral Researcher Rich Patrock observed Brazilian phorid flies, Pseudacteon tricuspis , bombarding approximately 30 percent of fire ant mounds they surveyed near experimental release sites in South Texas.

Patrock and Gilbert had previously released the ant-attacking flies weekly from early February through late March on a private ranch near Laredo.

“We are very encouraged by what we observed at our study site,” Gilbert said. “The Laredo area has been very hot and dry most of the time since we released the last laboratory-produced phorids on the site two months ago. Therefore, seeing the next generations appear now tells us that these Brazilian flies can somehow complete their life cycle under tough Texas conditions.

“We were also excited to see these phorids mating above ants that were swarming out of disturbed mounds and female phorids attacking worker fire ants that were carrying brood. The flies were also seen attacking workers foraging for food, and disrupting food gathering exactly as we see in Brazil.”

Adult Pseudacteon phorid flies has a brief (two- to five-day) life span. Females must in that time find mates and fire ant workers into which they inject single eggs. The next generation adult flies emerge some 40 days later from the host ant’s head. More than 16 South American phorid species are known that attack Solenopsis invicta, the red imported fire ant.

There are other Pseudacteon phorid flies native to Texas that attack several native fire ants including S. geminata and S. xyloni. These phorids show no interest in the imported ant, thus the need to import phorids specifically adapted to use the pest ant.

“While we are immensely encouraged and relieved to have gotten this far with the introduction of the tricupis phorid fly in Texas, this is merely another base camp on a long and complex journey,” Gilbert said. “Looking back, numerous researchers in our group have helped us make this event possible by exploring phorid biology in Brazil (Matt Orr), by experimentally measuring relative host specificity of various phorid fly species (Lloyd Morrison) and by developing an efficient phorid fly breeding program (Clare Wuellner and Christina Papp). Coordinated with those efforts were greenhouse experiments on release methods (Natasha Mehdiabadi) and, of course, intensive fieldwork at a natural release site (Rich Patrock).”

Gilbert noted also the importance of a collaboration with his Brazilian counterpart, Woodruff Benson at the University of Campinas, and his students who have facilitated the collection and export of phorids from Brazil to Texas. Also important was work with Sanford Porter of the U.S. Department of Agriculture-Gainesville, a former BFL colleague, who has exchanged knowledge of rearing technology and provided a supplemental source of fly stocks to increase numbers available for releases.

Gilbert emphasized that in Brazil, where fire ants are not viewed as pests, up to five species of phorid fly can be found around a single area– some species attacking when anteaters disturb mounds, some attacking along trails to food, some attacking more often in overcast conditions, some in sunny periods, some going after small workers and some after larger ones.

One major goal of his program is to find a matched set of phorid species that, acting as a group, will impose maximum impact on the ability of imported fire ants to compete with native ants in Texas. “Studying the life histories of 16 species of tiny South American flies, measuring their relative impacts on fire ants, and developing rearing technologies for those selected for introduction is a challenging task. These first steps with one species give us hope, but not euphoria,” Gilbert explained.

Currently, the UT Austin group has additional experimental releases underway at two sites around Austin and in a semi-natural tropical insectary that allows work to continue in winter and during drought. A few phorids have been seen at these sites as well, but not as obviously established as the Laredo population. Other releases of tricuspis phorids are being conducted by Jerry Cook and Bart Drees of Texas A&M using flies provided by the Gainesville and Austin rearing facilities.

Gilbert believes it will soon be known how well this phorid species can establish in Texas, and the BFL team already is busy developing assays to measure the effect of introduced phorids on fire ants in the field.

The fire ant and phorid fly program at Brackenridge Field Laboratory currently is supported by the State of Texas Imported Fire Ant Research and Management Plan and by the Robert Kleberg and Helen Kleberg Foundation. The latter of which also supports efforts of colleague Patricia Folgarait to find additional candidate phorid species in Argentina.

Gilbert said the cooperation between various agencies, universities and individual researchers to solve the fire ant problem in Texas was paralleled by the diversity of supporters for the BFL phorid fly project since 1994. These range from private ranchers, several private sources — including The Doughtery, Fondren and Ewing-Halsell foundations — the Houston Livestock Show and Rodeo Education Committee, the Texas Parks and Wildlife Department and, most recently, the State of Texas Fire Ant Initiative.

“Even if phorid flies don’t eventually solve the fire ant problem,” Gilbert said, “they have helped us see that the broader answer to pest fire ants involves careful management rather that eradication; if we wish to employ biological control we must consider the entire ecological system.” Gilbert points out that ranchers in Texas, dependant as many now are on income from wildlife and sensitive to the economic downside of standard control methods, were quick to jump on the idea of using phorid flies to reduce the impact of fire ants back in 1994.

They also were instrumental in encouraging the integrated approaches now being fostered through the Texas Experiment Station in College Station. “As far as phorids are concerned, at this point we are on definitely optimistic and on course, but it is not yet time to order phorids for your back 40!” Gilbert emphasized.

The State of Texas Fire Ant Program and linked web sites is available on the Internet at: http://fireant.tamu.edu/.