Thursday, December 08, 2005

ENV: Fire Ant Relief

One caution -- this is a press release, not a news article . . . passed on by Mike Quinn, thanks.

Off With Their Heads!
Bexar County Phorid Fly Release To Help with Fire Ant Control
Paul Schattenberg, Texas A&M University System Agricultural Program, Dec. 6, 2005

SAN ANTONIO – Heads will roll as the result of an upcoming phorid fly release in Bexar County. Fortunately, those heads will be attached to the bodies of thousands of red imported fire ants in the area.

While phorid flies have been established as a biological control for red imported fire ants in other Texas counties, their release here by Texas Cooperative Extension will be a first for Bexar County.

The release will be before year's end at Walker Ranch in northern San Antonio. Walker Ranch was chosen due to its existing fire ant mounds and the presence of sufficient trees to form a windbreak to protect the flies, as well as its water source.

Red imported fire ants are an invasive species accidentally introduced into the U.S. from South America around the 1930s, said Molly Keck, entomologist for Extension in Bexar County. Fire ants are now the dominant ant species in the eastern two-thirds of Texas. They are a concern because of their possible impact on human health, as well as on hatching reptiles, birds and other newborn animals.

In 2001, an economic impact study released by the Texas Imported Fire Ant Research and Management Plan showed Texans shell out more than $1.2 billion annually on fire ant damage and control. More than $700 million of that amount was for households.

Phorid flies were chosen as a biological control because they "parasitize" fire ants by depositing eggs which hatch into larvae that pupate inside the fire ant's head capsule, Keck said. Adult flies use chemical cues to locate fire ants and "dive-bomb" them, laying a torpedo-shaped egg in the ant's thorax. The maggot hatching from the egg then migrates to the ant's head.

"As the fly pupates, it releases enzymes which cause the head to fall off," she said. "The maggot continues to pupate in the decapitated head capsule, finally emerging as an adult fly." Currently, the main source of fire ant control is chemical.

"Many chemical controls are effective and work well against fire ants," Keck said. "But having an effective biological means of control is an important entomological and environmental objective. It provides us with another weapon in the arsenal to control fire ants."

Prior to a biological release, host specificity is established to eliminate any unintended economic or environmental consequences, Keck noted.

"The phorid fly species we'll be releasing is the Pseudacteon tricuspis," she said. "It is host-specific to red imported fire ants and has never been known to attack another organism."

The flies to be released are being provided by the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, said Dr. Bastiaan (Bart) Drees, professor of entomology at Texas A&M University in College Station.

"There have been similar successful releases throughout the southeastern U.S. and we feel confident this one will be equally worthwhile in supplementing red imported fire ant control efforts in Bexar County," he said.

Phorid flies will be shipped from the USDA rearing facility in Gainsville, Fla. Keck will receive hundreds of parasitized fire ant head capsules from which adult flies will emerge. As they emerge, they will be collected and released over a two-week period.

"The presence of adult flies next year will confirm the successful development and emergence of the first generation," Keck said. "After two months, all adults initially released will have died and new egg development would be complete."

Adult phorid flies must be released immediately after hatching because their life span is only a few days, she added.

Ten fire ant colonies will be opened and prepared and several will be monitored and the number of fire ant mounds at the release site will be recorded. The first study evaluation will take place two to three months after initial release.

Phorid fly activity and fire ant density will be evaluated during spring and fall, and the impact of the program will be monitored for several years.

"The main effect of the flies will be to disrupt fire ant foraging during the daytime and stress them so they have difficulty competing with other ant species," she said. "We hope that the introduction of this biological control will provide sustained repression of red imported fire ants in the county."

Similar biological control releases have resulted in a 10 percent to 30 percent reduction in the population of "target" species, Keck added.

Members of the integrative biology section of the University of Texas are currently planning a similar release within Bexar County in 2006. Keck and others involved in the Extension release are coordinating with them to ensure the integrity of their respective data. They will also share their results to get a better overall picture of phorid fly impact in the area.