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Battling the Imported Fire Ant
The imported fire ant Solenopis invicta was accidentally introduced from South America at the port of Mobile, Alabama in the late 1930's. This ant has had remarkable success in its invasion of the U.S. Since its arrival, it has negatively affected wildlife and overall biological diversity in the eastern half of Texas and the southern United States. The imported fire ant (IFA) entered Texas in 1957 and has increased its range over much of the state. While the drier conditions of the Southwest limit the ants' progress, the recent drought has in many ways increased human and fire ant encounters.
Negative interactions between people and wildlife often become more frequent as other species move into "people places" seeking moisture. This is also true of the imported fire ant. Under dry conditions, the IFA must burrow deeper underground to maintain a tolerable temperature. Not only does the IFA have certain temperature requirements, but also this voracious predator must intake a certain level of moisture to survive. An aggressive pest already, during a drought the IFA may be more likely to damage gardens, yards, homes and other structures in search of water.
We humans aren't the only ones affected by the IFA. Young wildlife can be particularly vulnerable. Although there have been numerous incidental observations of fire ants attacking and killing wildlife, limited research has been done regarding the IFAs impact on wildlife populations. It has been documented that these ants are attracted to moisture in the eyes, nose and mouth of young mammals and in the hatching eggs of ground nesting birds and reptiles. More damaging than direct attacks on individual animals is the intense competition for insects and seeds. The IFA can dramatically reduce the amount of food available for loggerhead shrikes, bobwhite quail, horned lizards and many other species. It is difficult to determine the exact relationship between the IFA and other species but it is obvious more research is needed to determine the long term effects of this ant at the ecosystem level.
Fire ants are one of the most studied species of insects in the world and with good reason. The IFA has an enormous economical and biological impact, especially in the United States. The success of their invasion is largely due to the aggressiveness and adaptability of the species which allows it to out-compete our native ants and the widespread use of non-selective aerial pesticides (until they were discontinued in 1977) which allowed the IFA to expand its range even faster. When we level the playing field with broad spectrum pesticides our native ants are easily out-competed by the IFA.
The Texas native fire ant Solenopis geminata is parasitized by two species of phorid flies. In its home range in South America, the imported fire ant is also affected by parasitic flies. These tiny flies use the ants as hosts for egg laying and in the process harrass the ants, reducing their foraging ability. A primary reason the imported fire ant has become such a problem in the U.S. is that our native species of flies paratisitize only our native fire ant and not its imported cousin.
Dr. Larry Gilbert and researchers from the University of Texas at Austin are working to introduce Pseudacteon flies from Brazil and Argentina which are species specific to the IFA. Funds from Texas Parks and Wildlife and Texas Department of Agriculture are helping to construct the first experimental rearing facility for these tiny flies, which are currently the best prospect for biological control of the imported fire ant.
Their research has also been funded by National Science Foundation, several private foundations, and the Houston Livestock Show and Rodeo Education Committee.
Written by Robert Perez
Robert Perez is the Program Assistant in the Upland Wildlife Ecology Program, Wildlife Division.
