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Red Imported Fire Ant Nemesis Gains Permanent Foothold in Florida

By Jim Core
May 19, 2004

The permanent establishment of a new species of phorid fly is bad news for the red imported fire ant, according to Agricultural Research Service scientists who are working to control the aggressive ant that has spread across the southern United States.

The establishment of the fly Pseudacteon curvatus is significant because it is the smallest of the decapitating flies. This means it can parasitize small worker ants--the most abundant workers in an ant colony. Phorid fly maggots live in the head capsules of their fire ant hosts, eventually decapitating them and pupating inside their heads. Phorid flies attack only fire ants.

ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla., recently reported that they collected P. curvatus flies from a research site southwest of Gainesville, one year after the flies were initially released. This confirms the first overwinter survival and permanent establishment of P. curvatus on red imported fire ants in the United States.

Sanford D. Porter, acting research leader of the ARS Imported Fire Ant and Household Insects Research Unit in Gainesville, and Juan Briano, director of the ARS South American Biological Control Laboratory in Argentina, originally collected P. curvatus in Argentina in October 2001. The flies were released at the Gainesville site in March 2003 and have been found in increasing numbers ever since.

According to Porter, another biotype of P. curvatus was previously established on hybrid fire ants, but it did not prefer red fire ants. The more recent establishment came from a biotype that prefers the much more abundant red imported fire ants.

There are about 20 species of phorid flies in South America that specifically attack fire ants. P. curvatus and P. tricuspis are the only ones known to be established here.

P. curvatus is one more natural enemy of fire ants that scientists can add to their arsenal of biological control agents. Fire ant populations are much greater in the United States than they are in South America, where natural enemies appear to keep them from being the dominant species.

ARS is the U.S. Department of Agriculture's chief scientific research agency.