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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGY, GENOMICS, AND INTEGRATED PEST MANAGEMENT OF INVASIVE ANTS

Location: Imported Fire Ant and Household Insects

Title: Establishment, dispersal, and competitive impacts of a third fire ant decapitating fly (Pseudacteon obtusus) in North Central Florida

Authors
item Porter, Sanford
item Calcaterra, Luis -

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 18, 2012
Publication Date: October 16, 2012
Citation: Porter, S.D., Calcaterra, L.A. 2012. Establishment, dispersal, and competitive impacts of a third fire ant decapitating fly (Pseudacteon obtusus) in North Central Florida. Biological Control. 64:66-74.

Interpretive Summary: Self-sustaining or classical biological control agents offer a hope for permanent wide-area control of imported fire ant populations in the United States. Escape from abundant natural enemies left behind in Argentina is a likely reason for unusually high fire ant densities in the United States. A scientist from the USDA-ARS Center for Medical, Agricultural and Veterinary Entomology (CMAVE) in Gainesville, FL cooperated with a scientist from the USDA-ARS, South American Biological Control Laboratory (SABCL) in Buenos Aires, Argentina to collect and release the decapitating fly Pseudacteon obtusus in Gainesville, FL as a self-sustaining biocontrol agent of red imported fire ants. This fly was selected because it is a common parasitoid of fire ants in large areas of Argentina and because it has a higher propensity of attacking fire ants along trails than the two decapitating fly species previously released. A rapidly expanding population (8-12 km/year) proved that the new decapitating fly was capable of thriving and successfully competing with the much more abundant Pseudacteon curvatus. Pseudacteon tricuspis , the first decapitating fly released, was effectively excluded from sample sites when faced with competition from both P. curvatus and P. obtusus. The addition of P. curvatus, the second parasitoid released, increased total parasitism pressure on fire ant populations by about 10 fold. The addition of P. obtusus, the third species, increased parasitism of larger fire ant workers, but did not measurably improve total pressure on red imported fire ants around Gainesville, FL. Releases of P. obtusus in several other states are in progress to assess its performance in other regions of the country.

Technical Abstract: Self-sustaining classical biological control agents offer a hope for permanent wide-area control of imported Solenopsis fire ants in the United States because escape from abundant natural enemies left behind in Argentina is a likely reason for unusually high fire ant densities in the United States. The fire ant decapitating fly Pseudacteon obtusus Borgmeier (Diptera: Phoridae) was released as a biocontrol agent of the red imported fire ant (Solenopsis invicta Buren) in Gainesville, FL because it is a common parasitoid of this ant in large areas of Argentina and because it has a higher propensity of attacking fire ants along trails than the two Pseudacteon species previously released. Field surveys of a rapidly expanding P. obtusus population (8-12 km/year) proved that this fly was capable of thriving and successfully competing with the much more abundant Pseudacteon curvatus Borgmeier. However, Pseudacteon tricuspis Borgmeier, the first decapitating fly released, was effectively excluded from sample sites when faced with competition from both P. curvatus and P. obtusus. Despite clear evidence for competitive exclusion, P. tricuspis abundance at sample sites was positively correlated with the abundance of its two competitors— probably because of moderate to strong covariability in the suitability of sample sites for all three congeners. The addition of P. curvatus, the second parasitoid released, increased total parasitism pressure on fire ant populations by about 10 fold. The addition of P. obtusus, the third species, did not measurably improve total guild pressure on red imported fire ants at roadside sample sites around Gainesville, FL., but study procedures were probably sufficient to detect only moderate to strong net changes in total fly populations. The performance of P. obtusus is expected to vary among habitats and in different regions and climates.

Last Modified: 11/24/2014