ARS | Publication request: Fire ant decapitating fly cooperative release programs (1994-2008): Two Pseudacteon species (P. tricuspis, P. curvatus) rapidly expand across imported fire and populations in the southeastern United States

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 8, 2010
Publication Date: February 18, 2011
Citation: Callcott, A., Porter, S.D., Weeks, R.D., Graham, L.C., Johnson, S.J., Gilbert, L.E. 2011. Fire ant decapitating fly cooperative release programs (1994-2008): Two Pseudacteon species (P. tricuspis, P. curvatus) rapidly expand across imported fire and populations in the southeastern United States. Journal of Insect Science. 2:1-25.

Interpretive Summary: Natural enemies of the imported fire ants (Solenopsis invicta Buren, S. richteri Forel, and their hybrid; Hymenoptera: Formicidae) include a suite of more than 20 phorid decapitating flies from South America in the genus Pseudacteon. Over the past 12 years, many researchers and associates have cooperated introducing several of these self-sustaining classical biological control agents to the United States. As a result, two species of flies, P. tricuspis Borgmeier and P. curvatus Borgmeier (Diptera: Phoridae), are well established across large areas of the southeastern United States. While many researchers have published local and state information about the establishment and spread of these flies, a compilation for the entire United States has not been available. Consequently, researchers with the USDA-APHIS, the USDA-ARS Center for Medical, Agricultural and Veterinary Entomology (CMAVE), Auburn University, Louisiana State University, and the University of Texas have cooperated to compile distribution data from both published and unpublished sources for the entire United States with the goal of presenting confirmed and estimated county level distributions for the fall of 2008. We also used documented rates of expansion to predict the distribution of these flies three years later in the fall of 2011. In the fall of 2008, eleven years after the first successful release, we estimate that P. tricuspis covered about 50% of the fire ant quarantined area and we estimate it will occur in almost 65% of the quarantine area by 2011. Complete coverage of the fire ant quarantined area will be delayed or limited by its slow expansion and frequent failure to establish in more northerly portions of the fire ant range and, perhaps, also by a preference for red imported fire ants (S. invicta). Eight years after the first successful release of P. curvatus, two biotypes of this species (one biotype predominantly preferring the black and hybrid imported fire ants and the other preferring the red imported fire ants) covered almost 60% of the fire ant quarantined area. We estimate they will cover almost 90% of the quarantine area by 2011 and fully cover the quarantine area by 2012 or 2013. The information in this paper is important because it shows that these two species of flies are expanding vigorously so that they will shortly impact fire ants across most if not all of the range of imported fire ants in the United States.

Technical Abstract: Natural enemies of the imported fire ants (Solenopsis invicta Buren, S. richteri Forel, and their hybrid; Hymenoptera: Formicidae) include a suite of more than 20 phorid decapitating flies from South America in the genus Pseudacteon. Over the past 12 years, many researchers and associates have cooperated introducing several of these self-sustaining classical biological control agents to the United States. As a result, two species of flies, P. tricuspis Borgmeier and P. curvatus Borgmeier (Diptera: Phoridae), are well established across large areas of the southeastern United States. While many researchers have published local and state information about the establishment and spread of these flies, a compilation for the entire United States has not been available. Consequently, we have compiled distribution data from both published and unpublished sources for the entire United States with the goal of presenting confirmed and estimated county level distributions for the fall of 2008. We also used documented rates of expansion to predict the distribution of these flies three years later in the fall of 2011. In the fall of 2008, eleven years after the first successful release, we estimate that P. tricuspis covered about 50% of the fire ant quarantined area and we estimate it will occur in almost 65% of the quarantine area by 2011. Complete coverage of the fire ant quarantined area will be delayed or limited by its slow expansion and frequent failure to establish in more northerly portions of the fire ant range and, perhaps, also by a preference for red imported fire ants (S. invicta). Eight years after the first successful release of P. curvatus, two biotypes of this species (one biotype occurring predominantly in black and hybrid imported fire ants and the other occurring in red imported fire ants) covered almost 60% of the fire ant quarantined area. We estimate they will cover almost 90% of the quarantine area by 2011 and fully cover the quarantine area by 2012 or 2013. Strategic selection of several distributional gaps for future releases will accelerate complete coverage of quarantine areas. However, some gaps may be best used for the release of additional species of decapitating flies because success rates of releases may be higher in areas without competing species of flies.