Natural enemies of the imported fire ants, Solenopsis invicta Buren S. richteri Forel (Hymenoptera: Formicidae), and their hybrid, include a suite of more than 20 fire ant decapitating phorid flies from South America in the genus Pseudacteon. Over the past 12 years, many researchers and associates have cooperated in introducing several species as classical or self-sustaining biological control agents in the United States. As a result, two species of flies, Pseudacteon tricuspis Borgmeier and P. curvatus Borgmeier (Diptera: Phoridae), are well established across large areas of the southeastern United States. Whereas many researchers have published local and state information about the establishment and spread of these flies, here distribution data from both published and unpublished sources has been compiled for the entire United States with the goal of presenting confirmed and probable distributions as of the fall of 2008. Documented rates of expansion were also used 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 that 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 this species' slow rate of spread and frequent failure to establish in more northerly portions of the fire ant range and also, perhaps, by its 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 the 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 these two biotypes will cover almost 90% of the quarantine area by 2011 and 100% 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 establishment rates may be higher in areas without competing species.

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A standard treatment and two candidate RIFA quarantine treatments were applied 21-23 May 1991 to a nonproduction field of common St. Augustine grass near Wadsworth, TX. Plots were 0.4 ha (210 x 210 ft) arranged in a CRD with 6 replicates per treatment. Granular formulations were applied with a Herd GT-77® granular applicator mounted on a John Deere AMT 600 all-terrain vehicle. Sprays were applied with a roller pump boom sprayer comprised of five KSS-3 spray tips spaced 0.9 m apart. The system was pressurized to 1.0-1.25 kg/cm2 and towed behind a Honda 300 all-terrain vehicle, providing a delivery rate of 115.5 liter/ha. RIFA population assessments were made in 0.1 ha circular subplots in the center of each treatment plot immediately prior to, and at 4, 8, 12, 20, and 36 wk after application using a population indexing system described elsewhere (Lofgren and Williams; 1982. J. Econ. Entomol. 75: 798-803). Data were analyzed for treatment differences using ANOVA and the Tukey test.