1. Phorid Flies In Alabama: Have fire ant populations been affected? Lawrence C. ‘Fudd’ Graham 1, Sanford D. Porter 2, and Vicky E. Bertagnolli 1 1 Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849-5413 2 USDA-ARS,CMAVE, P. O. Box 14565, Gainesville, FL 32604 Introduction When fire ants were introduced into Alabama in the early 1900's, almost all of their natural enemies were left behind in South America (Jouvenaz, 1990). As a result, fire ant densities are much higher in Alabama than they are in South America (Porter et al., 1997). Two species of imported fire ant occur in Alabama. The red imported fire ant, Solenopsis invicta, is located in the southern portion of the state and the black imported fire ant, Solenopsis richteri, is located in northwest Alabama. A hybrid of the two species populates the northern tier of Alabama. One group of natural enemies that have shown some promise in the battle against fire ants are phorid flies in the genus Pseudacteon (Porter, 2000). These flies have the unusual habit of decapitating fire ant workers. Pseudacteon tricuspis were released into S. invicta populations in Macon County and have been established since May 1999. Pseudacteon curvatus were released into hybrid fire ant populations in Talladega County and have been established since May 2000. Methods and Materials A release site and a corresponding control site approximately 9.5 kilometers apart were selected in each county. Grids were established at each site for bait stations and pit fall traps. Each grid had either 24 or 25 stations placed approximately 7.5 meters apart in a 6 x 4, 12 x 2, or 5 x 5 grid, depending on site topography. Sampling areas for population data were set up in conjunction with each grid and extended beyond the grid. In Macon County, sampling areas were 0.65, 0.75, and 0.82 acres at the release site and 0.59, 0.34, and 1.03 acres at the control site. In Talladega County, sampling areas were 0.42 and 0.31 acres at the release site and 0.28 and 0.31 acres at the control site. Data collected in each sampling area were total number of mounds and mound size (L x W). Mound size data were taken at the widest point on the mound and at 90 degrees to this measurement. In Macon County, data were collected at the release site and the control site just prior to release of phorid flies. In Talladega County, data were available for two years before the release. P. tricuspis reached the Macon County control site in mid- to late- summer of 2000. P. curvatus were found approximately 1.6 kilometers north of the control site in Talladega County in August 2002, but have not been found at the site. References Jouvenaz, D. P. 1990. Approaches to biological control of fire ants in the United States. In “Applied Myrmecology: World Perspective” (R. K. Vander Meer, K. Jaffe, and A. Cedeno, Eds.), pp. 620-27. Westview Press, Boulder CO. Porter, S. D., Williams, D. F., Patterson, R. S., and Fowler, H. G. 1997. Intercontinental differences in the abundance of Solenopsis fire ants (Hymenoptera: Formicidae): Escape from natural enemies? Environ. Entomol. 26 :373-84. Porter, S. D., 2000. Host specificity and risk assessment of releasing the decapitating fly Pseudacteon curvatus as a classical biocontrol agent for imported fire ants. Biol. Control 19: 35-47. Results Fig. 1. Field-reared P. tricuspis were found at the release site in fall of 1999. Flies reached the control site by fall of 2000. Once field-reared flies were established, the number of mounds decreased at both sites each sampling period until Spring 2002. Similarly, mound areas at both sites decreased each sampling period until Spring 2000. The white arrow on a graph indicates the approximate time field-reared phorids were first located at the site. Fig. 2. P. curvatus were first found at the release site in fall of 2000. As of fall 2002, flies had not yet reached the control site. As in Macon County, the number of mounds decreased each sampling period once field-reared flies were present. However, mound areas increased at the release site in 2002. Mound areas at the control site were low in May of 2001 and May of 2002. Droughts occurred in Alabama in 1999, 2000, and 2001. In addition, the coldest November and December on record were recorded in 2000. These environmental factors have influenced fire ant populations, as evidenced by the low number of mounds in May 2001 and reduction in mound areas in 2001 and 2002 at the Talladega County control site, where no phorids have been found. However, once field-reared phorids were present at a site, the number of mounds at that site began to decline. Further monitoring will be required to determine whether the presence of phorid flies will maintain fire ant populations at these lower numbers.