Establishment of the Phorid Fly, Pseudacteon curvatus, in Alabama for Biological Control of Imported Fire Ants

L. C. Graham1, V. E. Bertagnolli1, S. D. Porter2, H. D. Dorough3, and A. T. Kelley4

1Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama 36849-54132USDA-ARS Center for Medical and Veterinary Entomology, Gainesville, Florida 32604

3Auburn University, Alabama Cooperative Extension System, Talladega, Alabama 351604Department of Entomology and Plant Pathology, Mississippi State University, Starkville, Mississippi 39762-9775

Introduction Methods and Materials

Results and Discussion

References

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 primarily in the southern portion of the state. The black imported fire ant, Solenopsis richteri, is now only found in a small population located in northwest Alabama and northeast Mississippi. A hybrid of the two species populates the northern part 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 was released into S. invicta populations in southern Alabama and has been established since 1999. Pseudacteon curvatus was released into the hybrid fire ant population located in Talladega County in 2000.

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.

Fire ants were collected from a farm in Talladega County and were shipped to S. Porter in Gainesville, FL. The collected ants were identified as hybrids of S. invicta and S. richteri by their color and cuticular hydrocarbon patterns.

Once confirmation of a hybrid population was received, mounds at the site were individually marked with numbered flags. Approximately five grams of workers were collected from a mound and placed into a plastic container labeled to correspond to the mound number. Workers were collected from between five and eight mounds on a single date, beginning May 3, 2000.

The plastic containers with the workers inside were placed into a cooler with an ice pack and shipped overnight to S. Porter. The workers were exposed to a laboratory colony of P. curvatus for 2-3 days. The workers were then repackaged and shipped overnight back to our lab or to H. Dorough in Talladega County.

Exposed workers were returned to the field within 24 hours of receipt and were placed into the mound from which they were originally removed.

This process was repeated a total of six times. The last release of workers was May 31. Workers were collected from and returned to a total of 38 mounds.

x

xP. tricuspis, Macon Co., 1999

P. curvatus, Talladega Co., 2000

xP. tricuspis, Houston Co., 2000

Pseudacteon spp. release sites in Alabama

18 K*

P. tricuspis, Lowndes Co., 2001

x

1.1 K*

The search for a resident population of P. curvatus was initiated on June 16, 2000. The first siting of P. curvatus occurred on Aug. 10. Three flies were captured on Aug. 14 and were positively identified as P. curvatus. Flies were observed at the site again on Aug. 28 and Sep. 14 and 26.

In 2001, flies were found in May and July. On Aug 16, several areas around the release site were sampled. No flies were found to the south of the release site. However the phorids were found in mounds approximately 1.1 kilometers north of the release site. This is the first successful establishment of Pseudacteon curvatus in the United States.

P. curvatus ovipositor

Photo courtesy of S. Porter

Photo courtesy of S. Porter Photo courtesy of S. Porter

*Circles indicate movement in kilometers from release site.