Host Specificity and Risk Assessment of Releasing the Decapitating Fly Pseudacteon curvatus as a Classical Biocontrol Agent for Imported Fire Ants

Host specificity of the decapitating fly Pseudacteon curvatus was studied to determine whether this species is suitable for release as a classical biocontrol agent of imported fire ants in the United States. A series of no-choice tests with 19 species of ants from 12 genera showed that P. curvatus will not develop in ants outside the genus Solenopsis. P. curvatus successfully parasitized the native fire ants Solenopsis geminata and Solenopsis xyloni in no-choice tests, but rates of parasitism were considerably less than those with the imported fire ant Solenopsis invicta (6 and 35% of the rate for S. invicta, respectively). Paired preference tests showed that P. curvatus has a three- to fourfold preference for S. invicta over either of the native fire ants. Furthermore, flies reared from native fire ants still strongly preferred imported fire ants. P. curvatus was not attracted to vegetables, fruits, meat, prepared foods, carrion, or dung. This study indicates that release of P. curvatus poses only a small risk to native fire ants. The argument is made that this risk needs to be balanced against potential benefits to numerous other native organisms and a high probability that release of this fly will actually benefit native fire ants because impacts on imported fire ants will almost certainly be much greater than those on native fire ants.