Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/11/2008
Publication Date: 1/1/2009
Citation: Oi, D.H., Porter, S.D., Valles, S.M., Briano, J.A., Calcaterra, L.A. 2009. Pseudacteon decapitating flies (Diptera: Phoridae): Are they potential vectors of the fire ant pathogens Kneallhazia(=Thelohania)solenopsae (Microsporidia: Thelohaniidae)and Vairimorpha invictae (Microsporidia: Burenellidae)?. Biological Control. 48(3):310-315. Interpretive Summary: Pathogens and parasites from South America are being evaluated for the biological control of imported fire ants in the U.S. Scientists from the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida, and the USDA-ARS, South American Biological Control Laboratory in Hurlingham, Buenos Aires, Argentina, discovered that fire ant decapitating flies that developed in fire ants infected with the fire ant pathogen Kneallhazia (formerly Thelohania) solenopsae also acquired the pathogen. K. solenopsae was found in three species of flies (51% of pooled samples) and included flies collected from the field in Florida. This is the first report of a fire ant pathogen being detected in another fire ant biocontrol agent. Initial observations do not indicate detrimental effects of the pathogen on the flies. In contrast, Vairimorpha invictae was not detected in any of the flies. The finding of K. solenopsae in apparently healthy flies offers the possibility that the flies can transmit K. solenopsae, and perhaps facilitate the spread of the disease among fire ant populations.
Technical Abstract: Fire ant decapitating flies in the genus Pseudacteon were tested for their potential as hosts or vectors of two microsporidian pathogens of the red imported fire ant, Solenopsis invicta. Decapitating flies which attacked or were reared from S. invicta workers infected by Kneallhazia (=Thelohania) solenopsae or Vairimorpha invictae were tested for either pathogen by PCR tests or visual examination for spores using phase microscopy. Three species of fire ant decapitating flies acquired the pathogen, K. solenopsae. K. solenopsae was detected in 58% of pooled samples of Pseudacteon obtusus flies and 44% of pooled samples of Pseudacteon cultellatus that developed in K. solenopsae-infected fire ant workers. K. solenopsae was also found in 17% of pooled samples of field-collected Pseudacteon curvatus. In contrast, the microsporidium V. invictae was not detected in P. obtusus reared from V. invictae-infected S. invicta workers. Neither K. solenopsae nor V. invictae were detected in any of the hovering or ovipositing flies in the laboratory exposures, indicating no mechanical acquisition of the microsporidia occurred during oviposition activity. Greater than 92% of the P. obtusus that developed in K. solenopsae-infected ants survived and emerged as adults, thus indicating no detrimental effects of the microsporidium on fly development and emergence. These results indicate that Pseudacteon decapitating flies may be able to vector K. solenopsae but not V. invictae among fire ants. Further tests are planned to determine if flies containing K. solenopsae are capable of transferring this pathogen either during oviposition or by being consumed by fire ant larvae.