Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/23/2009
Publication Date: 4/12/2010
Citation: Oi, D.H., Valles, S.M., Briano, J. 2010. Laboratory host specificicty testing of the fire ant microsporidian pathogen Vairimorpha invictae (Microsporidia: Burenellidae). Biological Control. 53:331-336. Interpretive Summary: Insect pathogens from South America are being studied for the biological control of red imported fire ants (RIFA) 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, evaluated the potential of the pathogen Vairimorpha invictae, to infect two native North American fire ants, the tropical fire ant and the southern fire ant. In addition, the Argentine ant, an invasive pest ant established in the U.S. and other countries, was exposed to V. invictae to determine its susceptibility to the pathogen. Determining the susceptibility of non-target hosts to candidate biological control agents is an essential step in the approval process for their release in the U.S. Inoculations of laboratory colonies of the native fire ants and the Argentine ant did not result in any infections while 60% of the RIFA colonies were infected. In addition to the colony inoculations, V. invictae was not detected in the tropical and southern fire ants when their larvae were tended by V. invictae-infected adult RIFA. In contrast, V. invictae was detected in 40% of the RIFA larval groups tended by infected workers. These results are consistent with field surveys that indicated V. invictae specifically infects fire ants from a species group native to South America, and does not infect other non-ant arthropods. The results of this study combined with the field survey studies provide strong evidence that the release of V. invictae in the U.S. as a biological control agent pose little or no risk to U.S. native ants and other arthropods.
Technical Abstract: The host specificity of Vairimorpha invictae, a microsporidian pathogen of fire ants in South America, was assessed in the laboratory with the tropical fire ant, Solenopsis geminata, the southern fire ant, Solenopsis xyloni, and the Argentine ant, Linepithema humile. The two fire ant species are found in the U.S. and native to North America. The Argentine ant is a widespread, exotic species that co-occurs with the native North American fire ants as well as with the red and black imported fire ants, (Solenopsis invicta and Solenopsis richteri, respectively) in the U.S. Inoculations of V. invictae-infected S. invicta brood to laboratory colonies did not result in any infections of S. geminata, S. xyloni, or L. humile, while 60% of the S. invicta colonies were infected. In addition to the whole colonies inoculations, V. invictae was not detected in groups of S. geminata and S. xyloni larvae that were tended by V. invictae-infected adult, S. invicta workers. In contrast, V. invictae was detected in 40% of the S. invicta larval groups tended by infected workers. This was the first report of V. invictae transmission to larvae by infected adult worker ants. Exposure to V. invictae through infected brood and workers partially emulated possible field interactions between infected and uninfected ant species. These results are congruent with previous field surveys which indicate that the host range of V. invictae is limited to fire ants of the Solenopsis saevissima species group.