Field host range of the fire ant pathogens Thelohania solenopsae (Microsporida: Thelohaniidae) and Vairimorpha invictae (Microsporida: Burenellidae) in South America

We studied the field host specificity of the microsporidia Thelohania solenopsae and Vairimorpha invictae and their prevalence in the imported fire ants, Solenopsis invicta and S. richteri. Terrestrial ants were sampled by using bait traps and/or nest sampling at preselected sites in Argentina and Brazil. The sampling included the genera Solenopsis, Pheidole, Camponotus, Crematogaster, Linepithema, Brachymyrmex, Paratrechina, Dorymyrmex, and Wasmannia. The samples were examined under a phase-contrast microscope for the presence of microsporidian infections. The bait trap sampling revealed that: (1) T. solenopsae infected only S. richteri, S. invicta, and Solenopsis sp. at 6–67% of the sites and in 1.5–29% of the traps; (2) V. invictae infected only S. invicta at 6% of the sites and in 3% of the samples. The nest sampling revealed that: (1) T. solenopsae infected S. invicta, S. richteri, and S. macdonaghi, at 41–67% of the sites and in 11–58% of the colonies; (2) V. invictae infected the same species at 15–50% of the sites and in 2–26% of the colonies. We detected T. solenopsae and V. invictae in equal percentages of S. invicta sites (41%); however, the percentage of colonies infected with V. invictae was 20% and with T. solenopsae only 11%. At S. richteri sites, in contrast, T. solenopsae occurred at 46% of the sites and 15% of the colonies and V. invictae occurred at only 15% of the sites and 2% of the colonies. In S. macdonaghi, T. solenopsae was detected at 67% of the sites and 58% of the colonies, and V. invictae was detected at 50% of the sites and 26% of the colonies. This is the first report of V. invictae infecting S. macdonaghi. The proportion of S. richteri and S. invicta infected with T. solenopsae was similar. In contrast, the proportion of S. invicta infected with V. invictae was higher than S. richteri. We conclude that the microsporidia, T. solenopsae and V. invictae, show a very high specificity for Solenopsis ants in the field. It appears that T. solenopsae infects S. invicta and S. richteri equally but V. invictae may be more adapted to infect S. invicta.