BIOLOGICAL CONTROLÐMICROBIALS New Survey for the Fire Ant Microsporidia Vairimorpha invictae and Thelohania solenopsae in Southern South America, with Observations on Their Field Persistence and Prevalence of Dual Infections

The exploration for the Þre ant diseases Vairimorpha invictae Jouvenaz and Ellis (Microsporidia: Burenellidae) and Thelohania solenopsae Knell, Allen, and Hazard (Microsporidia: Thelohaniidae) was conducted from 2001 to 2005 in Argentina, Paraguay, Chile, Bolivia, and Brazil. A total of 2,064 colonies were sampled from 262 sites. Three sites with high prevalence of pathogens were monitored periodically for the persistence of the infections. V. invictae occurred at 12% of the sites and in 10%of the colonies. Except for one infected colony inBolivia, its distributionwas restricted to the eastern part of the region surveyed. The highest occurrence was in Santa Fe Province. T. solenopsae presented a much wider distribution. It occurred at 25% of the sites and in 13% of the colonies. The highest occurrencewas in Buenos Aires Province. This is the Þrst report of T. solenopsae in thenorthwest, in thewest, in centralArgentina, and inBolivia, and infectingS. interrupta(Santschi). Simultaneous infections were found at 4% of the sites and in 2.2% of the colonies. The periodical examination revealed high infection levels in most occasions. The prevalence of T. solenopsae ranged from 10 to 90% of the colonies, V. invictae from 0 to 60%, and dual infections from 0 to 50%. Each microsporidium exhibited a characteristic enzootic/epizootic wave. Successive epizootic levels observed in both infections provide amore constant pressure against Þre ant populations. These diseases are promising classical biological control agents of the imported Þre ants in the United States.