Prevalence of a microsporidian parasite in different social forms of the Red Imported Fire Ant, Solenopsis invicta, in its native range in Argentina

Authors: Ascunce, Marina; CALCATERRA, LUIS - Fuedei; SHOEMAKER, DEWAYNE - University Of Tennessee

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2025
Publication Date: 2/22/2025
Citation: Ascunce, M.S., Calcaterra, L.A., Shoemaker, D. 2025. Prevalence of a microsporidian parasite in different social forms of the Red Imported Fire Ant, Solenopsis invicta, in its native range in Argentina. Journal of Invertebrate Pathology. 210(108288). https://doi.org/10.1016/j.jip.2025.108288.
DOI: https://doi.org/10.1016/j.jip.2025.108288

Interpretive Summary: The Red Imported Fire Ant, Solenopsis invicta, was accidentally introduced to the southern U.S. in the late 1930s from South America. Long-term, sustained suppression approaches through biological control are needed to control these growing fire ant invasive populations. Among those natural enemies used in the U.S., there have been releases of a fungal-like microsporidian pathogen, Kneallhazia solenopsae. Thus, in this study, researchers characterized the prevalence and genetic diversity of this microsporidium in natural populations of Solenopsis invicta in Argentina. The goal is to characterize this natural enemy in its native environment. The information gained may be used to improve biological control methods in the U.S. The researchers analyzed ants from 559 nests and found that in 29 out of those 559 nests the microsporidium was present (5.19%). Interestingly, the microsporidium was found in both fire ant social forms single queen colony and multiple queen colony, which contrats the prevalence of this parasite in the U.S. populations where this microsporidium is absent in single queen colonies. Genetically, the microsporidian variant found in the fire ants from U.S. was different from the ones found in the native range. Further studies are needed to evaluate the pathogenicity of these native microsporidian variants.

Technical Abstract: We surveyed 559 colonies of the Red Imported fire ant, Solenopsis invicta, in its native range in Argentina, for the microsporidian parasite, Kneallhazia solenopsae, a natural enemy of this ant. The microsporidium was detected in 20 out of 508 monogyne and 9 out of 51 polygyne colonies corresponding to a 3.31% and 13.68% mean infection probability, respectively. In USA, K. solenopsae prevalence could reach 78% and is almost absent in monogyne colonies. A preliminary assessment showed that the K. solenopsae USA variant was genetically different from the ones in the native range supporting the idea that the USA variant might only infect polygyne colonies.