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United States Department of Agriculture

Agricultural Research Service


item Williams, David
item Knue, Gregory
item Becnel, James

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: The red imported fire ant was introduced into the United States from South America in the 1930's. It infests over 278 million acres in the United States and is a very serious medical and agricultural pest. During the past several decades numerous surveys have been made in South America and throughout the southern United States for potential biological control organisms of fire ants. A limited number of organisms have been identified mainly in South America. None has been found in imported fire ants in the U.S. It is believed that imported fire ants are much more abundant in the United States than in South America because they were introduced without any major natural enemies. The microsporidium Thelohania solenopsae is the most common pathogen in fire ants in Brazil and Argentina. During a recent survey of multiple queen field-collected colonies in Florida by Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL, this microsporidium was discovered in workers of the red imported fire ant. This is the first time this microsporidium has been found in the red imported fire ant in the U.S. We also discovered it in fire ant colonies from Mississippi and Texas.

Technical Abstract: The microsporidium, Thelohania solenopsae, is the most common pathogen in fire ants in Brazil and Argentina. It is an obligate intracellular pathogen which reduces population densities of fire ants. It has never been found in fire ants in the U.S. During a recent survey of colonies of the red imported fire ant, Solenopsis invicta, we discovered a microsporidium in workers. The spores appeared similar in size and shape to those of T. solenopsae. Sequence comparisons of the 16s rRNA genes of T. solenopsae from Argentina and the microsporidium found in S. invicta populations in Florida were indistinguishable. Therefore, this is the first time T. solenopsae has been found in S. invicta in the U.S. A total of 379 colonies was excavated in north central Florida and 86 (23%) of these were infected. Within infected colonies, workers had the highest infection rate (72%) followed by larvae (54%) and queens (31%). We have also examined polygynous colonies from Hurley, MS,(3 of 8 colonies were infected), Gulfport, MS (1 of 8 colonies was infected) and Thorndale, TX (5 of 7 colonies were infected). In addition, other ant species were also examined: S. geminata Fabricius (15), Dorymyrmex bureni (Trager) (9), Pheidole metallescens Emery (1), Pheidole moerens Wheeler (1), Camponotus floridanus (Buckley) (1), Trachymyrmex septentrionalis McCook (1), and Brachymyrmex depilis Emery (1) and all were negative for the microsporidium. At the present time, only polygynous S. invicta colonies have been found to be infected. This report documents for the first time a microbial pathogen in S. invicta in the U.S.

Last Modified: 10/19/2017
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