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United States Department of Agriculture

Agricultural Research Service


Location: Imported Fire Ant and Household Insects

Title: Pseudacteon spp. (Diptera: Phoridae) biological control agents of Solenopsis spp. (Hymenoptera: Formicidae) in Louisiana: statewide distribution and Kneallhazia solenopsae (Microsporidia: Thelohaniidae) prevalence

item Meszaros, Anna -
item OI, DAVID
item Beuzelin, Julien -
item Reay-Jones, Francis -
item Johnson, Seth -

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 25, 2014
Publication Date: N/A

Interpretive Summary: Imported fire ants infest over 140 million hectares in the United States and an estimated 6 billion dollars is spent annually to control and repair damage from this invasive pest. Fire ants entered the U.S. with few natural enemies, however, several fire ant decapitating phorid flies have been released in the U.S. since 1996 as biological control agents. In addition, a South American pathogen of fire ants, Kneallhazia (formerly Thelohania) solenopsae, was detected in the U.S. in 1996 and has spread both naturally and via releases. Interestingly, phorids can acquire the pathogen when it develops in infected fire ants. Scientists from the Center for Medical, Agricultural, and Veterinary Entomology, USDA, ARS, Gainesville FL, and Louisiana State University, Baton Rouge, LA worked cooperatively to quantify the spatial distribution of two of the flies, Pseudacteon tricuspis and Pseudacteon curvatus, and determine the pathogen’s distribution and prevalence in the Louisiana phorid fly populations. The phorid flies P. tricuspis and P. curvatus have expanded their range from seven release sites in Louisiana to occupy approximately 21,251 and 27,428 acres, respectively. P. curvatus essentially occupies the entire state of Louisiana and has spread faster than P. tricuspis despite the latter having more and earlier releases. K. solenopsae was detected in 34% of the 64 parishes and this is the first report of K. solenopsae in P. tricuspis. The pathogen does not harm the flies and its presence in them suggests it may be a vector of the pathogen. This study contributes to the understanding of the spatial distribution dynamics of fire ant biological control agents which may potentially guide future biological control releases for fire ants and other invasive ants.

Technical Abstract: Phorid flies, Pseudacteon spp. (Diptera: Phoridae), have been released in the United States since 1996 as biological control agents for imported fire ant, Solenopsis invicta Buren, Solenopsis richteri Forel, and their hybrid (Hymenoptera: Formicidae), management. A statewide survey was conducted in Louisiana during 2009 and 2010 to determine the distribution of Pseudacteon tricuspis Borgmeier and Pseudacteon curvatus Borgmeier, and to quantify the potential spatial association between the two species. Additionally, collected phorid flies were tested for the microsporidium Kneallhazia (=Thelohania) solenopsae (Knell, Allen, and Hazard), another natural enemy of fire ants, to establish a comprehensive account of the pathogen's distribution and prevalence in phorid fly populations. P. tricuspis and P. curvatus have expanded their range from four and three separate release sites, respectively, in Louisiana. By 2010, P. tricuspis and P. curvatus occupied approximately 86,600 km2 and 111,900 km2, respectively. Overall, P. curvatus was more abundant than P. tricuspis, with 41.9 and 9.8 females, respectively, collected on average per sampling site in 2009. Spatial Analysis by Distance IndicEs (SADIE) analyses suggested aggregation for the two phorid fly species. P. tricuspis collections were positively associated with P. curvatus collections, indicating that gaps and clusters of both species generally overlapped. K. solenopsae was detected in 22 of 64 parishes, and among 124 collection sites tested, 19% yielded positive responses for K. solenopsae. P. tricuspis males and females and P. curvatus females were found to harbor K. solenopsae. The present study is the first to detect K. solenopsae in P. tricuspis.

Last Modified: 8/19/2014
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