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Simple Summary: The Black Imported Fire Ant, Solenopsis richteri, was accidentally introduced to the southern U.S. in the 1930s from South America. Long-term, sustained suppression approaches through biological control are needed to control growing invasive fire ant populations. Among the natural enemies used in the U.S., there have been multiple releases of a fungal-like microsporidian pathogen, Kneallhazia solenopsae. In this study, researchers characterized the prevalence and genetic diversity of this microsporidium in native populations of S. richteri. The goal of these types of studies is to assess how the natural enemy acts in the native environment to improve biological control methods. The researchers analyzed ants from 219 nests and found that the microsporidium was present in 12.8% of the nests. Interestingly, within these S. richteri colonies, researchers found a social parasitic ant, Solenopsis daguerrei, and when those ants were analyzed, 3.9% of S. daguerrei ants tested positive for the microsporidium. The microsporidian variants found in both Solenopsis species were genetically similar. Further studies are needed to evaluate the pathogenicity of this microsporidian variant. Microsporidia are natural pathogens of arthropods and have been used as biological control against insect pests. In the United States, efforts to control the invasive Red Imported Fire Ant, Solenopsis invicta, and Black Imported Fire Ant, Solenopsis richteri, have included the use of the microsporidium, Kneallhazia solenopsae. However, there is limited information about the genetic differences among the microsporidian variants found in S. invicta and in S. richteri. In this study, we assessed the prevalence and genetic diversity of K. solenopsae in native populations of S. richteri in Argentina (South America). Additionally, we examined the social parasitic ant, Solenopsis daguerrei, which is found in some S. richteri nests, for the presence of this microsporidium. The survey of 219 S. richteri nests revealed K. solenopsae infections in all five sites analyzed, with 28 colonies (12.8%) positive for the microsporidium. Among the 180 S. daguerrei individuals collected, seven ants (3.9%) from three sites tested positive for K. solenopsae. Phylogenetic analyses of the microsporidian variants present in S. richteri and S. daguerrei based on partial small subunit ribosomal gene sequences (SSU rRNA) showed that both ant species shared the same variant, which is different from the ones found in S. invicta. Further studies are needed to determine the pathogenicity of genetically different K. solenopsae variants among Solenopsis species. [ABSTRACT FROM AUTHOR]

The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), is a stinging, invasive ant from South America that has plagued the southern US since the 1930s. It is currently established in parts of California, including the Coachella Valley. We introduced and established the fire ant decapitating phorid flies, Pseudacteon curvatus Borgmeier and Pseudacteon obtusus Borgmeier (Diptera: Phoridae); Solenopsis invicta virus 3 (Picornavirales: Solinviviridae) (SINV-3); and the microsporidian fire ant pathogen Kneallhazia solenopsae Knell, Allan, & Hazard (Microsporida: Thelohaniidae) for the biological control of fire ants in this region of California. This is the first establishment of fire ant decapitating phorid flies in California. In addition, we demonstrated human-mediated establishment of SINV-3 and K. solenopsae in hot, dry, but irrigated, urban desert habitat. [ABSTRACT FROM AUTHOR]

Sample collections of Solenopsis invicta Buren (Hymenoptera: Formicidae) were taken from 20 islands of the West Indies and evaluated for the presence of key pathogens and parasites of this invasive pest ant. We hypothesized that bottleneck events during the introduction of this ant species in the West Indies would have resulted in populations devoid, or nearly so, of natural enemies. Monogyne and polygyne social forms were found throughout the islands surveyed with monogyny being more prevalent (65%) compared with polygyny (35%). Among 254 samples, only 25 (~10%) tested positive for the presence of pathogens or parasites. The microsporidian Kneallhazia solenopsae was the most prevalent pathogen detected; it was found in 20 colonies. A second microsporidian species, Vairimorpha invictae, was shown to be present in a polygyne sample collected from St. Croix-the first detection of this pathogen outside South America. Similarly, Solenopsis invicta densovirus (SiDNV) was detected in one polygyne sample from Anguilla. SiDNV is not found in S. invicta U.S. populations, so this detection also represents the first geographic discovery outside of South America. Two species of Pseudacteon decapitating flies were found to have dispersed into the Bahamas. Utilization of the islands of the West Indies for release, establishment, and impact assessment of S. invicta natural enemies is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Kneallhazia solenopsae is a pathogenic microsporidium that infects the fire ants Solenopsis invicta and Solenopsis richteri in South America and the USA. In this study, we analyzed the prevalence and molecular diversity of K. solenopsae in fire ants from North and South America. We report the first empirical evidence of K. solenopsae infections in the tropical fire ant, Solenopsis geminata, and S. geminata × Solenopsis xyloni hybrids, revealing an expanded host range for this microsporidium. We also analyzed the molecular diversity at the 16S ribosomal RNA gene in K. solenopsae from the ant hosts S. invicta, S. richteri, S. geminata and S. geminata × S. xyloni hybrids from North America, Argentina and Brazil. We found 22 16S haplotypes. One of these haplotypes (WD_1) appears to be widely distributed, and is found in S. invicta from the USA and S. geminata from southern Mexico. Phylogenetic analyses of 16S sequences revealed that K. solenopsae haplotypes fall into one of two major clades that are differentiated by 2–3%. In some cases, multiple K. solenopsae haplotypes per colony were found, suggesting either an incomplete homogenization among gene copies within the 16S gene cluster or multiple K. solenopsae variants simultaneously infecting host colonies. [ABSTRACT FROM AUTHOR]

Abstract: A year-long survey was conducted to determine the seasonality and co-occurrence of four pathogens and a group of parasites in colonies of the red imported fire ant, Solenopsis invicta, in north-central Florida. Solenopsis invicta colonies were sampled and examined for the presence of Pseudacteon spp. (P. curvatus, P. tricuspis, P. obtusus) parasitic phorid flies, a microsporidian pathogen (Kneallhazia solenopsae) and 3 S. invicta viruses (SINV-1, SINV-2, and SINV-3) by PCR or RT-PCR methods. In addition, the social form designation of each colony (single- or multiple-queen) was determined by genotyping worker ants at the Gp-9 locus to determine if the pathogens or parasites were associated with monogyne or polygyne fire ant colonies. Seasonal variability was observed in the prevalence of all pathogens/parasites examined, with SINV-1, SINV-3, and K. solenopsae exhibiting pronounced seasonality. SINV-1 and K. solenopsae infections were most prevalent among colonies during warmer periods of the year, while SINV-3 was most prevalent during the cooler periods. As hypothesized, pathogens were found more commonly in polygyne colonies than in monogyne colonies. Infection comparisons by social form revealed higher infection rates of K. solenopsae and SINV-2 in polygyne colony samples compared with monogyne colony samples. The overall colony infection and parasitism rate among the 360 colonies sampled, regardless of social form, was 60.3% (SINV-1), 8.9% (SINV-2), 10.8% (SINV-3), 22.5% (K. solenopsae), and 8.1% (Pseudacteon flies). An interesting pattern was observed between the number of different pathogens or parasites detected in monogyne and polygyne colonies. The majority of monogyne colonies (>80%) were either uninfected or infected or parasitized with only a single pathogen/parasite while the majority of polygyne colonies (>55%) were infected or parasitized with 2 or more pathogens/parasites simultaneously. Higher pathogen/parasite prevalence among polygyne colonies is attributed to lower genetic relatedness (among nestmates), increased colony longevity, and the proclivity of polygyne colonies to share workers, brood and queens among their interconnected colonies. Evaluation of pairwise co-occurrence data indicated that the pathogens and fly parasites were usually independently distributed among host colonies; however, unknown local factors did cause several significant deviations from expected values. [Copyright &y& Elsevier]

Red imported fire ant, Solenopsis invicta Buren, workers were sampled from 26 colonies in Virginia during the 2007-2008 time period. Polymerase chain reaction (PCR) assays were used to determine colony social form (monogyny or polygyny) by genotyping ants at the Gp- 9 locus. Twenty of the colonies (76.9%) were found to be polygyne. Multiplex PCR was also used to detect the presence of several organisms currently being used as biological control agents for fire ants in the U.S., including the microsporidian parasite Kneallhazia solenopsae and Pseudacteon spp . parasitioid decapitating phorid flies in the sampled colonies. Kneallhazia solenopsae was detected in 11 of 26 colonies (42%). In addition, Pseudacteon spp. flies were detected in 2 (7.7%) colonies. The sampled colonies were examined by reverse transcription PCR (RT-PCR) for the presence of Solenopsis invicta viruses -1 and -2. Results indicated that 5 colonies were infected with SINV-1 (19%) and none were infected with SINV-2. This study is the first to characterize the red imported fire ant infestation in Virginia and documents the presence of biological control agents in this area. [ABSTRACT FROM AUTHOR]