Kneallhazia Research Articles

Prevalence and Genetic Diversity of a Microsporidian Parasite in the Black Imported Fire Ant and Its Social Parasitic Ant (Formicidae: Myrmicinae: Solenopsis) in Buenos Aires Province, Argentina.

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.

Introduction of Fire Ant Biological Control Agents into the Coachella Valley of California

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.

The Red Imported Fire Ant (Hymenoptera: Formicidae) in the West Indies: Distribution of Natural Enemies and a Possible Test Bed for Release of Self-Sustaining Biocontrol Agents

Abstract 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 sampl...

Mitigating the allergic effects of fire ant envenomation with biologically based population reduction

To describe the current efforts to use biological control agents to reduce fire ant population levels, thus ultimately reducing the number of human sting and allergic reaction incidents. Climate change and worldwide fire ant expansion will increase the frequency of human encounters and allergenic events, putting additional pressure on the public health sector. Six species of fire ant decapitating flies are now established in the United States. The microsporidium Kneallhazia solenopsae is well established and new fire ant hosts have been identified. The fire ant virus Solenopsis invicta virus 3 shows good potential for use as an environmentally friendly biopesticide because of its virulence and host specificity. During separate founding events in the United States, Australia, mainland China, and Taiwan, fire ants native to South America escaped their native pathogens and parasites. Consequently, fire ant populations in these introduced regions pose a serious public health threat to the human populations by envenomation and subsequent allergic reactions. Specific, self-sustaining biological control agents have been discovered, studied, and released into fire ant populations in the United States in an effort to re-establish an ecological/competitive balance, resulting in reduced fire ant densities and human exposure.

Molecular diversity of the microsporidium Kneallhazia solenopsae reveals an expanded host range among fire ants in North America

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.

Seasonal variation and the co-occurrence of four pathogens and a group of parasites among monogyne and polygyne fire ant colonies

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.

Characterization ofSolenopsis invicta(Hymenoptera: Formicidae) Populations in Virginia: Social form Genotyping and Pathogen/Parasitoid Detection

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 Gp9 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.Se realizó un muestreo de las obreras de la hormiga de fuego roja importada, Solenopsis invicta Buren, en 26 colonias en el estado de Virginia durante el período del 2007 al 2008. Se utilizaron ensayos de la reacción en cadena por la polimerasa (RCP) para determinar la forma social de la colonia (monoginia = una sola reina reproductive) o poliginia = reinas multiples) por medio del genotipo de las hormigas en el locus Gp-9. Se encontró que veinte de las colonias (76.9%) fueron poliginias. Se usó RCP múltiplex para detectar la presencia de varios organismos que estan usando actualmente como agentes de control biológico para las hormigas de fuego en los Estados Unidos, incluyendo el parasito microesporidiano Kneallhazia solenopsae, y la mosca Pseudacteon spp. (Diptera: Phoridae) que son parasitoides que decapitan las hormigas en las colonias muestreadas. Kneallhazia solenopsae fue detectado en 11 de las 26 colonias (42%). Además, se detectaron las moscas Pseudacteon spp. en dos (7.7%) de las colonias. Se examinaron las colonias muestreadas por la transcripción reversa de RCP (TR-RCP) para la presencia de los virus 1 y 2 de Solenopsis invicta. Los resultados indican que las 5 colonias fueron infectadas con SINV-1 (19%) y ninguna fue infectada con SINV-2. Este es el primer studio que caractiza la infestación de la hormiga de fuego roja importada en Virginia y documenta la presencia de agentes de control biológico en esta área.

Kneallhazia(=Thelohania)SolenopsaeInfection Rate ofPseudacteon curvatusFlies Determined by Multiplex PCR

A multiplex PCR method was developed and used to determine the infection rate of Kneallhazia solenopsae in individual Pseudacteon curvatus flies in north-central Florida. Among P. curvatus flies infected with K. solenopsae, 2 amplicons were produced, one of 800 nucleotides from the P. curvatus 18S rRNA gene, and one of 318 nucleotides from the K. solenopsae 16S rRNA gene. Multiplex PCR of DNA extracted from P. curvatus flies was capable of detecting 117.5 ± 82.7 K. solenopsae spore equivalents. The mean K. solenopsae infection rate of P. curvatus from 4 sites in Gainesville and Williston, Florida, was 12.3 ± 5.0%. The K. solenopsae infection rate for P. curvatus was independent of the K. solenopsae infection rate observed among S. invicta nests from where the fly collections took place. Not all P. curvatus flies that developed in K. solenopsae-infected fire ants were positive for K. solenopsae upon eclosion. Among 50 P. curvatus flies known to develop in K. solenopsae-infected S. invicta workers, 12 (24%) were positive for K. solenopsae at eclosion.

Pseudacteon decapitating flies (Diptera: Phoridae): Are they potential vectors of the fire ant pathogens Kneallhazia (= Thelohania) solenopsae (Microsporidia: Thelohaniidae) and Vairimorpha invictae (Microsporidia: Burenellidae)?

Fire ant decapitating flies in the genus Pseudacteon were tested for their potential as hosts or vectors of two microsporidian pathogens of the red imported fire ant, Solenopsis invicta. Decapitating flies that attacked or were reared from S. invicta workers infected by Kneallhazia (= Thelohania) solenopsae or Vairimorpha invictae were tested for either pathogen by polymerase chain reaction (PCR) tests or visual examination for spores using phase microscopy. Three species of fire ant decapitating flies acquired the pathogen, Kneallhazia solenopsae. K. solenopsae was detected in 58% of pooled samples of Pseudacteon obtusus flies and 44% of pooled samples of Pseudacteon cultellatus that developed in K. solenopsae-infected fire ant workers. K. solenopsae was also found in 17% of pooled samples of field-collected Pseudacteon curvatus. In contrast, the microsporidium V. invictae was not detected in P. obtusus reared from V. invictae-infected S. invicta workers. Neither K. solenopsae nor V. invictae were detected in any of the hovering or ovipositing flies in the laboratory exposures, indicating no mechanical acquisition of the microsporidia occurred during oviposition activity. Greater than 92% of the P. obtusus that developed in K. solenopsae-infected ants survived and emerged as adults, thus indicating no detrimental effects of the microsporidium on pupal development and emergence. These results indicate that Pseudacteon decapitating flies may be able to vector K. solenopsae but not V. invictae among fire ants. Further tests are planned to determine if flies containing K. solenopsae are capable of transferring this pathogen either during oviposition or by being consumed by fire ant larvae.

Biology and life-cycle of the microsporidium Kneallhazia solenopsae Knell Allan Hazard 1977 gen. n., comb. n., from the fire ant Solenopsis invicta

Thelohania solenopsae is a unique microsporidium with a life-cycle finely tuned to parasitizing fire ant colonies. Unlike other microsporidia of social hymenopterans, T. solenopsae infects all castes and stages of the host. Four distinctive spore types are produced: diplokaryotic spores, which develop only in brood (Type 1 DK spores); octets of octospores within sporophorous vesicles, the most prominent spore type in adults but never occurring in brood; Nosema-like diplokaryotic spores (Type 2 DK spores) developing in adults; and megaspores, which occur occasionally in larvae 4, pupae, and adults of all castes but predominantly infect gonads of alates and germinate in inseminated ovaries of queens. Type 2 DK spores function in autoinfection of adipocytes. Proliferation of diplokaryotic meronts in some cells is followed by karyogamy of diplokarya counterparts and meiosis, thereby switching the diplokaryotic sequence to octospore or megaspore development. Megaspores transmit the pathogen transovarially. From the egg to larvae 4, infection is inapparent and can be detected only by PCR. Type 1 DK spore and megaspore sequences are abruptly triggered in larvae 4, the key stage in intra-colony food distribution via trophallaxis, and presumably the central player in horizontal transmission of spores. Molecular, morphological, ultrastructural and life-cycle data indicate that T. solenopsae must be assigned to a new genus. We propose a new combination, Kneallhazia solenopsae.