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Title: LONG TERM STUDIES OF THE RED IMPORTED FIRE ANT, SOLENOPSIS INVICTA, INFECTED WITH THE MICROSPORIDIA VAIRIMORPHA INVICTAE AND THELOHANIA SOLENOPSAE IN ARGENTINA

Author
item BRIANO, JUAN

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2004
Publication Date: 6/1/2005
Citation: Briano, J.A. 2005. long term studies of the red imported fire ant, solenopsis invicta, infected with the microsporidia vairimorpha invictae and thelohania solenopsae in argentina. Environmental Entomology. 34: 124-132

Interpretive Summary: The red imported fire ant is a pest in the southern United States since its accidental introduction from South America around 1930. The classical biological control is a sound alternative to reduce the risk of chemicals in the environment. A study was conducted in Argentina, the native land of the red imported fire ant, where field plots were established and checked periodically to study the impact of two local diseases of fire ants. In a four-year period, the density of infected populations of fire ants diminished 69%. It was also observed that infected colonies were smaller than healthy ones. These results, combined with additional evidence reported previously, suggest that the infections have deleterious effect on native populations of fire ants and could be used in biological control programs in the United States.

Technical Abstract: A study was conducted on populations of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), infected with the microsporidia Vairimorpha invictae Jouvenaz and Ellis (Microsporida: Burenellidae) and Thelohania solenopsae Knell, Allen, and Hazard (Microsporida: Thelohaniidae). Fire ant populations and microsporidia prevalence were monitored 3-5 times per year from May 2000 to March 2004 in six field plots in northern Argentina. The mean population index per plot showed an overall reduction of 69%. The percentage of infection with V. invictae and T. solenopsae showed fluctuations that ranged from 29.2 to 2.1%. The highest infection rates were observed at the beginning of the study. A total of 394 colonies were sampled during the study, 325 (82.5%) were healthy and 69 (17.5%) were infected with microsporidia. The proportion of infected colonies with brood was 81% (56/69), similar to the proportion of healthy colonies with brood, 78% (255/325). The proportion of infected and healthy colonies in the population index categories was significantly different. Of the infected colonies with brood, 49.3% were medium and 1.4% were large in size. In contrast, healthy colonies were generally larger, with 29.7 and 10.4% being medium and large, respectively. The general environmental conditions in the area of the plots were appropriate for fire ant population growth, consequently, they do not explain the overall reduction in the populations. These results, combined with additional evidence reported previously, suggest that the infection with V. invictae and T. solenopsae has deleterious effect on native populations of S. invicta.