Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2010
Publication Date: 8/24/2010
Citation: Valles, S.M., Oi, D.H., Porter, S.D. 2010. Seasonal variation and the co-occurence of four pathogens and a group of parasites among monogyne and polygyne fire ant colonies. Biological Control. 54(3):342-348. Interpretive Summary: The red imported fire ant was introduced into the United States in the 1930s and currently infests about 300 million acres. It causes approximately $6 billion in damage annually and can pose a serious threat to human health from allergic reactions. Biological control agents are thought to provide the most sustainable, cost-effective and wide-reaching control of this ant in the USA. Indeed, the major biological control agents against the fire ant in the USA currently were discovered and/or released by scientists in ARS. Studies were conducted by ARS scientists at Imported Fire Ant and Household Insects Research Unit, Gainesville, Florida to ascertain whether the current biological control agents are equally impacting single queen and multiple queen colonies of the fire ant. Data indicate that the fire ant viruses (SINV-1, SINV-2, and SINV-3) and decapitating flies (Pseudacteon species) equally infect single and multiple queen colonies. However, the microsporidian, Kneallhazia solenopsae,is more prevalent in multiple queen colonies. Thus, additional research is required to improve infections of this biological control agent in single queen colonies.
Technical Abstract: A year-long survey of 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. S. invicta colonies were sampled and examined for the presence of Pseudacteon spp. (P. curvatus, P. tricuspis, P. obtusus) parasitic flies, a microsporidian pathogen (Kneallhazia solenopsae) and 3 Solenopsis 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 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 with only a single pathogen/parasite while the majority of polygyne colonies (>55%) were infected 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.