Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/3/2002
Publication Date: 4/1/2003
Citation: VALLES, S.M., PEREIRA, R.M. Hydramethylnon Potentiation in Solenopsis invicta by Infection with the Microsporidium, Thelohania solenopsae. BIOLOGICAL CONTROL. 2003. v. 27. p. 95-99. 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 significant economic losses in livestock and agricultural production and poses a serious threat to human health. Annually, 50% of people in infested areas are stung, occasionally with fatal consequences. A promising biological control agent of the red imported fire ant is Thelohania solenopsae, an intracellular parasite. Development of Thelohania solenopsae as a biological control agent will depend on elucidation of the life cycle. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have developed a molecular technique (PCR) capable of detecting Thelohania solenopsae at all stages of its development. This method is a significant improvement upon existing methods and will aid the discovery of the life cycle and its subsequent dissemination.
Technical Abstract: Laboratory and field evaluations were conducted in which hydramethylnon treatments were made against S. invicta individuals and colonies that were either infected or uninfected with Thelohania solenopsae. In laboratory experiments, polygynous T. solenopsae-infected colonies of S. invicta exhibited significantly greater cumulative mortality than uninfected colonies when exposed to hydramethylnon. By day 21, nearly 100% of the individuals in the T. solenopsae-infected colonies were dead while only about 50% of the individuals in the uninfected colonies were dead. In addition to a higher cumulative mortality among T. solenopsae-infected workers, queens from infected colonies also exhibited higher mortality than those from uninfected colonies. Similar results were observed in field studies in which fire ant infested pasture was treated with hydramethylnon. The number of T. solenopsae-infected colonies decreased much faster relative to uninfected colonies in the same area. The initial rate of decline was 1.3 mounds/plot/day among T. solenopsae-infected colonies compared with a decrease of 0.4 mounds/plot/day among uninfected colonies. Insecticide toxicity bioassay data supported our hypothesis that T. solenopsae infection can potentiate the toxicity of hydramethylnon. T. solenopsae-infected workers were 2.4-fold more susceptible to hydramethylnon than uninfected workers in toxicity bioassays.