RIFA is listed as one of the most destructive insects from a financial perspective. Areas fully infested with them become uninhabitable by humans, and they cannot be eradicated once firmly established.
DDT was found to be the most effective pesticide for use on red imported fire ants. We can thank the propaganda and lies originating from Rachel Carlson's book, Silent Spring for the continued prevalence of this invasive pest. For her efforts she may be featured on the next $20 bill after they ditch Andrew Jackson.