A 2-yr study of the impacts of the red imported fire ant, Solenopsis invicta Buren, on the success of Cyrtobagous salviniae Calder & Sands as a biological control agent of common salvinia, Salvinia minima Baker, was undertaken in southern Louisiana. Floating moats were constructed around 8 release sites where C. salviniae was introduced as a biological control agent. These moats were used to restrict access to the release site by red imported fire ants in half the quadrats. Moating was successful in limiting the number of red imported fire ants in the release sites over the course of the study (P < 0.0001). In 2010, locations where access by red imported fire ants was limited by the presence of a moat had lower biomass (P = 0.04) and higher populations of C. salviniae (P < 0.0001). Our study suggests that the presence of red imported fire ants negatively impacts the success of C. salviniae as a biological control agent.