Topical toxicity of four active ingredients on Atta sexdens workers

Abstract

Leaf-cutting ants are economically important pest insects in the Neotropical region. They forage on fresh leaves and flowers that serve as substrates for the cultivation of their mutualistic fungus, which they feed upon. The main active ingredient for their control is sulfluramid, but the restriction of its use is under discussion. In this study, the topical toxicity of four active ingredients on Atta sexdens workers was evaluated, determining the median lethal dose (LD50), median lethal time (LT50), and control efficiency, with the prospect of identifying them as potential contact formicides. Values of LD50 were obtained after observation of mortality and subsequent probit analysis. Sulfluramid presented the highest value (245.33 μg mL-1), followed by diafenthiuron (42.53 μg mL-1) and indoxacarb (7.29 μg mL-1). The imidacloprid LD50 was about 40-fold lower than the sulfluramid LD50 (6.27 μg mL-1). The LT50 values were higher for sulfluramid and diafenthiuron. Indoxacarb and imidacloprid presented control efficiency greater than 90%, and the linear model was significant for all active ingredients. The results obtained in this study indicate that indoxacarb and imidacloprid are fast-acting potential formicides for contact formulations, but not are feasible for use in formicide baits.