A new species of the genus Neotropiconyttus Kirkaldy, 1909 (Hemiptera: Heteroptera: Reduviidae: Harpactorinae: Harpactorini) is described and illustrated. Neotropiconyttus armandoi Gamboa & Gil-Santana, sp. nov. represents the first record of the genus for the Province of Napo in Colombia, and the first description of a male individual in the genus. The male specimen representing the new species was collected on a leaf of cacao (Theobroma cacao L.-Malvaceae). Its remarkable similarity in external coloration and structure with that of the true bug Monalonion dissimulatum Distant, 1883 (Hemiptera: Miridae) inhabiting cacao agroforestry systems suggests that the new species could be part of a mimetic complex that incorporates phytophagous and predator bugs. Comments and figures of type specimens of Neotropiconyttus alboannulatus (Stål, 1855) and Neotropiconyttus dama (Burmeister, 1838), and a key to the species of the genus are also provided.