We revise the genus Mecistostethus Marseul, sinking the monotypic genus Tarsilister Bruch as a junior synonym. Mecistostethus contains six valid species: M. pilifer Marseul, M. loretoensis (Bruch), comb. n., M. seagorum sp. n., M. carltoni sp. n., M. marseuli sp. n., and M. flechtmanni sp. n. The few existing records show the genus to be widespread in tropical and subtropical South America, from northern Argentina to western Amazonian Ecuador and French Guiana. Only a single host record associates one species with the ant
Pachycondyla striata Smith (Formicidae: Ponerinae), but it is possible that related ants host all the species.
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