A new species of Andricus Hartig 1840 (Hymenoptera: Cynipidae: Cynipini) is described from Panama: Andricus barriosi sp. nov. The new species induces galls on Quercus bumelioides Liebm. and Q. insignis M. Martens Galeotti (Fagaceae, sect. Quercus) and is the first species of the genus Andricus 'sensu lato' recorded from Panama. Andricus barriosi is part of a species complex that includes A. nievesaldreyi Pujade-Villar, A. georgei Pujade-Villar and A. maesi Pujade-Villar, which differ from the other species of the genus Andricus by having a characteristic striate-reticulate sculpture on the second metasomal tergum that is typically smooth in the other Andricus species. The diagnostic characters, gall description, distribution and biological data of the new species are given, and a key for the differentiation of the new species from related species is also provided.
Keywords: Hymenoptera, Cynipidae, oak gall wasps, Quercus, Chiriquí, Panama.