Gonatocerus deleoni Triapitsyn, Logarzo & Virla sp. n., reared from sentinel eggs of Tapajosa rubromarginata (Signoret) (Cicadellidae: Cicadellinae: Proconiini) on citrus plants, a new member of the ater species group of Gonatocerus Nees (Mymaridae), is described from the state of Mendoza, Argentina. Taxonomic notes and host association data are provided to help differentiate this new species from the morphologically similar but genetically distinct taxon, G. tuberculifemur (Ogloblin). The female of the latter is redescribed and the male is newly described. Gonatocerus deleoni, G. tuberculifemur, and three forms (different molecular clades) comprise the G. tuberculifemur complex. These forms are identified but not formally described because of lack of morphologically distinguishing features. The taxonomic conclusions are supported by molecular data, and by results of reciprocal cross-breeding experiments between most of them.Fil: Triapitsyn, Serguei V.. University of California; Estados UnidosFil: Logarzo, Guillermo Alejandro. United States Department of Agriculture. Agricultural Research Service; ArgentinaFil: de León, Jeese H.. United States Department of Agriculture. Agricultural Research Service; ArgentinaFil: Virla, Eduardo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentin
