none. A field study was carried out in Lapa, Parana, from June to October, 1977, in order to investigate the occurrence of natural enemies of barley crop aphids. Whole plant examination, water traps, and pitfall traps were used to estimate the populations. Aphid mortality by the entomogenous fungi Entomophthora spp. reached 21.2% in Metopolophium dirhodum (Walker, 1849) and 18.5% in Sitobion avenae (Fabricius, 1794), with the highest level after the peak of the aphids. A single species of parasitoid, Aphidius colemani Viereck, 1912 (Hym., Aphidiidae), was obtained from aphids, specially Schizaphis graminum (Rondani, 1852), Rhopalosiphum maidis (Fitch, 1856) and R. padi (Linnaeus, 1758). One hyperparasitoid was also found, Alloxysta brassicae (Ashmead, 1887) (Hym., Cynipidae). The most abundant predators were Allograpta exotica (Wiedmann, 1830) (Dip., Syrphidae) and Eriopis connexa (Germar, 1824) (Col. Coccinellidae). Some pupae of A. exotica were parasitized by Ethelurgus rufipes (Brethes, 1909) (Hym., Ichneumonidae) and Pachyneuron albutius Walker, 1843 (Hym., Pteromalidae).