A four-year field survey of wheat, barley, and corn generated data on 10 species of fungal pathogens, including eight Entomophthorales and two Hyphomycetes recovered from 2,930 cadavers of aphids infesting grains grown under irrigation in southwestern Idaho. Seven species of cereal aphids, including the Russian wheat aphid,Diuraphis noxia(Mordvilko); the potato aphid,Macrosiphum euphorbiae(Thomas);Metopolophium dirhodum(Walker); the corn leaf aphid,Rhopalosiphum maidis(Fitch); the bird-cherry oat aphid,R. padi(L.); the greenbug,Schizaphis graminum(Rondani); and the English grain aphid,Sitobion avenae(F.), were recorded as hostsof one or more species of entomopathogenic fungi. The fungi were identified asPandora neoaphidis(Remaudière&Hennebert) Humber,Conidiobolus obscurus(Hall&Dunn) Remaudière&Keller,C. coronatus(Costantin),C. thromboidesDrechsler,Entomophthora chromaphidisBurger&Swain,Neozygites fresenii(Nowakowski) Remaudière&Keller,Zoophthora radicans(Brefeld) Batko,Z. occidentalis(Thaxter) Batko,Beauveria bassiana(Balsamo) Vuillemin, andVerticillium lecanii(Zimmermann) Viégas.P. neoaphidiswas the most prevalent species annually in populations ofM. dirhodumandD. noxiaand also frequently infected other hosts.Conidiobolusspp. were secondary toP. neoaphidisin occurrence, commonly infecting several aphid species.E. chromaphidis, N. fresenii, Z. radicans, andZ. occidentaliswere recovered only occasionally and on fewer aphid species. Two Hyphomycetes,B. bassianaandV. lecanii, infected aphids in the field at very low levels compared with the Entomophthorales. All species, exceptN. freseniiandZ. occidentalis, were isolated from their aphid hosts with agar media (SDAY or SEMA, or both) or liquid insect tissue culture medium.