Triticum aestivum, breadwheat, Triticum turgidurn. durum wheat, Mayetiola destructor, Hessian fly, leaf pubescence, resistance. SUMMARY Grain yield reductions of both breadwheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum) caused by attacks of Hessian fly (Mayetiolu destructor SAY) are second perhaps only to those caused by inadequate soil moisture in Morocco. To identify effective sources of resistance, 817 entries of common wheat and durum wheat reported to be resistant to Hessian fly were evaluated under natural infestations in Morocco. A large number of genes conferring virulence are present in populations of Moroccan Mayetiolu.The genes HI, HZ. H3, hq. He, H7. Hs, Hg, Hlo, H11, H14, HIS, and H16 as well as the 'Marquillo', 'Kawvale' and PI 94587 resistance sources are not useful for cereal improvement in North Africa. 'Luso', which has the gene H12, also appeared susceptible in limited testing. Genotypes having the genes H5 and Hi3 were identified as significantly reducing larval survial in natural populations of Mayetiolu. Of 11 resistant breadwheats identified with unknown genes, seven were from Portugal and three were from the Soviet Union. Although none of the durums tested had high levels of resistance, the two most promising durums were from Portugal. It is proposed that initially Hs be deployed in durum wheats and H13 be used in common wheat improvement. Leaf pubescence appears of little use in reducing the larval survival of Muyetiolu.