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Hessian fly [Mayetiola destructor (Say)] is a serious pest of wheat (Triticum ssp.) in many wheat growing areas of the world. A number of genes (H1‐H26) that confer resistance to Hessian fly have been described. The linkage relationships of many of these genes, which are useful in breeding wheat for resistance to Hessian fly, are unknown. Testcross analyses were made in tetraploid durum wheat(Triticum turgidum L.) and tested to biotype D of Hessian fly to determine the linkage relationships among genes H9, H10, H12, H14, H15, H16 and HI7, all conferring resistance to biotype D. Also, monosomic 5A plants of susceptible cultivar Chinese Spring were crossed as seed parents to Purdue wheat (T. aestivum L. em Thell.) lines carrying gene H10 or H12. Testcross analyses indicated that six of these genes appear to occupy a single linkage block on wheat chromosome 5A in the order H9 to H15, HIO, H17, H16, and H12. Gene H14 did not appear to be within the linkage block H9 to H12. Additionally F2 plants derived from 41‐chromosome F1 plants and F1 families derived from F2 resistant plants were tested against biotype D. F2 segregation deviated significantly from 3 resistant : 1 susceptible and F3 families from resistant F2 plants deviated significantly from 1 resistant: 2 segregating for both crosses involving H10 and H12. Thus, monosomic analyses provided additional evidence that genes H10 and H12 are likely on chromosome 5A. Linkage between these genes would not seriously limit efforts to pyramid them in breeding for resistance to the Hessian fly because the linkage values are more than 20 centimorgans.

Forty-one accessions of primitive and wild wheats (Triticum species), 16 accessions of Aegilops species, and 20 accessions or cultivars of Agropyron species were evaluated for the first time for reaction to biotype L of Hessian fly (Mayetiola destructor). Three accessions of Triticum monococcum, 13 accessions of Aegilops species, and 13 accessions or cultivars of Agropyron species were found homogeneously resistant. Antibiosis was operative in some cases but in others there appeared to be physical resistance due to the presence of leaf pubescence or ligule. Pubescence of Triticum boeoticum was not effective in providing resistance.

Hessian fly (Mayetiola destructor) is a serious pest of wheat (Triticum spp.) and of the reported biotypes of Hessian fly, biotype L is described as the most virulent. Inheritance of resistance to Hessian fly biotype L was investigated in crosses of a resistant accession of Triticum monococcum, and two susceptible accessions of T. monococcum and one susceptible accession of T. boeoticum, all diploid wheats. F2 and testeross (backeross) families were classified for reaction to Hessian fly in the seedling stage and analysed by Chi-square goodness-of-fit tests for genetic segregation ratios of resistant or segregating families to susceptible families. Resistance was found to be simply inherited, controlled by one or two genes. This is the first report on the inheritance of resistance to Hessian fly in A-genome diploid wheats, and simple genetic control indicates possibility of transfer of this trait to cultivated wheats.

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