Breeding for resistance in wheat, Triticum spp L., to Hessian fly, Mayetiola destructor (Say), has been the most successful method of controlling damage from this pest. New genes for resistance are needed because virulence evolves in Hessian fly populations. Progenies of selected plants of eight durum wheat, Triticum durum Desf., introductions were compared for expression of resistance to Hessian fly Biotype L at temperatures of 19, 23, and 26°C. Biotype L is currently the most virulent biotype identified. The eight introductions had been shown previously to be resistant to Biotypes C, D, E, and L. All tested plants of the eight introductions were resistant to Biotype L at 19°C. At 23°C, all plants of four of the introductions were resistant, and four had from 88 to 98% resistant plants. At 26&C, all plants of three introductions were resistant, whereas five introductions had from 78 to 95% resistant plants. From testcross analyses, resistance in seven of the introductions appeared to be conferred by one, two, or three dominant or partially dominant independent genes. Resistances of CI3146‐6, CI3241‐2, and CI7335‐10 were different from genes H5, H9, H14, and H16 of tester stocks. The single gene resistance of CI3146‐6 was different from genes for resistance in CI3241‐2 and CI3984‐12. The two genes for resistance of CI7066‐1 were different from H9 and the two genes of CI7041‐3. Two lines, CI3170‐2 and CI3146‐6, appeared to have one gene in common.
