Hessian fly (Diptera : Cecidomyiidae) larval survival as affected by wheatresistance alleles, temperature, and larval density

The effects of allelic dosage of wheat resistance genes; larval density; an d temperature on the expression of resistance and on Hessian fly, Mayetiola destructor (Say), larval survival was studied in a growth chamber. Wheat p lants homozygous and heterozygous for resistance genes H3, H5, H7H8, H9, H1 0, and H11 expressed a high level of resistance as indicated by levels of p lant damage. Plants heterozygous for the H6 gene were only moderately resis tant. Little or no larval survival occurred on resistant plants homozygous and heterozygous for the H13 and H22 genes. However, significantly more lar vae survived on resistant plants heterozygous for the H3, H5, H6, H7H8, H9, H10, or H11 genes compared to the corresponding homozygous plants. Thus, l arval survival on resistant heterozyous plants rather than levels of plant damage appears to be the best criterion to determine if a resistance gene h as complete or incomplete dominance. Wheats with resistance genes H1H2, H7H 8, H11, and H13 expressed a high level of resistance across all egg (larval ) densities (5, 10, 20 eggs per plant) and temperature. Larval survival inc reased on resistant plants having H1H2 and H7H8 genes as egg density and te mperature (18, 24, 28 degrees C) increased, with the highest survival recor ded at 24 degrees C. Little or no larval survival occurred on resistant pla nts carrying the XII or H13 genes across density and temperature treatments .