Vera, C. L., Fox, S. L., DePauw, R. M., Smith, M. A. H., Wise, I. L., Clarke, F. R., Procunier, J. D. and Lukow, O. M. 2013. Relative performance of resistant wheat varietal blends and susceptible wheat cultivars exposed to wheat midge, Sitodiplosis mosellana (Géhin). Can. J. Plant Sci. 93: 59-66. Wheat midge, Sitodiplosis mosellana (Géhin), causes significant yield losses to spring wheat in western Canada. To mitigate these losses, midge-resistant wheat varietal blends, consisting of cultivars with the Sm1 midge resistance gene and containing 10% of a midge susceptible cultivar (interspersed refuge), were made available to farmers. To test their performance relative to conventional midge-susceptible cultivars, four varietal blends were grown during four consecutive growing seasons at eight locations in the provinces of Manitoba, Saskatchewan and Alberta, Canada, and compared with four conventional midge-susceptible cultivars. Midge damage varied from year to year during the 4-yr study. In general, the varietal blends, as a group, yielded more grain than the susceptible cultivars, especially when grown in environments with high (12.8%) seed damage. In environments with low (0.9%) seed damage, the varietal blend yield increases were smaller but still significant, suggesting that some of the varietal blends may be endowed with additional superior attributes, unrelated to midge resistance. The Sm1 gene was independent of time to heading and maturity, plant height, lodging and seed weight.