Seed damage and sources of yield loss by Sitodiplosis mosellana (Diptera: Cecidomyiidae) in resistant wheat varietal blends relative to susceptible wheat cultivars in western Canada

Spring wheat varieties with the Sm1 gene for resistance to wheat midge, Sitodiplosis mosellana (Gehin) (Diptera: Cecidomyiidae), were compared with susceptible wheat (Triticum Linnaeus; Poaceae) with respect to sources of yield loss and reduction in market value from wheat midge feeding damage. Four resistant varietal blends (90% Sm1 wheat plus 10% susceptible refuge) and four susceptible cultivars were grown in replicated experiments at eight locations in western Canada. Frequencies and 1000-kernel weights of undamaged and midge-damaged seeds were assessed before harvest by dissecting samples of ripe spikes, and after harvest in samples of cleaned grain. Spike data were used to estimate yield losses from reduced weight of damaged seeds and loss of severely damaged seeds (<= 8 mg) at harvest. Among midge-damaged seeds in spikes, few were severely damaged in resistant varietal blends, whereas most were severely damaged in susceptible cultivars. Cleaned, harvested grain of resistant varietal blends and susceptible cultivars had similar frequencies of midge damage and were assessed similar market grades. The primary benefit of midge-resistant wheat was reduced yield loss due to seed damage by wheat midge larvae. Resistant wheat did not protect against loss of market grade, but market value could increase due to larger yields.