Identifying new sources of genetic resistance to wheat stem sawfly in wild wheat species

A major pest of cultivated wheat, the wheat stem sawfly (Cephus cinctus Norton) has been a prevalent pest for over 100 years. It is difficult to estimate the damage of this insect, but conservative calculations estimate grain-yield loss to exceed 30% and the economic losses exceed $350 million annually. This estimate does not include Colorado, so we expect the current figure to be much higher.  Most economic loss is caused when the larva reaches the final instar when it creates a hibernaculum (stub) by cutting the stem above ground level just before harvest, which causes the wheat head to fall. Fallen stems are difficult to harvest and are easily blown away. Host plant resistance is considered the most effective way to manage wheat stem sawfly. The most common resistance mechanism is solid pith expression which impedes movement and increases larval mortality. However solid-stemmed cultivars yield lower when compared to hollow-stemmed cultivars and pith expression can be highly variable. There are a few other sources of resistance that have been identified but their effectiveness and durability have not been examined. Due to the limited options for resistance traits in elite germplasm, we decided to evaluate diverse wheat genetic resources for additional alleles. We used wild wheat species from the Wheat Genetics Resource Center to screen for novel wheat stem sawfly resistance alleles. Growing the wild wheat varieties in the greenhouse and infesting them in an outdoor setting allowed us to examine potential antixenosis and antibiosis resistance traits.