The most effective way to reduce losses caused by the wheat stem sawfly (WSS; Cephus cinctus Norton (Hymenoptera: Cephidae) is to grow cultivars that express the solid-stem phenotype. The major locus SSt1 associated with this phenotype was previously mapped to chromosome 3BL in durum and common wheat. However, discrepancies between current wheat assemblies within the mapped genomic region have major implications both on the size of the interval, and the gene composition contained within. Comparative genomic analysis between assemblies for Svevo (durum) and Chinese Spring (wheat) identified putative structural variation within the region including large- and small-scale inversions, and sequence divergence. For this reason, we focused on detailed investigation of the SSt1 genomic interval in durum wheat. These studies revealed that the physical interval of SSt1 in the durum reference sequence spans 2.5 Mb and contains 56 genes. To determine the expression of these genes, RNA-Seq was performed on a panel of six durum cultivars with varying levels of stem-solidness, including a loss-of-function (hollow-stemmed) mutant line, “Pithless-1”, that was generated via EMS mutagenesis of the solid-stemmed cultivar CDC Fortitude. This study identified thirty-one high-confidence genes that were expressed within the SSt1 interval, of which only eight were differentially expressed between CDC Fortitude and Pithless-1. A single gene (TRITD3Bv1G280530) encoding a putative Dof (DNA-binding with one finger) transcription factor was differentially expressed between contrasting stem-types for solidness in the RNA-Seq panel. Moreover, whole genome sequencing revealed that CDC Fortitude carries multiple copies of TRITD3Bv1G280530, whereas a cluster of nine genes that includes TRITD3Bv1G280530 is deleted in Pithless-1. Copy number variation involving TRITD3Bv1G280530 was investigated using a qPCR assay in a diversity panel of 96 durum cultivars. The findings from this study showed increased copy number was associated with stem-solidness. Work is currently underway to define the functions of the identified candidate genes using gene overexpression in Pithless-1, combined with high-throughput screening of additional mutant populations. Molecular markers developed from this work are currently being used to select for WSS resistant lines in Canadian wheat breeding programs.