As a major pest of wheat, the wheat stem sawfly (Cephus cinctus Norton) causes yield loss by larval feeding in the stem lumen during crop development. Successful feeding and development results in girdled stems of the mature crop - which typically lodge. Yield loss estimates at harvest are historically based on detailed measurement of outcomes of individual stems using life table classification for mortality (dying due to plant defense, parasitoids, or unknown) - or survival to stem girdling in infested stems. These estimates are incomplete because at the stem level, uninfested stems are treated as single entities. Yet, the architecture of wheat plants typically yields several stems (or tillers) per seed planted, with tillers arising from the base of the primary stem early in development. Potential interactions between uninfested and infested stems of the same plant could cause yield outcomes for these systemic connections via mechanisms of either compensation, tolerance, or loss. Using detailed greenhouse experiments to characterize the yield outcomes for all stems of infested plants shows that neither positive compensation nor static tolerance is likely. Rather yield loss appears to be systemic, with varying outcomes possible in uninfested stems, depending on whether primary stems or tillers are impacted. Losses due to wheat stem sawfly injury in wheat plants were found to be greater than for the infested stems only, making it likely that broad estimates of regional yield impacts are too conservative.