How insect herbivores alter plant physiology is often unknown, so not surprisingly the interaction of plant resistance with insect injury is similarly uncertain. The recent discovery of a new virulent population of Russian wheat aphid, Diuraphis noxia (Mordvilko), induces responses from resistant wheat that indicates the aphid has found a way to circumvent resistant genes. The avirulent aphid population compared with the new virulent aphid population may give insight into how this insect alters the physiology of a plant. The impact aphid feeding has on physiological responses of resistant (Prairie Red) and susceptible (TAM 107) wheat was documented through the following photosynthetic responses: carbon exchange measurements, carbon assimilation (A-Ci) curves, chlorophyll fluorescence kinetic measurements, invertase activity measurements, and glucose concentrations. Results for these methods will be presented at the meeting.