Technical Abstract: The impact of feeding injury by the Russian wheat aphid, Diuraphis noxia (Mordvilko), and bird cherry oat aphid, Rhopalosiphum padi (L.), (Hemiptera: Aphididae) on susceptible and resistant wheat, Triticum aestivum L., near-isogenic lines ‘Tugela’ (susceptible), Tugela-Dn1 (antibiotic), -Dn2 (tolerant), and -Dn5 (antixenotic) was evaluated by assessing photosynthetic parameters. Photosynthesis and closely related parameters, pigment composition, and non-structural carbohydrates were measured at 1, 3, and 9 d after aphids were introduced on plants maintained under greenhouse conditions. Overall, R. padi had a higher reproductive capacity within a period of 9 d compared to D. noxia on all lines except for Tugela-Dn2. Although the visible injury symptoms associated with aphid injury can be highly species specific, the data indicate that photosynthetic reduction is a common physiological pattern of wheat response to aphid feeding, irrespective of chlorosis elicitation. Although both aphids negatively affected net photosynthesis, D. noxia had a greater impact than R. padi, even when aphid numbers were considerably fewer (100-150 aphids per plant) for D. noxia compared to R. padi (greater than 200 aphids per plant). The photosynthetic pigment and carbohydrate quantification data suggest that the initial net photosynthesis reduction elicited by aphid feeding may not be directly related to the light reaction portion of the photosynthetic pathway via pigment losses. It is also unlikely that source-sink manipulation is the primary cause for the observed short-term inhibition of photosynthesis.