Abstract:Two wheat varieties, MY169 (susceptible) and KOK1679 (resistant) were planted in controlled chambers under elevated CO2 (0.7 mL/L) and ambient CO2 concentrations (0.35 mL/L, as control) conditions for 30 d. Feeding behaviors of wheat aphids, Sitobion avenae (Fabricius), on seedling plants were observed and recorded with electrical penetration graph (EPG). Increased number of potential drop waveform (pd waveform), prolonged total time of mechanical stylet penetration (total time of C waveform), delayed initial time of 1st probing from phloem (time to 1st E2 waveform) and extended sustaining time of passive ingestion were observed in S. avenae fed on wheat plants grown under elevated CO2 than that under ambient CO2 condition. The change of feeding behavior of wheat aphids was probably resulted from the change of host plants grown under elevated CO2 concentration condition.