Abstract: Effects of atmospheric CO₂ concentrations (350, 550 and 700 μl/L) and soil water levels (40%, 60% and 80% field water capacities, FWC) on the population dynamics of the wheat aphid, Rhopalosiphum padi (L.) feeding on spring wheat were examined in opentopped field chambers. Results showed that: (1) Aphid density increased significantly with rising atmospheric CO₂ concentrations, the highest density occurring on wheat grown at 700 μl/L CO₂ and 60% FWC treatment; (2) Atmospheric CO₂ concentration and soil water level had significant effects on chemical components in the wheat foliage: water, soluble proteins, soluble carbohydrates, starch and tannin increased with the rising atmospheric CO₂ and FWC. Content of DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3one) increased as atmospheric the CO₂ concentration rose with the lowest DIMBOA content occurring in the 60% FWC treatment; (3) Aphid density was positively correlated with the contents of water, soluble proteins, soluble carbohydrates and starch, and negatively correlated with the contents of DIMBOA and tannin, in foliage of treated wheat. These results suggest that aphid populations will grow more rapidly in future climate conditions, especially in semiarid areas since increasing CO₂ and changes in soil moisture will alter the chemical composition of host plants.

Key words: atmospheric CO concentration, field water capacity, spring wheat, Rhopalosiphum padi, chemical composition of wheat foliage