Impacts of elevated CO₂ on the population abundance and reproductive activity of aphid Sitobion avenae Fabricius feeding on spring wheat

Spring wheat ( Triticum aestivum L. cv. Kehan 50) plants were grown in pots under three atmospheric CO 2 concentrations (ambient, 550 and 750 p.p.m.) in field open‐top chambers (OTCs), with half of the plants subjected to aphid ( Sitobion avenae Fabricius) infestation. Increase in CO 2 levels increased host plant growth and grain yield, and decreased 1000‐grain dry weight compared with ambient CO 2 . On the contrary, aphids had a negative effect on 1000‐grain dry weight. Host plants grown at elevated CO 2 generally had greater ear starch, sucrose, glucose, total non‐structure carbohydrates (TNCs), ratio of TNC : nitrogen, free amino acids and soluble protein and less ear fructose and nitrogen. However, the aphids did not affect the ear nitrogen and ratio of TNC : nitrogen. The responses of apterous and alate aphids to enrichment CO 2 atmosphere were different. Local population of aphids, including apterous and alate forms infested on host plants in OTCs, increased with elevated atmospheric CO 2 concentrations. Emigrating alate aphids captured on sticky yellow paper decreased with rising CO 2 . CO 2 affected the reproductive activity of alate aphids. The alate forms deposited more offspring on plants grown at 550 and 750 p.p.m. CO 2 compared with ambient CO 2 . Both population abundance of local aphids and reproductive activity of alate aphids correlated positively with ear starch, sucrose, glucose, TNCs, raito of TNC : nitrogen and free amino acids, while negatively with ear fructose and nitrogen. Moreover, emigration population abundance was related negatively with ear starch, sucrose, glucose, TNCs, ratio of TNC : nitrogen and free amino acids and positively with ear fructose and nitrogen.