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 CO2 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 CO2 levels increased host plant growth and grain yield, and decreased 1000-grain dry weight compared with ambient CO2. On the contrary, aphids had a negative effect on 1000-grain dry weight. Host plants grown at elevated CO2 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 CO2 atmosphere were different. Local population of aphids, including apterous and alate forms infested on host plants in OTCs, increased with elevated atmospheric CO2 concentrations. Emigrating alate aphids captured on sticky yellow paper decreased with rising CO2. CO2 affected the reproductive activity of alate aphids. The alate forms deposited more offspring on plants grown at 550 and 750 p.p.m. CO2 compared with ambient CO2. 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.