Impacts of atmospheric CO2 concentrations and soil water on the population dynamics, fecundity and development of the bird cherry-oat aphid Rhopalosiphum padi.

The impacts of elevated CO₂ and soil water on the population dynamics, adult fecundity and nymphal period of the bird cherry-oat aphid Rhopalsiphum padi (Linnaeus) were evaluated in three experiments: (i) Combined effects of CO ₂ and soil water on aphid populations. Spring wheat was grown in pots at three CO₂ concentrations (350, 550 and 700 ppm) and three soil water levels (40%, 60% and 80% of field water capacity, FWC) in field open-top chambers (OTC) and infested with the bird cherry-oat aphid. Aphid population dynamics were recorded throughout the growing season; at the same time, adult fecundity and duration of the nymphal period were recorded. Chemical composition of spring wheat leaves was also analyzed. (ii) Indirect effects of CO ₂ concentrations and soil water on aphid adult fecundity and nymphal period. The experiment was conducted with the leaf discs method in the laboratory. Aphids were reared on leaf discs excised from the treated wheat in OTC with different CO₂ and soil water levels. (iii) Direct effects of CO ₂ concentrations on aphid adult fecundity and nymphal period. Aphids were reared on leaf discs excised from the wheat grown under natural conditions. The experiment was conducted with the leaf disc method in OTC with the three CO₂ concentrations. It was found that the direct effect of CO₂ concentration on aphid population parameters was minor. CO₂ and soil water affected aphid population indirectly through their effects on wheat characteristics. The aphid population under 550 ppm CO₂ was far larger than the one under 350 ppm CO₂, whereas the population under 700 ppm CO₂ was slightly higher than that under 550 ppm CO₂. The largest aphid population was obtained with the 60% soil water treatment, regardless of CO₂ treatment. The effects of CO₂ concentration on aphid population were, however, not significantly correlated with soil water level. Adult fecundity increased with CO₂ concentration, the highest fecundity being achieved under 60% FWC treatments. The nymphal period was not affected by CO₂ concentration. The shortest period occurred under 60% FWC. Atmospheric CO₂ and soil water had significant effects on the chemical composition of the wheat leaves. Aphid population size was positively correlated with leaf water content, concentrations of soluble proteins, soluble carbohydrates and starch, and negatively correlated with DIMBOA and tannins concentrations. [ABSTRACT FROM AUTHOR]