Elevated CO2 and O3 alter the feeding efficiency of Acyrthosiphon pisum and Aphis craccivora via changes in foliar secondary metabolites

Elevated CO2 and O-3 can affect aphid performance via altering plant nutrients, however, little is known about the role of plant secondary metabolites in this process, especially for aphids feeding behaviors. We determined the effects of elevated CO2 and O-3 on the growth and phenolics of alfalfa (Medicago sativa) and feeding behaviors of the pea aphids (Acyrthosiphon pisum) and cowpea aphids (Aphis craccivora). Elevated CO2 improved plant growth, but could not completely offset the negative effects of elevated O-3. Elevated O-3 increased foliar genistin content at the vegetative stage, increased ferulic acid at the reproductive stage, and elevated CO2 increased those at both stages. Simultaneously elevated CO2 and O-3 increased foliar ferulic acid content at the reproductive stage and increased genistin content at both stages. For pea aphids, feeding efficiency was reduced under elevated CO2 at the reproductive stage and decreased under elevated O-3 at the vegetative stage. For cowpea aphids, feeding efficiency was increased under elevated CO2 at the vegetative stage and decreased under elevated O-3 at both stages. Simultaneously elevated CO2 and O-3 decreased both aphids feeding efficiency. We concluded that CO2 and O-3 independently or interactively had different effects on two aphids feeding behaviors through altering foliar ferulic acid and genistin contents.