Response of amino acid changes in Aphis gossypii (Glover) to elevated CO₂ levels

Effects of elevated CO 2 levels on the amino acid constituents of cotton aphid, Aphis gossypii (Glover), fed on transgenic Bacillus thuringiensis (Berliner) (Bt) cotton [ Cryl A(c) ], grown in ambient and double‐ambient CO 2 levels in closed‐dynamics CO 2 chambers, were investigated. Lower amounts of amino acids were found in cotton phloem under elevated CO 2 than under ambient CO 2 levels. However, higher amounts of free amino acids were found in A. gossypii fed on elevated CO 2 ‐grown cotton than those fed ambient CO 2 ‐grown cotton, and the contents of amino acids in honeydew were not significantly affected by elevated CO 2 levels. A larger amount of honeydew was produced by cotton aphids feeding on leaves under elevated CO 2 treatment than those feeding on leaves under ambient CO 2 treatment, which indicates that A. gossypii ingests more cotton phloem because of the higher C:N ratio of cotton phloem under elevated CO 2 levels. Moreover, the amino acid composition was similar in bodies of aphids ingesting leaves under both CO 2 treatments, except for two alkaline amino acids, lysine and arginine. This suggests that the nutritional constitution of the phloem sap was important for A. gossypii . Our data suggest that more phloem sap will be ingested by A. gossypii to satisfy its nutritional requirement and balance the break‐even point of amino acid in elevated CO 2 . Larger amounts of honeydew produced by A. gossypii under elevated CO 2 will reduce the photosynthesis and result in the occurrence of some Entomophthora spp.