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Keywords:

  • amino acids;
  • cotton aphid;
  • elevated CO2;
  • honeydew;
  • phloem sap

Abstract

Effects of elevated CO2 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 CO2 levels in closed-dynamics CO2 chambers, were investigated. Lower amounts of amino acids were found in cotton phloem under elevated CO2 than under ambient CO2 levels. However, higher amounts of free amino acids were found in A. gossypii fed on elevated CO2-grown cotton than those fed ambient CO2-grown cotton, and the contents of amino acids in honeydew were not significantly affected by elevated CO2 levels. A larger amount of honeydew was produced by cotton aphids feeding on leaves under elevated CO2 treatment than those feeding on leaves under ambient CO2 treatment, which indicates that A. gossypii ingests more cotton phloem because of the higher C:N ratio of cotton phloem under elevated CO2 levels. Moreover, the amino acid composition was similar in bodies of aphids ingesting leaves under both CO2 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 CO2. Larger amounts of honeydew produced by A. gossypii under elevated CO2 will reduce the photosynthesis and result in the occurrence of some Entomophthora spp.