Response of the pea aphid ( Acyrthosiphon pisum) to variation in dietary levels of sugar and amino acids: the significance of amino acid quality

Abstract

Growth, survivorship and food intake were measured for newborn pea aphids maintained on one of 25 chemically-defined diets varying in sucrose and amino acid content (200–1000 and 50–250 mM, respectively), with amino acids comprising 20:80 essential/non-essentials (e:n). Survivorship varied positively with dietary amino acid concentration, while dry weight growth was strongly affected by concentration of amino acids and sucrose, and also by the ratio of sucrose to amino acids (s:aa). Peak performance was achieved on the diet containing 800 mM sucrose and 200 mM amino acids. This was a lower s:aa ratio than that which supported maximal growth in previous experiments for aphids reared on diets containing 50:50 e:n. Comparison of plots for final dry weight against s:aa ratio indicated that the 20:80 e:n amino acid mixture supported growth ca. 60% of that on the 50:50 e:n mix. When the scaling of the s:aa ratio was adjusted accordingly, the plots for 20:80 and 50:50 e:n converged in all but elevation; a difference which represented the extra growth costs of feeding on 20:80 e:n diets. Analysis of diet consumption showed that these costs were associated with, and perhaps attributable to, inhibition of compensatory feeding.