Effect of dietary leucine concentration on pea aphid (A. pisum) performance and behaviour.
A. Aphid growth for different leucine concentrations in the diet. The results (means ± SE, n = 54) are expressed as a percentage of the aphid growth on the 20 mM leucine control diet and compared using a Tukey–Kramer HSD test. Conditions with different letters show statistically different means at 95% confidence level.
B. The behavioural response of A. pisum to variations in dietary leucine concentration has been evaluated in choice tests, comparing the different tested concentrations with the control diet. Diet Preference Index (DPIx) quantifies the choice of test diet over the control (1 is complete preference of the tested diet over the control, −1 is the reverse). Statistical significance is given following a Wilcoxon non-parametric signed rank test testing DPIx = 0 at 95% confidence level: • no significant difference between the observed DPIx and 0; DPIx lower than 0; ▴ DPIx higher than 0. Similar assays with valine and isoleucine showed no significant choice for these amino acids.