thiamine hydrochloride (Sigma–Aldrich, St. Louis, MO, USA) was added to different final concentrations to the nutrient solution for 5 days, and the additions were stopped 24 h before placing aphids on the plants. Seed soaking: surface
sterilized seeds were soaked with aeration in water (control) or different concentrations of thiamine during 10 h for barley or 8 h for pea