To evaluate the effect of thiamine treatments on plant defence
against aphids, barley seeds were soaked in different concentrations
of thiamine or the vitamin was added to the nutrient solutions to
plants cultivated in vermiculite/perlite. Adult mixed instar aphids
(R. padi) were added to the plant and aphid numbers were counted
after 1 week. Seed soaking or addition of thiamine to the nutrient
solution resulted in reduced aphid population growth to ca. 60% to
70% on the treated plants as compared to on control plants (Fig. 1).