A rubber tube (10 cm×0.05 cm diameter, Pherobio Technology
Co. Ltd., Beijing, China) as the releaser loaded with 10
L candidate volatile substances was hung in wheat fields
at a height of 10 cm above the top of wheat plant, and five
releasers were used completely randomized design in each
single plot. The first introduction of releasers was made on
22 April (at the setting stage of wheat), and chemicals were
subsequently supplied every 7 d until aphid counting ended