Abstract: In nature plant terpenoids play multiple ecological roles. Many phytophagous insects use them as kairomones to locate their host plants. This is also the case for Lobesia botrana, which is the main pest of European vineyards. It was found that a specific blend of the terpenoids (E)-β-caryophyllene, (E)-β-farnesene and the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene emitted by grapevine was attractive to L. botrana females, and the attractiveness was shown to be dependent on the kairomone ratio. In this work, we generated stable grapevine transgenic lines with altered (E)-β-caryophyllene and (E)-β-farnesene emission compared to natural plants. Thus, we modified the ratio between these two kairomones in vivo, and tested how it affected L. botrana behaviour.