The influence of copper on adults of the Colorado potato beetle (Leptinotarsa decemlineata Say) was studied. The adults were treated by the contact fungicide Kuprikol 50, which is used to control down powder mildew (Phytophtora infestans de Bary). Copper content was determined by radio-nuclide X-ray fluorescence analysis using a 238Pu exciting source. The obtained results contribute to the control measures against the Colorado potato beetle and to the question of the resistance of Colorado potato beetle towards pyrethroide insecticides.