The effect of some terpenoid lactones (monocyclic δ-hydroxy-γ-lactone; bicyclic δ-hydroxy-γ-spirolactone and bicyclic δ-hydroxy-γ-lactone) and azadirachtin on feeding and growth of Leptinotarsa decemlineata Say larvae was studied. Among lactones bicyclic δ-hydroxy-γ-spirolactone showed a strong feeding deterrency. Larvae treated with this compound consumed 0.163 cm² (per larva) of potato leaves during 6 days, whereas control larvae ate 0.892 cm². When lactones were used, a slight increase in body weight was observed. Azadirachtin, in comparison with lactones, much stronger reduced food consumption and growth rate of insects.