The effect of some terpenoid lactones (monocyclic ó-hydroxy-v-lactone: bicyclic &-hydroxy-y-spirolactone and bicyclic &-hydroxy-y-lactone) and azadirachtin on feeding and growth of Leptinotarsa decemlineata Say larvae was studied. Among lactones bicyclic 6-hydroxy-y-spirolactone showed a strong feeding deterrency. Larvae treated with this compound consumed O.I63 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.