【Background】Stress can lead to plant volatiles components and contents to change. This change can increase or reduce the searching behavior of natural enemies. 【Method】In this experiment, tobacco leaves infested by aphids were first exposed to eight insecticides as the stress factor. Then the search behavior response of Harmonia axyridis (Pallas) var.spectabilis, H.axyridis (Pallas) ab.Conspicua and H.axyridis (Pallas) ab.Bimaculata were measured using a Y-tube olfactometer. 【Result】The results showed that the three varieties of H.axyridis did not show any preference when exposed to intact tobacco leaves. H.axyridis however selected tobacco leaves infested by Myzus persicae at a rate of 70%~74%. When infested tobacco was sprayed with omethoate, H.axyridis varieties selected at rates of 32%, 36% and 34%; When exposed to fipronil+perchloric, the rates were 36%, 38% and 36%; When tobacco leaves was sprayed with spinosad, the rates were 40%, 42% and 38%. The preferences of the ladybirds to tobacco leaves exposed to these three insecticides were weak obviously. Two insecticides, imidacloprid and acetamiprid only slightly affected the search behavior of ladybirds (rates varying between 60% and 68%). When infested tobacco was sprayed with beta-cypermethrin, H.axyridis varieties selected at rates of 80%, 82% and 80%; When exposed to lambda-cyhothrin, the rates were all 78%; When exposed to cyfluthrin, the rates were 76%, 78% and 76%. The preferences of the ladybirds to tobacco leaves exposed to these three insecticides were strong. 【Conclusion and significance】Insecticides can probably change plant volatiles components and contents, but different insecticides have different effects.